The laboratory test is said to have already detected viral genetic material, even after pasteurization or heat treatment. What the researchers have found so far is causing concern among experts: one in five samples contained components of the avian influenza virus A/H5N1.
The strange thing about the infected cows is that they do not have much virus in their throats, says Danish expert Lone Simonsen. In contrast, their milk production is unusual. It is very thick milk, and it is full of this virus. For that reason, warnings have been issued in the U.S. not to drink unpasteurized milk and milk products, says Lone Simonsen.
So far, two people in the U.S. have been infected. This has already led some countries in South America to temporarily impose import restrictions on American meat.
It is not yet clear how wild birds could have transmitted the virus to cows in the U.S. According to the Science Media Center, everything happening in the U.S. can be traced back to one single case. Possibly this cow, via an infected udder, contaminated the milking machines and/or the gloves of the farm workers.
This assumption is supported by the observation that the pathogen multiplies rapidly, especially in the udders — unlike in the airways, where the pathogen could only be detected in small amounts.
But the high viral load in the udders causes other problems. “This means the virus is not only spread with every drop of milk that enters the environment, but that all the equipment needed for milk production can become contaminated with an infectious virus,” says Schwemmle in an interview with Die Welt. It is very difficult to bring such widespread contamination under control.