Residents in the Midwest are generally aware that ticks carry the bacteria that cause Lyme disease. But ticks are responsible for other fatal diseases as well. The worst is Powassan disease, which kills about 10 percent of its victims and leaves half of the survivors with permanent neurological damage.

Ticks carry other patho-gens that cause such human diseases as anaplasmosis, babesiosis, ehrlichiosis, Rickettsia parkeri, Rocky Mountain Spotted Fiver, Southern Tick Associated Rash Disease, tick-borne relapsing fever, tularemia and Rickettsiosis.  Like mosquitoes, ticks are capable are capable of carrying, supporting and injecting more kinds of disease-causing microbes than almost any other creature.



Description

Ticks are close relatives of mites and spiders. In fact, they may have evolved from mites more than 94 million years ago.

Ticks have eight legs and a flat, hard body. Like many of their arthropod relatives, ticks hatch from eggs and grow through four distinct stages: egg, six-legged larva, eight-legged nymph and adult. Adult ticks are approximately the size of a poppy seed. Ticks, like crabs and lobsters, have a hard covering that they must shed periodically to grow. They generally live for two years.

The biggest problem ticks have is finding an appropriate host for their next blood meal. (Ticks must have a blood meal at every stage to survive and grow.) Ticks cannot fly; they crawl slowly and generally cannot travel without help. Ticks can crawl on a blade of grass or twig and using their lower legs for leverage wait for the right host to come along. They hold their upper pair of legs outstretched, waiting to climb aboard.

Ticks do not see well but have an extremely sensitive and rapid response to a whiff of carbon dioxide or to the faint odor of butyric acid exuded from the skin of many animals. They can feed from mammals, birds, reptiles and amphibians.

Depending on the tick species and its stage of life, preparing to feed can take from 10 minutes to two hours. When the tick finds a feeding spot, it grasps the skin and cuts into the surface. The tick then inserts its feeding tube. Many species also secrete a cement-like substance that keeps them firmly attached during the meal. The feeding tube can have barbs that help keep the tick in place. Ticks can also secrete small amounts of saliva with anesthetic properties so that the animal or person cannot feel that the tick has attached itself.



Lyme Disease

Some ticks will attach to a host and suck the blood slowly for several days. If the host has certain blood-borne infections, such as the Borrelia burgdorferi spirochete, the agent that causes Lyme disease, the tick may ingest the pathogen and become infected. Once infected, a tick can transmit infection throughout its life.  Transmission of B. burgdorferi generally requires at least 36 hours of tick attachment.

Lyme disease is the most widespread tick-borne disease in the United States, but it is not confined to this continent. Researchers have even located infected ticks that helped spread disease on seagulls and albatrosses in the Arctic Ocean and in Antarctica. Some 30,000 cases are reported to the Centers for Disease Control (CDC) each year, but most cases go unreported because the symptoms are mild or mimic other diseases. The CDC recently estimated that there may be 300,000 cases a year in this country.  

Many scientists contributed to today’s understanding of Lyme disease but a team from the Yale School of Medicine is widely credited with the discovery. Dr. Stephen Malawista and Allen Steere, then a postdoctoral student, defined the ailment.  

The story began in 1975, when two mothers — one from Lyme, Connecticut, and the other from adjacent Old Lyme, were distressed by the odd rashes, neurological symptoms and swollen joints that their families and others were experiencing. Unable to find answers, each approached Yale independently.  The initial diagnosis was juvenile rheumatoid arthritis, but the disease had never been known to appear in bunches. Doctors at Yale counted 51 cases, a rate about 100 times what was expected to occur in a combined population of 12,000 in the two towns. The cases also occurred almost exclusively in warm weather months. Because the disease was clustering, it looked like there had to be a vector — something like an insect to transmit the disease.

Malawista and his associates made the compelling link between ticks and the disease by noting that cases were 30 times more frequent on the east side of the Connecticut river, where Lyme is situated, than on the west side. Ticks feed and breed on deer, and there are far more deer on the east side.

Prevention

Several points in the transmission cycle provide opportunities to prevent Lyme disease. However, no prevention strategy can be effective unless people who are at risk accept it.

People can be cautioned to avoid tick-infested areas. Second, there is good evidence that removal of ticks within 36 hours after attachment will reduce the risk of infection. Daily tick checks are thus advised.

People can also wear protective clothing, tuck their pants into their socks and use repellents.

For tick control, the most consistently effective method is to spray or otherwise broadcast acaricides onto vegetation where the ticks live. Acaricides are pesticides that kill ticks and mites.

Max Sherman is a medical writer and pharmacist retired from the medical device industry. He has taught college courses on regulatory and compliance issues at Ivy Tech, Grace College and Butler University. Sherman has an unquenchable thirst for knowledge on all levels.  Eclectic Science, the title of his column,  will touch on famed doctors and scientists, human senses, aging,  various diseases, and little-known facts about many species, including their contributions to scientific research. He can be reached by email at  [email protected].