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New tick-borne virus puts the bite on Missouri farmers

CDC

The Lone Star tick, or A. americanum, shown here, may be responsible for the spread of a never-before-seen virus that hospitalized two Missouri farmers.

When two Missouri farmers wound up hospitalized with fever, fatigue, low blood cell counts and elevated liver enzymes in 2009, doctors suspected ticks were to blame.

Both men recently had reported tick bites, including a 57-year-old whose wife plucked a single critter off his abdomen with tweezers and a 67-year-old man who figured he was bitten 20 times a day for two weeks while rebuilding fences on his 40-acre farm.

"I was getting worse and worse," recalled Robert Wonderly, now 60, of Sheridan, Mo., the victim with the single bite.

The men had all the symptoms of ehrlichiosis, a potentially dangerous bacterial infection spread by, yes, ticks. But when scientists cultured samples of the farmers’ blood, the bacteria were nowhere to be found.

“We placed it into the culture and then we didn’t get anything,” recalled Dr. William L. Nicholson, a research microbiologist who specializes in emerging and zoonotic infectious with the Centers for Disease Control and Prevention. “And that, to us, indicated that we had something else in there that we weren’t testing for.”

That something turned out to be an entirely new virus discovered only through sophisticated genetic analysis conducted by Nicholson’s colleagues at the CDC’s Viral Special Pathogens branch. The scientists reported their findings in this week's issue of the New England Journal of Medicine.

“This particular virus has never been detected before,” said Nicholson. “This is unique to the world.”

So far, the Missouri men are the only known victims of the new germ, which has been identified as a phlebovirus, part of the Bunyaviridae family of potentially serious bugs. Hantavirus, spread by deer mice, comes from that group. So does the deadly Crimean-Congo hemorrhagic fever.

But Nicholson, along with state and local health officials, has been scouring the region where the men were infected. They’re looking for additional signs of what has been dubbed “the Heartland virus,” after Heartland Regional Medical Center in St. Joseph, Mo., where the men were treated -- and because it was discovered in the nation’s heartland.

The new virus appears to be very rare. Although there are plenty of phleboviruses around -- more than 70 -- they are divided by the ways that they’re spread. Some are carried by sand flies, for instance. Others, like the Rift Valley fever virus, are spread by mosquitoes.

The only other tick-borne phlebovirus known to cause disease in humans is called SFTSV -- severe fever with thrombocytopenia syndrome virus -- which was recently identified in central and northeastern China.

“Even though the Chinese virus is similar, it is still quite distinct,” said Nicholson.

Researchers were able to identify the Heartland virus by using electron microscopes and next-generation genomic sequencing including total RNA analysis.

It’s not clear yet exactly how the new virus may be spread. Ticks appear to be the culprits. Nicholson and others suspect that A. americanum, the Lone Star tick found widely in northwestern Missouri and elsewhere, may be be a carrier. But other critters may be responsible as well. It’s also not clear what animals may serve as hosts, noted Dr. Scott M. Folk, the infectious disease expert at Heartland Regional who treated the two farmers.

Finding those answers will be imperative, because although the Heartland virus appears to be rare, it may not be.

“It could be responsible for more illness than we think,” Folk said.

In many ways, the new virus is just one more tick-borne problem to worry patients and doctors. The CDC lists 10 tick-borne diseases in the U.S.

The best-known is Lyme disease, which infected about 30,000 people in the U.S. in 2010. Other infections include anaplasmosis and ehrlichiosis, which affect about 1,000 people each a year, and babesiosis, which infected about 1,100 people in the U.S. last year, the CDC said. There's also Rocky Mountain Spotted Fever, an old disease that still strikes about 2,500 people a year.

Pat Smith, president of the Lyme Disease Association Inc., believes the new virus should help bolster growing awareness of the problem of tick-borne diseases and encourage people to realize that they can be serious.

“Maybe you don’t have Lyme. Maybe you have something else,” Smith said. “They can make you sick for a long time.”

The CDC encourages people to check for ticks after they’ve been outdoors, to use insecticides to kill ticks and to monitor dogs and other animals to prevent ticks from being brought indoors.

The two Missouri men were hospitalized for nearly two weeks and took a couple months to recover. Wonderly, who also works at the local Energizer Eveready Battery Co. in nearby Maryville, says he still has problems with short-term memory, fatigue and headaches three years after the infection.

The second victim, now 70, who agreed only to be identified by his first name, Larry, said he's fine now. Neither man seemed much impressed with being infected by a never-before-seen virus, though both are glad it didn't turn out to be worse. 

"I guess I never give it much thought," said Wonderly. "But I was glad they saved my life."

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