Fear that bird flu is spreading quietly as asymptomatic equine infections are confirmed

Scientists’ discovery that horses in Mongolia were infected with bird flu – and that these infections were not accompanied by visible symptoms – has raised fears that the virus is spreading undetected to other animals and even people.

H5N1 influenza has been spreading rapidly among dairy cows in several US states since spring 2023. North America is home to 30 percent of the world’s horse population, with many horses exposed to the virus on farms.

“We are witnessing the unceasing spread of H5N1 at a geographic level. “The virus has expanded its spread around the world and with that we have seen more mammalian species becoming infected,” said Professor Pablo Murcia from the MRC University of Glasgow Center for Virus Research. He is the lead author of a study that found antibodies to bird flu are present in the blood of horses.

“In addition, H5N1 viruses were not considered transmissible among mammals. “But that perception has changed with outbreaks in fur-bearing animals, minks and foxes in Europe, pinnipeds – sea lions – in South America and dairy cattle in the US,” Murcia said Newsweek.

“The more the virus begins to spread to new species of mammals, the greater the chances of adapting to mammals in general – and of course we are mammals – and, furthermore, the greater the chance that humans will come into contact with it,” said he.

Murcia’s team, along with an international team of scientists including research groups from the United States and Mongolia, decided to conduct a series of H5N1 antibody tests in herds of horses in two regions of Mongolia: a wetland that supports a large population of wild birds, and a dry area with low bird density.

Horses infected with bird flu

The results, published in the online journal Emerging Infectious Diseases, show that horses were infected with bird flu in different areas of Mongolia over several years.

There were no reports of respiratory disease outbreaks in the herds studied, suggesting that the animals that tested positive for H5N1 antibodies may have suffered asymptomatic infections. This raises concerns about a silent spread of bird flu.

“Given the large horse population in the U.S., combined with the prevalence of H5N1 in birds and now cows, it is reasonable to assume that horses in the U.S. have a higher chance of exposure to H5N1,” Murcia said.

“Cases of H5N1 on dairy farms suggest that cows can transmit the virus to humans,” he said.

reference

Damdinjav, B., Raveendran, S., Mojsiejczuk, L., Ankhanbaatar, U., Yang, J., Sadeyen, J.-R., Iqbal, M., Perez, DR, Rajao, DS, Park, A. , Viana, M. & Murcia, P.R. (2024). Evidence of influenza A(H5N1) spillover infections in horses, Mongolia. Emerging Infectious Diseases, 31(1). https://doi.org/10.3201/eid3101.241266