US health authorities have just confirmed a second case of Bourbon virus, a rare illness doctors believe to be spread by ticks. The virus—which was first found only a year ago in, in Kansas—is the latest among a slew of newly discovered tick-borne pathogens.
This time, the virus turned up in Oklahoma in May, when a patient there reported a fever, acute muscle and joint pain, diarrhea, and a rash, reports the Tulsa World. State epidemiologists matched the virus to one discovered in Bourbon county, Kansas (hence the name).
Fortunately, the Oklahoma patient made a full recovery, despite the lack of any known treatment. The 50-year-old Kansas man who suffered the first recorded case wasn’t so lucky. In June 2014, less than two weeks after symptoms first appeared, he died of multiple organ failure. The patient told health authorities that he suffered frequent tick bites, and had removed a blood-filled tick from his shoulder shortly before falling ill.
Many of the diseases that ticks give to humans—Lyme disease and Rocky Mountain spotted fever, for example—are caused by bacteria, which means they can usually be treated with antibiotics. Viruses can’t, which makes Bourbon and another recently discovered tick-borne disease called Heartland virus particularly pernicious.
Both viruses are a reminder of how little scientists understand about tick-borne pathogens, says Keith Clay, a professor of biology at Indiana University. “We’re constantly discovering new bacteria and viruses in ticks,” says Clay. “I don’t think we have a full understanding of the range of microbes associated with ticks.”
In the case of Bourbon virus, we don’t even know which tick it’s associated with. Those most commonly found in Oklahoma include the American dog tick, known for spreading Rocky Mountain spotted fever, and the Lone Star tick, which transmits ehrlichiosis, tularemia, something called southern tick-associated rash illness (STARI, for short), and (probably) Heartland virus.
Many tick populations appear to be expanding. For instance, 10 or 15 years ago, Clay hardly ever encountered Lone Star ticks in southern Indiana, where he conducts field studies. Now the species is the area’s most abundant.
Scientists aren’t clear what exactly is helping the Lone Star tick and other species colonize America—or what’s behind the apparent uptick in tick-borne diseases. Changing climate might be making new areas hospitable for certain tick species. It also might be changing how ticks interact with the other animals they feed on. Probably the biggest factor, says Clay, is how human alteration of the environment is upping the abundance or proximity of deer, mice, birds, and other critters ticks like to feed on.
These factors also influence how easily and often ticks spread disease. For instance, warmer temperatures mean longer springs and autumns, increasing the likelihood that newly hatched ticks will feed on previously infected animals.