By Randy Dotinga
MONDAY, July 22 (HealthDay News) -- While a type of tick-borne disease known as Heartland virus appears to be extremely rare -- only two cases in humans have been reported so far -- a new study finds it is lurking in ticks in northwestern Missouri.
The researchers haven't issued anything other than the usual warnings about avoiding contact with ticks that may harbor disease. Still, "there's another tick-borne pathogen out there to be careful of," said study author Harry Savage, a medical entomologist with the U.S. Centers for Disease Control and Prevention.
Heartland virus is indeed rare, he said, but reports on it may be spotty because a test for it is not readily available.
Lyme disease is the most well-known infection spread by ticks, but there are several others. The infection known as Heartland virus -- so named because it was discovered in the middle of the country -- is unusual because it's spread by a virus, not a bacteria.
Two farmers from northwestern Missouri were diagnosed with the illness in 2009 after coming in contact with ticks. The virus causes "fever, headaches, mild diarrhea and low white blood [cell] counts," Savage said.
Both of the men were hospitalized with severe illness but recovered.
Last year, researchers fanned out across northwestern Missouri -- to the north and northwest of Kansas City -- and gathered a whopping 56,428 ticks at 12 locations, including at the farms of the infected men. The ticks were caught in the wild and taken off horses and dogs.
The researchers report that they found the virus in a species known as the lone star tick. The infection rate was about one in 500 ticks, Savage said.
It appears that the ticks became infected at the larval stage when they bit an animal that harbored the virus. Then the ticks reached the nymph stage and looked for blood meals from, say, humans, Savage added.
Investigators identified the first cases with the help of the CDC. Now, Savage said, researchers are working on a test to identify the virus in infected people.
However, it's not clear how helpful a test will be. Because the disease comes from a virus, antibiotics can't be used to treat it.
Is the virus -- which Savage said may have lurked around for thousands of years -- concerning? That's also not clear, said another expert who studies infectious disease.
"If these two cases represent the severe end, then there may be many other milder cases that are going undiagnosed," said Dr. Lucas Blanton, an instructor at University of Texas Medical Branch at Galveston. "Until more patients are studied, I do not think we know the full implications of this virus."
Blanton said physicians should consider possible infection with Heartland virus if the tick-borne disease it mimics -- ehrlichiosis -- fails to improve when antibiotics are given.
The public, meanwhile, should continue to recognize the risk of ticks and rely on protective clothing, insect repellents and checking their skin for signs of ticks, he said.
In addition, the CDC recommends showering soon after going outdoors, removing attached ticks from the body with tweezers, and calling a doctor if illness develops after a tick bite.
The new study was published online July 22 in the American Journal of Tropical Medicine and Hygiene.