46. TICKS

Ticks really tick off a lot of people. These small, spider-like, parasitic arachnids bite their animal hosts and after they latch onto the skin of their victim, they feast on blood. Ticks can sense an animal’s body temperature, scent, and breath as they lie in wait on leaves or in grass for a passing host. Often ticks attach themselves to body parts that the host cannot see, such as the scalp, back, and legs. Mammals, birds, reptiles, and amphibians can all provide blood meals for ticks.

A tick bite often causes local skin irritation with redness, swelling, and itching. Some people are allergic to components in tick saliva that can send a victim into life-threatening anaphylactic shock and, strangely, lead to a meat allergy. Not all ticks transmit disease, but those that do can spread serious infections caused by bacteria, viruses, and protozoa.

Perhaps the most well-known tick-borne disorder is Lyme disease. Lyme disease is named after the city of Lyme, Connecticut, where an outbreak of the illness was discovered in 1975. The Centers for Disease Control and Prevention (CDC) reports that there were 26,203 confirmed cases and 10,226 probable cases of Lyme disease in the United States in 2016. The disease is caused by a bacterium called Borrelia burgdorferi. Deer and mice are carriers of B. burgdorferi, and the bacterium is transferred to ticks (e.g., Ixodes scapularis, black-legged tick, or Ixodes pacificus, Western black-legged tick) when they feed on the blood of these animals. Infected ticks then transmit the bacteria to humans (and other animals) when they bite. Symptoms of Lyme disease usually start with a gradually expanding rash at the site of the tick bite. As the bacteria spread through the body, a person may experience joint pains, general aches, chills, fever, and headache. Several weeks after the infecting bite, people with Lyme disease may experience a stiff neck, facial palsy, tingling or numbness in the extremities, headache, sore throat, and severe fatigue. Untreated Lyme disease may result in pain and swelling of the large joints, heart abnormalities (Lyme carditis), and neurological symptoms such as confusion and memory problems. Early treatment of Lyme disease with appropriate antibiotics often results in rapid and complete recovery, but late-stage Lyme disease is more difficult to treat, and symptoms may continue for many months.

Southern tick-associated rash illness (STARI) is sometimes mistaken for Lyme disease because both disorders are transmitted by tick bites and both result in circular rashes. STARI also causes some of the same symptoms as Lyme disease such as fatigue, headache, and body pains. However, STARI has been linked to the lone star tick (Amblyomma americanum); these ticks do not harbor B. burgdorferi, the bacteria associated with Lyme disease. The pathogen responsible for STARI is not known.

Another well-known tick-borne disease is Rocky Mountain spotted fever (RMSF). This disease is caused by bacteria in the rickettsia group. In the United States, the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni), and brown dog tick (Rhipicephalus sanguineus) can become infected with rickettsia bacteria. The bites of these infected ticks can cause fever, headaches, rash, nausea, and pain. Approximately 3,500 cases of RMSF were reported to the CDC in 2014. The initial illness associated with RMSF can leave some people with lingering health effects such as hearing loss, paralysis, and other neurological problems.

Different bacteria are responsible for several other tick-borne diseases, including anaplasmosis, African tick-bite fever, and tularemia. Symptoms of these diseases usually include fever, fatigue, headache, and muscle pain and can progress to serious illness involving the nervous, respiratory, and cardiovascular systems.

Ticks can also carry viruses that cause illness in people. Bourbon virus, Colorado tick fever, and Heartland virus have all been linked to tick bites and result in fever, headaches, body pains, and fatigue. Unfortunately, there are no medications or vaccines to prevent these viruses.

Babesiosis is a tick-borne disease caused by protozoan parasites (Babesia microti). These single-celled parasites target and reproduce in red blood cells of the host organism. In the United States, babesiosis is transmitted by the same ticks responsible for Lyme disease. People infected with B. microti may feel tired, lose their appetite, and have fever, nausea, sweats, and body aches. In healthy people, the infection may resolve itself, but victims who have spleen problems or take immunosuppressant medications may have serious complications and health risks.

If diseases caused by bacteria, viruses, and protozoa weren’t enough, ticks have another way to transmit disease: neurotoxic saliva. Many species of ticks release a chemical neurotoxin into their saliva when they bite. This chemical attacks the nervous system, causing tick paralysis, which often starts in the feet and legs and moves progressively higher in the body. When this happens, removal of the tick, at least some species, usually results in quick and complete recovery. But if the tick is not removed and the paralysis affects breathing, a person can die.

The best way to prevent tick-borne diseases is to avoid tick bites. Long-sleeved pants and shirts, boots, and hats should be worn by people traveling through areas where ticks are found. Insect repellents, including those containing DEET or permethrin, can also be effective in warding off ticks. When appropriate, people should check their bodies, especially the scalp, underarms, and legs, to ensure that they are free of ticks.

If a tick is found on your skin, it should be removed quickly and properly. Ticks should be removed by grasping them as close to their mouthparts as possible. For example, tweezers can be inserted between the tick’s mouth and host’s skin and pulled straight out. It is important to remove the head of the tick and avoid squeezing or pulling the tick by its body. After the tick is removed, wash the bite area with soap and water.

Many people like to get outdoors and commune with nature. To ensure that you don’t return home with any unwanted blood-sucking ticks, wear appropriate clothing, apply insect repellent, and do a body check.

SUMMARY

Preventability (78)

Dress appropriately, use insect repellent, and do body checks when you are in areas shared by ticks.

Likelihood (22)

Most ticks do not carry diseases, and a tick bite does not necessarily transmit disease. Rapid removal of a tick can reduce the likelihood of disease transmission, and appropriate antibiotic treatment for bacterial infections can resolve some tick-borne illnesses.

Consequence (67)

A tick bite can cause symptoms ranging from mild skin irritation that clears up in several days to severe health problems.

REFERENCES

Cabezas-Cruz, A., Mateos-Hernández, L., Pérez-Cruz, M., Valdés, J. J., de Mera, I. G. F., Villar, M., & de la Fuente, J. (2015). Regulation of the immune response to α-Gal and vector-borne diseases. Trends in Parasitology, 31, 470–476.

Centers for Disease Control and Prevention. (2017, July 25). Tickborne diseases of the United States. Retrieved from https://www.cdc.gov/ticks/diseases/index.html

Centers for Disease Control and Prevention. (2018, January 19). Lyme disease. Retrieved from https://www.cdc.gov/lyme/index.html

Pecina, C. A. (2012). Tick paralysis. Seminars in Neurology, 32, 531–532.