Natural science Bird flu cases in humans in the USA often go undetected

Numerous human infections with the H5N1 avian flu virus on dairy farms in the USA apparently go undetected. Tests have revealed an infection rate of seven percent, reported the US health authority CDC.

A total of 115 blood samples were taken from employees on farms in two states between June and August for the investigation. 8 of the samples showed that the employees had recently contracted the H5N1 avian 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.

H5N1 avian influenza is currently widespread in wild birds around the world, and many wild mammals are also infected. In addition, the virus has recently led to outbreaks in 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.

Frequency of transmission to humans unclear

The CDC now states that the 46 cases are likely only a portion of the actual cases. "Despite ongoing efforts to monitor dairy workers for illness, test for H5N1, and provide antiviral treatment, several factors have prevented a comprehensive understanding of the extent of cow-to-human transmission." For example, employees are often not seriously ill and some farms do not want to participate in testing.

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.

SDA