Release of sequences from recent swine pandemic H1N1 isolates indicates the virus is now transmitting between swine herds in the United States. The two most recent isolates had low reactor G158E, which has been found in low reactors. (Snip) that change was appended onto a sub-clade in Minnesota and Illinois, indicating the H1N1 is transmitting between swine in those two states. The swine sub-clade in MN and IL was linked to isolates frequently found in Ukraine, Russia, and Norway which also had strong associations between D225G/N and fatal human cases. (Snip) another pandemic H1N1 sub-clade found in a patient in San Diego has also been found in swine in Illinois and Iowa (Snip) providing additional evidence for pandemic H1N transmission between swine herds in IL and IA.
Earlier reports of pandemic H1N1 jumping from humans to swine appeared to be isolated. The swine outbreaks were linked to humans associated with the farms. (Snip) these latest examples are clear evidence for transmission from swine to swine over a wide area in the United States. The swine isolates have unique polymorphisms not found in human cases but found in published sequences from three gene segments (HA, NA, MP). In the most recent series, the same virus is in A/swine/IL/5265-1/2010, A/swine/IL/5265-2/2010, and A/swine/IA/35573/2009.
The multiple examples of H1N1 in swine over a wide geographical area raise concerns that pandemic H1N1 could become endemic in swine. It is easily passed from swine to swine and generally produces mild or asymptomatic infections.
These jumps into swine lead to acquisition of new swine polymorphisms, and the genetically modified H1N1 in swine can jump back into human populations because the HA is easily transmitted to and between humans. The changes in pandemic H1N1 raise concerns that the genetic evolution could follow the same path as 1918, which has an equal mix of human and swine H1N1 polymorphisms in all eight gene segments. The sequences required multiple recombination events, as is being observed in the 2009/2010 pandemic H1N1 isolates from swine.
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