CDC: No Human H5N2 Cases So Far

OMAHA (DTN) -- H5N2, the highly contagious avian flu strain blamed for nearly 8 million poultry deaths in North America, has not yet infected humans, but federal officials aren't ruling out the possibility the virus will transmit to humans at some point.

Alicia Fry, a medical officer with the Centers for Disease Control's National Center for Immunization and Respiratory Diseases, Influenza Division, Epidemiology and Prevention Branch, said at a news conference Wednesday at least 100 farm workers and others potentially exposed to H5N2 on poultry farms in the infected states have been monitored and so far there are no human cases.

"We don't know very much about these viruses, as they only recently have been identified," Fry said. "We're following the situation very closely. At this time, it looks like the H5 viruses in North America are different" than in those identified in Asian poultry, "where it caused a cluster of human cases."

At this point, there's no way to know if or when H5N2 may jump to humans, she said.

"It is possible we will see human infections," Fry said. That could occur, she said, in humans who have had direct, close and prolonged contact with infected birds.

"While we are cautiously optimistic it is not going to occur in humans, we are taking genetic analysis, and we're not finding increased illness in people or spread among people. People in contact with birds should take precautions to protect against infection -- observe birds only from a distance. Avoid birds that appear sick. You should monitor your own health for flu-like symptoms."

H5N2 continues to sweep through the poultry industry, and the number of infected farms continues to grow. Late Wednesday afternoon, USDA reported 13 more infected turkey flocks in Minnesota, adding another 370,000 turkeys that died or will have to be destroyed.

David Swayne, USDA Southeast Poultry Research Laboratory director, said his lab is working on a potential vaccine for birds. If a vaccine is developed, he said then it would have to be determined whether it would be used.

Fry said the CDC also is in the process of developing a potential human vaccine if needed. That includes identifying a potential "seed" virus that could be used to create a vaccine.

"We don't have a need to go further than that at this point," she said. "We have these candidate viruses available."

Avian influenza is a highly contagious viral disease that can quickly spread between various types of birds. It is carried by free-flying waterfowl such as ducks, geese and shorebirds. It can spread rapidly to domestic flocks through infected food or water, or through contact with infected wild birds. The outbreaks of avian influenza occurring across the U.S. are not considered to be a threat to public health or the food supply.

PATHWAYS INVESTIGATED

USDA Chief Veterinary Officer John Clifford said investigators are not sure how the virus found its way into a 3.8-million-bird chicken hen house in Harris, Iowa, this week, to other farms.

"We're looking at a multitude of possibilities," he said. "As we review them, the industry is taking them very, very seriously to address those gaps as soon as possible."

For those farmers with backyard turkey or chicken flocks, Clifford said there are a number of things they can look for to tell whether their livestock may have H5N2.

When it comes to turkeys, he said, the birds will go off water and feed, and then it takes "only hours" to become lethargic. Clifford said infected turkeys show signs of "star gazing" or staring into space, "followed by rapid death."

With chickens, he said they tend to see a drop-off in egg production and show the same symptoms as turkeys.

"There have not been a lot of respiratory symptoms in chickens," Clifford said.

"Every worker needs clean footwear and to wash their hands. Many of the facilities infected are close to lakes. With backyard flocks, if you're near wildfowl, keep your birds enclosed as best as they can."

WATER SUPPLIES

Swayne said backyard flocks should not be drinking surface water, as the source could be contaminated with H5N2. Instead, those flocks should have access to municipal water supplies.

While consistently warmer temperatures would help stem the spread of H5N2, he said there are other factors affecting the spread of the virus among poultry.

Swayne said as sunshine becomes more readily available later in the spring and into the summer, H5N2 should begin to subside. In addition, the virus thrives in humid conditions.

"Ultraviolet light will kill the virus," he said.

Clifford said it is too soon to tell whether H5N2 will spread to states on the East Coast. At this point, the virus has been identified in three of the four major flyways in North America, he said.

"These birds don't stay in one flyway," Clifford said. "We would anticipate in the fall that we're likely to see (the virus) in all four flyways."

Swayne said, "We can't predict what's going to happen in the future. Once birds go to the northern breeding grounds, we're not sure if they'll bring it back south or not."

There have been concerns about whether the virus can spread from one poultry house to another. To this point, only one case -- in Washington State -- showed evidence of the virus spreading laterally within a single farm.

"We continue to look at the potential for lateral spread," Clifford said. "This could have spread laterally within a farm itself -- one house to another."

Todd Neeley can be reached at todd.neeley@dtn.com

Follow him on Twitter @toddneeleyDTN

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