When it comes to transmitting infectious agents to humans, few vectors are as efficient as ticks, the parasitic cousins of spiders. The diversity of pathogens carried by ticks, from bacteria and viruses to parasites, reveals why they are often referred to as “walking syringes.” Below is a growing laundry list of diseases caused by the bite of ticks that inhabit the continental U.S.
Lyme disease is caused by the bacterial spirochete Borrelia burgdorferi, which is transmitted by the blacklegged or deer tick (Ixodes scapularis) principally in the northeastern and upper midwestern U.S. and by the western blacklegged tick (I. pacificus) along the Pacific coast. Typical symptoms include fever, headache, fatigue, and a characteristic skin rash called erythema migrans. If left untreated, infection can spread to joints, the heart, and the nervous system. Nervous system disease can result in headaches, cognitive deficit, brain ‘fog’, depression, and suicidality.
Borrelia mayonii infection has recently been described as a cause of illness in the upper midwestern U.S. It has been found in deer ticks and B. mayonii is the only species besides B. burgdorferi known to cause Lyme disease in North America. B. mayonii causes fever, headache, and neck pain in the days after infection and can cause arthritis after a few weeks of illness. Unlike B. burgdorferi, B. mayonii can also cause nausea and vomiting and large, widespread rashes.
Borrelia miyamotoi infection has recently been described as a cause of illness in the U.S. It is transmitted by the deer tick and has a range similar to that of Lyme disease. Patients with this infection commonly experience fever, chills, and headache. Other common symptoms included body and joint pain and fatigue but developing a rash is rare.
Babesiosis is caused by malaria-like parasites that infect red blood cells. Most human cases of babesiosis in the U.S. are caused by Babesia microti. B. microti is transmitted by the deer tick and is found primarily in the northeast and upper Midwest. In the continental United States and Canada another species of Babesia, B. duncani, is responsible for causing a more severe but rarer form of babesiosis. Patients can experience nonspecific flu-like symptoms but many infected people (approximately 40%) feel fine and do not have any symptoms.
Anaplasmosis is caused by the bacterium Anaplasma phagocytophilum. It is transmitted by tick bites primarily from deer ticks in the northeastern and upper midwestern U.S. and I. pacificus along the Pacific coast. Patients experience symptoms similar to Lyme disease early on but can also experience nausea, vomiting, diarrhea, and loss of appetite. Prolonged illness can result in respiratory failure, bleeding problems, organ failure and death.
Ehrlichiosis is caused by several species of the bacteria Ehrlichia. They are transmitted by the lone star tick (Amblyomma americanum), found primarily in the southcentral and eastern U.S. Symptoms are similar to that seen with anaplasmosis except confusion is common during early disease and severe inflammatory damage to the brain is associated with late disease.
Powassan disease is caused by a virus transmitted by the deer tick and the groundhog tick (I. cookei). Cases have been reported primarily from northeastern states and the Great Lakes region. Initial symptoms can include fever, headache, vomiting, and weakness. Powassan virus can also cause severe disease, including infection of the brain (encephalitis) or the membranes around the brain and spinal cord (meningitis). Severe illness is associated with confusion, loss of coordination, difficulty speaking, and seizures.
Heartland virus cases have been identified in the Midwestern and southern United States. Studies suggest that Lone Star ticks can transmit the virus. Most patients have fever, fatigue, decreased appetite, headache, nausea, diarrhea, and muscle or joint pain. Patients also can have lower than normal counts of white blood cells that help fight infections and platelets, which help clot blood.
Bourbon virus infection has been identified in a limited number of patients in the Midwest and southern United States. Because so few cases have been reported a full accounting of symptoms is lacking but they appear similar to those experienced by patients with Heartland virus disease.
Rocky Mountain spotted fever (RMSF) is caused by the bacterium Rickettsia rickettsii that is transmitted by mites and by the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (D. andersoni), and the brown dog tick (Rhipicephalus sanguineous) in the U.S. The first sign of many spotted fevers is generally a dark scab at the site of a mite or tick, known as an eschar. Eschars usually develop a few days to a week following the bite of an infected vector. Other signs and symptoms are not specific to RMSF and tend to mimic other tick-borne diseases (TBDs). However, the disease can rapidly progress to a serious and life-threatening illness. This can include damage to blood vessels resulting in amputation, hearing loss, paralysis, and mental disability.
Colorado tick fever (CTF) is caused by a virus transmitted by the Rocky Mountain wood tick (D. andersoni). It is a rare disease that occurs primarily in the Rocky Mountain states at elevations of 4,000 to 10,500 feet. Like RMSF, CTF can present like other TBDs. About half of patients have a “biphasic” fever, which means they have several days of fever, feel better for several days, and then have a second short period of fever and illness. Most patients have mild disease and recover completely. However, weakness and fatigue may last several weeks.
Rickettsia parkeri rickettsiosis, also known as Pacific Coast tick fever, is transmitted to humans by the Gulf Coast tick (A. maculatum). Caused by a bacterial species of Rickettsia this spotted fever is less severe than RMSF; however, it can be difficult to distinguish from the other spotted fevers, especially during early stages of the disease.
364D rickettsiosis (Rickettsia phillipi, proposed) is transmitted to humans by the Pacific Coast tick (D. occidentalis ticks). This is a new disease that has been found in California and presents very similar to other spotted fevers.
Tickborne relapsing fever (TBRF) is caused by a bacterial infection that results it recurring bouts of fever, headache, muscle and joint aches, and nausea. TBRF is transmitted to humans through the bite of infected soft ticks. of the genus Ornithodoros. Soft ticks differ in two important ways from the more familiar “hard ticks” (e.g., the deer tick and the dog tick). First, the bite of soft ticks is brief, usually lasting less than half an hour. Second, soft ticks do not search for prey in tall grass or brush. Instead, they live within rodent burrows and humans typically come into contact with soft ticks when they sleep in rodent-infested cabins. Thus far TBRF has been reported in 15 states: Arizona, California, Colorado, Idaho, Kansas, Montana, Nevada, New Mexico, Ohio, Oklahoma, Oregon, Texas, Utah, Washington, and Wyoming.
Tularemia is caused by the bacterium Francisella tularensis and is transmitted to humans by the dog tick (D. variabilis), the wood tick (D. andersoni), and the lone star tick (A. americanum). Unlike other TBDs, F. tularensis can also be transmitted by mosquitos and deer flies. Tularemia occurs throughout the U.S. and can be contracted through skin contact with infected animals, drinking contaminated water, and inhaling contaminated aerosols or agricultural and landscaping dust. Illness ranges from mild to life-threatening. All forms are accompanied by fever, which can be as high as 104 °F.
STARI (Southern tick-associated rash illness) is transmitted via bites from the lone star tick (A. americanum), found in the southeastern and eastern U.S. Curiously, the causative agent of STARI is yet to be discovered. Researchers once hypothesized that STARI was caused by the spirochete, B. lonestari; however, further research did not support this idea. Patients with STARI are difficult to distinguish from those with early Lyme disease. However, STARI has not been linked to arthritis, neurologic disease, or chronic symptoms.
Hopefully, what you are left appreciating is the fact that tick bites can result in a wide range of diseases, some of which can be quite debilitating while a few can often be lethal if left untreated.
Watch the video below to learn steps to prevent a tick bite as well as what to do if you should get a tick bite. For more info on GLA's Be Tick AWARE tick bite prevention program, visit BeTIckAware.org.
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Timothy Sellati, P.h.D.
Chief Scientific Officer at Global Lyme Alliance
Timothy J. Sellati, PH.D. is Chief Scientific Officer at Global Lyme Alliance As GLA’s Chief Scientific Officer, Dr. Sellati leads GLA’s research initiatives to accelerate the development of more effective methods of diagnosis and treatment of Lyme and other tick-borne diseases.