Avian flu and human flu, the interaction that worries scientists and the CDC’s measures in the USA

The outbreak of the H5N1 avian virus in US livestock continues to be a concern. After having jumped species and infected dozens of dairy cattle herds in various states of the Union, the virus is now causing concern for possible (even if unlikely) interactions with human influenza viruses that could lead to […]

The outbreak of the virus in US livestock remains of concernavian H5N1. After having made the jump to species and infected dozens of dairy cattle farms in various states of the Union, the virus is now worrying about what could be the possible (even if unlikely) consequences interactions with human influenza viruses which could lead to a particularly dangerous combination for humans.

That’s why the U.S. Centers for Disease Control and Prevention (CDC) presented the agency’s recommendations that the country’s influenza surveillance systems continue to operate at enhanced levels through the summer. CDC Principal Deputy Director Nirav D. Shah stressed the importance of remaining vigilant and outlined a plan to influenza virus monitoring nationwide for the summer season, which is a time when flu activity and testing typically declines. The goal of this plan is to maintain increased awareness of circulating influenza viruses, given the ongoing H5N1 outbreak among US poultry and dairy cattle.

Specifically, Shah called for jurisdictions to work with clinical laboratories to increase the submission of positive influenza virus specimens to public health laboratories for subtyping. Subtyping is a process that determines whether the influenza A sample is a common, seasonal influenza virus or a new virus such as H5N1. Monitoring is all the more important considering a recent preprint study, according to which cows have the same receptors for influenza viruses as humans and birds. The authors took tissue samples from the lungs, trachea, brains and mammary glands of calves and cows and stained them with compounds they knew would attach to different types of sialic acid receptors. They cut the colored tissues very thinly and observed them under the microscope. What they saw was surprising: The tiny sacs of milk-producing breasts, called alveoli, were filled with sialic acid receptors and had both the type of receptors associated with birds and those more common in humans. Nearly every cell examined contained both types of receptors, said the study’s lead author, Dr. Charlotte Kristensen, a postdoctoral researcher in veterinary pathology at the University of Copenhagen.

This discovery raised concern because one of the ways flu viruses change and evolve is by exchanging pieces of their genetic material with other flu viruses. This process, called replenishment, requires a cell to be infected by two different influenza viruses at the same time. “If you introduce both viruses into the same cell at the same time, you could essentially have hybrid viruses coming out of it,” said study author Dr. Richard Webby, director of the Center for Studies on the Ecology of Influenza in Animals and Birds at the World Health Organization. To be infected with two influenza viruses at the same time – an avian influenza virus and a human influenza virus – a cell should have both types of sialic acid receptors, which cows have, which was not known before this study. But scholars consider it a rare event, also due to the time of year. For something like this to happen, a cow infected with the avian flu virus would have to contract a different flu strain than an infected human.