A New Tick-Borne Illness, and a Plea to Consider the Insects

A tick’s mouth parts under 40x magnification.

In the summer of 2009, two men from northwest Missouri showed up at Heartland Regional Medical Center in St. Joseph, tucked up against the Kansas border 50 miles north of Kansas City. The men were seriously sick. They had high fevers, fatigue, aches, diarrhea and disordered blood counts: lower than normal amounts of white blood cells, which fight infection, and also lower than normal platelets, cells that control bleeding by helping blood to clot. But they had none of the diseases that were high on the differential diagnosis, the list of possible causes that doctors work their way down as they try to figure out what has gone wrong: no flu, no typhus, no Clostridium difficile, and none of the serious foodborne illnesses — no Salmonella, no Shigella, and no Campylobacter.

The two men had one thing in common, though: About a week before being hospitalized, each remembered, he had been bitten by a tick.

From that memory — teased out by an alert infectious-disease physician who was called to consult on the illness of both men — has come an unnerving discovery: a heretofore unknown tick-borne illness, technically a phlebovirus, that has been named Heartland virus in honor of the medical center where it was identified.

The discovery was recounted in a “brief report” in the New England Journal of Medicine last week. The two farmers, who both recovered, are the first known victims. But local physicians, along with staff from the Centers for Disease Control and Prevention who helped analyze the cases with rapid whole-genome sequencing, are sure there are more. In NEJM, they point out that the cause of these two men’s illnesses was only discovered because the men were so sick that physicians needed to look hard at what was going on, and add:

Although these two patients had severe disease, the incidence of infection with the novel virus and range of disease severity are currently unknown. Given the largely nonspecific symptoms observed, this virus could be a more common cause of human illness than is currently recognized.

There are two things worth thinking about in this report. The first is that it reinforces something that we tend to forget: Significant new diseases are startlingly common. In the past 40 years, at least one per year – sometimes several in a year – has been recognized for the first time or freshly linked to a causative organism. The World Health Organization published a list in 1996 (updated by the Journal of Infection in 2000). Some highlights, counting backward: There was Nipahvirus in 1998; H5N1 flu in 1997; new variant CJD (“mad cow”) in 1996; Hendravirus in 1995; Sabia virus (the cause of Brazilian hemorrhagic fever) in 1994; and Sin nombre (the cause of hantavirus pulmonary syndrome) in 1993. Going back to 1977, a banner year, there was Ebolavirus, Hantaan virus, and also Legionella, responsible for the 1976 outbreak of Legionnaires’ disease that made people wonder whether the U.S. Bicentennial celebrations were being attacked by biological weapons.

But the other thing worth thinking about is how many of those new diseases are vectorborne, transmitted by arthropods such as ticks or by insects such as mosquitoes. Heartland is one of three new tick-borne diseases identified just in the past two years, preceded by Noerlichia mikurensis in Sweden in 2010 and severe fever with thrombocytopenia syndrome virus (SFTSV) in China last year. In the United States, Lyme disease is thought of as the major tickborne bad actor — but over the past two years, health authorities have been coming to grips with the unappreciated toll of other tick-related diseases, including erlichiosis, anaplasmosis, STARI, and babesiosis, which is moving into the blood supply. That’s not even to mention the toll of long-standing insect-borne diseases: malaria, one of the top five infectious killers in the world, along with rapidly rising dengue.

When we indulge in cultural fascination with scary new diseases, we tend to look to the animal kingdom — bats in the movie Contagion, whose scenario was based on the discovery of Nipahvirus, or monkeys in just about any account of Ebola. Like Gulliver among the Lilliputians, we have difficulty believing we can be brought down by something we can barely see. (In some cases literally: The tick suspected of transmitting Heartland, Amblyoma americanum, is half the size of a sesame seed.) But this summer has already been marked by the largest West Nile virus epidemic since the disease was recognized in the Americas, in a new and more virulent form, in 1999. Heartland is another reminder that we seldom consider the risks from insects and arthropods, and that we should.

Cite: McMullan LK, Folk SM, Kelly AJ et al. “A New Phlebovirus Associated with Severe Febrile Illness in Missouri.” 2012. N Engl J Med 2012; 367:834-841
Photo: Flickr/SpeciousReasons/CC


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