Seasonal thermal energy storage (or STES) is the
storage of heat or cold for periods of up to several months. The thermal
energy can be collected whenever it is available and be used whenever
needed, such as in the opposing season. For example, heat from solar
collectors or waste heat
from air conditioning equipment can be gathered in hot months for space
heating use when needed, including during winter months. Waste heat
from industrial process can similarly be stored and be used much later.
Or the natural cold of winter air can be stored for summertime air conditioning.
STES stores can serve district heating systems, as well as single
buildings or complexes. Among seasonal storages used for heating, the
design peak annual temperatures generally are in the range of 27 to
80 °C (81 to 180 °F), and the temperature difference occurring in the
storage over the course of a year can be several tens of degrees. Some
systems use a heat pump to help charge and discharge the storage during
part or all of the cycle. For cooling applications, often only
circulation pumps are used. A less common term for STES technologies is
interseasonal thermal energy storage.
There
are several types of STES technology, covering a range of applications
from single small buildings to community district heating networks.
Generally, efficiency increases and the specific construction cost
decreases with size.
Underground thermal energy storage
UTES (underground thermal energy storage), in which the
storage medium may be geological strata ranging from earth or sand to
solid bedrock, or aquifers. UTES technologies include:
ATES (aquifer thermal energy storage).
An ATES store is composed of a doublet, totaling two or more wells into
a deep aquifer that is contained between impermeable geological layers
above and below. One half of the doublet is for water extraction and the
other half for reinjection, so the aquifer is kept in hydrological
balance, with no net extraction. The heat (or cold) storage medium is
the water and the substrate it occupies. Germany’s Reichstag building has been both heated and cooled since 1999 with ATES stores, in two aquifers at different depths.
In the Netherlands there are well over 1,000 ATES systems, which are now a standard construction option.
A significant system has been operating at Richard Stockton College (New Jersey) for several years.
ATES has a lower installation cost than BTES because usually fewer
holes are drilled, but ATES has a higher operating cost. Also, ATES
requires particular underground conditions to be feasible, including the
presence of an aquifer.
BTES (borehole thermal energy storage). BTES stores can be constructed wherever boreholes
can be drilled, and are composed of one to hundreds of vertical
boreholes, typically 155 mm (6.102 in) in diameter. Systems of all sizes
have been built, including many quite large.
The strata can be anything from sand to crystalline hardrock, and
depending on engineering factors the depth can be from 50 to 300 metres
(164 to 984 ft). Spacings have ranged from 3 to 8 metres (9.8 to
26.2 ft). Thermal models can be used to predict seasonal temperature
variation in the ground, including the establishment of a stable
temperature regime which is achieved by matching the inputs and outputs
of heat over one or more annual cycles. Warm-temperature seasonal heat
stores can be created using borehole fields to store surplus heat
captured in summer to actively raise the temperature of large thermal
banks of soil so that heat can be extracted more easily (and more
cheaply) in winter. Interseasonal Heat Transfer uses water circulating in pipes embedded in asphalt solar collectors to transfer heat to Thermal Banks
created in borehole fields. A ground source heat pump is used in winter
to extract the warmth from the Thermal Bank to provide space heating
via underfloor heating.
A high Coefficient of Performance is obtained because the heat pump
starts with a warm temperature of 25 °C (77 °F) from the thermal store,
instead of a cold temperature of 10 °C (50 °F) from the ground.
A BTES operating at Richard Stockton College since 1995 at a peak of
about 29 °C (84.2 °F) consists of 400 boreholes 130 metres (427 ft) deep
under a 3.5-acre (1.4 ha) parking lot. It has a heat loss of 2% over
six months.
The upper temperature limit for a BTES store is 85 °C (185 °F) due to
characteristics of the PEX pipe used for BHEs, but most do not approach
that limit. Boreholes can be either grout- or water-filled depending on
geological conditions, and usually have a life expectancy in excess of
100 years. Both a BTES and its associated district heating system can be
expanded incrementally after operation begins, as at Neckarsulm,
Germany.
BTES stores generally do not impair use of the land, and can exist under
buildings, agricultural fields and parking lots. An example of one of
the several kinds of STES illustrates well the capability of
interseasonal heat storage. In Alberta, Canada, the homes of the Drake Landing Solar Community
(in operation since 2007), get 97% of their year-round heat from a
district heat system that is supplied by solar heat from solar-thermal
panels on garage roofs. This feat – a world record – is enabled by
interseasonal heat storage in a large mass of native rock that is under a
central park. The thermal exchange occurs via a cluster of 144
boreholes, drilled 37 metres (121 ft) into the earth. Each borehole is
155 mm (6.1 in) in diameter and contains a simple heat exchanger made of
small diameter plastic pipe, through which water is circulated. No heat
pumps are involved.
CTES (cavern or mine thermal energy storage).
STES stores are possible in flooded mines, purpose-built chambers, or
abandoned underground oil stores (e.g. those mined into crystalline
hardrock in Norway), if they are close enough to a heat (or cold) source
and market.
Energy Pilings. During construction of large buildings, BHE
heat exchangers much like those used for BTES stores have been spiraled
inside the cages of reinforcement bars for pilings, with concrete then
poured in place. The pilings and surrounding strata then become the
storage medium.
GIITS (geo interseasonal insulated thermal storage). During
construction of any building with a primary slab floor, an area
approximately the footprint of the building to be heated, and > 1 m
in depth, is insulated on all 6 sides typically with HDPE
closed cell insulation. Pipes are used to transfer solar energy into
the insulated area, as well as extracting heat as required on demand. If
there is significant internal ground water flow, remedial actions are
needed to prevent it.
Surface and above ground technologies
Pit Storage.
Lined, shallow dug pits that are filled with gravel and water as the
storage medium are used for STES in many Danish district heating
systems. Storage pits are covered with a layer of insulation and then
soil, and are used for agriculture or other purposes. A system in
Marstal, Denmark, includes a pit storage supplied with heat from a field
of solar-thermal panels. It is initially providing 20% of the
year-round heat for the village and is being expanded to provide twice
that. The world's largest pit store (200,000 m3 (7,000,000 cu ft)) was commissioned
in Vojens, Denmark, in 2015, and allows solar heat to provide 50% of
the annual energy for the world's largest solar-enabled district heating
system.
Large-scale thermal storage with water. Large scale STES water storage tanks can be built above ground, insulated, and then covered with soil.
Horizontal heat exchangers. For small installations, a heat exchanger of corrugated plastic pipe can be shallow-buried in a trench to create a STES.
Earth-bermed buildings. Stores heat passively in surrounding soil.
Salt hydrate technology This technology achieves significantly higher storage densities than water-based heat storage.
Conferences and organizations
The International Energy Agency'sEnergy Conservation through Energy Storage (ECES) Programme
has held triennial global energy conferences since 1981. The
conferences originally focused exclusively on STES, but now that those
technologies are mature other topics such as phase change materials (PCM)
and electrical energy storage are also being covered. Since 1985 each
conference has had "stock" (for storage) at the end of its name; e.g.
EcoStock, ThermaStock.
They are held at various locations around the world. Most recent were
InnoStock 2012 (the 12th International Conference on Thermal Energy
Storage) in Lleida, Spain and GreenStock 2015 in Beijing.
EnerStock 2018 will be held in Adana, Turkey in April 2018.
The IEA-ECES programme continues the work of the earlier International Council for Thermal Energy Storage
which from 1978 to 1990 had a quarterly newsletter and was initially
sponsored by the U.S. Department of Energy. The newsletter was initially
called ATES Newsletter, and after BTES became a feasible technology it was changed to STES Newsletter.
Use of STES for small, passively heated buildings
Small
passively heated buildings typically use the soil adjoining the
building as a low-temperature seasonal heat store that in the annual
cycle reaches a maximum temperature similar to average annual air
temperature, with the temperature drawn down for heating in colder
months. Such systems are a feature of building design, as some simple
but significant differences from 'traditional' buildings are necessary.
At a depth of about 20 feet (6 m) in the soil, the temperature is
naturally stable within a year-round range,
if the draw down does not exceed the natural capacity for solar
restoration of heat. Such storage systems operate within a narrow range
of storage temperatures over the course of a year, as opposed to the
other STES systems described above for which large annual temperature
differences are intended.
Two basic passive solar building technologies were developed in
the US during the 1970s and 1980s. They utilize direct heat conduction
to and from thermally isolated, moisture-protected soil as a seasonal
storage medium for space heating, with direct conduction as the heat
return method. In one method, "passive annual heat storage" (PAHS),
the building’s windows and other exterior surfaces capture solar heat
which is transferred by conduction through the floors, walls, and
sometimes the roof, into adjoining thermally buffered soil.
When the interior spaces are cooler than the storage medium, heat is conducted back to the living space.
The other method, “annualized geothermal solar” (AGS) uses a separate
solar collector to capture heat. The collected heat is delivered to a
storage device (soil, gravel bed or water tank) either passively by the
convection of the heat transfer medium (e.g. air or water) or actively
by pumping it. This method is usually implemented with a capacity
designed for six months of heating.
A number of examples of the use of solar thermal storage from across the world include: Suffolk One
a college in East Anglia, England, that uses a thermal collector of
pipe buried in the bus turning area to collect solar energy that is then
stored in 18 boreholes each 100 metres (330 ft) deep for use in winter
heating. Drake Landing Solar Community
in Canada uses solar thermal collectors on the garage roofs of 52
homes, which is then stored in an array of 35 metres (115 ft) deep
boreholes. The ground can reach temperatures in excess of 70 °C which is
then used to heat the houses passively. The scheme has been running
successfully since 2007. In Brædstrup,
Denmark, some 8,000 square metres (86,000 sq ft) of solar thermal
collectors are used to collect some 4,000,000 kWh/year similarly stored
in an array of 50 metres (160 ft) deep boreholes.
Liquid engineering
Architect Matyas Gutai obtained an EU grant to construct a house in Hungary
which uses extensive water filled wall panels as heat collectors and
reservoirs with underground heat storage water tanks. The design uses
microprocessor control.
Small buildings with internal STES water tanks
A
number of homes and small apartment buildings have demonstrated
combining a large internal water tank for heat storage with roof-mounted
solar-thermal collectors. Storage temperatures of 90 °C (194 °F) are
sufficient to supply both domestic hot water and space heating. The
first such house was MIT Solar House #1, in 1939. An eight-unit
apartment building in Oberburg, Switzerland was built in 1989, with three tanks storing a total of 118 m3
(4,167 cubic feet) that store more heat than the building requires.
Since 2011, that design is now being replicated in new buildings.
In Berlin, the “Zero Heating Energy House”, was built in 1997 in as part of the IEA Task 13 low energy housing demonstration project. It stores water at temperatures up to 90 °C (194 °F) inside a 20 m3 (706 cubic feet) tank in the basement.
A similar example was built in Ireland in 2009, as a prototype. The solar seasonal store consists of a 23 m3 (812 cu ft) tank, filled with water, which was installed in the ground, heavily insulated all around, to store heat from evacuated solar tubes during the year. The system was installed as an experiment to heat the world's first standardized pre-fabricated passive house in Galway, Ireland.
The aim was to find out if this heat would be sufficient to eliminate
the need for any electricity in the already highly efficient home during
the winter months.
Use of STES in greenhouses
STES is also used extensively for the heating of greenhouses.
ATES is the kind of storage commonly in use for this application. In
summer, the greenhouse is cooled with ground water, pumped from the
“cold well” in the aquifer. The water is heated in the process, and is
returned to the “warm well” in the aquifer. When the greenhouse needs
heat, such as to extend the growing season, water is withdrawn from the
warm well, becomes chilled while serving its heating function, and is
returned to the cold well. This is a very efficient system of free cooling, which uses only circulation pumps and no heat pumps.
Treatments for influenza include a range of medications and therapies that are used in response to disease influenza. Treatments may either directly target the influenza virus itself; or instead they may just offer relief to symptoms of the disease, while the body's own immune system works to recover from infection.
The two main classes of antiviral drugs used against influenza are neuraminidase inhibitors, such as zanamivir and oseltamivir, or inhibitors of the viral M2 protein, such as amantadine and rimantadine.
These drugs can reduce the severity of symptoms if taken soon after
infection and can also be taken to decrease the risk of infection.
However, virus strains have emerged that show drug resistance to both classes of drug.
Consult a physician early on for best possible treatment
Remain alert for emergency warning signs
Warning signs are symptoms that indicate that the disease is becoming
serious and needs immediate medical attention. These include:
Difficulty breathing or shortness of breath
Pain or pressure in the chest or abdomen
Dizziness
Confusion
Severe or persistent vomiting
In children other warning signs include irritability, failing to wake
up and interact, rapid breathing, and a blueish skin color. Another
warning sign in children is if the flu symptoms appear to resolve, but
then reappear with fever and a bad cough.
Antiviral drugs
Antiviral drugs
directly target the viruses responsible for influenza infections.
Generally, anti-viral drugs work optimally when taken within a few days
of the onset of symptoms. Certain drugs are used prophylactically, that is they are used in uninfected individuals to guard against infection.
Four licensed influenza antiviral agents are available in the United States: amantadine, rimantadine, zanamivir, and oseltamivir.
They are available through prescription only. These drugs fall into
categories as either M2-inhibitors (admantane derivatives) or
neuraminidase inhibitors as illustrated in the following table.
Note: Neuraminidase inhibitors are approved for prophylaxis use in children and adults.
In Russia and China a drug called arbidol
is also used as a treatment. Testing of the drug has predominantly
occurred in these countries and, although no clinical trials have been
published demonstrating this is an effective drug, some data suggest
that this could be a useful treatment for influenza.
Peramivir
Peramivir, an experimental anti-influenza drug, developed by BioCryst Pharmaceuticals has not yet been approved for sale in the United States.
This drug can be given as an injection, so may be particularly useful
in serious cases of influenza where the patient is unconscious and oral
or inhaled drug administration is therefore difficult.
In October 2009, it was reported that the experimental antiviral drugPeramivir had been effective in treating serious cases of swine flu. On October 23, the U.S. Food and Drug Administration (FDA) issued an Emergency Use Authorization
for Peramivir (now expired), leading to wider and faster availability
for patients. Since the FDA's decisions and actions are closely watched
around the world, this move is likely to also increase demand for
Peramivir internationally.
Interferons
Interferons
are cellular signalling factors produced in response to viral
infection. Research into the use of interferons to combat influenza
began in the 1960s in the Soviet Union, culminating in a trial of 14,000 subjects at the height of the Hong Kong Flu
of 1969, in which those treated prophylactically with interferon were
more than 50% less likely to suffer symptoms, though evidence of latent
infection was present. In these early studies leukocytes were collected from donated blood and exposed to a high dose of Newcastle disease,
causing them to release interferons. Although interferon therapies
became widespread in the Soviet Union, the method was doubted in the
United States after high doses of interferon proved ineffective in
trials. Though the 1969 study used 256 units of interferon, subsequent
studies used up to 8.4 million units. It has since been proposed that
activity of interferon is highest at low concentrations. Phase III trials in Australia are planned for 2010, and initial trials are planned in the U.S. for late 2009.
Interferons have also been investigated as adjuvants to enhance to effectiveness of influenza vaccines.
This work was based on experiments in mice that suggested that type I
interferons could enhance the effectiveness of influenza vaccines in
mice.
However, a clinical trial in 2008 found that oral dosing of elderly
patients with interferon-alpha actually reduced their immune response to
an influenza vaccine.
Viferon is a suppository of (non-pegylated) interferon alpha-2b, ascorbic acid (vitamin C), and tocopherol (vitamin E) which was reported in two small studies to be as effective as arbidol. It is sold in Russia for $4–$9 per suppository depending on dose.Another interferon alfa-2b medicine, "Grippferon", nasal drops, is used for treatment and emergency prevention of Influenza and cold. Its manufacturers have appealed to the WHO to consider its use against avian influenza
and H1N1 Influenza 09 (Human Swine Flu), stating that it was used
successfully in Russia for eight years, but that "the medical profession
in Europe and the USA is not informed about this medicine".
Drug resistance
Influenza viruses can show resistance to anti-viral drugs. Like the development of bacterial antibiotic resistance, this can result from over-use of these drugs. For example, a study published in the June 2009 Issue of Nature Biotechnology emphasized the urgent need for augmentation of oseltamivir (Tamiflu) stockpiles with additional antiviral drugs including zanamivir
(Relenza) based on an evaluation of the performance of these drugs in
the scenario that the 2009 H1N1 'Swine Flu' neuraminidase (NA) were to
acquire the tamiflu-resistance (His274Tyr) mutation which is currently
widespread in seasonal H1N1 strains.
Yet another example is in the case of the amantadines treatment may lead
to the rapid production of resistant viruses, and over-use of these
drugs has probably contributed to the spread of resistance.
In particular, this high-level of resistance may be due to the easy
availability of amantadines as part of over-the-counter cold remedies in
countries such as China and Russia, and their use to prevent outbreaks of influenza in farmed poultry.
On the other hand, a few strains resistant to neuraminidase
inhibitors have emerged and circulated in the absence of much use of the
drugs involved, and the frequency with which drug resistant strains
appears shows little correlation with the level of use of these drugs.
However, laboratory studies have shown that it is possible for the use
of sub-optimal doses of these drugs as a prophylactic measure might
contribute to the development of drug resistance.
During the United States 2005–2006 influenza season, increasing incidence of drug resistance by strain H3N2
to amantadine and rimantadine led the CDC to recommend oseltamivir as a
prophylactic drug, and the use of either oseltamivir or zanamivir as
treatment.
Over-the-counter medication
Antiviral drugs are prescription-only medication in the United States. Readily available over-the-counter medications do not directly affect the disease, but they do provide relief from influenza symptoms, as illustrated in the table below.
Children and teenagers with flu symptoms (particularly fever) should avoid taking aspirin as taking aspirin in the presence of influenza infection (especially Influenzavirus B) can lead to Reye's syndrome, a rare but potentially fatal disease of the brain.
Off-label uses of other drugs
Several generic prescription medications might prove useful to treat a potential H5N1 avian flu outbreak, including statins, fibrates, and chloroquine.
Nutritional supplements and herbal medicines
Malnutrition can reduce the ability of the body to resist infections and is a common cause of immunodeficiency in the developing world. For instance, in a study in Ecuador, micronutrient deficiencies were found to be common in the elderly, especially for vitamin C, vitamin D, vitamin B-6, vitamin B-12, folic acid, and zinc, and these are thought to weaken the immune system or cause anemia and thus place people at greater risk of respiratory infections such as influenza.
Seasonal variation in sunlight exposure, which is required for vitamin
D synthesis within the body, has been proposed as one of the factors
accounting for the seasonality of influenza.
A meta-analysis of 13 studies indicated some support for adjunctive
vitamin D therapy for influenza, but called for more rigorous clinical
trials to settle the issue conclusively.
The activity of N-acetylcysteine (NAC) against influenza was first suggested in 1966.
In 1997 a randomized clinical trial found that volunteers taking
1.2 grams of N-acetylcysteine daily for six months were as likely as
those taking placebo to be infected by influenza, but only 25% of them experienced clinical symptoms, as contrasted with 67% of the control group. The authors concluded that resistance to flu symptoms was associated with a shift in cell mediated immunity from anergy toward normoergy, as measured by the degree of skin reactivity to seven common antigens such as tetanus and Candida albicans.
Several animal studies found that in a mouse model of lethal
infection with a high dose of influenza, oral supplementation with one
gram of N-acetylcysteine per kilogram of body weight daily increased the
rate of survival, either when administered alone or in combination with
the antiviral drugs ribavirin or oseltamivir. NAC was shown to block or reduce cytopathic effects in influenza-infected macrophages, to reduce DNA fragmentation (apoptosis) in equine influenza-infected canine kidney cells, and to reduce RANTES production in cultured airway cells in response to influenza virus by 18%. The compound has been proposed for treatment of influenza.
Elderberry
A few news reports have suggested the use of an elderberry(Sambucus nigra) extract as a potential preventative against the 2009 flu pandemic. The preparation has been reported to reduce the duration of influenza symptoms by raising levels of cytokines.
However, the use of the preparation has been described as "imprudent"
when an influenza strain causes death in healthy adults by cytokine storm leading to primary viral pneumonia.
The manufacturer cites a lack of evidence for cytokine-related risks,
but labels the product only as an antioxidant and food supplement.
"Kan Jang"
The mixture of Eleutherococcus senticosus ("Siberian ginseng") and Andrographis paniculata, sold under the trade name Kan Jang, was reported in the Journal of Herbal Pharmacotherapy to outperform amantadine in reducing influenza-related sick time and complications in a Volgograd pilot study of 71 patients in 2003. Prior to this, an extract of Eleutherococcus senticosus was shown to inhibit replication of RNA but not DNA viruses in vitro. Among nine Chinese medicinal herbs tested, Andrographis paniculata was shown to be most effective in inhibiting RANTES secretion by H1N1 influenza infected cells in cell culture, with an IC50 for the ethanol extract of 1.2 milligrams per liter.
Green Tea
High dietary intake of green tea
(specifically, catechins and theanine that is found in tea products)
has been correlated with reduced risk of contracting influenza, as well
as having an antiviral effect upon types A and B.
Specifically, the high levels of epigallocatechin gallate, epicatechin
gallate, and epigallocatechin present in green tea were found to inhibit
influenza virus replication. Additionally, topical application has been suggested to possibly act as a mild disinfectant.
Regular dietary intake of green tea has been associated with stronger
immune response to infection, through the enhancement of T-Cell
function.
Passive immunity
Transfused antibodies
An alternative to vaccination used in the 1918 flu pandemic
was the direct transfusion of blood, plasma, or serum from recovered
patients. Though medical experiments of the era lacked some procedural
refinements, eight publications from 1918-1925 reported that the
treatment could approximately halve the mortality in hospitalized severe
cases with an average case-fatality rate of 37% when untreated.
Bovine colostrum might also serve as a source of antibodies for some applications.
Ex vivo culture of T lymphocytes
Human T lymphocytes can be expanded in vitro using beads holding specific antigens to activate the cells and stimulate growth. Clonal populations of CD8+ cytotoxic T cells have been grown which carry T cell receptors specific to influenza. These work much like antibodies but are permanently bound to these cells. (See cellular immunity).
High concentrations of N-acetylcysteine have been used to enhance
growth of these cells. This method is still in early research.
Avian influenza, known informally as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds. The type with the greatest risk is highly pathogenic avian influenza (HPAI). Bird flu is similar to swine flu, dog flu, horse flu and human flu
as an illness caused by strains of influenza viruses that have adapted
to a specific host. Out of the three types of influenza viruses (A, B, and C), influenza A virus is a zoonotic infection with a natural reservoir almost entirely in birds. Avian influenza, for most purposes, refers to the influenza A virus.
Though influenza A is adapted to birds, it can also stably adapt and sustain person-to-person transmission. Recent influenza research into the genes of the Spanish flu
virus shows it to have genes adapted from both human and avian strains.
Pigs can also be infected with human, avian, and swine influenza
viruses, allowing for mixtures of genes (reassortment) to create a new virus, which can cause an antigenic shift to a new influenza A virus subtype which most people have little to no immune protection against.
Avian influenza strains are divided into two types based on their pathogenicity: high pathogenicity (HP) or low pathogenicity (LP). The most well-known HPAI strain, H5N1, appeared in China in 1996, and also has low pathogenic strains found in North America.
Companion birds in captivity are unlikely to contract the virus and
there has been no report of a companion bird with avian influenza since
2003. Pigeons can contract avian strains, but rarely become ill and are
incapable of transmitting the virus efficiently to humans or other
animals.
Between early 2013 and early 2017, 916 lab-confirmed human cases of H7N9 were reported to the World Health Organization (WHO).
On 9 January 2017, the National Health and Family Planning Commission
of China reported to WHO 106 cases of H7N9 which occurred from late
November through late December, including 35 deaths, 2 potential cases
of human-to-human transmission, and 80 of these 106 persons stating that
they have visited live poultry markets. The cases are reported from
Jiangsu (52), Zhejiang (21), Anhui (14), Guangdong (14), Shanghai (2),
Fujian (2) and Hunan (1). Similar sudden increases in the number of
human cases of H7N9 have occurred in previous years during December and
January.
History
The
most widely quoted date for the beginning of recorded history of avian
influenza (initially known as fowl plague) was in 1878 when it was
differentiated from other diseases that caused high mortality rates in
birds. Fowl plague, however, also included Newcastle disease
until as recently as the 1950s. Between 1959 and 1995, there were 15
recorded occasions of the emergence of HPAI viruses in poultry, but
losses were minimal. Between 1996 and 2008 however, HPAI outbreaks in
poultry have occurred at least 11 times and 4 of these outbreaks have
involved millions of birds.
In the 1990s, the world's poultry population grew 76% in
developing countries and 23% in developed countries, contributing to the
increased prevalence of avian influenza.
Before the 1990s, HPAI caused high mortality in poultry, but infections
were sporadic and contained. Outbreaks have become more common due to
the high density and frequent movement of flocks from intensive poultry production.
Influenza A/H5N1 was first isolated from a goose in China in 1996. Human infections were first reported in 1997 in Hong Kong. Since 2003, more than 700 human cases of Asian HPAI H5N1 have been reported to the WHO,
primarily from 15 countries in Asia, Africa, the Pacific, Europe, and
the Middle East, though over 60 countries have been affected.
Genetics
Genetic factors in distinguishing between "human flu viruses" and "avian flu viruses" include:
PB2: (RNA polymerase): Amino acid (or residue) position 627 in the PB2 protein encoded by the PB2 RNA gene. Until H5N1, all known avian influenza viruses had a Glu at position 627, while all human influenza viruses had a Lys.
HA: (hemagglutinin): Avian influenza HA viruses bind alpha 2-3 sialic acid receptors, while human influenza HA viruses bind alpha 2-6 sialic acid receptors. Swine influenza
viruses have the ability to bind both types of sialic acid receptors.
Hemagglutinin is the major antigen of the virus against which
neutralizing antibodies are produced, and influenza virus epidemics are
associated with changes in its antigenic structure. This was originally
derived from pigs, and should technically be referred to as "pig flu".
Subtypes
There
are many subtypes of avian influenza viruses, but only some strains of
five subtypes have been known to infect humans: H5N1, H7N3, H7N7, H7N9,
and H9N2. At least one person, an elderly woman in Jiangxi Province, China, died of pneumonia in December 2013 from the H10N8 strain, the first human fatality confirmed to be caused by that strain.
Most human cases of the avian flu are a result of either handling
dead infected birds or from contact with infected fluids. It can also
be spread through contaminated surfaces and droppings. While most wild
birds have only a mild form of the H5N1 strain, once domesticated birds
such as chickens or turkeys are infected, H5N1 can potentially become
much more deadly because the birds are often in close contact. H5N1 is a
large threat in Asia with infected poultry due to low hygiene
conditions and close quarters. Although it is easy for humans to
contract the infection from birds, human-to-human transmission is more
difficult without prolonged contact. However, public health officials
are concerned that strains of avian flu may mutate to become easily
transmissible between humans.
Spreading of H5N1 from Asia to Europe is much more likely caused
by both legal and illegal poultry trades than dispersing through wild
bird migrations, being that in recent studies, there were no secondary
rises in infection in Asia when wild birds migrate south again from
their breeding grounds. Instead, the infection patterns followed
transportation such as railroads, roads, and country borders, suggesting
poultry trade as being much more likely. While there have been strains
of avian flu to exist in the United States, they have been extinguished
and have not been known to infect humans.
Birds that have died of avian influenza. The virus is spread by contact between healthy and unhealthy birds.
Avian influenza is most often spread by contact between infected and
healthy birds, though can also be spread indirectly through contaminated
equipment.
The virus is found in secretions from the nostrils, mouth, and eyes of
infected birds as well as their droppings. HPAI infection is spread to
people often through direct contact with infected poultry, such as
during slaughter or plucking.
Though the virus can spread through airborne secretions, the disease
itself is not an airborne disease. Highly pathogenic strains spread
quickly among flocks and can destroy a flock within 28 hours; the less
pathogenic strains may affect egg production but are much less deadly.
Although it is possible for humans to contract the avian
influenza virus from birds, human-to-human contact is much more
difficult without prolonged contact. However, public health officials
are concerned that strains of avian flu may mutate to become easily
transmissible between humans.
Some strains of avian influenza are present in the intestinal tract of
large numbers of shore birds and water birds, but these strains rarely
cause human infection.
Five manmade ecosystems have contributed to modern avian
influenza virus ecology: integrated indoor commercial poultry,
range-raised commercial poultry, live poultry markets, backyard and
hobby flocks, and bird collection and trading systems including cockfighting.
Indoor commercial poultry has had the largest impact on the spread of
HPAI, with the increase in HPAI outbreaks largely the result of
increased commercial production since the 1990s.
Village poultry
In
the early days of the HPAI H5N1 pandemic, village poultry and their
owners were frequently implicated in disease transmission. Village poultry, also known as backyard and hobby flocks, are small flocks raised under extensive
conditions and often allowed free range between multiple households.
However, research has shown that these flocks pose less of a threat than
intensively raised commercial poultry with homogenous genetic stock and poor biosecurity.
Backyard and village poultry also do not travel great distances
compared to transport of intensively raised poultry and contribute less
to the spread of HPAI.
This initial implication of Asian poultry farmers as one broad category
presented challenges to prevention recommendations as commercial
strategies did not necessarily apply to backyard poultry flocks.
H5N1
The highly pathogenic influenza A virus subtype H5N1 is an emerging avian influenza virus that is causing global concern as a potential pandemic threat. It is often referred to simply as "bird flu" or "avian influenza", even though it is only one of many subtypes.
H5N1 has killed millions of poultry in a growing number of
countries throughout Asia, Europe, and Africa. Health experts are
concerned that the coexistence of human flu viruses and avian flu
viruses (especially H5N1) will provide an opportunity for genetic
material to be exchanged between species-specific viruses, possibly
creating a new virulent influenza strain that is easily transmissible
and lethal to humans. The mortality rate for humans with H5N1 is 60%.
Since the first human H5N1 outbreak occurred in 1997, there has
been an increasing number of HPAI H5N1 bird-to-human transmissions,
leading to clinically severe and fatal human infections. Because a
significant species barrier exists between birds and humans, the virus
does not easily spread to humans, however some cases of infection are
being researched to discern whether human-to-human transmission is
occurring.
More research is necessary to understand the pathogenesis and
epidemiology of the H5N1 virus in humans. Exposure routes and other
disease transmission characteristics, such as genetic and immunological
factors that may increase the likelihood of infection, are not clearly
understood.
The first known transmission of H5N1 to a human occurred in Hong Kong
in 1997, when there was an outbreak of 18 human cases; 6 deaths were
confirmed. None of the infected people worked with poultry. After
culling all of the poultry in the area, no more cases were diagnosed.
In 2006, the first human-to-human transmission likely occurred when 7
members of a family in Sumatra became infected after contact with a
family member who had worked with infected poultry.
Although millions of birds have become infected with the virus
since its discovery, 359 people have died from H5N1 in twelve countries
according to World Health Organization reports as of August 10, 2012.
As an example, the H5N1 outbreak in Thailand
caused massive economic losses, especially among poultry workers.
Infected birds were culled and slaughtered. The public lost confidence
with the poultry products, thus decreasing the consumption of chicken
products. This also elicited a ban from importing countries. There were,
however, factors which aggravated the spread of the virus, including
bird migration, cool temperature (increases virus survival) and several
festivals at that time.
A mutation in the virus was discovered in two Guangdong patients
in February 2017 which rendered it more deadly to chickens, inasmuch as
it could infect every organ; the risk to humans was not increased,
however.
Controversial research
A
study published in 2012 in Science Magazine reported on research
findings that allowed for the airborne transmission of H5N1 in
laboratory ferrets. The study identified the 5 mutations necessary for
the virus to become airborne and immediately sparked controversy over
the ethical implications of making such potentially dangerous
information available to the general public. The study was allowed to
remain available in its entirety, though it remains a controversial
topic within the scientific community.
The study in question, however, created airborne H5N1 via amino
acid substitutions that largely mitigated the devastating effects of the
disease. This fact was underscored by the 0% fatality rate among the
ferrets infected via airborne transmission, as well as the fundamental
biology underlying the substitutions. Flu viruses attach to host cells
via the hemagluttinin proteins on their envelope. These hemagluttinin
proteins bind to sialic acid receptors on host cells, which can fall
into two categories. The sialic acid receptors can be either 2,3 or
2,6-linked, with the species of origin largely deciding receptor
preference. In influenzas of avian origin 2,3-linkage is preferred, vs.
influenzas of human origin in which 2,6-linkage is preferable.
2,3-linked SA receptors in humans are found predominantly in the lower
respiratory tract, a fact that is the primary foundation for the
deadliness of avian influenzas in humans, and also the key to their lack
of airborne transmission. In the study that created an airborne avian
influenza among ferrets it was necessary to switch the receptor
preference of the host cells to those of 2,6-linkage, found
predominantly in humans' upper respiratory tract, in order to create an
infection that could shed aerosolized virus particles. Such an
infection, however, must occur in the upper respiratory tract of humans,
thus fundamentally undercutting the fatal trajectory of the disease.
H7N9
Influenza A virus subtype H7N9 is a novel avian influenza virus first reported to have infected humans in 2013 in China. Most of the reported cases of human infection have resulted in severe respiratory illness.
In the month following the report of the first case, more than 100
people had been infected, an unusually high rate for a new infection; a
fifth of those patients had died, a fifth had recovered, and the rest
remained critically ill. The World Health Organization (WHO) has identified H7N9 as "...an unusually dangerous virus for humans." As of June 30, 133 cases have been reported, resulting in the deaths of 43.
Research regarding background and transmission is ongoing. It has been established that many of the human cases of H7N9 appear to have a link to live bird markets.
As of July 2013, there had been no evidence of sustained
human-to-human transmission, however a study group headed by one of the
world's leading experts on avian flu reported that several instances of
human-to-human infection were suspected.
It has been reported that H7N9 virus does not kill poultry, which will
make surveillance much more difficult. Researchers have commented on
the unusual prevalence of older males among H7N9-infected patients. While several environmental, behavioral, and biological explanations for this pattern have been proposed, as yet, the reason is unknown. Currently no vaccine exists, but the use of influenza antiviral drugs known as neuraminidase inhibitors in cases of early infection may be effective.
The number of cases detected after April fell abruptly. The
decrease in the number of new human H7N9 cases may have resulted from
containment measures taken by Chinese authorities, including closing
live bird markets, or from a change in seasons, or possibly a
combination of both factors. Studies indicate that avian influenza
viruses have a seasonal pattern, thus it is thought that infections may
pick up again when the weather turns cooler in China.
In the four years from early 2013 to early 2017, 916 lab-confirmed human cases of H7N9 were reported to WHO.
On 9 January 2017, the National Health and Family Planning
Commission of China reported to WHO 106 cases which occurred from late
November through December. 29, 2016. The cases are reported from
Jiangsu (52), Zhejiang (21), Anhui (14), Guangdong (14), Shanghai (2),
Fujian (2) and Hunan (1). 80 of these 106 persons have visited live
poultry markets. Of these cases, there have been 35 deaths. In two of
the 106 cases, human-to-human transmission could not be ruled out.
Affected prefectures in Jiangsu province closed live poultry
markets in late December 2016, whereas Zhejiang, Guangdong and Anhui
provinces went the route of strengthening live poultry market
regulations. Travellers to affected regions are recommended to avoid
poultry farms, live bird markets, and surfaces which appear to be
contaminated with poultry feces. Similar sudden increases in the number
of human cases of H7N9 have occurred in previous years during December
and January.
Domestic animals
A chicken being tested for flu
Several domestic species have been infected with and shown symptoms
of H5N1 viral infection, including cats, dogs, ferrets, pigs, and birds.
Birds
Attempts
are made in the United States to minimize the presence of HPAI in
poultry through routine surveillance of poultry flocks in commercial
poultry operations. Detection of a HPAI virus may result in immediate
culling of the flock. Less pathogenic viruses are controlled by
vaccination, which is done primarily in turkey flocks (ATCvet codes: QI01AA23 (WHO) for the inactivated fowl vaccine, QI01CL01 (WHO) for the inactivated turkey combination vaccine).
Cats
Avian influenza in cats
can show a variety of symptoms and usually lead to death. Cats are able
to get infected by either consuming an infected bird or by contracting
the virus from another infected cat.
Global impact
In 2005, the formation of the International Partnership on Avian and Pandemic Influenza
was announced in order to elevate the importance of avian flu,
coordinate efforts, and improve disease reporting and surveillance in
order to better respond to future pandemics. New networks of
laboratories have emerged to detect and respond to avian flu, such as
the Crisis Management Center for Animal Health, the Global Avian
Influenza Network for Surveillance, OFFLU,
and the Global Early Warning System for major animal diseases. After
the 2003 outbreak, WHO member states have also recognized the need for
more transparent and equitable sharing of vaccines and other benefits
from these networks.
Cooperative measures created in response to HPAI have served as a basis
for programs related to other emerging and re-emerging infectious
diseases.
HPAI control has also been used for political ends. In Indonesia,
negotiations with global response networks were used to recentralize
power and funding to the Ministry of Health. In Vietnam policymakers, with the support of the Food and Agriculture Organization of the United Nations (FAO),
used HPAI control to accelerate the industrialization of livestock
production for export by proposing to increase the portion of
large-scale commercial farms and reducing the number of poultry keepers
from 8 to 2 million by 2010.
Stigma
Backyard
poultry production was viewed as "traditional Asian" agricultural
practices that contrasted with modern commercial poultry production and
seen as a threat to biosecurity. Backyard production appeared to hold
greater risk than commercial production due to lack of biosecurity and
close contact with humans, though HPAI spread in intensively raised
flocks was greater due to high density rearing and genetic homogeneity.
Asian culture itself was blamed as the reason why certain
interventions, such as those that only looked at placed-based
interventions, would fail without looking for a multifaceted solutions.
Indonesia
Press
accounts of avian flu in Indonesia were seen by poultry farmers as
conflating suspected cases while the public did see the accounts as
informative, though many became de-sensitized to the idea of impending
danger or only temporarily changed their poultry-related behavior. Rumors also circulated in Java
in 2006. These tended to focus on bird flu being linked to big
businesses in order to drive small farmers out of the market by
exaggerating the danger of avian influenza, avian flu being introduced
by foreigners to force Indonesians to purchase imported chicken and keep
Indonesian chicken off the world market, and the government using avian
flu as a ploy to attract funds from wealthy countries. Such rumors
reflected concerns about big businesses, globalization, and a distrust
of the national government in a country where "the amount of
decentralization here is breathtaking" according to Steven Bjorge, a WHO
epidemiologist in Jakarta in 2006.
In the context a decentralized national government that the
public did not completely trust, Indonesian Health Minister Siti Fadilah
Supari announced in December 2006 that her government would no longer
be sharing samples of H5N1 collected from Indonesian patients. This
decision came as a shock to the international community as it disrupted
the Global Influenza Surveillance Network (GISN) coordinated by the WHO
for managing seasonal and pandemic influenza. GISN is based on countries
sharing virus specimens freely with the WHO which assesses and
eventually sends these samples to pharmaceutical companies in order to
produce vaccines that are sold back to these countries.
Though this was initially seen as an attempt to protect national
sovereignty at all costs, it was instead used for a domestic political
struggle. Prior to Indonesia's dispute with the GISN, the Ministry of
Health, already weak due to the decentralized nature the government, was
experiencing further leakage of funding to state and non-state agencies
due to global health interventions. By reasserting control over public
health issues and funding by setting itself up as the sole Indonesian
representative to the WHO, the Ministry of Health made itself a key
player in the management of future international funds relating vaccine
production and renegotiated benefits from global surveillance networks.
Economic
Approximately 20% of the protein consumed in developing countries come from poultry.
In the wake of the H5N1 pandemic, millions of poultry were killed. In
Vietnam alone, over 50 million domestic birds were killed due to HPAI
infection and control attempts. A 2005 report by the FAO totaled economic losses in South East Asia around US$10 billion.
This had the greatest impact on small scale commercial and backyard
producers relative to total assets compared to industrial chains which
primarily experience temporary decreases in exports and loss of consumer
confidence. Some governments did provide compensation for culled
poultry, it was often far below market value (close to 30% of market
value in Vietnam), while others such as Cambodia provide no compensation
to farmers at all.
As poultry serves as a source of food security and liquid assets, the most vulnerable populations were poor small scale farmers.
The loss of birds due to HPAI and culling in Vietnam led to an average
loss of 2.3 months of production and US$69–108 for households where many
have an income of $2 a day or less. The loss of food security for vulnerable households can be seen in the stunting of children under 5 in Egypt. Women are another population at risk as in most regions of the world, small flocks are tended to by women. Widespread culling also resulted in the decreased enrollment of girls in school in Turkey.
Prevention
People
who do not regularly come into contact with birds are not at high risk
for contracting avian influenza. Those at high risk include poultry farm
workers, animal control workers, wildlife biologists, and
ornithologists who handle live birds.
Organizations with high-risk workers should have an avian influenza
response plan in place before any cases have been discovered.
Biosecurity of poultry flocks is also important for prevention. Flocks
should be isolated from outside birds, especially wild birds, and their
waste; vehicles used around the flock should be regularly disinfected
and not shared between farms; and birds from slaughter channels should
not be returned to the farm.
With proper infection control and use of personal protective equipment
(PPE), the chance for infection is low. Protecting the eyes, nose,
mouth, and hands is important for prevention because these are the most
common ways for the virus to enter the body. Appropriate personal
protective equipment includes aprons or coveralls, gloves, boots or boot
covers, and a head cover or hair cover. Disposable PPE is recommended.
An N-95 respirator and unvented/indirectly vented safety goggles are also part of appropriate PPE. A powered air purifying respirator (PAPR) with hood or helmet and face shield is also an option.
Proper reporting of an isolated case can help to prevent spread. The Centers for Disease Control and Prevention
(US) recommendation is that if a worker develops symptoms within 10
days of working with infected poultry or potentially contaminated
materials, they should seek care and notify their employer, who should
notify public health officials.
For future avian influenza threats, the WHO suggests a 3 phase, 5 part plan.
Phase: Pre-pandemic
Reduce opportunities for human infection
Strengthen the early warning system
Phase: Emergence of a pandemic virus
Contain or delay spread at the source
Phase: Pandemic declared and spreading internationally
Reduce morbidity, mortality, and social disruption
Conduct research to guide response measures
Vaccines for poultry have been formulated against several of the
avian H5N1 influenza varieties. Control measures for HPAI encourage mass
vaccinations of poultry though The World Health Organization has
compiled a list of known clinical trials of pandemic influenza prototype
vaccines, including those against H5N1.
In some countries still at high risk for HPAI spread, there is
compulsory strategic vaccination though vaccine supply shortages remain a
problem.
For village poultry farmers
During
the initial response to H5N1, a one size fits all recommendation was
used for all poultry production systems, though measures for intensively raised birds were not necessarily appropriate for extensively
raised birds. When looking at village-raised poultry, it was first
assumed that the household was the unit and that flocks did not make
contact with other flocks, though more effective measures came into use
when the epidemiological unit was the village.
Recommendations involve restructuring commercial markets to
improve biosecurity against avian influenza. Poultry production zoning
is used to limit poultry farming to specific areas outside of urban
environments while live poultry markets improve biosecurity by limiting
the number of traders holding licenses and subjecting producers and
traders to more stringent inspections. These recommendations in
combination with requirements to fence and house all poultry, and to
limit free ranging flocks, will eventually lead to fewer small
commercial producers and backyard producers, costing livelihoods as they
are unable to meet the conditions needed to participate.
A summary of reports to the World Organisation for Animal Health in 2005 and 2010 suggest that surveillance and under-reporting in developed and developing countries is still a challenge. Often, donor support can focus on HPAI control alone, while similar diseases such as Newcastle disease, acute fowl cholera, infectious laryngotracheitis, and infectious bursal disease still affect poultry populations. When HPAI tests come back negative, a lack of funded testing for differential diagnoses can leave farmers wondering what killed their birds.
Since traditional production systems require little investment
and serve as a safety net for lower income households, prevention and
treatment can be seen as less cost-effective than letting poultry die.
Effective control not only requires prior agreements to be made with
relevant government agencies, such as seen with Indonesia, they must
also not unduly threaten food security.
Culling
The interior of a barn showing infected birds who have been killed by suffocation with foam.
Culling is used in order to decrease the threat of avian influenza transmission by killing potentially infected birds. The FAO
manual on HPAI control recommends a zoning strategy which begins with
the identification of an infected area (IA) where sick or dead birds
have tested positive. All poultry in this zone are culled while the area
1 to 5 km from the outer boundary of the IA is considered the
restricted area (RA) placed under strict surveillance. 2 to 10 km from
the RA is the control area (CA) that serves as a buffer zone in case of
spread. Culling is not recommended beyond the IA unless there is
evidence of spread.
The manual, however, also provides examples of how control was carried
out between 2004 and 2005 to contain H5N1 where all poultry was to be
stamped out in a 3 km radius beyond the infected point and beyond that a
5 km radius where all fowl was to be vaccinated. This culling method
was indiscriminate as a large proportion of the poultry inside these
areas were small backyard flocks which did not travel great enough
distances to carry infection to adjacent villages without human effort
and may have not been infected at all. Between 2004 and 2005, over 100 million chickens were culled in Asia to contain H5N1.
The risk of mass culling of birds and the resulting economic
impact led to farmers who were reluctant to report sick poultry. The
culls often preempted actual lab testing for H5N1 as avian flu policy
justified sacrificing poultry as a safeguard against HPAI spread.
In response to these policies, farmers in Vietnam between 2003 and 2004
became more and more unwilling to surrender apparently healthy birds to
authorities and stole poultry destined for culls as it stripped poultry
of their biosocial and economic worth. By the end of 2005, the
government implemented a new policy that targeted high-risk flock in the
immediate vicinity of infected farms and instituted voluntary culling
with compensation in the case of a local outbreak.
Not only did culling result in severe economic impacts especially
for small scale farmers, culling itself may be an ineffective
preventative measure. In the short-term, mass culling achieves its goals
of limiting the immediate spread of HPAI, it has been found to impede
the evolution of host resistance which is important for the long-term
success of HPAI control. Mass culling also selects for elevated
influenza virulence and results in the greater mortality of birds overall.
Effective culling strategies must be selective as well as considerate
of economic impacts to optimize epidemiological control and minimize
economic and agricultural destruction.
People-poultry relations
Prevention
and control programs must take into account local understandings of
people-poultry relations. In the past, programs that have focused on
singular, place-based understandings of disease transmission have been
ineffective. In the case of Northern Vietnam, health workers saw poultry
as commodities with an environment that was under the control of
people. Poultry existed in the context of farms, markets,
slaughterhouses, and roads while humans were indirectly the primary
transmitters of avian flu, placing the burden of disease control on
people. However, farmers saw their free ranging poultry in an
environment dominated by nonhuman forces that they could not exert
control over. There were a host of nonhuman actors such as wild birds
and weather patterns whose relationships with the poultry fostered the
disease and absolved farmers of complete responsibility for disease
control.
Attempts at singular, place-based controls sought to teach
farmers to identify areas where their behavior could change without
looking at poultry behaviors. Behavior recommendations by Vietnam's
National Steering Committee for Avian Influenza Control and Prevention
(NSCAI) were drawn from the FAO Principles of Biosecurity.
These included restrictions from entering areas where poultry are kept
by erecting barriers to segregate poultry from non-human contact, limits
on human movement of poultry and poultry-related products ideally to
transporters, and recommendations for farmers to wash hands and footwear
before and after contact with poultry.
Farmers, pointed to wind and environmental pollution as reasons poultry
would get sick. NSCAI recommendations also would disrupt longstanding
livestock production practices as gates impede sales by restricting
assessment of birds by appearance and offend customers by limiting
outside human contact. Instead of incorporating local knowledge into
recommendations, cultural barriers were used as scapegoats for failed
interventions. Prevention and control methods have been more effective
when also considering the social, political, and ecological agents in
play.
