from Infectious Disease Special Edition, September 27, 2017
by IDSE News Staff
Ticks are nasty little survivors, outlasting even dinosaurs as they resist drought, tolerate cold and go for months without a blood meal. University of Cincinnati researchers are demonstrating just how hardy they are.
Researchers at the UC McMicken College of Arts and Sciences are examining the tick’s defenses, looking for ways to prevent tick-borne illnesses, such as Lyme disease. They are studying the distribution of ticks in southwestern Ohio, the diseases they carry and their ability to withstand Midwest winters.
“There are still so many things we don’t know about ticks,” said UC assistant professor Joshua Benoit, PhD, who is supervising the research. “They’re known for transmitting even more diseases than mosquitoes.”
Four species are found in southwestern Ohio. They are shaped like a watermelon seed but can vary in size from a poppy seed to the head of a pushpin, with eight legs and a hard protective shell. Hungry for a meal, they climb to the tip of a blade of grass or a twig and wave their extra-long, hook-tipped forelegs in the air, a behavior called “questing,” until a rabbit, deer, dog or human brushes past. They can detect carbon dioxide from their would-be host so they are ready to latch onto fur or denim, if given the chance.
Ticks have ferocious barbed mouth parts like ratchets that allow them to pierce deeply into the skin and remain embedded while feeding on the host’s blood. They transmit diseases through their saliva.
Students in UC’s Department of Biological Sciences regularly collect ticks at local parks. Surveillance research begins at UC’s Center for Field Studies northwest of Cincinnati, next to Miami Whitewater Forest. On a recent morning, UC postdoctoral fellow Andrew Rosendale, PhD, and students Alicia Fieler, Benjamin Davies and Madisen Kimbrel dragged flags made of fleece over bushes and meadows full of summer wildflowers to collect ticks for their study.
Back at Dr. Benoit’s biology lab, the students measure the levels of lipids, proteins and glycogen in the tick specimens. Higher fat content is an indication of good nutrition. They can also identify what diseases, if any, the ticks carry.
Once tick eggs hatch, the baby parasites seek a blood meal in each of their next three life cycles: larvae, nymph and adult. They live for up to six years.
Dr. Rosendale, a co-author of numerous studies on ticks, said the goal of the research is to find ways to slow or halt the spread of disease. “We want to find better ways to kill them by studying the mechanisms of resistance of ticks to pesticides.”
Fossil evidence suggests that ticks fed on dinosaurs and other Cretaceous Period creatures 90 million years ago. Today, ticks contract Borrelia burgdorferi and other bacteria from animals, such as mice, that serve as reservoirs for the bacteria.
“Ticks carry countless diseases. New ones are identified all the time,” Dr. Benoit said.
Besides Lyme disease, ticks in many midwestern and northeastern states are known to carry diseases such as anaplasmosis, ehrlichiosis and Rocky Mountain spotted fever. The bite of some Lone Star ticks in Kentucky and Indiana has been linked to an immune response that causes some people to become allergic to red meat, a disorder called alpha-gal. “It’s a bizarre condition. People talk about it but it’s relatively rare,” Dr. Benoit said.
Doctors need to be vigilant about tick-borne illnesses, even those not commonly observed in this area, said Carl J. Fichtenbaum, MD, an infectious disease specialist at the University of Cincinnati Medical Center and the Cincinnati Veterans Affairs Medical Center.
“Lyme is uncommon here. We see a handful of cases each year,” he said. “Someone goes to Cape Cod for vacation and gets bitten by a tick and comes back with an infection.”
Typically, patients with Lyme disease complain of flu-like symptoms: headache, fever, and achy joints or muscles, he said. “They may get the characteristic bull’s-eye rash around the bite, but that doesn’t happen in everyone.”
Unlike mosquitoes, which transmit viruses such as West Nile or Zika in their bite, ticks transmit bacteria when they bite people, Dr. Fichtenbaum said. “With tick-borne diseases, we don’t have immunity to bacterial infections. We can get infected over and over again. Our body isn’t capable of fending it off.”
A course of antibiotics cures most tick-borne diseases. Dr. Fichtenbaum said surveillance efforts such as UC’s ongoing study are invaluable in helping doctors understand the likelihood of patients contracting diseases from local ticks.
“I think it’s great to sample the population of animals and insects to understand zoonosis,” he said. “It’s always good if we’re keeping track of what’s out there so we know the possibilities.”
So far, B. burgdorferi has not been found in the ticks that Dr. Benoit’s team has collected locally. But one species, the dog tick, is a known carrier of RMSF, which causes headache and fever and, sometimes days later, a spotted rash. It’s prevalent in midwestern and mid-Atlantic states.
About 30,000 cases of Lyme disease are reported each year to the CDC. The disease was observed in patients across 40 states in 2015. But this does not capture all diagnosed cases or the many suspected cases that go undiagnosed each year, the agency said. A 2015 study by the CDC used health insurance claims between 2005 and 2010 to estimate that 329,000 people contract Lyme disease each year in the United States.
“The vast majority of research into tick-borne illness is where Lyme disease is prevalent, in the Northeast and upper Midwest,” Dr. Rosendale said. “It hasn’t received a lot of attention in Ohio because historically Lyme disease hasn’t been as common. We didn’t have the blacklegged tick here. But recently we’ve been seeing more and more of that species, and so Lyme disease is becoming more of an issue.”
Some tick species appear to be expanding their range, which means the diseases they carry could be an emerging concern, Dr. Rosendale said.
A UC study, published in 2016, suggests that ticks have little difficulty surviving a typical Ohio winter (Ticks Tick Borne Dis 2016;7:1155-1161). Drs. Benoit and Rosendale et al examined the cold tolerance of the American dog tick using exposure to temperatures as low as –9° F. They determined that no ticks survived more than two hours at that temperature. But ticks could withstand temperatures just above 0° F, and most survived temperatures in the 20s for at least two weeks.