FAQ: Tick-Borne Diseases
Although Lyme disease is the most prevalent tick-borne infection in the U.S, ticks can transmit 20 diseases, according to the CDC. Some of these -- like Rocky Mountain spotted fever, Powassan virus and ehrlichiosis -- can be fatal. And while tick populations are not on the rise, they have expanded their range to all 50 states, says Christopher Paddock, MD, of the CDC.
The blacklegged tick -- which can transmit Powassan, Lyme disease, babesiosis, and anaplasmosis, for example -- is now in almost half of all U.S. counties. CDC data show that ticks are responsible for more emerging diseases than mosquitoes -- 95% of all vector-borne diseases, Paddock says. Ticks are also believed to transmit the Bourbon virus, which is suspected in the death of a Missouri woman in June.
Paddock says it’s difficult to predict from year to year how many cases of tick-borne diseases they'll see. Not all ticks bite humans, and most tick bites do not result in infection.
“But there are many billions of ticks and thousands of cases of tick disease in the U.S.,” says Paddock, who specializes in spotted and typhus fevers.
Here’s what you need to know about tick-borne illnesses.
Q. How is Rocky Mountain spotted fever transmitted, and are cases on the rise?
A. The Arizona Department of Health Services reported seven cases of the disease in the first 4 months of 2017, Paddock says. It’s most commonly transmitted by the American dog tick in the eastern United States and the brown dog tick in the West.
Although relatively rare, Native American reservations in southeast Arizona have seen epidemic levels of the disease. Between 2002 and 2014, public health officials reported more than 300 cases of Rocky Mountain spotted fever in the region, and more than 20 people have died from the disease.
Q. Why are cases of Rocky Mountain spotted fever on the rise?
A. A large population of free-roaming dogs carry the ticks. When humans come into contact with the dogs, the ticks bite and infect them, Paddock says. The explosion of Arizona cases has occurred in a low-income area where many people can’t afford treatments to prevent ticks for their dogs. They might also not have the resources to neuter or spay the dogs to keep down their numbers, he says.
Outside of Arizona, the disease is typically clustered in the “tick belt” that stretches from Oklahoma to North Carolina. According to the CDC, more than 3,000 cases of the disease are reported each year, most from Oklahoma, Arkansas, Missouri, Tennessee, and North Carolina.