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Avian Influenza

Avian influenza (AI) is one of the biggest concerns in the poultry industry today. While not as widespread as some other pathogens, AI outbreaks have occurred in many parts of the world, causing devastating losses from the rapid spread and exceptionally high death rates of the "high-pathogenic" (HP) forms of the virus. The potential economic "ripple effect" of trade restrictions, food shortages, industry job loss, and reduced consumer confidence necessitates a strong focus on AI control measures.


The term "avian influenza" encompasses numerous viruses that infect domestic poultry as well as other species and are broadly divided into two sub-types based on virulence:


  • High-pathogenic (HP) forms, which most notably include many (but not all) of the H5 and H7 strains, cause severe systemic disease that can wipe out entire flocks within days (some strains may cause low pathogenic disease but carry the risk of viral mutation to high pathogenicity)
  • Low-pathogenic (LP) forms, including mostly H9N2  strains, have much milder effects but still adversely affect productivity, especially in combination with other pathogens, such as the infectious bronchitis virus, E. coli bacteria, etc., which may lead to what is known as the “respiratory complex”.


   Some AI virus strains have infected humans, causing illness and even death and raising understandable public health concerns. While such zoonotic infections are rare, they further underscore the need for industry action.


Disease Management Approaches


Vaccination has become increasingly important in avian influenza control, but is only one tool in what must be a multi-pronged approach. AI strains spread quickly, and while vaccines can prevent infection and reduce viral shed, they must be used in conjunction with strong biosecurity and sanitation both during and after outbreaks. Accurate strain diagnosis is necessary to identify appropriate vaccines, and it's critical to continue monitoring status of vaccinated flocks as well as wider epidemiologic conditions.


Controlling High-Pathogenic AI


HP AI is one of the only avian diseases designated "List A" by the World Organisation for Animal Health (OIE) for its "serious socio-economic or public health consequence," and outbreaks can trigger international trade restrictions. To date, most mature poultry markets follow the OIE's "stamping out" policies, culling infected and adjacent flocks to contain the disease.


In less established markets, however, widespread culling is simply not economically viable, as the local industry cannot sustain such losses. Vaccines offer an alternative approach, and for safety purposes inactivated and vector vaccines are most widely used. But for several reasons, implementing HP AI vaccination programs can be more complex than for other avian diseases:


  • Tremendous AI strain diversity, requiring multiple unique vaccines (sometimes custom-made) and strong diagnostic tools
  • The "moving target" of constant overall strain evolution, and risk of antigenic drift or shift mutation
  • Varying country regulations, some of which prohibit importation of live vaccines or allow only local vaccine production

All continents are potential AI targets, and outbreaks have been described in most parts of the world. Some territories may suffer from enzootic conditions with more persistent risk of outbreak. Global vigilance by industry, agricultural authorities, and other stakeholders is crucial.

See the OIE’s web page on current HP AI outbreaks


Considerations for Low-Pathogenic AI


The LP forms of AI don't get as much public, media, or regulatory attention, but the strains are actually far more widespread both geographically and in number of birds affected—for example, currently the most common LP strain, H9N2, is circulating in a large swathe of countries in Africa and Asia. The LP strains cause respiratory disease that is aggravated by the presence of other pathogens and reduces bird productivity. But perhaps most importantly, H5 and H7 strains can mutate to the far more virulent HP forms, so controlling their spread through vaccination is still a high priority.


Merial’s Solutions**


 In the highly complex environment of AI management, Merial is an industry leader, providing effective vaccines for the most common strains in approved markets** along with tools for building strong control strategies. Currently our AI solutions include:


  • TROVAC AIV H5, a vector vaccine (available in some markets**) that uses the fowl pox virus as a vector to carry protection against the H5 strains of AI
  • GALLIMUNE Flu and FLUVAC ranges, our lines of inactivated vaccines (available in some markets**), include various AI products for the high-pathogenic H5 and H7 strains as well as the low-pathogenic H9N2 strain (some in combination with other diseases)


 Brand and product availability vary across markets, but we are always evolving our offerings to address new needs. Merial maintains an active presence in the regions most affected by avian influenza. Our teams keep a close watch on the wider epidemiologic landscape, local regulations, and changing policies to help guide our R&D efforts and fast-track approval of urgent priorities.

 Our customer solutions also include the expertise of our Veterinary Services teams, who provide diagnostic and monitoring tools and knowledge to identify AI threats and develop a plan of action. And Merial's Vaccination Technologies & Services (VTS) group delivers comprehensive on-site support, including audits and consulting to optimize biosecurity and hygiene practices.


More About Avian Influenza*


 Outbreaks of avian influenza date back to the 1870s, and the disease was historically called "fowl plague." In the 1950s it was discovered to be caused by a type A influenza virus, and the term avian influenza (or more informally, "bird flu") came into common usage. With the growth of the global poultry population in the 1990s, prevalence of the AI virus has increased worldwide.


The virus is categorized into high-pathogenic (HP) and low-pathogenic (LP) forms, and these are grouped into sub-types based on molecular characteristics designated with "H" (1-16) and N (1-9). Most AI sub-types are LP, but the H5 and H7 strains in particular are highly pathogenic to chickens, turkeys, and some other domestic birds. The virus is shed through birds' feces and respiratory secretions, and while not airborne, spreads rapidly through contact in the physical environment.


Clinical signs vary by sub-type. LP strains may cause sub-clinical infection, mild respiratory symptoms (coughing, sneezing, sinusitis, etc.), and/or drops in egg production. Both morbidity and mortality tends to be low, but co-infection with other respiratory pathogens exacerbate the disease.


HP strains cause severe systemic disease with extremely high mortality, up to 100% within days. Death may be sudden, with no prior clinical signs, but some symptoms may be seen in advance, including:


  • Lethargy and loss of appetite
  • Drops in egg production
  • Facial swelling
  • Eye and nose discharge
  • Diarrhea (often greenish)


Diagnostic tools can help differentiate the virus from other respiratory diseases with similar symptoms, but often sudden death is the characteristic sign of AI.


*  Merial produces and markets several vaccines against avian influenza. However, be aware that NOT all aspects of the disease mentioned on this page are addressed by a vaccine. Always consult the product label for exact vaccine indications.

** Many of Merial’s avian vaccines are only marketed and available in certain countries, sometimes under different trade names. Speak to your Merial representative or contact us to find out what’s available in your region.


To find out exactly which Merial avian products and vaccination equipment options are available in your region, talk to your Merial representative or contact us now.

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