Tick-borne diseases on the move

Jun 17, 2017

Residents of the Northeastern U.S. have become increasingly familiar with Lyme disease, which is transmitted by ticks. But the tick population in this country is spreading and growing, and along with it, so are the diseases they carry.

This week on “Take Care,” Dr. Richard Ostfeld, senior scientist at the Cary Institute of Ecosystem Studies, a not-for-profit research institution in Millbrook, New York, discusses the latest information on ticks and tick-borne diseases. The Cary Institute examines the science behind environmental solutions. Ostfeld also teaches at Rutgers University and the University of Connecticut, and has authored the book, "Lyme Disease: The Ecology of a Complex System."

By far the most common disease transmitted by the blacklegged tick, also knows as the deer tick, is Lyme disease. Ostfeld says it is several times more prevalent than other tick-borne diseases. But cases of all of them are on the rise.

“The more we look inside ticks and people who get tick bites, the more of these pathogens and diseases we discover. And I think that’s likely to continue,” Ostfeld said.

Lyme disease is a bacterial disease, as are most other tick-borne diseases. The primary exception is Powassan virus, which Ostfeld calls the one important viral disease transmitted by ticks.

The blacklegged tick is found throughout much of the eastern half of the U.S. and up through southeastern Canada. There is also a western blacklegged tick in California and Oregon.

But even though ticks are found in large parts of the country, Ostfeld says distribution of tick-borne diseases is more restricted. For example, he says there is not much reported disease in the Southeastern U.S. Most of these diseases tend to be found in the Northeast, between Maine and Virginia, stretching west to western New York, western Pennsylvania and the Upper Midwest – including Wisconsin, Minnesota, Michigan, Illinois, North Dakota and South Dakota.

“These tick-borne diseases are on the move. They are increasing in their geographic range, but all of them seem to overlap in that sort of Northeastern and Upper Midwest area,” Ostfeld said.

There tend to be more reported cases of tick-borne disease every year, Ostfeld says. And the geographic range of ticks and the diseases is spreading. Those two factors might not be caused by the same things, but the reasons could overlap, Ostfeld says.

As the climate warms, tick are now occupying places that were too harsh an environment for them 10 or 20 years ago. Ostfeld says that explains tick populations’ movement to the north & up in elevation. But ticks are also spreading to the south, which is not caused by climate warming. Ostfeld says scientists don’t know what is contributing to ticks’ southward expansion.

The increase in the numbers of cases is in part due to expanding tick populations. But also, says Ostfeld, we’re doing a better job of detecting actual cases. That’s in large part because of increasing awareness by patients and health care providers. So, the statistics on tick-borne diseases are more accurate now. But Ostfeld says the true number of tick cases in the U.S. is still underreported.

Most of these tick-borne diseases share in common a set of early symptoms and signs. These tend to be flu-like symptoms -- fever, chills, muscle aches, lethargy. But since tick bites typically happen in May, June or July, patients should realize that’s not flu season, says Ostfeld. If they are feeling those symptoms and live in tick-borne epidemic zones, it’s critical seek medical attention right away, he says.

The Powassan virus is different. Ostfeld calls it “not a disease you ever want to get.”

Powassan causes swelling of the brain. So it often presents with headache or other neurologic symptoms. Powassan’s early symptoms can include partial paralysis, dizziness and disorientation, Ostfeld says.

Powassan virus is not easily treatable. Doctors can treat the symptoms, but little can be done to treat the disease, says Ostfeld. With the bacterial tick-borne diseases, an antibiotic can help clear the infection. But because Powassan is viral, an antibiotic is not an option.

Ostfeld calls Powassan “a scary disease.” The bad news is it can kill people, and does so in more or less than 10 percent of detected infections. Those who survive have a 50-50 chance of long term or even permanent disability. But Ostfeld says the good news is it’s quite rare – the rarest of all the tick-borne diseases. There are only a handful of cases in given year. The chance of exposure is low, but if you are, exposed, Ostfeld says it’s a huge problem.

Ostfeld also says those who are worried about tick-borne diseases should be comforted by the fact that this is a rapidly developing field of study. Scientists are discovering new information about ticks and tick-borne diseases and some of that information is being and will be turned into lasting remedies.