PSA members can view Dr. Spackman’s full presentation here.
As highly pathogenic avian influenza virus (HPAIV) continues to spread, gaining a better understanding of transmission remains a key component to preventing the virus. PSA recently hosted Dr. Erica Spackman, Distinguished Senior Research Scientist with the Exotic and Emerging Avian Viral Diseases Research unit at the U.S. National Poultry Research Center, USDA-Agricultural Research Service, on a webinar to discuss the latest on what it known.
Typically, farm-to-farm transmission or how the virus is entering the premises is first considered, but Dr. Spackman says another aspect that should be considered is what is occurring at the host level.
As a virus family, Dr. Spackman explains that Influenza A has a wide range of hosts and is often coined the “promiscuous virus.” She notes, “If you throw enough virus at a species, it will be infected at some point. It’s what happens after infection that matters.”
What’s important to note about avian influenza, she says, is that individual strains will adapt to the host species through the process of circulating in that host.
“Flu is very sneaky. It knows every way to mutate that a virus can. A lot of times, more than one marker can confer the same adaptation, so it can be really difficult to tease out what is allowing host adaptation to occur.”
While migratory waterfowl have been identified as the species spreading the virus, Dr. Spackman said the natural host reservoir species is specifically dabbling ducks. Spillover has been occurring through other species, possibly through an environmental source rather than direct transmission.
There is also an issue with “bridge hosts” that link the reservoir to the susceptible population. Currently, domestic poultry and dairy cattle are serving as bridge hosts, although Dr. Spackman says it could be argued that dairy cattle have become reservoirs as the virus is adapting.
In the case of the H5N1, poultry are acting as a bridge host between the ducks and the people who work on the farms, are cleaning up, or are culling the infected flocks.
“It’s very situation specific, and on some levels, this does make a subtle difference in what’s happening with transmission, because this virus is well adapted and at high levels in the species for a long time.”
The current virus is also much more infectious in chicken and turkeys than it was in 2015. “It is much harder to combat this using biosecurity, because we have something that transmits way better.”
Even so, how the animal is exposed matters as research has shown that infection from intranasal inoculation is lower than if it were to occur through eating or drinking.
Airborne transmission
According to Dr. Spackman, preventing airborne transmission is hard to control and is not well understood.
Aerosols. Transmission can occur through aerosols—super small airborne particles. Dr. Spackman explains that many times, the virus will actually be covered in mucus, which protects it.
Airborne transmission can also occur directly between hosts, or when an aerosol is deposited on a surface and made airborne again somehow.
Fomites and Dander. In the case of poultry, transmission is occurring via fomites like dust, feathers, and equipment.
Particularly in growing feathers, it has been found that the growing cells inside the feather shaft are full of the virus, and the feather shaft seems to help protect it.
Research has also shown that the virus can survive in the feathers of a carcass longer than in the heart, thigh muscle and breast muscle.
Dander. Sampling has revealed dander is also playing a role A recent study from The Netherlands found waterfowl DNA at air inlets in poultry houses. If waterfowl are shedding virus with dander in it, could that possibly be getting into the poultry houses, Dr. Spackman poses.
Particularly noteworthy, Dr. Spackman says increasing humidity levels has been shown to make a big difference in lowering transmission.
PCR samplings have also revealed that the virus is not detected more than 250-300 ft from an infected poultry house. When it is detected, quantities are generally low.
Critters on infected farms
While there is evidence of infection on farms in mice, birds such as starlings, swallows, rock pigeons, and robins—things that tend to live around the poultry houses—it is unclear whether these critters were infected from the environment or the birds, Dr. Spackman says. It is also unclear what role small animals are playing.
Some experimental work with low pathogenic avian influenza has also been done in skunks, rabbits and raccoons. Findings showed infection could occur, but that virus shed varied.
Research on house flies and blowflies with the virus found they are picking it up from the environment through ingestion. However, the virus does not replicate in the gut and dies quickly, usually within 24-48 hours.
Virus in the environment
Soil and sediment. Sandy material does not appear to transmit the virus well, but it does appear birds can get it from denser material.
Feed. Dr. Spackman says this comes up a lot in relation to animal disease transmission, but different studies have shown there is no evidence this is occurring for HPAIV in poultry. Further, one study showed the virus didn’t even survive 24 hours, she notes.
Water. Research has shown the natural environment and temperature of water allows the virus to survive months. One study done on pond water found that HPAIV was still infectious for mallard ducks as long as 226 days. All of the samples where the virus persisted were in colder waters.
Manure. Temperature matters, but there are a lot of variables. For the most part, the virus was short lived in manure. Porous material, in general, does not transmit the virus well, Dr. Spackman explains.
Spread more limited
Dr. Spackman says that while there is currently more focus on what is being done wrong, farm-to-farm spread during this outbreak has been much more limited than in the past. Additionally, vaccination, if applied correctly, is an important tool as it is known to halt transmission and preserve production.
Key takeaways
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Flu infects lots of species, but everything varies by dose, host, strain, and other factors.
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Transmission can occur by many routes. Location, location, location is key.
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In different situations, different factors will matter, including sanitation, hygiene, visitor control, and farm maintenance.
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Are critters carrying the virus or are they just mechanical vectors?
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Vaccination does halt transmission and preserve production.
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Increasing humidity levels makes a big difference in lowering transmission.
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Virus is not detected more than 250-300 ft from an infected poultry house.
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Hard to separate transmission route in small geographical routes.
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Experience is providing the most information.
PSA members can view Dr. Spackman’s full presentation here. The entire library of past PSA webinars can also be accessed here.