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.
He 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 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.
Q. How long does a tick have to stick to you to transmit Rocky Mountain spotted fever or other infections?
A. The tick can transmit infection in 3 hours or less. For Lyme disease, it typically takes 36 to 48 hours for the tick to transmit the infection.
Q. What are symptoms of Rocky Mountain spotted fever?
A. They aren’t much different from a flu — fever, headache, muscle aches. But within 3-10 days, a rash will spread to your torso until it becomes spotted. At that point, the disease may be doing serious damage to your organs. Some people go on to develop permanent disabilities like gangrene, learning disabilities, and problems walking, says Paddock.
Q. How is Rocky Mountain spotted fever treated?
A. Like Lyme and most other bacterial tick-borne infections, it’s treated with the antibiotic doxycycline in the first 5 days after a tick bite. About a quarter of people with the disease who are not treated with doxycycline die within 8 or 9 days, Paddock says.
“The frustrating component is that there isn’t a lot to go on in the first 3 days of the illness,” he says. As many as 40% of people who get the disease don’t report it right away. Knowing whether your area has a higher prevalence of the disease can help diagnose it more quickly.
Q. What about other tick-borne diseases?
A. Both anaplasmosis, transmitted by the blacklegged tick, and ehrlichiosis, transmitted by the lone star tick, are on the rise. The CDC first started tracking them in 1999.
The number of ehrlichiosis cases rose sharply between 2000 and 2008 — when 961 cases were reported — and then dropped steadily until 2010. But the numbers climbed again, reaching 1,288 in 2015. The death rate from the disease has remained about 1% since 2010. Paddock attributes the rise to better disease identification and public awareness.