Mongolia may well prove to be a hot spot for the emergence of novel strains of the equine influenza virus (EIV), according to researchers.
Horses are critical to the livelihood of Mongolian herders, providing transportation and food products, and playing important cultural roles. With an estimated 3.3 million horses, there are likely more horses today in Mongolia than people.
Major outbreaks of equine flu have been frequent among Mongolia’s horses, with five occurring since 1970.
Mongolian University of Life Sciences researchers Alexandra Sack and her colleagues sought to estimate the prevalence of EIV infection among horses and Bactrian camels with influenza-like illness between these major outbreaks, known as epizootics.
In 2016–2017, the study team periodically carried out surveillance for the virus in four provinces.
In all, nasal swabs were collected from 680 horses and 131 camels.
Just seven of the horse swabs proved positive for evidence of influenza A virus using molecular-based qRT-PCR testing. Two more were suspected of being positive.
None of the camel specimens had molecular evidence of infection, the researchers reported in the journal Pathogens.
None of the nine horse specimens actually yielded an influenza A virus under further testing.
None of the 131 herder households surveyed as part of the study had recently vaccinated their horses against the equine flu virus, the authors noted.
It seems likely that sporadic outbreaks of equine flu were regular occurrences in multiple Mongolian provinces.
“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,” they said.
Equine influenza is caused by influenza A virus. Two subtypes, H7N7 and H3N8, historically caused infections in horses. However, H7N7 has not been isolated in horses since the late 1970s.
EIV H3N8 is divided into European and American strains.
Historically in Mongolia, three outbreaks with high mortality rates have been recorded from the 1970s to 1990s. Records estimate a 20–30% death rate for all three outbreaks.
The most recent reported outbreak, in 2011–2012, occurred in all 21 of the country’s provinces.
They noted that EIV-positive horses were found in 2016 at Mongolia’s national Naadam horse race, which raised the risk of another national outbreak.
The researchers reported that, across three of the provinces from which samples were collected, no-one had vaccinated their horses for EIV in the past year, and only nine (6.9%) reported ever vaccinating their horses against the virus.
“Only 29 households (22.1%) reported knowing that there is a vaccine for EIV, even though over 85% knew about EIV.”
More than 95% of households reported that they would be willing to give an EIV vaccine to their horses if it was free, and 115 households were willing to pay 100 MNT (US$0.04).
“There is a desire to protect horses from EIV, but a gap exists between that desire and the current knowledge and practice,” the researchers said.
They said there was serious concern of the potential for transmission of existing or potentially new EIV strains from horses to people.
A recent review of the evidence found evidence in support of occasional transmission of EIV, specifically H3N8, to people. “The same paper observed that horses have been infected with other strains of influenza, including H1N8, H5N1, H7N1, and H9N2.
“This increases the risk for the emergence of novel influenza viruses.”
They continued: “Many historical human influenza outbreaks had been preceded or were less commonly followed by equine outbreaks.
“One review of the historical records in Europe from 1688 to 1888 found 56 years with documented outbreaks of human or equine influenza. Out of the 56 outbreaks, both horses and humans were affected in 21 years, humans only in 25 years, and horses only in 10 years.
“Some of the largest EIV outbreaks with smaller accompanying human influenza outbreaks occurred in 1727, 1750, 1760, and 1872.
“Human and equine EIV outbreaks occurred in the past, and a novel EIV or reemergence of H7N7 could allow them to return.”
The study team said, outside of racehorses, EIV still had the potential to be devastating to Mongolian herder families.
The evidence had shown that EIV was endemic in Mongolia between large-scale outbreaks, the authors said.
The study team comprised Sack, Ulziimaa Daramragchaa, Maitsetseg Chuluunbaatar, Battsetseg Gonchigoo, Boldbaatar Bazartseren, Nyamdorj Tsogbadrakh and Gregory Gray. They are variously affiliated with the Mongolian University of Life Sciences in Ulaanbaatar; Duke University in Durham, North Carolina; the National Center for Zoonotic Diseases in, Ulaanbaatar; Duke-Kunshan University, China; and the Duke-NUS Medical School in Singapore.
Low Prevalence of Enzootic Equine Influenza Virus among Horses in Mongolia
Alexandra Sack, Ulziimaa Daramragchaa, Maitsetseg Chuluunbaatar, Battsetseg Gonchigoo, Boldbaatar Bazartseren, Nyamdorj Tsogbadrakh and Gregory C. Gray.
Pathogens 2017, 6(4), 61; doi: 10.3390/pathogens6040061