Low Prevalence of Enzootic Equine Influenza Virus among Horses in Mongolia

Abstract

Horses are critically important for Mongolian herders’ livelihoods, providing transportation and food products, and playing important cultural roles. Equine influenza virus (EIV) epizootics have been frequent among Mongolia’s horses, with five occurring since 1970. We sought to estimate the prevalence for EIV infection among horses and Bactrian camels with influenza-like illness between national epizootics. In 2016–2017, active surveillance for EIV was periodically performed in four aimags (provinces). Nasal swabs were collected from 680 horses and 131 camels. Seven of the horse swabs were “positive” for qRT-PCR evidence of influenza A (Ct value ≤ 38). Two more were “suspect positive” (Ct value > 38 and ≤ 40). These nine specimens were collected from four aimags. None of the camel specimens had molecular evidence of infection. Despite serial blind passage in Madin-Darby Canine Kidney cells (MDCK) cells, none of the nine horse specimens yielded an influenza A virus. None of the 131 herder households surveyed had recently vaccinated their horses against EIV. It seems likely that sporadic EIV is enzootic in multiple Mongolian aimags. This finding, the infrequent use of EIV vaccination, periodic prevalence of highly pathogenic avian influenza, and the mixing of domestic and wild equid herds suggest that Mongolia may be a hot spot for novel EIV emergence.

Absence of adaptive evolution is the main barrier against influenza emergence in horses in Asia despite frequent virus interspecies transmission from wild birds

“…Since 1974 there have been five EIV epizootics documented in Mongolia: 1974–1975, 1983–1984, 1993–1994, 2007–2008, and 2011 [28]. As vaccination coverage in the country is seemingly very low [42], it can be reasonably assumed that most seropositive horses have acquired EIV immunity by natural infection, which is known to induce a potent immunological response. Since all AIVs studied here possess the same subtype as EIV (H3), the high seroprevalence of the latter could provide enough pre-existing immunity against H3 AIVs, thus acting as an effective barrier against AIV emergence in horses.…”

Equine Influenza Virus in Asia: Phylogeographic Pattern and Molecular Features Reveal Circulation of an Autochthonous Lineage

“…Besides, EIV was also reported in India (2008 and2009) and Mongolia (2008Mongolia ( , 2012Mongolia ( , and 2016. Phylogenetic analyses showed that all Indian and Mongolian strains were similar to the FC2 viruses circulating in China between 2007 and 2008 (9,(15)(16)(17). Finally, EIV was also detected in Kazakhstan during 2007 and 2012, and the isolates were closely related to Mongolian and Chinese FC2 strains (18).…”

A Comprehensive Review on Equine Influenza Virus: Etiology, Epidemiology, Pathobiology, Advances in Developing Diagnostics, Vaccines, and Control Strategies

“…Similarly, there was no positive case observed out of 131 camels tested. This study reported a sporadic incidence of enzootic EIV in Mongolia (Sack et al, 2017 ).…”