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An update on avian flu in the United States

November 9, 2015

For many years, we have heard about avian and other types of flu outbreaks across the globe. Unlike strains that infect land animals, bird or avian flu has the ability to spread over long distances, making detection and eradication of these viruses difficult.


Highly pathogenic flu strains detected in commercial hens and turkeys

For many years, we have heard about avian and other types of flu outbreaks across the globe. Unlike strains that infect land animals, bird or avian flu has the ability to spread over long distances, making detection and eradication of these viruses difficult. Each year, scientists at the U.S. Centers for Disease Control and Prevention (CDC) formulate a flu vaccine for public inoculations. The developed serum is based on the flu strains that are considered most likely to be contagious to humans in the coming year. While some years the inoculations are less effective than in other years, they have prevented widespread flu pandemics.

To gather the necessary information, researchers monitor and test migrating birds for flu strain infection. In fact, millions of tests on migrating birds were completed prior to 2015 without a single positive avian flu virus detected in the United States.

Flu strain naming conventions

  • What’s with HxNy? Flu strains are classified as A, B or C – with A and B being responsible for the seasonal flu epidemics each winter in North America. (Type C strains are very mild and typically do not cause influenza.)
  • Type A strains are subgrouped by the presence of two proteins on the surface of the virus – hemagglutinin (H) and neuraminidase (N). There are 18 different H subtypes and 11 different N subtypes. So, when scientists refer to H1N1, they are referring to a Type A influenza virus with the subtype 1 proteins of both H and N. While it remains a bit of a mystery for the general public, such nomenclatures help scientists differentiate between strains.

In January 2015, something changed. Highly pathogenic sub-strains of H5N1, H5N2 and H5N8 were detected in 14 commercial hens and turkeys. These were the first reported infections of these sub-strains originating in U.S. birds. The infections may have been caused by migrating birds crossing from Asia across Canada into the Midwestern United States, home to most of the U.S.’s commercial poultry farms. Feces from infected birds spread the virus. Despite stringent biosecurity controls to prevent the transmission of viruses, these sub-strains are highly pathogenic and the slightest lapse in biosecurity can result in widespread infection. In the case of these viruses, a single infected hen can wipe out the entire population within one or two days.

Since being detected, the three sub-strains have spread to poultry farms in more than 12 U.S. states. Subsequently, the CDC and the United States Department of Agriculture (USDA) required farmers to cull more than 40 million birds, resulting in increased retail egg prices and a possible shortage of turkeys for holiday dinners.

The CDC and USDA remain concerned that fall migrations could further spread the virus to Mid-Atlantic States where the U.S. broiler chicken industry is located. The broiler industry farms are taking extra precautions to help prevent viral spread to their business. If these farms are infected, the U.S. could see a shortage of broiler chickens in grocery stores and restaurants, in addition to a shortage of turkeys.

From a human transmission standpoint, none of these viruses have infected humans in the United States, but concerns remain. The highly pathogenic avian strain could mutate with other avian flu viruses to create a new strain, which could potentially infect humans and lead to a new flu pandemic. Currently, the CDC is working to create a vaccine to prevent a human pandemic. In the interim, aside from biosecurity controls being followed by the affected poultry industries, individuals should avoid close and prolonged contact with wild birds, including ducks, geese, osprey and others.

1963 2003 2009 2011 2012 2014

H7N3 infects poultry in the United Kingdom


H5N1, common in domestic poultry in Asia and the Middle East, infects 650 people in 15 countries


H1N1, or “swine flu” spreads from pigs to humans, causing a worldwide pandemic


H9N2 infects land-based birds and a small number of people in Southeast Asia


H1N2 causes a small number of human infections in the United States


H10N8, known to infect only wild and domestic birds, is detected in a Chinese woman


H7N7, which infects chickens, discovered accidentally while researching H7N9, a strain that killed 40 people in China


H3N2 causes 296 human infections in the United States after having close contact with pigs


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