This morning, the New England Journal of Medicine published a brief report on two cases of a new virus discovered in Missouri.
The virus has been named “Heartland virus” after the medical center that treated the infected patients.
In June 2009, two farmers from northwestern Missouri were admitted to the hospital. Both cases were experiencing fever, nausea, diarrhea, and anorexia. Doctors tested them for the bacteria Ehrlicia chaffeensis, Ehrlichia ewingii and Ehrlichia muris-like (all causing human ehrliciosis), clostridium difficile, Salmonella, shigella, and campylobacter. All results were negative. The cases were hospitalized for 10 to 12 days, and released. Both experienced four to six weeks of recurring head aches, short-term memory problems and anorexia, but have since recovered.
What scientists from the CDC discovered is a new phlebovirus, from the family Bunyaviridae (which includes Hantavirus and Crimean-Congo fever). There are more than 70 different phleboviruses, which are often categorized by how they are transmitted. They can be carried by sand flies, mosquitoes, and ticks.
In the NEJM report, the authors state that not all of Koch’s postulates have been filled, but their findings strongly suggest a new phlebovirus.
As a sidebar, Robert Koch was one of the most influential bacteriologist in history. His teachings and accomplishments are impressive, vast, and significant. In 1905, he won the Nobel Prize for Physiology or Medicine. He is frequently cited today as the developer of certain postulates that are to be met before one could say that a certain microorganism is the cause of a specific disease. His four postulates are 1:
- The parasite occurs in every case of the disease in question and under circumstances which can account for the pathological changes and clinical course of the disease.
- It occurs in no other disease as a fortuitous and nonpathogenic parasite.
- After being fully isolated from the body and repeatedly grown in pure culture, it can induce the disease anew.
- It must be recoverable from the experimentally infected host.
Traditionally, a pathogen is considered to be the cause of a disease only after all postulates have been met. There are, of course, exceptions. The germs associated with leprosy and syhpilis are well known but cannot be grown in a pure culture so the 3rd postulate remains unachievable.
This novel virus is most closely related to the severe fever with thrombocytopenia virus syndrome (SFTSV), also transmitted by ticks, and discovered recently in China. Based on the two cases, it seems that symptoms of infection with Heartland virus are fever, fatigue, nausea and anorexia. Scientists were not able to isolate the virus in the tick because the ticks that bit the two patients were not available for study. However, the hypothesis is that the Ambylomma americanum, or Lone Star tick, is the culprit. In recent ecological studies, 99.9 percent of ticks collected from south and central Missouri were Lone Star ticks, indicating their substantial prevalence in the area. According to the CDC, the geographic distribution of these ticks ranges from the south and central U.S. states and reaches along the eastern coast from Florida to Maine.
The Lonestar Tick already carries three diseases: ehrliciosis, Southern tick-associated rash illness, and tularemia.
As with all tick-borne illnesses, the CDC recommends avoiding wooded and bushy areas with high grass and leaves, using repellents with 20 percent or more DEET, using permethrin on clothing, gear (boots, socks, tents), and always check your body after coming in from outdoor excursions. Ticks can also be on pets or clothing, so it is important to check your pets and to wash your cloths on high heat. Permethrin products should be used with caution around house cats as it is highly toxic to them.
(1) Evans, AS. (1976). Causation and Disease: The Henle-Koch Postulates Revisited. Yale Journal of Biology and Medicine 49 (2) 175-195