Avian Flu, the Virus Travels in Milk. But a Sneeze Can Be Enough: The Study

A ‘sneeze’ in a crowded stable. Contagion by the highly pathogenic avian influenza virus H5N1 among cows on US farms it could have also occurred through respiratory transmission, although this is not the mode of transmission that is driving the current epidemic among cattle, which remains in infected milk. This is the hypothesis advanced by a study available in preprint version on the BioRxiv platform. For the authors – as reported by ‘Nature’ online – cows could become infected by breathing in aerosols loaded with viruses.

I study

Several teams have conducted experiments to better understand the infections recorded in dairy cows in several U.S. states. Amy Baker and colleagues at the U.S. Department of Agriculture (USDA) in Ames, Iowa, infected cows and calves with the specific H5N1 strain isolated from Texas cattle early in the outbreak. They exposed four year-old female calves to a virus-laden fog through a mask that covered the animals’ noses and mouths. All infected animals produced neutralizing antibodies against the virus, confirming that they were infected. Calves showed mild symptoms, and researchers isolated infectious virus from the upper airways of two of them. The study’s findings, it says, suggest that in an environment where hundreds of animals are kept in close quarters, the virus could spread through the respiratory tract.

Before the outbreak, researchers did not know that influenza A viruses, such as H5N1, could spread in cows.. Scientists were quick to raise concerns that if H5N1 spread effectively through the respiratory system in cattle, it would be harder to control and would increase the risk of it spreading to humans, given the close contact cows have with people. But because the animals in the study did not shed large amounts of the virus in their respiratory tracts, it is probably not a major source of spread at this point, says Thomas Peacock, a virologist at Imperial College London.

Colleague Wendy Barclay, a virologist at the same university, agrees that because low levels of infectious virus were detected in animals despite their exposure to high doses of H5N1, airborne transmission is probably not efficient, nor can it “explain what’s happening at the moment.” “That doesn’t mean the virus can’t change if this epidemic continues at the current rate,” Peacock adds. “What we need to do now is keep a close eye on the virus.”