Experiment Infects Cattle with H5N1

Four calves were experimentally inoculated with the virus. Despite they remained healthy, several animals shed low amounts of virus, detected by inoculation of nasal swab fluid into embryonated chicken eggs and onto MDCK cells.

Since 1997, an epidemic of highly pathogenic avian influenza virus (HPAIV) subtype H5N1 has spread in Asia, causing fatal infections in poultry, wild birds, and mammals, including humans.

Scientists working for the Federal Ministry of Food, Agriculture and Consumer Protection in Germany, say that knowing the susceptibility to the disease of species living in close proximity to humans and poultry, such as cattle and water buffalo, would be help people determine further areas of risk.

Serologic examinations have indicated that calves might be susceptible to influenza A virus however, so far only 1 strain has been identified as a cattle strain. A correlation between influenza A virus infection, reduced milk yield, and respiratory symptoms in dairy cows was assumed in the late 1990s and has received recent attention. Nevertheless, to our knowledge, no data about the susceptibility of cattle to infections with HPAIV have been reported.

Conclusions

According to the scientists the findings show that H5N1 has the potential to infect bovine calves, at least after high-titer intranasal inoculation, and that conventional HI tests may underestimate such infections.

Furthermore, asymptomatic shedding of HPAIV (H5N1) by infected calves and subsequent seroconversion seem to be possible, and even low levels of HPAIV (H5N1) might be sufficient to induce a detectable antibody response in contact calves.

However, the possibility that the infectivity detected in the contact calf at 1 dpi was the result of residual inoculum cannot be ruled out. Although the question whether calf-to-calf transmission of HPAIV (H5N1) occurs could not be definitely answered by the study, bird-to-calf transmission resulting in seroconversion is probable.

The incidence of clinical infections of cattle with HPAIV (H5N1) in disease-endemic regions should be low. However, the data indicates that serum from bovine species would be a valuable source of additional information about transmission events, especially in regions like Asia and Egypt, where HPAIV (H5N1) is endemic and probability of contact between poultry and cattle is high. The NP-ELISA is currently the assay of choice for the evaluation of bovine serum, and the VN test should be used for confirmation.

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