The Centers for Disease Control and Convention has completed susceptibility testing for influenza antiviral medications that are used for seasonal influenza and confirmed that the avian influenza A (H5N1) virus is susceptible to all commercially available FDA-approved and recommended neuraminidase inhibitor antivirals. Testing to confirm susceptibility to baloxavir marboxil, a different antiviral medication, will take longer and is ongoing. The CDC is collaborating with the USDA, the Food and Drug Administration and state public health and animal health officials to address the emerging infectious disease using a One Health approach.

Since March 25, H5N1 has been confirmed in dairy cattle in eight states: 12 herds in Texas, six each in New Mexico and Michigan, four in Kansas, two in Idaho, and one in Ohio, North Carolina and South Dakota. Only one associated human case to date has been linked to the outbreak in dairy cows and was reported by Texas on April 1. The CDC continues to work to better characterize the virus from the human case.

The CDC is also studying human sera (blood) from people vaccinated against A(H5) to confirm that existing A(H5N1) candidate vaccine viruses will provide protection against the A(H5N1) virus isolated from the human case in Texas. The CDC says manufacturers could use these CVVs to make a vaccine if needed. Preliminary genetic analysis had suggested two existing CDC CVVs would offer protection against the virus isolated from the human case in Texas.

Commercial milk supply safe

While the USDA has noted the presence of the virus has been detected in raw milk, the FDA says pasteurization is likely to inactivate the virus. However the process is not expected to remove the presence of viral particles. Some of the samples collected have indicated the presence of HPAI using quantitative polymerase chain reaction testing.

The FDA is completing a large representative national sample, to better understand the extent of these findings. Because qPCR findings do not represent actual virus that may be a risk to consumers, the agency is further assessing any positive findings through egg inoculation tests. To date, they have seen nothing that would change the assessment that the commercial milk supply is safe.  

Bovine symptoms, biosecurity measures

While H5N1 is associated with high morbidity and mortality in birds, dairy cattle reportedly recover with supportive treatment and little to no mortality. Common clinical signs in affected cows include low appetite, reduced milk production and abnormal appearance of milk (thickened, discolored).

According to the USDA, wild migratory birds are believed to be the original source of the virus. However, the investigation to date also includes some cases where the virus spread was associated with cattle movements between herds, and from dairy cattle premises back into nearby poultry premises.

The American Veterinary Medical Association urges veterinarians and producers to practice good biosecurity, test cattle before necessary movements, minimize cattle movements and isolate sick cattle.