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Bird Flu and Chickens

A couple of weeks ago, I wrote a post on factors, such as bird flu, affecting the cost of eggs. Even as egg prices have decreased slightly where I live, HPAI still abounds. What is it? How is it spread? And are people at risk? These are just some of the questions I’ll answer as we discuss bird flu and chickens.

What is HPAI

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While there are 4 types of influenza viruses (A-D), type A viruses are the main ones identified in causing worldwide flu epidemics. Further, whereas types B, C, and D have been detected in other species, including humans, only type A has been recognized to infect birds. Also, avian influenza, a subtype of type A, is labeled as either high or low pathogenicity in relation to genetic features. Thus, HPAI, or highly pathogenic avian influenza is a severely contagious illness caused by influenza type A virus.

History of Bird Flu

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According to the CDC, bird flu was first documented in 1878 in Northern Italy. Fowl plague, its moniker, was characterized by high mortality. And by 1901, it was concluded that fowl plague was caused by a filterable virus. But it wasn’t until 1955 that fowl plague was revealed to be a type A influenza virus. Moreover, in 1981, the term fowl plague was replaced by highly pathogenic avian influenza (HPAI) at the First International Symposium on Avian Influenza.

Then, in 1996, HPAI H5N1 was first observed in domestic waterfowl in Southern China. Additionally, bird flu was subsequently detected in people in 1997, something previously not thought possible.

More recently, as of 2021-2022, a new H5N1 virus with a wild bird adapted gene popped up. Furthermore, it’s caused the biggest outbreak Europe and the US have seen to date.

How does Bird Flu Spread

black and white digital sketch of a chicken sneezing on another chicken with a sign advising them to stay 6 feet apart if ill
Digital Art, Courtesy of Sarah Smith

Given that avian flu is so infectious, how does it spread? Well, based on the USDA website, bird flu spreads directly from bird to bird. However, it can also spread indirectly by coming into contact with something that’s infected. For instance, suppose someone tracks feces from a contaminated farm back to their own farm, and then their chickens walk and peck the ground where said person tracked contaminated feces, picking up the virus. That’s just one example of how bird flu can spread to birds.

Bird flu has caused over 200 million poultry deaths in a host of countries so far.  Additionally, an unprecedented number of non-poultry birds, including wild birds, have died due to the disease. Plus, because of migration patterns of wild birds, they help the virus circulate. Thus, wild birds, rodents, and people are all possible sources of presenting the disease to domestic birds. But what about other vectors?

What are Vectors

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vector noun

2 a: an organism (such as an insect) that transmits a pathogen from one organism or source to another

“Vector.” Dictionary, Merriam-Webster, Accessed 19 Feb. 2023.

Over 2 decades ago my father-in-law was asked to assist veterinarians in Great Britain as they were dealing with foot and mouth disease. While he was there, he remarked on how there were a ton of flies on the dead and diseased cattle. He finally mentioned it to someone in charge, even asking what they were doing about the vectors. Unfortunately his observations were not well received, as he was told to keep his mouth shut.

I found this memory poignant, especially in light of all the affected birds from this latest outbreak of HPAI. What are we doing about other vectors? We’re aware of animal, human, and bird vectors that spread the disease. Though, I could only find a couple of examples online, in the US, that even hinted that flies might be vectors. However, this study done over a decade ago didn’t come right out and say that flies spread bird flu. It advised that the flies carried it in the study, so it was possible. But, more tests would be needed.

Though, in the event you want evidence that flies spread diseases, check this site out. It details HPAI outbreak in Japan during 2003-2004, and was linked to the blow fly, a relative of the common house fly. Also, according to the same study above, flies were listed as mechanical vectors. But what’s the difference between mechanical and biological vectors? And what are wild birds and mammals when they spread avian flu to chickens?

Mechanical and Biological Vectors

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Mechanical vectors, such as flies, pick up an infectious agent and physically transmit it in a passive way. And a biological vector is one in whose body the pathogen develops and multiplies before passing on to another host. Mosquitos are biological vectors for West Nile virus.

Honestly I couldn’t find what wild birds were, whether biological or mechanical. However, since we’re told that birds spread the disease from bird to bird, it would seem they are also mechanical. Although, we’re told as well that wild aquatic birds are natural reservoirs for the virus. Plus, in the intervening years we don’t see the disease before it resurfaces, and it’s mutated, indicates a biological vector is at work. Interestingly enough, birds are reservoir hosts for West Nile virus.

Wildlife, especially mammals, are reservoirs for an enormous diversity of viruses.

1Faculty of Health Sciences, Curtin University, Perth, Western Australia, Australia
2Burnet Institute, Melbourne, Australia
3CSIRO Australian Animal Health Laboratory, Private Bag 24, Geelong, Victoria 3220, Australia
John S Mackenzie: ua.ude.nitruc@eiznekcaM.J
4Address: 20A Silver Street, Malvern, Vic 3144, Australia.

And according to the CDC, aquatic birds, including shore birds and wild waterfowl like ducks are considered reservoirs, or natural hosts, for bird flu viruses.

Symptoms of H5N1 HPAI in Poultry

dead brown and red chicken on the grass

Birds infected with the virus may show one or more of the following:

  • sudden death
  • lack of energy
  • reduction in egg production
  • soft-shelled or misshapen eggs
  • swelling around head, neck, and eyes
  • purple discoloration on head and legs
  • gasping for air (difficulty breathing)
  • nasal discharge, coughing, and sneezing
  • incoordination (stumbling or falling down)
  • twisting of the head or neck
  • and/or diarrhea

What You Can Do

Biosecurity is currently the best policy if you have backyard birds. Read below for recommendations:

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  • Disinfect clothes, shoes, egg trays, vehicles, crates, etc.
  • Don’t expose cleaned and disinfected tools and equipment to wild birds.
  • Wash hands and shoes before and after entering chicken yard (area).
  • Buy birds from reputable sources; and isolate for at least 30 days to observe for any signs of illness before mixing with the rest of your flock.
  • Restrict visitors on and off of your property, especially from having contact with your flock.
  • Don’t visit other poultry farms, and avoid visitors that have poultry.
  • Keep wild birds and rodents out of the coop and poultry areas.
  • Don’t let your birds have contact with migratory waterfowl or other wild birds.
  • Secure feed and water to guard against contamination.
  • And have a written biosecurity plan.
  • Finally, if you’re working around sick birds, wear PPE; and visit the CDC site for more info.

In the past, simply culling birds and the heat from summer seemed to keep the virus in check. However, with this latest outbreak, it hung around. And now, some countries are even considering poultry vaccines for H5N1. It’s a measure of desperation. Costs and the need to have a vaccine for all of the strains are just a couple of reasons vaccines haven’t been used before.

Are People at Risk

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Poultry and wild birds aren’t the only animals being affected by avian flu since 2021. Thus far, several mammals in both Europe and the US have been infected by H5N1. Red fox, opossum, raccoons, a coyote, striped skunks, harbor and grey seals, a bottlenose dolphin, a fisher, 3 types of bears, a mountain lion, a bobcat, an Amur tiger and an Amur leopard all have been found positive for the H5N1 virus in the US.

Likewise, seals in Scotland, sea lions in Peru, and lastly, mink in Spain have also been identified with the virus. Given that mink seemed to pass the virus between themselves gave virologists concern. Furthermore, past studies have revealed mink to be vulnerable to avian and human influenza A viruses.

The high seroprevalence of combined avian and human influenza viruses suggests a strong likelihood of co-infections and thus farmed mink could serve as “mixing vessels”…. 

aKey Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing, People’s Republic of China
bDepartment of Biostatistics, University of Michigan, Ann Arbor, Michigan, USA
cChinese Academy of Sciences (CAS) Key Laboratory of Pathogenic Microbiology and Immunology, Center for Influenza Research and Early-Warning (CASCIRE), Institute of Microbiology, Beijing, People’s Republic of China
dSchool of Public Health (Shenzhen), Sun Yat-sen University, Guangdong, People’s Republic of China
eSchool of Veterinary Medicine and Science, University of Nottingham, Nottingham, UK
CONTACT Jinhua Liu nc.ude.uac@hjl
*Honglei Sun and Fangtao Li contributed equally to this work.

Nevertheless, the CDC advised that humans lack the type of cell receptor in the upper respiratory tract that H5N1 viruses use to cause the disease. Plus, according to WHO, this current strain of H5N1 has caused less than 10 infections worldwide. And only 1 was in the US. In addition, it mainly affects those who have close contact with sick birds. Moreover, there have been no known human-to-human transmissions of the H5N1 virus that’s presently spreading globally among birds.

In Summary

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Bird flu has been around a long time. And each time it returns, it’s changed a little bit more. Further, there are a number of ways bird flu can spread to poultry. Additionally, even though it’s been identified in some mammals, the threat to humans is still considered low.

However, if you see any of the symptoms listed above in your birds, you are encouraged to contact your agricultural extension office/agent, local veterinarian, local animal health diagnostic laboratory, or the State veterinarian; or call USDA toll free at 1-866-536-7593.

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