Experts have warned dairy producers to assume the worst when taking steps to secure their premises against HPAI infections.

As the outbreak of highly pathogenic avian influenza (HPAI) continues to affect US dairies, experts have warned producers to practice stringent biosecurity measures in order to stamp out emerging infections before they've spread.

The advice comes as California recorded its 96 dairy herd to be infected with the virus in just 6 weeks; making the state the worst-hit since the start of the outbreak in March 2024. In comparison, states such as Idaho (34), Colorado (64) and Texas (26) have reported considerably smaller number of dairy herd infections even though the virus was detected in these states earlier in the outbreak. A total of 295 dairy herds in 14 states have been affected so far, according to CDC.

What's also worrying experts is the higher infection and mortality rate across Californian dairies, where up to 60% of cows are infected and 10-15% of those die, according to anecdotal reports cited by nonprofit California Dairy Research Foundation (CDRF).

The organization also claims that at least half of new herd infections had not been linked to movement of animals, suggesting the virus was spreading just as effectively through contaminated equipment or visitors.

Reflecting on the 10% mortality rate across infected dairy herds in California, Dr. Alex Hamberg, Pennsylvania State Veterinarian, said during a Center for Dairy Excellence conference call: "That's a pretty substantial number. That's almost a third of all cases since the inception of this event have occurred within the last 30 days.

"This thing continues to grow; it continues to expand. We are by no means on the downward trend here."

While Pennsylvania is yet to record a positive case of HPAI in dairy cattle, the state was vulnerable to infections 'because we are so densely populated with both cattle and poultry', he added.

"We're still getting more farms detected at an increasing rate nationwide, and it does have a pretty negative effect on affected dairy farms. So it's really key that we have good surveillance and good biosecurity here in Pennsylvania so that if it ever does come here, we can contain it and stamp it out quickly rather than have a more prolonged and expansive event like what we're seeing in Michigan and Texas and Colorado and California."

Hamberg added that researchers need 460 farms to enrol in the state's voluntary testing programs in order to gain 'statistically significant data' about the state's dairy herd; with less 100 farms including a processor taking part currently. More information about the voluntary program and how to apply is available here.

On the same dairy industry call, Dr. Ernest Hovingh, DVM, PhD, a Penn State professor and expert in biosecurity and infectious disease management, also highlighted the importance of on-farm biosecurity - and warned farmers to think holistically when it comes to their prevention and containment strategies.

"Movement of cattle is certainly a big thing, whether they're clinical or pre-clinical," he explained. "There's also been quite a few herds that have not said they've imported any animals into the herd over the preceding period of time before they became infected. That certainly suggests there's other routes of infection that we need to consider seriously as well.

"And that fits with good biosecurity practices and principles as well that we shouldn't just focus on one risk factor, but think of everything. So whether it's people coming onto the farm, manure coming onto the farm, whether that's any equipment, whether that's on equipment, whether that's on people's shoes, that also has to be considered."

"And then by the same token, if a producer or a service provider is leaving a premises, you have to assume that the premises is infected and you're not taking anything with you," he added.

Dr. Hovingh then reminded those on the call of 'three basic things' farms should require of a visitor coming onto their farm:

With 18 human cases of avian influenza infections now confirmed in the US since 2022 - including 7 following exposure to infected dairy cows - epidemiologist Miriam, Wamsley, PhD, warned farmworkers 'could become co-infected with seasonal flu and other variants of avian flu'.

"And if somebody is co-infected, those flus can re-combine and cause a new flu virus, which could be make a person infected with both very sick.

"Additionally, it could possibly make it easier for human to human transmission, which currently has not occurred with this strain of avian influenza.

"So I really would like to encourage everybody to get out there and get that flu shot. It's really important for anybody that has exposure to animals," she concluded.