Minks in Spanish breeding have bird flu, possible mutual contamination

Avian flu was diagnosed in a mink farm in northwestern Spain last October. The minks may have infected each other with the virus, researchers say. That would be the first evidence that the currently present bird flu virus can pass from mammal to mammal.

Spanish and Italian researchers have been studying the outbreak in mink farming. This was probably caused by the food that the minks received, often leftovers from poultry. It is also possible that minks in semi-open housing have come into contact with wild seabirds that were infected with bird flu.

The mortality rate among the mink rose relatively high in a short period of time, up to 4.3 percent per week. This means that at the peak of the outbreak in breeding with 52,000 animals, more than 2,200 minks died. Dead animals that were examined often had severe pneumonia and a bloodied snout.

According to researchers, the rising, high mortality rate is an important indication that the minks have infected each other. “It is unlikely that contamination in all those deaths was through the feed or contact with wild seabirds,” says Thijs Kuiken, virologist at the Erasmus Medical Center.

The researchers do not dare to conclude that the minks in Spanish breeding have actually infected each other with the avian flu virus. “They are waiting for further research from the laboratory, where, among other things, the contagiousness of the avian flu virus is studied from ferret to ferret,” says Kuiken.

Ferrets are also mustelids and are most similar to humans in terms of infectivity. How efficiently the virus passes from ferret to ferret is a good measure of the efficiency with which the virus could pass from human to human. The World Health Organization (WHO) calls the chance of spreading from person to person small.

There is, however, a known case of a 9-year-old girl in Ecuador that has become infected with the avian flu virus, probably via poultry in the backyard of her house.

Minks, like all mustelids, are susceptible to infection with influenza viruses. Minks are kept for their fur, which is widely used in the fur industry.

Due to the many corona outbreaks in the remaining mink farms in the Netherlands, those companies were closed more quickly in 2020. The ban on fur farming would not actually take effect until 2024.