Study finds H7N8 infection dynamics different for turkeys
A series of tests with low-pathogenic and highly pathogenic strains of H7N8 avian flu involved in Indiana poultry farm outbreaks in 2016 found that turkeys are highly susceptible and show different symptoms than infected chickens do. Researchers from the US Department of Agriculture's (USDA's) Southeast Poultry Research Laboratory reported their findings yesterday in PLoS One.
In January 2016, highly pathogenic H7N8 was detected on an Indiana turkey farm, followed by nine more outbreaks at nearby turkey farms that involved the low-pathogenic form of the virus. Genetic testing has shown that both viruses are similar to a low-pathogenic H7N8 detected in wild ducks. To better gauge the risk to poultry, the USDA researchers used both strains to assess infectious dose, shedding, clinical illness, and transmissibility in chickens, turkeys, and mallards.
The lowest mean infectious dose for both virus types was seen in turkeys, and only turkeys showed clinical signs when infected with the low-pathogenic virus. Highly pathogenic H7N8 was deadly for both chickens and turkeys, but clinical signs were different: neurologic symptoms were observed only in turkeys. Also, turkeys had respiratory symptoms after infection with the low-pathogenic virus.
Mallards could be infected by and were able to transmit both viruses, but they didn't show clinical signs. Another key finding was that the mallards were able to contract the virus from chickens.
The mean death time for turkeys infected with H7N8 was shorter than for the highly pathogenic H5N2 virus that struck Midwestern states in 2015, which could mean that H7N8 outbreaks could be easier to control, since the events would be recognized earlier. However, both H7N8 viruses had mean infectious doses that were lower than H5N2 and were more transmissible among turkeys.
Researchers said Indiana's rapid depopulation of infected turkey flocks likely played a major role in limiting the outbreaks, and the lower infectious dose in turkeys and epidemiologic links between turkey farms probably limited the outbreak to turkeys.
May 8 PLoS One abstract
China reports more high-path H7N9 outbreaks in poultry
In the latest avian flu outbreak developments, China reported more highly pathogenic H7N9 detections at live-poultry markets and farms, and Bulgaria reported one more H5N8 outbreak in wild birds, according to the latest notifications from the World Organization for Animal Health (OIE).
China, which reported the highly pathogenic form of H7N9 for the first time in February, noted more outbreaks that occurred from Feb 23 to Apr 28 in three provinces: Hunan in the south-central region, Guangdong in the south, and Hebei in the north.
The Hunan province events began toward the end of February in Chenzhou, striking backyard birds and a livestock market. Guangdong province reported three livestock market detections in three different cities in early March, and Hebei province reported an outbreak that began on Apr 28 at a layer farm that killed 5,000 birds and led to the culling of 25,000.