Bird flu in cattle: situation and prospects

Bird flu is severely affecting US dairy farms. Only 34 farms are officially infected, but a representative analysis of commercial milk detected virus fragments in 20% of samples. We explain the situation and what the degree of threat is in Europe.

What is known about avian influenza on US dairy farms?
At the end of March, the presence of bird flu was reported on dairy farms in the United States. So far, the disease has affected 34 farms in 9 states. In any case, the scope of the disease is believed to be much larger, as analysis of representative samples by the US Food and Drug Administration found traces of viral particles in 1 in 5 commercial milk samples collected from supermarkets.

Genomic analysis of the virus shows that transmission from poultry to cows occurred in late December 2023 or early January 2024. The virus has since spread between different farms in 9 states. Most states have now restricted the importation of animals and testing is required for the movement of farm animals.

Is it safe for people to consume commercial milk in the United States?
The virus is completely destroyed by heat treatment of milk (pasteurized or ultra-pasteurized). No samples of commercial milk were found to contain infectious avian influenza virus.

Consumption of UHT or pasteurized milk is completely safe.

What is done with milk from farms where the disease has been detected?
It is removed from the food chain. Authorities are urging farms to pasteurize milk before discarding it or using it as calf feed. Otherwise, it may become a source of infection.

What effect does avian influenza have on cows on affected US farms?
Infection with the virus causes decreased milk production, loss of appetite and various other symptoms (fever, dehydration, increased milk supply, mastitis…).

Affected animals are estimated to recover within 7–10 days, with little to no mortality.

Is there transmission of the virus among the herd?
Yes, although it is not yet clear how the virus spreads within the herd. Between 5 and 20% of cows on a farm become ill with avian influenza. Therefore, farm biosecurity is very important, including the movement of people, vehicles and objects. The hypothesis that is being worked on is that milk is one of the main factors of infection.

What do they do with diagnosed cows?
Currently, sick cows are isolated from other animals until they recover.

To date, the virus has not been detected on meat farms.

Does bird flu also affect meat farms?
So far, avian influenza has not been detected on meat farms. Health authorities in the United States are testing farms and slaughterhouses for the virus, but so far have had no success. Therefore, it is considered that beef is completely safe to eat, although it is always recommended to cook it at a sufficient internal temperature, as this eliminates possible viruses.

What is the threat level for European dairy farms?
The infection in dairy cattle in the United States is linked to the H5N1 strain, which has not been detected in Europe, a spokesman for the European Food Safety Authority (EFSA) told Politico. “We are closely monitoring the situation and its possible developments,” they said at EFSA.

Do poultry farms have avian flu vaccines? And for meat farms?
Avian influenza vaccine trials have been successfully developed in the United States for poultry production, although they are not yet in use due to various factors that need to be considered (circulating strains, impact of vaccination on meat marketing, etc.). There is also the possibility of developing vaccines for beef farms, but these are not yet available.

Is it possible to infect humans with bird flu?
Until now, bird flu has rarely been transmitted to humans, although there is a risk of mortality when it does. As for outbreaks on farms, in Spain a worker at a poultry factory in Guadalajara was identified as sick, and in the United States a worker at a meat farm in Texas was also infected, although only with conjunctivitis.

With avian flu beginning to spread to mammals, suggesting a possible mutation driving the move, health authorities in the US and Europe are concerned.

More information