What is avian leukosis? Is it a food safety concern?

What is avian leukosis?

Avian leukosis belongs to a family of viruses termed “retroviruses.”  It is confined to birds and cannot spread to humans or any other species.  Like all retroviruses, avian leukosis is relatively weak and does not survive well outside of the bird.  The virus impacts the bird’s immunity, and can eventually form lesions on the bird’s internal organs such as the liver or spleen.

How often does avian leukosis occur?

According to the U. S. Department of Agriculture’s (USDA) Food Safety and Inspection Service (FSIS), avian leukosis is a “rare manifestation” in broiler chickens.1  From as early as 1984, avian leukosis was present in only 0.017 percent of young chickens slaughtered.2  That number is less than 0.001% today, or one-one thousandth of one percent.

Nearly all birds are vaccinated against the sources of avian leukosis.  Along with vaccine pressure, modern breeding practices and biosecurity have effectively eliminated the virus from commercial broiler and breeder flocks.

Is avian leukosis a food safety concern? Can it make someone sick?

USDA’s FSIS and other health agencies have recognized avian leukosis “is not transmissible to humans” and “does not present a human health concern,” a fact the agency has acknowledged since at least 1997.3 The viruses that cause leukosis are species-specific and cannot be transmitted to humans.  The National Institutes of Health (NIH) has declared these viruses are not “associated with disease in adult humans.”4 Comprehensive literature reviews of the viruses that cause leukosis have also concluded that there is no apparent risk to public health.5

In the rare occurrence avian leukosis is found on a chicken liver or spleen, are the other parts of the bird, like the breast or wings, affected?

No.  In the extremely rare occasion that these lesions may occur, they are easily found on the bird’s organs, such as the liver or the spleen, and the organs are discarded.  The disease is local and not systemic, meaning it is confined to the organ and does not spread to other parts of the bird.


A Change in Regulations

In March of 2019, the National Chicken Council petitioned FSIS to vacate prior avian leukosis condemnation regulations because the disease does not impact the whole chicken – it only impacts a specific part of the chicken.  In July of 2020, because of overwhelming scientific evidence (?), FSIS granted the petition and in March 14, 2022 FSIS published a proposed rule in the Federal Register.

In August 2023, FSIS finalized the proposed rule.  It allows for the removal of extremely rare lesions suspected to be caused by avian leukosis from the bird during processing.  The rule no longer requires the whole chicken to be discarded, thus reducing food waste.  This became effective September 18, 2023.

Amending the current regulations was scientifically supported by public health and agency scientists for reasons such as:

  • Avian leukosis does not present a food-safety risk
  • Avian leukosis cannot infect humans
  • Modern understandings of the avian disease are much more advanced than when FSIS first developed its policy
  • Leukosis is not a systemic disease
  • Modern vaccination and breeding programs have all but eliminated avian leukosis

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