In an unexpected turn of events, yesterday Cornell University and the University of Wisconsin announced that the canine influenza outbreak which we looked at last week (see CDC Statement On Canine Influenza In Chicago) – which was presumed to be due to the canine H3N8 virus – was in fact sparked by the first appearance of the Korean H3N2 virus in North America.
First the statement from Cornell University, then I’ll be back with more.
April 12, 2015 By Joe Schwartz
ITHACA, N.Y. – The canine influenza outbreak afflicting more than 1,000 dogs in Chicago and other parts of the Midwest is caused by a different strain of the virus than was earlier assumed, according to laboratory scientists at Cornell University and the University of Wisconsin. Researchers at Cornell say results from additional testing indicate that the outbreak is being caused by a virus closely related to Asian strains of influenza A H3N2 viruses, currently in wide circulation in southern Chinese and South Korean dog populations since being identified in 2006. There is no evidence that it can be transmitted to humans.
The outbreak in the Midwest had been attributed to the H3N8 strain of virus, which was identified in the U.S. dog population in 2004 and has been circulating since. The H3N2 virus had not been previously detected in North America. The outbreak in Chicago suggests a recent introduction of the H3N2 virus from Asia.
Testing of clinical samples from the outbreak conducted at The New York State Animal Diagnostic Laboratory at Cornell indicated that the virus was Influenza A. Further testing led researchers to believe a new strain was at fault. Subsequent testing, carried out with the assistance of the Wisconsin Veterinary Diagnostic Laboratory, identified the new subtype as H3N2. The National Veterinary Services Laboratories in Ames, IA is sequencing two isolates from this outbreak, which were isolated at Cornell, to facilitate rapid complete characterization of the viruses.
Both Influenza strains can cause high fever, loss of appetite, coughing, nasal discharge, and lethargy. Symptoms may be more severe in cases caused by the H3N2 virus. Some infected dogs may not show symptoms at all.
H3N2 has caused infection and respiratory illness in cats.
Up until a little over a decade ago, dogs were considered largely immune to influenza infection. In 2004, however, the equine H3N8 virus mutated enough to adapt to a canine host, and began to spread among greyhounds in Florida (see EID Journal article Influenza A Virus (H3N8) in Dogs with Respiratory Disease, Florida).
Since then canine H3N8 has been sporadically reported across much of the United States. It is considered a `canine specific’ virus, and there have been no reports of human infection.
The canine influenza story suddenly became more complex in 2008, when the EID Journal reported on the 2007 Transmission of Avian Influenza Virus (H3N2) to Dogs in Korea. Analyses showed that the HA and NA genes of the A/canine/Korea/01/2007 (H3N2) isolate were closely related to those identified in 2003 from chickens and doves in South Korea.
The authors wrote:
Because all genes of the canine isolates were of avian influenza virus origin, we concluded that the entire genome of the avian influenza virus had been transmitted to the dogs. Transmission of avian influenza A virus to a new mammalian species is of great concern, because it potentially allows the virus to adapt to a new mammalian host, cross new species barriers, and acquire pandemic potential.
Over the next few years this Korean H3N2 virus spread into China, and in 2011 we learned from a study that appeared in the Journal of General Virology, that in 2010 it had begun to infect cats as well (see Korea: Interspecies Transmission of Canine H3N2).
D.S. Song, D.J. An, H.J. Moon, M.J. Yeom, H.Y. Jung, W.S. Jung, S.J. Park, H.K. Kim, S.Y. Han, J.S. Oh, B.K. Park, J.K. Kim, H. Poo, R.G. Webster, K. Jung and B.K. Kang
In the last 4 years, incidences of endemic or epidemic respiratory diseases associated with canine influenza H3N2 virus in Asian dogs have been reported in countries such as South Korea and China. Canine species were considered to be the new natural hosts for this virus.
However, at the beginning of 2010, influenza-like respiratory signs, such as dyspnea, were also observed among cats as well as in dogs in an animal shelter located at Seoul, South Korea. The affected cats showed 100% morbidity and 40% mortality.
We were able to isolate a virus from the lung specimen of a dead cat that had suffered from the respiratory disease, in embryonated chicken eggs. The 8 viral genes isolated were almost identical to those of the canine influenza H3N2 virus suggesting interspecies transmission of canine influenza H3N2 virus to the cat.
As with the equine and canine strains of H3N8, we’ve not seen any evidence of human infection with this canine H3N2 virus.
But like all influenza viruses, canine H3N2 is a continually moving target. It can not only evolve via antigenic drift, it can also pick up entire gene segments from other flu viruses via antigenic shift (aka reassortment).
And last summer we saw evidence of just such an event, in a report appearing in the journal Epidemiology & Infection, that found a new reassortment of the canine H3N2 virus – one that had picked up the M (matrix) gene from the 2009 H1N1 pandemic virus (see Canine H3N2 Reassortant With pH1N1 Matrix Gene).
If that sounds vaguely familiar, in 2011 (see MMWR: Swine-Origin Influenza A (H3N2) Virus Infection in Two Children) we saw a similar reassortment of swine-origin influenza A (H3N2) virus and the 2009 influenza A (H1N1) virus, producing a swine variant H3N2v with the M gene from pH1N1.
The CDC has speculated that `This M gene may confer increased transmissibility to and among humans, compared to other variant influenza viruses.’ – CDC HAN 2012 – but once again, we’ve seen no evidence to date that canine H3N2 has transmitted to humans.
So where does this leave us?
While one cannot predict these things, the introduction of an avian-origin mammalian-adapted influenza A virus into North America certainly requires watching. This imported virus now has the ability to encounter – and possibly reassort with – a fresh supply of influenza viruses, including canine H3N8.
The National Veterinary Services Laboratories, in Ames, Iowa is sequencing two isolates from this outbreak to further characterize the virus. Once completed, that should tell us a lot more about the origin, and evolutionary path of this virus (including the source of its M gene).
Until then, the press release from Cornell University closes with the following advice:
Veterinary professionals are advised that diagnostic testing of samples from sick pets can be done using a broadly targeted Influenza A matrix reverse transciptase-polymerase chain reaction assay (Rt-PCR). The canine-specific Influenza A H3N8 Rt-PCR in use in several laboratories will not detect this virus. Serology is also currently not available as the H3N2 virus is different enough from H3N8 that antibodies may not cross react. However, an H3N2-specific serologic assay is under development and will be available soon.
It is not known if the current vaccine will provide any protection from this new virus. It does protect against H3N8, which is in circulation in some areas. Other preventive advice remains the same: In areas where the viruses are active, avoid places where dogs congregate, such as dog parks and grooming salons.
Owners of symptomatic dogs and cats should consult their veterinarians about testing and treatment.