What do we know about the bird flu infecting US farms?

Bird flu has been infecting poultry farms in the West and Midwest. With large scale chicken farms affected and increasing numbers of birds being destroyed to contain the spread, GENeS has reached out to experts to find out what we know about current strains of the virus.


Dr. Rodrigo Gallardo, Assistant Professor of Population Health & Reproduction, University of California, Davis (webpage):

Expertise: avian virology, specifically in RNA viruses and their capabilities of mutation, recombination and variation.

“We don’t know as much as we would like about the H5N2 virus currently affecting the U.S. poultry industry, but the USDA Southeast Poultry Research Laboratory did some preliminary characterizations of H5N8 and H5N2 in chickens, turkeys and ducks. These two viruses that have been detected in the Pacific flyway and H5N2 in the Mississippi and Central flyways, as well as in the commercial poultry industry. Infection in the domestic poultry industry has been for the most part H5N2, though H5N8 has also been detected in wild birds in the US, and in two commercial farms in California.

“USDA traced back these viruses to other isolations of highly pathogenic avian influenza (HPAI). They concluded that a virus isolated in China in 1996 developed into the H5N8 strain which subsequently got mixed with North American avian influenza viruses – H*N2 – and that genetic reassortment produced the H5N2 that is affecting the poultry industry in the U.S.

“When characterizing the H5N2 and H5N8 viruses in chickens and turkeys, USDA investigators saw that the dose of the virus that was needed to produce disease in poultry was greater than common HPAI viruses, and that in experimental conditions the viruses were not easily transmitted from infected to contact birds. Also, common HPAI viruses kill chickens in approximately three days, but these viruses cause mortality after approximately nine days.

“USDA investigators also infected ducks and tested transmissibility, finding that transmission was easy between Mallard ducks, without causing disease, and we know that waterfowl have been linked to these outbreaks. We don’t know too much about the route of transmission between wild and domestic birds because it’s been so recent that there hasn’t been enough time to research the ecology/epidemiology of the virus. There is no information about the role of non-migrant waterfowl, which could be carriers.

“Although these viruses are experimentally not as pathogenic in commercial poultry species as other HPAI viruses, they still induce a huge concern because they are exotic diseases causing severe economic losses to the industry and the country. In the US we have one of the best surveillance systems in the world. Whenever these viruses are detected, the authorities USDA/APHIS take over performing quarantines and depopulating flocks in order to eradicate the disease. The action the country has taken is the appropriate including surveillance, biosecurity and eradication in the face of an avian influenza detection.”


Dr. Daniel R. Perez, Georgia Research Alliance Distinguished Investigator and Caswell S Eidson Chair in Poultry Medicine, University of Georgia (webpage):

Expertise: pathogenesis and transmission of influenza viruses, developing approaches for in vivo reverse genetics, live attenuated vaccines and testing of alternative antivirals.

“I trust the biosecurity efforts that take place in commercial US poultry operations. Knowing that the virus is spreading at a unexpected rate, I would expect that biosecurity controls, prevention and diagnostic efforts to be re-emphasize. I would also anticipate that, if deficiencies are found, then improvements will be made. 

“I think it is important to separate the actual number of infected birds versus the number of infected flocks. Culling is an effort to curtail virus spread. If effective, I would not anticipate major evolutionary pressure on the current virus. If the virus were to persist in some wild animal population, then we may end up having the risk of the virus to return to poultry and, perhaps, with some alterations. However, this is all new and the US has been fairly effective at keeping avian flu away from poultry, I do not have a reason to think that we will fail in this instance.”


Dr. Jürgen A. Richt, Regents Distinguished Professor & KBA Eminent Scholar, Kansas State University (webpage):

Expertise: diagnosing and treating zoonotic diseases; emerging diseases of livestock focusing mainly on viral and prion diseases; influenza viruses, especially swine and avian influenza viruses.

“The H5N2 virus is highly pathogenic to domesticated poultry; to turkey, pheasants and chickens. It is most likely that wild birds picked up this virus along migratory pathways on the Pacific flyway. Infected wild birds then probably came through Canada and into the West of the USA and the first isolates of H5N2 were made in the state of Washington.

“The virulence of the older H5N1 avian flu virus varied in wild birds, and the same is likely to be true of H5N2. In some duck species the viruses are virulent, in others they are not so virulent. If the virus replicates in the GI tract and doesn’t kill them, the birds carry the virus around with them. If there are not very good biosecurity measures in poultry farms the wild birds could mingle and contaminate domesticated birds, for which the viruses are deadly.

“One of the questions is whether avian-like influenza viruses have a tendency to mutate and become mammalian-like. This is something we need to avoid; it is something that could happen and which we have to look for. We also need to look at whether the viruses mutate when they come from a wild host into domesticated poultry host and what the genetic consequences of this transmission are. That’s why USDA and others are sequencing these viruses and analyze their genomes in detail.

“There is not much published yet about the North American H5N2 viruses. The big question mark is over the pathogenicity of the virus for mammalian species. I have not seen any studies done with the virus in mammalian models, and these studies need to be done. Only from studies in non-human primates and ferrets, which are surrogate models for humans, can we make a full risk assessment about whether this virus might be dangerous to human health.

“We have seen that some of these highly pathogenic influenza viruses, such as H7 or H5, have the ability to replicate in humans and cause disease, so we have to be careful. I would think they could potentially be human pathogens but the studies have to be done in surrogate models first.”


Declared interests (see GENeS register of interests policy):

No interests declared

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