33.5 million birds and rising, why is avian flu so hard to stop?

Avian flu has been confirmed on poultry farms in fifteen U.S.  states, with over 33.5 million birds infected and numbers continuing to rise. Destroying infected flocks to eradicate the highly pathogenic viruses presents a significant biosecurity challenge, and researchers are scrambling to understand how the viruses move between wild species and domestic birds.

Building on previous comments gathered by GENeS, we asked researchers for comments on why the outbreak is proving hard to control, and how infected flocks can be disposed of safely. New comments may be added to this page as they come in.


Dr. Carol Cardona, Pomeroy Endowed Chair, Veterinary Biomedical Sciences Department, University of Minnesota (webpage):

Expertise: avian influenza and other viral diseases in poultry; viral and host factors that determine transmissibility and viral adaptation. Dr Cardona holds the only endowed chair in avian medicine in the U.S. 

“One of the things making the outbreak so difficult to contain is that, like all highly pathogenic avian influenza (HPAI) viruses, the virus replicates to high levels within the host. If you think about a disinfectant like a hand sanitizer that kills 99.99% of bacteria, some of these birds have such high levels of virus – we’re talking about 1010, 1012, 1012 – killing 99.99% still leaves you with a huge amount. Our poultry producers are used to dealing very well with low pathogenicity viruses, but those don’t replicate to a high level. So adjusting to that presents an incredible challenge.

“This is the first time we’ve had a Eurasian virus outbreak in North America, and all the way along it has been unusual. It’s different from other viruses in the way it’s been able to adapt and move within species, and it has a lot of surprises up its sleeve. The fact that H5N8 was found in Indiana is a very strong indication that it’s coming from wild birds. But despite looking, it has so far been found very rarely in the wild. Where it is coming from remains a big question.

“The process of looking for viruses in wildfowl usually coincides with hunting season, when hunters kill the birds and samples can be collected and tested. For the most part that’s not happening now. To get the broader picture requires things like trapping and capturing birds, picking up environmental samples, and coordinating with banding efforts. Looking in blood for antibodies would indicate which birds had the virus and would give a broader picture of all the species involved. Which ones have been involved in the movement of the virus to the different locations it’s appearing in? Which ones are involved in spreading it to farms or to amplifying it? We really have very little information about that.

“There has been some overestimation of the role of warm weather in putting an end to the outbreak. In Minnesota, when we have had spring introductions of influenza in the past, their endpoint has been around the middle of May. That means the ending of viruses coming from wild birds into turkey flocks, which is not the same thing as the end of an outbreak. Contamination can still occur between farms.Heating up will definitely kill the virus in the environment but in Minnesota that type of weather won’t typically happen until mid July. The weather is going to help but it’s not a silver bullet. If transmission is happening from farm to farm and the virus returns with migrating birds in the fall, could we maintain it all year round under a worst-case scenario? We probably could.”


Dr. Shafiqur Rahman, Associate Professor, Department of Agricultural and Biosystems Engineering, North Dakota State University (webpage):

Expertise: environmentally friendly animal waste management; livestock and poultry carcass composting.

“There are several options for disposing livestock and poultry mortalities, including rendering, incineration, alkaline hydrolysis, burial and composting. Each option has a set of advantages and disadvantages, however composting is recognized as an effective method of disposal by the USDA-APHIS to manage emergency management of mortalities like avian influenza (AI).

“Composting is the preferred method of carcass disposal since it can be implemented rapidly on farms at minimum cost. Composting can be done in-house or offsite, but it is a preferred option to do in-house composting of AI infected birds to minimize environmental concerns (e.g., groundwater and air pollution), disease transmission especially airborne disease, and to avoid public nuisance. If it is not possible to do in-house composting, on-farm outside composting is allowed, provided the composting site is suitable for constructing large amounts of windrows, and runoff and leachate from the composting pile is not causing any surface water pollution or environmental concerns.

“Once killed, birds need to be disposed of quickly. To kill AI virus, it is important to maintain a sustainable temperature of >131 Fahrenheit for at least 3-5 days. A properly constructed composting pile can generate temperatures ranging from 130-155 Fahrenheit within 48-72 hours of construction.  At that temperature, AI virus may be killed, but composting is not complete. In the case of in-house composting, it is recommended to keep the pile at least 2-3 weeks before turning. It may take months for bones to decompose, but once finished the compost can be used as a green fertilizer.”


Dr. Henry Wan, Associate Professor in Systems Biology, Mississippi State University (webpage):

Expertise: Genomic dynamics, evolution and ecology of influenza A viruses

“The highly pathogenic avian influenza viruses that are causing outbreaks in North America are genetic reassortant viruses between the ‘Gs/Gd-like’* H5N1 virus from Eurasia and low pathogenic avian influenza viruses from North America. Reassortant viruses arise when genetic materials from two different viruses intermix. This can happen when an animal is co-infected with two viruses.

“These outbreaks have been challenging to contain for several reasons. First, during the past two decades, a large number of Gs/Gd-like H5 variants have emerged, and some of these variants have genetic material from viruses originating in domestic and/or wild birds. Many of these virus variants became panzootic – affecting animals of many species over a large geographical area – and caused outbreaks in domestic poultry across Asia, Europe, and Africa for a number of years. Second, bi-directional transmission of the virus between domestic poultry and wild birds does not seem uncommon. Last, the movements of domestic poultry or migratory waterfowl could introduce a virus variant from one region to another, and further contributing to the circulation of H5 influenza viruses and ongoing outbreaks.

“Current knowledge about the behavior of the viruses in wild host species is still limited. There are many wild host species for influenza viruses, and these species are very different from each other, just as humans are different from monkeys even though both are mammals. The same virus could be highly pathogenic to one avian species (wild or domestic) but not to another. The Gs/Gd-like H5 viruses are highly pathogenic to domestic poultry, such as turkey and chicken, but only some of these viruses cause death among ducks and geese. Such a pathogenic discrepancy could be associated with differences in the birds’ genetic backgrounds and immune systems. For example, ducks have a functional retinoic acid–inducible gene 1, but chickens do not. This gene serves as an intracellular sensor for viral replication and can activate an anti-viral response that can protect ducks against the virus.

“When a large number of birds are infected with influenza virus, the virus will reproduce and evolve very rapidly. This rapid reproduction and evolution will facilitate emergence of a virus that is more transmissible among domestic poultry.”

* A/goose/Guangdong/1/1996(H5N1)-like


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No further interests declared

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