September 25, 2024

 

Concerns over bird flu spread as California, US reports new cases in dairy herds

 

After three more herds in California, US, tested positive for bird flu, questions are being raised about whether the true extent of the outbreak in the US is larger than recognised, given the lack of biosecurity and limited testing, The Guardian reported.

 

The US Department of Agriculture (USDA) revealed the new cases, bringing the total number of affected herds in California to eight this month.

 

"We are really not testing enough," said Meghan Davis, an associate professor at Johns Hopkins Bloomberg School of Public Health. "The lack of testing has actually been one of the most startling things for me, in terms of watching the response to this outbreak unfold."

 

California is now the 14th US state to report H5N1 cases in dairy cows since the outbreak was first identified in March. Recently, New Mexico and Michigan also reported more cases in dairy herds.

 

However, several states and localities have resisted testing, both among animals and people. In Missouri, the first patient to test positive after no known contact with animals had a close contact fall ill at the same time. Despite this, the contact was not tested for the flu and has not undergone a blood test to check for H5N1 antibodies.

 

In Colorado, nine cases were discovered in July among 109 poultry workers who reported symptoms and agreed to testing. This represents only a fraction of the 663 workers who were exposed to H5N1-positive chickens, according to a recent report from the US Centres for Disease Control and Prevention (CDC).

 

The continued low levels of testing, even among workers with confirmed exposures, demonstrate the limits of federal agencies in responding to the outbreak. Experts are concerned that the virus is more widespread than reported, and every new case in animals increases the risk of human infections.

 

In response to the outbreak, farms near the affected herds in California will conduct bulk milk sampling, according to Eric Deeble, deputy undersecretary for marketing and regulatory programs at USDA.

 

Bulk testing of milk can reveal cases among cows that appear healthy. After Colorado implemented this type of testing, officials discovered positive cases in 11 more herds.

 

Meghan Davis commented, "It'd be really great to see USDA step in with some very strong recommendations" around efforts like bulk milk testing.

 

US officials have considered bulk-testing mandates "since day one," but they have not been implemented nationwide. Deeble mentioned in a call last month that Colorado's success might be unique to the state and might not be applicable to the rest of the country.

 

Testing all animals is a considerable task, according to Steve Grube, chief medical officer for the Centre for Food Safety and Applied Nutrition at the US Food and Drug Administration (FDA), during an August briefing. Currently, the USDA only requires H5N1 testing for lactating dairy cows moving across state lines.

 

Deeble expressed confidence that the existing testing accurately reflects the status of animals moving between states, although movement within states is monitored less closely. He added, "I do feel like the response is adequate."

 

The source of H5N1 in California remains unclear. The cases could indicate a lapse in interstate testing, circulation of the virus before testing protocols were introduced in April, or transmission through wildlife or contaminated equipment such as trucks.

 

A USDA report in June indicated that human activity, such as the movement of transportation vehicles between herds and rearing practices, was likely contributing to the spread of the virus. Other biosecurity concerns include open-air dairy operations and the reuse of water in cow stalls, which may be contaminated by other cows or wildlife. Large dairies often send calves to "calf ranches" where they are raised with cows from other states, potentially facilitating the spread of disease.

 

Sequencing of samples from the first three herds in California indicates that the strain is closely related to the one circulating among dairy cows in other states, according to Deeble, suggesting that the infections were not caused by a new spill over event from the bird flu strain circulating among wild birds in North America since 2022.

 

The strain found in cows has also infected other animals, including wild and domesticated birds, cats, and mice, raising concerns about its spread to more animals.

 

H5N1 vaccines for cows are currently undergoing testing, and vaccines for humans are in production, although they have not yet been approved for use. No human cases have been reported in California so far, but the state has issued a health alert for providers to monitor for potential H5N1 cases in people.

 

While no poultry flocks have been affected by this outbreak, bird flu was detected in San Francisco wastewater in June, though the source of the contamination remains unclear.

 

As California leads the nation in dairy production, accounting for 20% of the US milk supply, a widespread outbreak could have significant economic impacts on farmers, especially if the virus continues to circulate.

 

Farm workers, who are at the highest risk of contracting the virus from sick animals, could create new risks for others if their illnesses and the illnesses of the animals they care for are going undetected.

 

-      The Guardian