Bad development

Bird flu often goes undetected in humans in the USA

Researchers fear that the virus can adapt better to mammals if it circulates widely in them (symbolic image).

(Bild: IAKOV FILIMONOV stock.adobe)

The USA is currently causing headaches with regard to the further spread of the H5N1 bird flu virus. Apparently, numerous human infections with the pathogen on dairy farms in the United States are never detected.

"Despite ongoing efforts to monitor dairy workers for illness, test for H5N1, and provide antiviral treatments, several factors have prevented a comprehensive understanding of the extent of cow-to-human transmission," explains the U.S. Centers for Disease Control and Prevention (CDC).

Testing of employees on farms where the virus was detected in cows revealed an infection rate of seven percent. A total of 115 blood samples were taken from employees on farms in two states between June and August for the investigation.

Eight of the samples showed that the employees had recently been infected with the H5N1 bird flu virus. Only some of them had mild symptoms of illness. According to the CDC, all of the employees tested stated that they were milking cows or cleaning the milking parlor. According to current research, H5N1 is mainly transmitted between cows via milk.

Full extent unclear
H5N1 avian influenza is currently widespread in wild birds around the world, and many wild mammals are also infected. The virus has also recently led to outbreaks on poultry farms and dairy farms in the USA. However, the extent of the outbreak is largely unclear due to a lack of data.

Since April of this year, the CDC has recorded 46 cases in humans, mainly among employees of dairy and poultry farms, with mild cases. Human-to-human transmission has not yet been detected. The CDC continues to assess the risk to the general population as low.

The CDC now states that the 46 cases are probably only part of the actual infections. For example, employees are often not seriously ill and some companies do not want to participate in testing.

Fear of mutations
Researchers fear that the virus can adapt better to mammals if it circulates widely in them. A study published in August showed transmission from mammal to mammal, including between animal species, for example from cows to cats. Mutations of the virus that would lead to improved transmissibility of H5N1 to humans have not yet been discovered.