Warm weather and plenty of sunshine are the factors most likely to halt, at least for now, the series of H5N2 avian flu outbreaks plaguing poultry farms across the Midwest, US Department of Agriculture (USDA) officials said today, a few hours before an onslaught of 13 new outbreaks in Minnesota was reported.
"When warm weather comes in consistently across the country I think we'll stop seeing new cases," John Clifford, DVM, the USDA's chief veterinary officer, said at a morning press conference about the virus that has spelled death for millions of turkeys and chickens in recent weeks.
"I can't predict what will happen in the fall, but we need to prepare and that's what we're doing," he added.
His comments came in the wake of four more turkey-farm outbreaks reported late yesterday, three in Minnesota and one in South Dakota. And late this afternoon the USDA and Minnesota officials reported that the virus has hit 13 more turkey farms in the state, while Wisconsin officials reported two H5 outbreaks on chicken and turkey farms in different counties, with test results on the specific subtype awaited.
Virus can't take the heat
In response to a question about whether cool weather is prolonging the H5N2 siege, Clifford said, "We know that this virus doesn't like heat, so when it gets up to a certain level of temperature the virus doesn't survive easily."
David Swayne, DVM, PhD, director of the USDA's Southeast Poultry Research Laboratory in Athens, Ga., added that the increased sunshine in spring and summer means more ultraviolet light, which kills flu viruses.
"It's hard to predict a particular date and say we'll have a drop-off in cases," he said, noting that temperature and humidity are factors as well. "Dryness also helps reduce the life of the virus in the environment."
More than 3 million birds culled
Clifford said more than 3.5 million birds have been culled so far to prevent the virus from spreading. The number doesn't include the huge chicken layer facility in northwestern Iowa that was identified as an outbreak site 2 days ago, he said.
The USDA had said the farm in Osceola County had 5.3 million chickens, but the owner of the farm, Sonstegard Foods, later said it had only 3.8 million birds there, according to media reports yesterday. Either way, the farm is by far the biggest to be affected so far.
The H5N2 virus is known to exist in some wild waterfowl, which can shed it in their feces. But how it is getting into poultry barns remains unknown, and officials shed no new light on that at the briefing.
"We're looking into a multitude of possibilities," said Clifford.
In opening the briefing, Clifford said officials and farmers have succeeded in keeping the virus from spreading from infected farms to others nearby. "We've had very good success in being able to address these things once we've been able to find these outbreak situations. We've been able to contain lateral spread," he said.
But he later qualified that, commenting that with the many recent outbreaks and epidemiologic investigations incomplete, "I don't want to say there's been no lateral spread."
In response to a question, he said USDA officials are considering the possibility that the virus may go airborne in certain circumstances.
Avian flu viruses do not spread easily through the air, he said, but added that some of the affected Minnesota farms are close to lakes, and winds in the region have been high recently. "Were talking about wind carrying potential feathers or dust or other things that could carry the virus and moving it into [poultry] houses," he said.
A University of Minnesota swine health expert told CIDRAP News today that he is part of a group that has been approached by the USDA about a possible air sampling study to look for the virus.
Peter Davies, BVSc, PhD, a professor of swine health and production, said USDA officials contacted him last week. "They told us they were interested in having some testing done, to explore the possibility whether the virus could be detected in the air in proximity to the barns," he said. "It's sort of contingent on finding a suitable farm and USDA contacting us to say they'd like us to test. We're really waiting for them to give us the go-ahead."
Davies noted that he was a coauthor of a study published last year on the detection of porcine epidemic diarrhea virus in aerosols. He said he didn't know if the USDA has already done any research on airborne transmission of the H5N2 virus, and Clifford didn't spell out any such effort.
Davies stressed that several other University of Minnesota personnel also are involved in the potential project, including graduate student Carmen Alonso, DVM; Montserrat Torremorell, DVM, PhD, an associate professor in veterinary population medicine; and Peter Raynor, PhD, an environmental sciences associate professor in the School of Public Health.
In other comments at the briefing, officials noted the concern that the virus could spread farther east through summertime mingling of migratory birds that use different flyways. Thus far the virus has been found in the Pacific, Central, and Mississippi flyways.
Clifford commented that the virus has adapted well to migratory birds, has been found in three flyways, and has caused two outbreaks in Ontario, all of which suggest the possibility of eastward spread. Noting that with birds there is some "crossover and mixing" between the flyways, he said, "If we see it in the fall, we're likely to see it in more flyways."
Swayne added, "Once they [migratory birds] go in summer to their northern breeding grounds, we're not sure if they'll bring the virus back [in the fall] or if it'll burn itself out. But we have to prepare for that possibility."
Low risk to humans
Alicia Fry, MD, MPH, a flu expert with the Centers for Disease Control and Prevention, noted that the H5 viruses now circulating in the United States have not been known to infect humans, but said that possibility can't be ruled out.
"While we are cautiously optimistic, we must be prepared for that possibility," she said. "We're creating candidate vaccine viruses which could be used to make a vaccine for people if needed." She characterized that as a routine step taken when any new flu virus emerges.
Later she commented, "At this point we don't know very much about these viruses because they're new, but we do know if we look at their genes we don't see any genetic markers which in the past have been associated with more severity or more transmission to humans, so that's a good sign."
Fry also cautioned the public to avoid contact with sick-looking or dead domestic birds or poultry and their droppings. Anyone who has had contact with infected birds should watch for any flu-like symptoms, she added. She also noted that at least 100 people who were exposed to infected birds have been monitored, with no illnesses.
Swayne noted that his lab is developing a seed strain for a potential poultry vaccine against H5N2 and will test it in chickens and turkeys. The decision whether to eventually use it will be up to regulatory officials.
Signs of infection in birds
Responding to a question, Clifford said that when turkeys are infected, "They'll go off water and feed and once they start doing that, it doesn't take very long, we're talking hours, for the birds to become very lethargic."
They show "a little twisting of the neck, followed pretty rapidly by death. . . . In chickens you see a drop in egg production, and some of the same symptoms, going off feed and lethargy. We're not seeing a lot of respiratory signs in turkeys."
Minnesota, Wisconsin report more outbreaks
Fifteen new avian flu outbreaks were reported today, 13 in Minnesota turkeys and 2 in Wisconsin. The Wisconsin outbreaks were in chickens at a commercial egg farm and at a commercial turkey farm. Outbreaks have now been detected in five Wisconsin counties.
The USDA's Animal and Plant Health Inspection Service (APHIS) said that Minnesota reported 13 new H5N2 outbreaks at commercial turkey farms in five different counties that have already battled the virus. The outbreaks, confirmed on Apr 20 and 21, struck birds in Kandiyohi (5 outbreaks), Meeker (3), Stearns (3), Otter Tail (1), and Redwood (1) counties. Most of the affected counties are located in the central part of the state, though Redwood County is southwest of that area and Otter Tail County is northwest of the main outbreak region.
The 5 new outbreaks in Kandiyohi County—the state's top turkey producer—raised the county's total of 15.
Details on flock size are still pending for 3 of the outbreaks, with the affected birds in today's other 10 outbreaks totaling 430,300, according to the report. The Minnesota Board of Animal Health (MBAH) now lists a total of 44 affected farms, with 2.57 million turkeys, in 15 counties.
Minnesota is the United States' leading turkey producer, raising about 46 million birds each year.
Meanwhile, Wisconsin's Department of Agriculture (WDA) said H5 avian influenza has been detected in a chicken flock in Jefferson County and in birds at a commercial turkey farm in Chippewa County, raising the state's outbreak total to five.
The Jefferson County farm houses 800,000 chickens, and all surviving birds will be destroyed to curb the spread of the virus. Agriculture officials will conduct surveillance and testing at other farms near the facility to check for virus spread.
Jefferson County, in the southeastern corner of the state, was the first county to report an H5 outbreak, on Apr 13. Other virus detections occurred in Barron, Juneau, and Chippewa counties, which led to the culling of 400,000 birds.
Earlier today the WDA said an H5 outbreak was detected in a flock of 87,000 turkeys in Chippewa County. The Associated Press (AP) reported that Hormel Foods has confirmed that the facility is owned by its Jennie-O Turkey Store division. Chippewa County is in west-central Wisconsin, and the outbreak announced today is its first.
Wisconsin had already banned poultry movements in three affected counties and added Chippewa County to the list today, according to the WDA.
Yesterday's Minnesota outbreaks involved a farm with 301,000 turkeys in Wadena County, the county's first outbreak; Cottonwood County's second incident, on a farm with 30,000 turkeys; and a Kandiyohi County outbreak on a farm with 61,000 birds.
In South Dakota, a turkey farm in the northeastern county of Spink was also hit by the virus, in the state's sixth outbreak, the USDA reported late yesterday.
Apr 22 USDA Blog post by Clifford on avian flu outbreaks
MBAH updates on avian flu
Apr 22 WDA statement on Jefferson County outbreak
Apr 22 WDA statement on Chippewa County outbreak
Apr 22 AP story
Mar 27 CIDRAP News story on H5N2 vaccine development