A report in the May 10th edition of Science reported that virus isolated from dairy cows in Texas will be evaluated at the Federal Research Institute for Animal Health in Riems. This facility is equipped with high security facilities capable of housing adult cattle at Biosafety Level-3. The Institute in Germany will conduct studies to ascertain incubation period, organs affected and duration of shedding of virus. The research program will also evaluate contact spread either by direct contact with milk or by aerosol. The question arises as to why this research is not to be conducted at the new National Bio and Agro-Defence Facility (BADF) in Kansas. It is presumed that the BL-3 housing for large animals is not yet functional. The emergence of Bovine influenza-H5N1 confirms the need for a functional BADF.
A critical component will be evaluation of sialic receptors to H5N1. Scientists in Denmark determined that bovine mammary tissue is receptive to both human and duck influenza viruses. This creates the potential for dairy cows to become “mixing vessels” for viruses or for viruses to undergo recombination events as is known to occur in swine.
Currently with the BSL-3 experiments, numerous laboratories are undertaking genomic assays to detect possible mutations in both avian and bovine viruses that could extend the range of hosts including humans. A mutation has been identified that increases the ability of polymerase of H5N1 to function in mammals.
Scientists appear to be responding to the possible risk of bovine influenza-H5N1 extending to other species. Field epidemiologic research is underway with screening of workers from affected dairy herds in Michigan although critical field research that should be conducted by USDA-APHIS in cooperation with the Centers for Disease Control and Prevention is lagging. Justifiably APHIS has imposed restrictions on movement of lactating cows from affected herds and is requiring assay of pooled milk samples that may indicate herd infection.
At the present time, risk to the U.S. human population appears extremely low. This is based on the limited number of cases of human infection among poultry farm and dairy-herd workers and the fact that the virus is inactivated by pasteurization of milk and by thorough cooking of meat.