The past few weeks have been busy with a surge in avian influenza activity. According to the World Health Organization (WHO
), the most concerning of the avian influenza strains, are subtypes A(H5N1), A(H7N9), and A(H9N2).
In past cases and outbreaks of avian influenza, interaction and direct contact with infected animals and contaminated environments were key modes of transmission. While transmission between humans has been limited and considered inefficient, public health officials still worry about healthcare-associated cases due to invasive medical care and prolonged close contact. The world of avian influenza has seen two recent updates in the past week in countries literally a world apart: a recent surge of cases in China and an outbreak among birds at a poultry farm in Tennessee.
WHO released their most recent situation update
on avian influenza and human interaction in China on February 27, 2017. A recent investigation into two human A(H7N9) cases found that the individuals had prevalent exposure to both sick and dead poultry. At the time of the report, none of the 105 close contacts of the individuals (who are under monitoring) had developed symptoms.
WHO reported that genetic sequencing of the cases found “changes at the cleavage site of the hemagglutinin (HA) gene suggestive of being highly pathogenic to poultry.” The genetic sequencing analysis points to the evolving nature of the virus; however, it has not changed the risk for human-to-human transmission. As WHO noted, “there is no evidence that a change in the virus from low pathogenic to high pathogenic avian influenza virus has an impact on the pathogenicity or transmissibility in humans.”
Despite this change, WHO stated that the likelihood of community-level spread, or epidemic levels, remains low. Surveillance and control efforts at the animal level may be challenged due to this viral change; however, WHO feels confident that the risk for an epidemic is minimal.
The CDC also released an update in their Morbidity and Mortality Weekly Report
regarding human A(H7N9) cases
, which included an overview of the annual epidemics in China since 2013. The CDC's comments mirror those of WHO in terms of the perceived low risk to the public; however, they did note that of all the 12 novel influenza A viruses assessed in their Influenza Risk Assessment Tool, A(H7N9) viruses have the highest risk score and a moderate-high potential pandemic risk.
Following the WHO news release, it was announced last week that the US Department of Agriculture (USDA) had confirmed an outbreak of highly pathogenic H7 avian influenza (HPAI) in a commercial poultry farm in Tennessee. The chicken breeder in which the infected birds were found is a contracted farmer with Tyson Food Inc
., which is the biggest chicken meat producer in the United States. Although there is no reported risk for transmission of contaminated chicken meat, public health officials are reporting that 73,500 birds will be culled to help stop the spread of infection.
Tyson released a statement
on March 5, 2017 regarding the case, noting that “all flocks located within a six-mile radius of the farm will be tested and will not be transported unless they test negative for the virus.”
The outbreak was first identified when 700 birds died and public health officials were first notified of an outbreak around March 1, 2017. The USDA’s Animal and Plant Inspection Services is currently awaiting additional testing to identify the extract strain of HPAI in the birds.
Additional testing, surveillance, and precautions are ongoing, but this is yet another outbreak of a disease which has resulted in the culling of over 48 million chickens and turkey since late 2014.
: WHO’s recent updated press release
has reported an additional 28 cases of A(H7N9) in China, which has brought the total case counts to 1421 laboratory-confirmed cases since 2013. WHO is advising travelers to countries with reported outbreaks to avoid poultry farms and areas where poultry may be slaughtered. Ongoing surveillance is encouraged; however, WHO is not advising special screening at ports of entry since human cases of A(H7N9) still remain unusual.