The equine flu virus which infected horses in a mountainous and remote region of the Soviet Union in the late 1970s has been traced back to a subtype circulating in Europe, raising the intriguing question as to how it made it so far behind the Iron Curtain.
Researchers in Kazakhstan have delved into the genetic make-up of the equine influenza A virus which was behind the 1977 outbreak in Kirgizia, a former Soviet republic which is now Kyrgyzstan.
They compared its genetic make-up with all available H7N7 equine influenza viruses in public databases in a bid to figure out the potential source of the introduction of the virus to the Central Asian region.
Kobey Karamendin and his colleagues, writing in the journal Pathogens, described their analysis of the equine fluvirus known as A/equine/Kirgizia/26/1974 (H7N7) using virus deposited in the National Collection of Microorganisms at the Research Institute for Biological Safety Problems in Kazakhstan.
The virus was found to be closely related to the London/1973 strain previously isolated in Europe. The study team said the Kirgizia virus shared a maximum nucleotide sequence identity at 99% with it.
They said the virus responsible for the Kirgizia outbreak did not have any specific genetic signatures and could be considered an epizootic strain of the 1974 virus that spread in Europe.
The researchers said the large population of horses in Central Asia – more than 20 million – provided a strong basis for sustained transmission and evolution of the equine flu virus in equine hosts.
“It is hard to say how the European sublineage virus could reach the mountainous region of Soviet Central Asia because of the strict regime and closed borders during the communist era in Kirgizia,” they said.
Unfortunately, no epidemiological data is available about this outbreak from the Soviet era. They supposed that the H7N7 virus ultimately circulated in the wider region, which includes Kazakhstan, Kirgizstan, China and Mongolia.
Equine flu cases due to the H7N7 subtype — responsible for the Kirgizia cases — have not been reported since the end of the 1970s.
The last serological evidence indicating the circulation of this serotype was recorded in the 1990s in horses in Central Asia. This is when antibodies were last found in unvaccinated horses.
The H7N7 subtype is now considered to be no longer circulating in horses.
The equine flu viruses currently circulating in horses worldwide belong to the H3N8 subtype consisting of two lineages — American and Eurasian.
Karamendin was joined in the research by Aidyn Kydyrmanov and Marat Sayatov, from the Institute of Microbiology and Virology in Kazakhstan; and Vitaliy Strochkov, Nurlan Sandybayev and Kulaysan Sultankulova, from the Research Institute for Biological Safety Problems in Gvardeyskiy, Kazakhstan.
Retrospective Analysis of the Equine Influenza Virus A/Equine/Kirgizia/26/1974 (H7N7) Isolated in Central Asia
Kobey Karamendin, Aidyn Kydyrmanov, Marat Sayatov, Vitaliy Strochkov, Nurlan Sandybayev and Kulaysan Sultankulova.
Pathogens 2016, 5(3), 55; doi: 10.3390/pathogens5030055