A recent study challenged some commonly held beliefs about how the H5N1 bird flu behaves in cattle. While it was previously thought that the virus usually caused only mild illness and that asymptomatic animals did not spread the disease, new findings have shed light on a different reality. The study, conducted by Kiril Dimitrov, DVM, PhD, and his colleagues, revealed some startling information about the behavior of H5N1 in dairy cattle.
One of the most surprising findings of the study was that cattle mortality rates were actually higher than expected during outbreaks. In fact, on two of the nine farms studied, the mortality rate was twice the normal rate. This challenges the notion that H5N1 always produces only mild illness in cattle. The fact that almost a third of nasal swabs from asymptomatic animals tested positive for the virus further emphasized the severity of the situation.
The study also found evidence of subclinical infection in some cows, with viral RNA being detected in nasal swabs and urine samples. Interestingly, animals with clinical illness shed the virus at a lower frequency in nasal swabs and urine. This has important implications for the transmission of the virus between farms. The researchers discovered that cow-to-cow transmission occurred after apparently healthy cows from one farm were transported to another.
Key symptoms of H5N1 in cattle were also confirmed by the study, including decreased feed intake, respiratory signs, lethargy, dehydration, and abnormal milk production. Despite the severity of the illness, most cattle were able to recover within 5 to 14 days and return to their pre-outbreak health status. However, the virus spread not only among cattle but also to other animals on or near the farm, such as cats, raccoons, and wild birds.
The study concluded that the spread of H5N1 in dairy cattle and the evidence of mammal-to-mammal transmission are unprecedented. This highlights the need for efficient biosecurity practices and enhanced surveillance efforts on affected and non-affected farms. The study’s findings underscore the importance of preventing and controlling the infection and further spread of HPAI H5N1 in dairy cattle to reduce the risk of the virus adapting in this new mammalian host species and decreasing the pandemic risk to humans.
Overall, the study provides valuable insights into the behavior of H5N1 bird flu in cattle and underscores the importance of continued research and vigilance in monitoring and controlling the spread of the virus.
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