How UPenn scientists are tracking bird flu and developing a vaccine

Pennsylvania is among the states across the country ramping up efforts to guard against a growing bird flu outbreak. The situation captured the national spotlight last week after California declared a state of emergency over the virus’ toll on its cattle population.

Steps being taken in Pennsylvania include increased testing for H5N1 in birds and among cattle and raw milk. The state issued a quarantine order in April that required dairy cattle to be tested for avian flu before they entered the state, and last month began requiring regular testing of milk samples from tanker trucks that take raw milk to be pasteurized at processing plants.

The University of Pennsylvania’s veterinary researchers are working closely with the state to track the spread of bird flu in agricultural settings. Penn’s immunologists are also developing a vaccine for the highly contagious virus.

So far, the virus has not been a serious threat to humans. The vast majority of cases among humans — including the first serious case, reported last week — were among people who had direct contact with an infected animal.

» READ MORE: What to know about the bird flu outbreak as California declares a state of emergency

Pennsylvania has so far seen no cases of bird flu in cattle and has not detected a case of the virus in domestic birds in at least a month.

Here’s a look at what Penn scientists are paying attention to as they track the virus.

The current outbreak is caused by a strain of the H5N1 virus that began circulating among birds in the United States in 2020, and spread to the cattle population about a year ago.

To date, the vast majority of bird flu cases among humans have been linked to direct contact with an infected animal, such as a bird or cow.

“It would be a disaster if we start detecting a lot of infections without a known animal source, if there was any evidence of human-to-human transmission,” said Scott Hensley, a professor of microbiology at Penn. “That’s what’s required for a virus to turn into a pandemic virus.”

The H5N1 virus binds poorly to human respiratory cells, which means it is not able to easily spread from one person to another.

The virus could become a bigger threat to humans if it mutates and becomes better able to latch on to receptors in the respiratory system.

“Any time you have an avian virus where there’s low levels of human immunity, any time you have a situation with a virus that’s coming into a lot of contact with humans, you worry it’s going to begin to be able to mutate and replicate,” Hensley said.

The approaching flu season adds to those concerns.

When people contract two types of respiratory virus — for instance, seasonal influenza and bird flu — the viruses can mix together and exchange genetic material. That could lead to a strain of bird flu that is better able to latch on to human respiratory cells and be passed on from one person to another, Hensley said.

“We are in a really precarious time right now,” he said.

The emergence of bird flu in cattle surprised researchers when cases first began turning up last year. “We had no idea cows could even get influenza — this was a total shock,” Hensley said.

Scientists initially assumed that the virus would spread among cattle the same as it would among humans — through the respiratory system, he said.

But they now believe that the virus binds to mammary gland cells in cows’ udders, and is spread through contaminated milk.

Commercial dairy farms use milking machines on multiple cows before cleaning them, putting healthy cows in contact with milk from sick cows, Hensley said.

(Public health officials have cautioned against drinking raw, unpasteurized milk because it can contain the virus. The high-heat pasteurization process deactivates the virus.)

At their testing lab in Kennett Square, Penn veterinary researchers are regularly testing samples from domestic birds and cattle — about 4,000 in the last month, said Eman Anis, an assistant professor in the department of pathobiology at Penn’s veterinary school.

Penn’s lab is one of three such sites in the state that helps agricultural officials monitor diseases in livestock.

After avian flu began spreading to cattle, the lab updated its testing devices to handle samples taken from milk, Anis said.

“We have not found avian flu in any milk, and we hope to stay like that,” Anis said.

The lab also regularly monitors for H5N1 in birds, testing samples from both domestic and wild flocks. At one point in 2023, Pennsylvania had more cases of avian flu in domestic birds than any other state in the country. But the virus has not been detected here in birds in at least 30 days, according to state data.

If bird flu is detected in cattle in the state, Anis said, case loads will increase significantly at the Kennett Square lab, so lab administrators are training more staff and stocking up on testing supplies to prepare.

Hensley leads a team developing a vaccine that could one day help protect humans and animals from the virus.

Penn’s H5N1 vaccine uses the same messenger RNA (mRNA) technology used in COVID-19 vaccines.

» READ MORE: Penn mRNA scientists Karikó and Weissman win Nobel Prize

Traditional vaccines are made by growing a live virus, then deactivating or weakening it. When given to humans, it causes a reaction that allows the body to build immunity to the virus.

Vaccines made with mRNA use bits of genetic code to instruct the body to produce proteins that block the virus from binding to cells.

Penn’s vaccine is currently in clinical trials among cattle. Researchers expect to publish results as early as January.