avian influenza

Wild birds

Since the mid-1970s, avian influenza viruses have been isolated from avian species representing most of the major families of birds throughout the world. Stallknecht and Shane (1988) in their review of surveillance studies listed 88 species of birds, covering 12 orders, which have been found to excrete influenza virus. The actual number of naturally infected or susceptible species is probably much greater because these surveys have been selective with respect to the species sampled, the geographical locations examined and the time of year sampling occurred. Most avian influenza viruses have been isolated from ducks, although other wild birds may also be infected including other waterfowl, shorebirds, and gulls and other seabirds. Wild birds and their excreta are considered to be a major source of avian influenza virus. Most avian influenza virus infections of wild birds are asymptomatic.

Domestic poultry

Turkeys are more commonly infected than chickens probably because of differences in husbandry systems. Preventing direct contact with free-flying birds and protecting domestic poultry from contact with the faeces of wild birds is an important way to prevent initial introduction of avian influenza into domestic poultry. Modern commercial chicken farms are made wild bird-proof. Turkeys, however, are often raised on open ranges, and this has resulted in outbreaks of primarily low pathogenicity avian influenza. Also at risk to avian influenza are poultry raised outdoors for organic or free-range markets, domestic ducks raised on ponds frequented by wild ducks, live poultry markets with multiple bird sources and multi-directional movement of birds, and small farm enterprises that raise multiple poultry species and such birds having access to outdoor areas.

Avian influenza viruses occur worldwide in both wild and domestic birds. Migratory birds, especially waterfowl are believed to be important reservoir hosts, and shed the virus in their respiratory and ocular secretions as well as in faeces. These birds frequently introduce avian influenza viruses into local, non-migratory, wild bird populations. Infected wild birds can transmit the virus to domestic birds such as chickens and turkeys. Asymptomatic carrier birds may also transmit the virus.

Avian influenza notifiable to OIE is defined as an infection of poultry caused by any influenza A virus with high pathogenicity (HPAI) and by H5 and H7 subtypes with low pathogenicity (H5/H7 LPAI). Influenza A viruses with high pathogenicity in birds other than poultry, including wild birds, are also notifiable.

Since 2002 a number of serious outbreaks of HPAI have occurred in different regions of the world with massive disruption to international trade, the culling of millions of birds, and transmission to humans resulting in disease and mortality.

The only country in Africa that reported cases of HPAI to the AU-IBAR in 2011 was Egypt. The country reported a total of 306 outbreaks that involved a morbidity of 218,797 and mortality of 31,851 birds. With the exception of Egypt, there has been a significant reduction in the number of HPAI outbreaks being reported on the African continent. The countries that have reported cases of HPAI in recent years include Egypt (2009, 2010, 2011), South Africa (2010) and Togo (2008).

Countries reporting avian influenza in 2011 to AU-IBAR 

The distribution map associated with this datasheet illustrates occurrence of notifiable avian influenza in poultry.

Editor's note: the clinical signs table in this datasheet refers to highly pathogenic avian influenza (HPAI).

Avian influenza (AI) is difficult to diagnose and false positives are not uncommon in preliminary tests. Virus isolation in specific-pathogen-free embryonated eggs or cell cultures is conventionally considered the method of choice for the detection and identification of avian influenza viruses. This is a reliable and specific technique although it is time-consuming and expensive. However, the time between clinical suspicion and laboratory confirmation of AI can be long because of the logistics of sending samples to laboratories and their capacity for providing high throughput of sensitive and specific assays is often limited. Although very accurate, virus isolation is of limited value for control and eradication purposes, because avian influenza is a highly contagious disease and the prompt identification of infection is crucial. In order to shorten the time between receipt of samples in a laboratory and diagnosis there has been widespread application of molecular techniques based on the amplification of specific nucleic acid sequences by polymerase chain reaction (PCR), ligase chain reaction and nucleic acid sequence-based amplification (NASBA). Real-time PCR (Brown, 2006) is increasingly being used, as it enables rapid diagnosis in part due to automation, and also because the PCR products are detected, and quantified, during the DNA amplification process, without requiring a subsequent separate detection process. The development of portable instruments for application of molecular technologies in field offers prospects for radically changing diagnostic approaches for AI in the future (Cattoli and Capua, 2006).

Clinical Diagnosis

Clinical signs of avian influenza vary according to the host, strain of virus, vaccinal immunity, secondary infections and environmental conditions. In some flocks the only evidence of the infection is seroconversion, i.e. the birds infected with a LPAI virus may only develop a detectable antibody titre to avian influenza virus. Birds infected with LPAI virus often develop respiratory, enteric, or reproductive disease. Decreased feed intake and a drop in egg production are some of the earliest and most predictable signs of disease. Birds infected with LPAI may show mild depression with a significant decrease in egg production. Other clinical signs for LPAI include excessive lacrimation, sinusitis, diarrhoea, coughing and sneezing.

Birds with HPAI may show some of the clinical signs of LPAI, but infected poultry usually have swollen heads, facial oedema with swollen and cyanotic unfeathered skin (comb, wattles, snood, feet and legs) and nervous signs such as paresis, paralysis, torticollis, and opisthotonus. Other clinical signs include severe depression and inappetence as well as a significant decline in egg production. Infection with the HPAI virus may cause sudden death with little or no overt signs (mortality can reach 100%). However, none of these signs can be considered pathognomonic. Differential diagnosis should consider acute fowl cholera, velogenic Newcastle disease, and respiratory diseases such as infectious laryngotracheitis.

Laboratory Diagnosis

Diagnosis of avian influenza is made by the isolation of the virus, molecular detection of specific nucleic acids or identification of specific proteins. Serological methods may be used as additional diagnostic tools, but, used alone, are unsuitable for a detailed identification.

The virus can be isolated from variety of sources including faeces, tracheal swabs and cloacal swabs. Inoculation of embryonated SPF chicken eggs is the preferred method of growing avian influenza A viruses but avian cell tissue culture can be used. The presence of haemagglutination activity in allantoic fluids of inoculated 9- to 11-day-old embryonating chicken eggs after incubation for 4-7 days at 35-37°C indicates a high probability of either influenza A virus or Newcastle disease virus infection.

The presence of influenza A virus can be confirmed in the allantoic fluid using agar gel immunodiffusion tests by demonstrating the presence of the nucleocapsid or matrix antigens, which are common to all influenza A viruses. The method for definitive antigenic sub-typing of influenza A viruses recommended by the WHO Expert Committee (1980) involves the use of highly specific antisera against haemagglutinin and neuraminidase subtypes, generally in a reference laboratory. Alternatively, the allantoic fluid can be tested for avian influenza virus type A nucleoprotein or matrix protein by solid phase ELISA test such as Directigen or by detection of avian influenza viral nucleic acids in a reverse transcriptase polymerase chain reaction assay. The antigen or nucleic acid detection tests can also be used to identify avian influenza virus directly in respiratory or cloacal swabs, or tissue homogenates from affected birds.

Further information concerning the pathogenicity of avian influenza subtypes may be obtained by sequencing part of the genome of the virus, where the amino acid make-up of the cleavage site of the haemagglutinin has great significance as an indicator of pathogenicity. Essentially, high pathogenicity H5 and H7 subtype strains have one or more pairs of basic amino acids (arginine, lysine) at the HA1-HA2 cleavage site, rendering the haemagglutinin cleavable by ubiquitous furin proteases present in many cells of organs throughout the body of poultry species. Consequently AIVs with such cleavage sites can replicate in many visceral and other organs and are consequently highly pathogenic. In contrast, low pathogenicity strains generally have only individual basic amino acids, not pairs, in the cleavage site. Proteases able to cleave such cleavage sites are not present in organs throughout the body, thereby restricting replication largely to respiratory and enteric organs where these proteases are present.

Prevention is based on biosecurity measures that include avoiding contact between poultry and wild birds, in particular waterfowl, avoiding introduction of birds of unknown disease status into flocks, control of human traffic, proper cleaning and disinfection procedures, and one age group per farm ('all in-all out') breeding systems.

When outbreaks have occurred, all birds in the flock must be slaughtered and the carcasses disposed. Restocking should not occur for at least 21 days.

Immunization and vaccines

Antibodies against the haemagglutinin play the major role in protection following immunization or exposure. These antibodies are protective against the homologous haemagglutinin subtype but not against heterologous subtypes; i.e. H5 vaccine protects against an H5 but not an H7 avian influenza virus.

Several types of commercial vaccines are available, listed though not necessarily endorsed by the Food and Agriculture Organisation (see: Avian Influenza Vaccine Producers and Suppliers for Poultry, June 2009). The largest type is inactivated whole AIV oil emulsion vaccines of H5 or H7 subtypes. These consist of various AIV isolates i.e. all eight genes from the respective AIV isolate, or comprise the H5 and N1 or N3 genes from AIVs plus the six internal protein genes from human A/Puerto Rico/8/34 virus, known as PR8. The PR8 virus has been used for many decades as the basis for human inactivated influenza vaccines, containing the HA and NA genes of a prevailing human influenza virus. PR8 genes confer high productivity in embryonated chicken eggs. There are also some live recombinant virus vectored vaccines against AIV. Two such vaccines comprise an avian poxvirus as the vector, producing H5 or both an H5 and N1 proteins. Another vectored vaccine comprises live Newcastle disease virus (LaSota) producing H5 haemagglutinin.

The use of AI vaccines around the world in poultry is not well documented. It is believed that the largest single use of inactivated avian influenza vaccine (H5N2 strain) has occurred in China (since December 2003 to present). Indonesia has also used H5 inactivated AI vaccine. In Mexico, both inactivated and recombinant fowlpox vaccines have been used since January 1995. Pakistan began using H7 inactivated AI vaccine following epizootics (in 1995, 1998, 2000 and 2003) of H7N3 HPAI and H9N2 LPAI (Naeem and Siddique, 2006). H9N2 inactivated vaccines are used in many countries in Asia, the Middle East and Eastern Europe. The USA also has considerable experience with the use of killed vaccines, primarily in turkeys. In the state of Minnesota in the 1980s and early 1990s vaccines were used successfully to control outbreaks of AI in turkeys. More recently, several large layer flocks have been vaccinated in Connecticut after an H7N2 LPAI outbreak (Suarez et al., 2006). H7 inactivated vaccine has been used in a high-risk area of northern Italy.

In areas where inadequate resources preclude eradication, flocks may be immunized using autogenous inactivated vaccines or recombinant vectored products. These vaccines are effective in preventing disease and reducing the amount of virus shed into the environment, but have the disadvantage of making it difficult to distinguish between infected and vaccinated birds. Vaccination suppresses clinical occurrence of disease but the virus may persist in the poultry population of the affected region unless adequate biosecurity and surveillance measures are undertaken. In most developed countries, vaccines are banned or discouraged because they may interfere with control policies and may also result in export bans on poultry products. However, during the devastating epidemics of HPAI in the 1990s and early 2000s, the mass slaughter of animals raised serious ethical questions. These epidemics showed that the use of emergency vaccination is an essential element in disease control (Clercq and Goris, 2004). With the development of tests or vaccines that will allow differentiation of vaccinated birds from those infected with the field virus, vaccines may come into greater use (Capua et al., 2003; Ellis et al., 2004; Swayne et al., 2006; Zhao et al., 2006).

Table: Types of vaccines available

Information from the Food and Agriculture Organisation (FAO), June 2009.

Vaccines and vaccination to control avian influenza - update 2005

By kind permission of the author, Dr David Swayne, Laboratory Director, Southeast Poultry Research Laboratory, USDA/ARS, and ProMED-mail (http://www.promedmail.org), the following is provided as background information on the use of vaccines for control of avian influenza (AI) in poultry (first published as: ProMED-mail. Avian influenza, poultry vaccines: a review. ProMED-mail 2005; 7 March: 2005 16:32:05 -0500 (EST). <http://www.promedmail.org>. Accessed 7 March 2005).

"1. Vaccination should be viewed and used only as a single tool in a comprehensive control strategy that includes: 1) biosecurity, 2) education, 3) diagnostics and surveillance, and 4) elimination of AI virus infected poultry. One or more of these components are used to develop AI control strategies to achieve one of 3 goals or outcomes (Swayne, 2004): 1) Prevention - preventing introduction of AI; 2) Management - reducing losses by minimizing negative economic impact through management practices; or 3) Eradication - total elimination of AI.

2. Protection against avian influenza is the result of immune response against the hemagglutinin protein (HA), of which there are 15 different HA subtypes, and to a lesser extent against the neuraminidase protein (NA), of which there are 9 different NA subtypes (Suarez & Schultz, 2000; Swayne & Halvorson, 2003). Immune responses to the internal proteins, such as nucleoprotein or matrix protein, are insufficient to provide field protection. Therefore, there is no one universal AI vaccine. Practically, protection is provided against the individual hemagglutinin subtype(s) included in the vaccine.

3. Experimental and field studies have shown that properly used vaccines will accomplish several goals: 1) protect against clinical signs and death, 2) reduced shedding of field virus if vaccinated poultry become infected, 3) prevent contact transmission of the field virus, 4) provide at least 20 weeks protection following a single vaccination for chickens (this may require 2 or more injections in turkeys or longer-lived chickens), 5) protect against challenges by low to high doses of field virus, 6) protect against a changing virus and 7) increase a birds resistance to avian influenza virus infection (Swayne, 2003; Capua et al., 2004). These positive qualities are essential in contributing to AI control strategies. Most AI vaccine studies and field use have focused on chickens and turkeys because of their high death rates and the high concentrations of Highly Pathogenic Avian Influenza (HPAI) virus excreted into the environment by these species. However, with the changing epidemiology of the H5N1 HPAI virus in Asia, the infection of domestic ducks and geese has become a very important contributor to the maintenance and spread of the H5N1 HPAI virus. Experimentally, vaccines have been shown to significantly reduce AI virus replication and shedding in domestic ducks and geese and thus decrease environmental contamination (especially in ponds, lakes and rivers) and prevent contact transmission. Proper vaccination of domestic ducks and geese will have a positive impact on control of H5N1 HPAI in Asia.

4. A wide variety of vaccines have been developed and examined in the laboratory for potential use in the field. However, only vaccines from 2 technologies are licensed and used in poultry: inactivated whole avian influenza virus vaccines and a recombinant fowlpox virus vectored vaccine with an H5 AI gene insert (from AI virus A/turkey/Ireland/83 (H5N8)). These 2 vaccine technologies have been shown to produce safe, pure and potent vaccines. Both vaccine technologies require handling and injection of individual birds.

5. The quantity of AI vaccine used around the world in poultry is not well documented, but reliable information suggests the largest single use has been 2 billion doses of inactivated H5N2 avian influenza vaccine in China (December 2003 - present). Indonesia also uses H5 inactivated AI vaccine. In Mexico, an AI vaccination program has been used since January 1995, with over 1.3 billion doses of inactivated vaccine and 850 million doses of recombinant fowlpox have been used. H5N2 HPAI has been eradicated (last isolate was in June 1995), but H5N2 LPAI (low pathogenic avian influenza) still circulates in central Mexico. Pakistan began using H7 inactivated AI vaccine in 1995, with use in 3 regions following epizootics of H7N3 HPAI (1995, 2001 and 2004). By contrast, with low pathogenicity (LP) AI, H9N2 inactivated vaccines have been and are used in many countries within Asia, the Middle East and Eastern Europe, but the number of doses is unknown. Vaccines for control of LPAI have been used sporadically. Recently, H7 inactivated vaccine is being used in a high risk area of Northern Italy and in one chicken layer company in the USA to control LPAI.

6. Historically, AI virus strains selected for manufacturing of inactivated vaccines have been based on LPAI viruses obtained from field outbreaks that have homologous hemagglutinin protein; i.e. H5 vaccine virus obtained from an H5 LPAI outbreak. Rarely, HPAI strains have been used to manufacture inactivated vaccines, because, to be done properly, such production requires specialized high biocontainment manufacturing facilities which are uncommon in the world. Contrary to rumor, HPAI strains do replicate to sufficient titer in embryonating eggs to be used in inactivated AI vaccines, but their use is discouraged because of biosecurity and biosafety manufacturing concerns. Furthermore, LPAI strains, with fewer biosecurity and biosafety concerns for manufacturing, protect against HPAI viruses of the same hemagglutinin subtype.

7. Vaccine strains have been shown to provide protection against diverse field viruses (88-100 percent similarity to the challenge virus hemagglutinin) isolated over a 38 year period (Swayne et al., 2000b). Recently, both North American and Eurasian lineages of AI vaccine viruses from 1968-1986 have been shown to be protective against the most recent 2003-2004 Asian H5N1 HPAI viruses (Swayne, 2004). This broad and longer-term protection efficacy of poultry AI vaccines, as compared to the need for frequent change of human influenza vaccine strains, is potentially the result of the following: 1) poultry vaccines use proprietary oil-emulsion-adjuvant technology which elicits more intense and longer-lived immune response in poultry than alum-adjuvant influenza vaccines, 2) the AI virus immune response in poultry appears to be broader than in humans, 3) the immunity in the domestic poultry population is more consistent because of greater host genetic homogeneity than is present in the human population, and 4) vaccine use in poultry is targeted to a relatively young, healthy population as compared to humans, in whom the vaccine is optimized for groups with the highest risk of severe illness and death.

8. The protection efficacy of individual poultry AI vaccines should be evaluated every 2-3 years to assure they are still protective against circulating virus strains. For example, a recent study demonstrated the 1994 Mexican H5N2 vaccine strain is no longer protective against circulating H5N2 LPAI viruses in Central America, and a change in vaccine strains is needed (Lee et al., 2004a). With the H5N1 AI virus in Asia circulating as only an HP strain, future vaccines may require the use of reverse genetics (Liu et al., 2003; Lee et al., 2004b) to generate new LPAI vaccine strains, or, other molecular techniques to produce vectored vaccine products, such as new recombinant fowlpox virus vaccines. Some of these products use patented technologies and will require legal clarification before use in the field.

9. "Sterilizing immunity" is not feasible in the field. Some experiments have reported "sterilizing immunity," but closer examination indicated such studies used very few experimental birds without statistical evaluation, used a very low virus challenge, or used low sensitive virus isolation/detection methods. In the field, vaccines will reduce replication of challenge virus in respiratory and GI tracts and thus reduce the environmental load of virus and virus transmission. However, the protection in conventional poultry in the field will always be less than that seen in specific-pathogen-free poultry under laboratory conditions because of other factors, such as improper vaccination technique, reduced vaccine dose, immunosuppressive viruses and improper storage & handling of vaccines. The other 4 components of a control strategy, as presented in item 1, are essential, because vaccines and their use are not perfect.

10. Economics and animal health control drive the use of vaccines in poultry. Vaccines are used in geographic areas of highest risk and in the agricultural sector affected, or at greatest risk to be affected. In the USA, inactivated AI vaccines cost on average USD 0.05/dose and another USD 0.05-0.07 for labor and equipment to administer. In examining new vaccine technologies, such adoption will only occur when protection is as good as or better than existing technologies, and the product is cost effective (Swayne, 2004). If the cost is prohibitively high, the farmer or company will not be able to use the vaccine.

11. When deciding to use AI vaccine in poultry, a simple animal health algorithm, in decreasing order of application, should be used: 1) high risk situations - e.g. as suppressor vaccine in the outbreak zone or as ring vaccination outside the outbreak zone; 2) rare captive birds, such as those in zoological collections; 3) valuable genetic poultry stock, such as pure lines or grandparent stocks whose individual value is high; 4) long-lived poultry, such as egg layers or parent breeders; and, lastly, 5) meat production poultry.

12. Several issues which must be resolved before deciding to use AI vaccines: 1) the vaccine strain must be of the same hemagglutinin subtype and be shown in animal studies to be protective against the circulating field virus, 2) standardized manufacturing of vaccines must be followed to produce consistent and efficacious vaccines, 3) policies must be established for proper storage, distribution and administration of the vaccine; 4) adequate serological or virological surveillance must be done to determine whether the field virus is circulating in vaccinated flocks; and 5) an exit strategy must be developed to prevent permanent use of vaccine. In addition, for inactivated whole AI vaccines, the following should be addressed: 1) the need for adequate AI viral antigen content to elicit a protective immune response, either by establishing a minimum hemagglutinin protein content in the vaccine (e.g. minimum of 1-5 micrograms/dose if using generic adjuvant system, less antigen is needed if a proprietary systems gives higher titers) or by demonstration of a high level of protection as measured by _in vivo_ challenge studies or the presence of a minimal hemagglutination inhibition (HI) antibody titer in vaccinated birds (e.g. minimum of 1:32-1:40 HI test); 2) the need for a good oil emulsion adjuvant system; and 3) the establishment of a high level of biosecurity practice for vaccination crews that enter farms to prevent accidental spreading of field virus. If using recombinant fowlpox vaccine, the vaccine should only be administered to one day-old chickens in hatchery, which will give good protection, improved biosecurity and a high degree of quality control. Before new vaccine technologies should be used in the field, assessment of safety in target species, environmental impact to non-target species, purity and efficacy must be demonstrated.

13. Surveillance must be conducted on vaccinated flocks to determine whether the field virus is circulating and the control strategy is working. This should be done by both serological and virological surveillance of vaccinated and non-vaccinated flocks. For serological surveillance, several methods can be used to identify infections by field virus in vaccinated populations: 1) placement of unvaccinated sentinel birds and looking for antibodies against AI viruses, such as in ducks, 2) if using inactivated vaccine, looking for specific antibodies against the neuraminidase of the circulating field virus in vaccinated birds (if using an inactivated vaccine strain with a different neuraminidase subtype than the circulating field virus (Capua et al., 2003)) or looking for antibodies against the non-structural protein (Tumpey et al., 2005), or 3) if using recombinant fowlpox vaccine, looking for antibodies to nucleoprotein/matrix protein. For virological surveillance, examination for specific AI viral nucleic acids or proteins, or isolation of the virus, could be used to determine whether the field virus is circulating. This is best done on sentinel birds that are showing clinical signs or who die. Alternatively, examination of dead poultry from vaccinated populations will give an indication of whether the field virus is circulating.

14. Recently, 2 new vaccines for use in China have been reported (ProMED 20050207.0415 and 20050210.0456): 1) recombinant fowlpox-H5N1 AI vaccine, and 2) a reverse genetic produced influenza A inactivated vaccine. The new recombinant fowlpox vaccine is a live, injectable vaccine for chickens and uses the same technology as the previously licensed recombinant-fowlpox-virus-AI-H5 vaccine (cDNA copy of the AI hemagglutinin gene from A/turkey/Ireland/83 (H5N8)), but includes inserted cDNA copies of AI hemagglutinin (H5) and neuraminidase (N1) genes (both from A/goose/Guangdong/3/96 (H5N1)) (Qiao et al., 2003). This type of vaccine can only be used in one-day-old chickens and not in older birds in which immunity to fowlpox virus will inhibit replication of the vaccine virus and prevent development of effective immunity (Swayne et al., 2000a). The other new vaccine is a traditional inactivated oil emulsion AI vaccine, but unlike current inactivated AI vaccines, the new vaccine virus is not an H5 LP or HPAI field virus. The vaccine virus was produced by reverse genetics using the 6 internal genes from a human influenza vaccine strain (PR8) and the hemagglutinin and neuraminidase genes from A/goose/Guangdong/3/96 (H5N1) AI virus. The use of PR8 internal genes imparts the characteristic of growth to high virus content in embryonating chicken eggs used in the manufacturing process and thus produces a high concentration of the protective hemagglutinin protein in the vaccine. Another change in the vaccine virus: the portion of the gene that codes the hemagglutinin proteolytic cleavage site has been changed from a sequence of an HP to an LPAI virus, thus, the vaccine virus is a LPAI virus and can be manufactured at a lower level of biosafety. Both vaccines require handling and injection of individual birds. Data published or presented at scientific meetings indicate that these new vaccines are as efficacious as the existing licensed vaccines, but no data have been presented to demonstrate they provide superior protection."

National and international control policy

The virulent form of avian influenza (fowl plague) is included in the OIE (World Organisation for Animal Health) list of notifiable diseases, which means that outbreaks are notifiable to the OIE and restrictions to movement of birds and poultry products are enforced.

Many countries have regulations aimed at preventing avian influenza, which involve trade embargoes on importation of birds and avian products from countries not declared highly pathogenic avian influenza (HPAI) -free. HPAI virus is considered an exotic pathogen in most European countries, the USA and Australia. Exotic outbreaks of HPAI are eradicated by implementing an intensive programme comprising rapid diagnosis, slaughter and disposal of affected flocks, quarantine of the affected area and concurrent surveillance with disposal of flocks with positive antibody titres to avian influenza. Restrictions on movement of flocks and poultry products from infected areas are imposed.

Farm-level control

It is important to have adequate biosecurity to prevent AI introduction from other poultry flocks. Preventing direct contact with wild and migratory birds that may carry the virus, and protecting domestic poultry from contact with the faeces of wild birds are also ways of preventing avian influenza. Implementation of strict biosecurity measures at the local farm level can limit dissemination of avian influenza virus. However, the prevention of avian influenza in developing countries is extremely difficult because feed is delivered in bags, and because small-scale producers distribute eggs and live broilers through dealers to regional markets.

Cleaning and disinfection

The virus remains viable for a long time in tissues and faeces. Effective disinfection procedures involve complete removal of all organic material because influenza viruses are well protected from inactivation in such material. Disinfectants of many types (glutaraldehyde plus formaldehyde; glutaraldehyde and quaternary ammonium salts; chlorocresols; oxidising disinfectants; iodophores; quaternary ammonium salts) are effective against influenza virus. However, professional advice should be sought as these differ with respect to efficacy in the presence of organic matter and in relation to low temperatures.