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New Tick-borne Heartland Virus Identified in Missouri

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Centers for Disease Control and Prevention (CDC) investigators have identified a new virus, thought to be transmitted by ticks, after 2 men in Missouri came down with an unexplained illness with fever and blood cell abnormalities, according to a report in the August 30, 2012, New England Journal of Medicine.

The 2 men (one age 57, the other 67) -- both farmers from northwestern Missouri -- independently sought care in June 2009 for illness characterized by fever, fatigue, loss of appetite, diarrhea, and low levels of white blood cells and platelets. The men recalled being bitten by ticks within 7 days before the onset of symptoms. Both were hospitalized for about 12 days, had a prolonged recovery lasting more than a month, and 1 has reported persistent headaches and fatigue.

The men were initially suspected to have bacterial infections, but antibiotics were not effective. Researchers then tested the men for several potential causes including Salmonella, Shigella, Clostridium difficile, and various Ehrlichia species, a type of tick-borne bacteria that cause diseases known as ehrliciosisin humans.

Electron microscope examination revealed a previously unknown virus of the phlebovirus genus, part of the Bunyaviridae family; researchers have named it the "Heartland virus." Various known phleboviruses -- which may be transmitted by ticks, mosquitos, or sandflies -- cause illness ranging from mild fever to fatal hemorrhagic fever.

The CDC team said that although Koch's postulates -- a set of criteria proposed by Robert Koch for establishing that a particular pathogen causes a specific disease -- have not been completely fulfilled, "we believe that this phlebovirus, which is novel in the Americas, is the cause of this clinical syndrome."

If the link is confirmed, the Heartland virus would be the first of some 70 known phleboviruses found to cause human disease in the Western Hemisphere. It is not clear how common the virus is, or how long it has been around, since it causes common, non-specific symptoms that could be attributed to influenza or other infections. Its closest known relative may be "severe fever with thrombocytopenia syndrome virus," which was discovered in China last year.

Further study is needed to determine whether ticks were the responsible vector in the Missouri cases. The most common type of tick in that area -- the lone star tick, or Amblyomma americanum -- is currently the prime suspect, since the virus is genetically similar to other tick-borne phleboviruses; however, researchers have not ruled out mosquitoes or sandflies. Investigators are now searching for mammals and bird hosts. There has been no evidence of person-to-person transmission.

The best current advice for avoiding infection, the CDC team advised, is to take precautions against tick bites, including avoiding tick habitat like tall grass and woodlands, wearing long pants and long sleeves, and using effective insect repellents such as DEET.

9/5/12

Reference

LK McMullan, SM Folk, AJ Kelly, et al. A New Phlebovirus Associated with Severe Febrile Illness in Missouri. New England Journal of Medicine 367:834-841. August 30, 2012.