Federal scientists have isolated a virus in ticks that has never before appeared in the Western Hemisphere and are calling on other scientists to look for evidence of the disease-causing pathogen.
Virus hunters from the Centers for Disease Control and Prevention said the virus causes an illness nearly identical to ehrlichiosis, a tick-borne disease that is caused by a bacterium.
The newfound pathogen, known as a phlebovirus, was isolated in 2009 in two Missouri men who doctors knew had been bitten by ticks but whose disease didn’t respond to antibiotics, which are useless against viral pathogens.
Dr. William L. Nicholson, chief of pathogen biology and disease ecology at the CDC, said the unexpected appearance of a phlebovirus in the United States stunned his research team.
“This is the first time a phlebovirus has infected humans in the Western Hemisphere,” he said.
Both men developed a fever and a significant drop in blood platelets, which are critical in the formation of blood clots. One suffered fatigue and recurrent headaches after leaving the hospital, but doctors could not attribute those symptoms to the infection. The other reported fatigue, short-term memory loss and anorexia four to six weeks after discharge. Those symptoms, doctors now say, have abated.
Dr. Bruce Hirsch, a specialist in infectious diseases at North Shore University Hospital in Manhasset, N.Y., said the discovery opens a new window on tick-borne diseases. “The authors of the study are naming the virus the Heartland virus,” Hirsch said, noting the pathogen is in the same viral family as those that cause Rift Valley fever in Africa and a severe fever syndrome in China. That illness is also typified by a dramatic decline in blood platelets.
Although Lyme and ehrlichiosis are tick-borne diseases, they are caused by bacteria. Babesiosis, another tick-transmitted illness, is caused by organisms known as protozoa. The discovery of a phlebovirus, analysts said, adds to the known number of viral species that can be carried by the eight-legged arachnids. To date, nearly 40 other viruses are known to be transmitted through tick bites.
Nicholson and his colleagues are zeroing in on the lone star tick as the probable culprit. Yet, though genetic studies so far point to ticks as vectors, Nicholson noted that he and his team are also investigating other biting insects, especially mosquitoes.
Nicholson’s research was published Thursday in the New England Journal of Medicine.
It isn’t the only research to turn up a new disease-causing pathogen in ticks.
In Connecticut, Dr. Durland Fish of Yale University is continuing research into a tick-transmitted bacterium he discovered with a team of Russians. The pathogen, known as Borrelia miyamotoi, causes high fevers and leaves patients vulnerable to relapsing fevers.
Fish and his colleagues reported their discovery last September after more than a decade of research. Ticks used in his study were collected from a variety of sites on Long Island as well as in Westchester County, New Jersey and his own state.
“Ticks can carry a greater variety (of pathogens]) than any other vector, more varieties than mosquitoes,” Fish said.