Updated: May 19, 2020
There are approximately 850 species of ticks and they rank second only to mosquitos in importance as insect vectors of human disease (1). Tick borne disease was first described nearly 2500 years ago. In the early 18th century, European doctors described patients with signs and symptoms of what today we know as Lyme disease. This was followed by several other discoveries that led to better understanding of tick borne diseases.
Ticks are the most common insect vectors of disease in the United States. For those of us that enjoy outdoor activities, ticks are unavoidable. Ticks may also affect those who don’t participate in outdoor activities, as pets may bring them into the home.
The overall warming noted around the globe has expanded the season which ticks are found and the window of opportunity for exposure to them. As a result of the warmer weather ticks are now found higher altitudes.
Once a tick initiates feeding, the feeding organ (hypostome) enters the skin of the host. The hypostome has hundreds of barbs pointed in reverse direction from entry into the skin to help anchor the tick.
Ticks transmits a variety of infectious agents. The main tick borne diseases in the United states are discussed below.
The most important diseases caused by Borrelia species in the United States include Lyme disease.
Doctors from the Yale School of Medicine investigated a cluster of cases of arthritis in children near Old Lyme, Connecticut in the 1970s. Further studies helped elucidate this as an arthropod borne illness that like any infection, responded to antibiotics.
Lyme disease surveillance started in 1982 at the Centers for Disease Control and Prevention (CDC) and this disease became reportable in 1991. In 2000, Lyme disease accounted for more than 90% of all cases of vector borne disease in the United States (2).
Anyone can become infected with Lyme disease, but there are two peaks: children 5 to 14 years old and adults 50 to 59 years of age. Lyme disease is a global problem and has been diagnosed or found on all continents (3,4).
Lyme disease has multiple constitutional, skin, nerve, cardiac and musculoskeletal symptoms. The most common being vague muscle pains, headache, fatigue, neck stiffness and bone pain. These symptoms are difficult to distinguish from simple viral infections which may lead to misdiagnosis.
The disease process in broken down to three stages. It usually begins as a localized infection with constitutional findings and symptoms, this is where the typical red, round rash appears (stage 1). Within days, the spirochetes spread through the blood and nerves, cardiac and joint abnormalities develop (stage 2). And finally, chronic infection of the joints, nerves, skin or even eyes may occur months or years later (stage 3).
The CDC has established a surveillance case definition for Lyme disease. This requires exposure to ticks in an endemic area and a skin lesion that is larger than 5cm. By this definition, exposure requires outdoor activities in the past 30 days of the onset of skin lesion. An endemic area is considered one where there has been at least two confirmed cases of Lyme disease. Unfortunately this definition is used for reporting and not helpful in actual individual diagnosis.
While there are several blood tests, many reveal non specific findings. Culture is the gold standard for diagnosis but is difficult to obtain. Another option is to biopsy the skin lesion.
Ultimately the best clinical diagnosis of Lyme disease is based on history, risk and a physician with a good knowledge of the disease process.
Most symptoms of Lyme disease improve spontaneously without treatment (3). However, treatment with appropriate antibiotics will shorten the recovery time in all stages of the disease.
The risk of serious complications in untreated patients with a known tick bite is low because less than 5% of those bitten in endemic areas become infected. Secondly, most people with an identified tick bite remove it before it has been attached for the 36-48 hours required for the tick to cause infection.
And lastly, nearly 90% of those who get infected develop the typical rash, which makes diagnosis easier.
Of these, three potentially transmit disease. They include Rocky Mountain spotted fever, Q fever and ehrlichial infections. It is important to note that exposure to crushed ticks, or fluids from these ticks may transmit rickettsiae.
Rocky Mountain Spotted Fever
This disease was first recognized in the Snake River Valley area of Idaho in 1896. Dr. Howard Ricketts established the epidemiology of this disease and also realized that ticks were the vector for transmitting this disease. The causative organism was named Rickettsia rickettsii.
A sudden onset of chills and fevers in a person with a history of tick exposure. Rocky Mountain spotted fever produces a disseminated vasculitic rash (5) in up to 90% of those with the disease. The rash usually begins on the wrists, hands, ankles and feet and spreads centripetally.
Initially it is a small blanching reddish lesion that evolves into a larger more pronounced and non blanching lesion. Finally the rash turns dark red to black.
Immunocompromised patients are the least likely to have this rash but are most likely to die from this disease (6). Other symptoms include minor headache to encephalopathy, seizures, ataxia and delirium. Gastrointestinal symptoms are also very common.
Early diagnosis and treatment significantly reduce the morbidity and nearly eliminates the chance of dying from this disease. For this reason, some doctors treat if they suspect Rocky Mountain spotted fever even before a definitive diagnosis. Serology is the confirmatory test but is not perfect.
Antibiotics are recommended for those living or recreating in endemic areas if they develop any of the constitutional symptoms of Rocky Mountain spotted fever such as headache, fever and muscle aches. Patients started on early antibiotic treatment are three times less likely to die from this disease (7).
First described in 1937 in Australia, this zoonotic disease in found worldwide and affects both wild and domestic animals (8). Aerosol spread of the causative agent Coxiella burnetii is the usual mode of transmission to humans.
Fortunately this is relatively rare and only about 10 cases are reported in the United States per year.
The most common clinical manifestation is flu like symptoms such as fevers, headache, and muscle aches.
Serologic testing is used to diagnose Q fever.
Antibiotics are the mainstay of treatment and the drug and duration of therapy depend on acute or chronic disease.
Ehrlichiosis was discovered in the mid 1980s in rural areas of Arkansas. There were several cases of a febrile disease that had many of the symptoms of Rocky Mountain spotted fever (9).
There are two basic forms of ehrlichiosis in humans: human monocytic ehrichiosis (HME) and human granulocytic ehrichiosis (HGE).
Human Monocytic Ehrlichiosis (HME)
Although reported in 46 states, it is found predominantly in south central and southeastern United States. It is primarily transmitted in the months of March through November.
Human Granulocytic Ehrlichiosis (HGE)
This disease occurs in the north-central and northeastern parts of the United States.
Clinically, HME and HGE are very similar. Within a week or two after exposure to an infected tick, malaise, back pain, gastrointestinal symptoms and fevers up to 102 F(39 C) develops. The majority of those infected require hospitalization (10,11). This disease can be fatal.
Generally speaking, those who are immunocompromised, older than 60 and those who have not received appropriate antibiotics within one week of the onset of symptoms are the most likely to die (12).
Lab tests are available to confirm diagnosis.
Appropriate antibiotic therapy is the mainstay of treatment.
Tick borne viral diseases
Colorado Tick Fever
This is the only tick borne virus that occurs with any significant frequency in the United States. Typically only adult ticks can transmit the virus to humans.
The fever is similar to dengue fever, with fevers up to 104F (40C) for a few days followed by a brief remission period before another fever episode of similar duration. Severe complications can occur especially in young children less than 10 years of age.
This is usually a clinically diagnosis, but laboratory diagnosis is available.
Treatment is non specific and is entirely supportive. Recovery usually takes several weeks but infection generally confers lifelong immunity.
These are pleomorphic protozoan parasites and more than 70 species have been described (13). Transmission is via a tick bite.
There is a gradual onset of malaise, anorexia, and fatigue, followed by several days of fever, sweats and muscle pains. The incubation period is anywhere from one to four weeks after the tick bite and most people don’t recall a tick bite when they develop symptoms. Most people with normally functioning spleens recover without specific therapy, however prolonged fatigue and malaise is common (14).
Babesiosis should be considered in any person with unexplained fevers who lives in or has traveled to an endemic region in the midsummer months. Especially if there has been an history of a tick bite. Diagnosis is confirmed by a blood smear showing the parasite.
Those with mild symptoms usually recover without treatment. Antibiotic therapy should be considered in those who are immunocompromised, don’t have a functional spleen or the elderly (15).
The best prevention is awareness of ticks and the diseases they can transmit. Proper clothing should consist of light colors to make it easier to spot the ticks.
Insecticides containing diethyl toluamide (DEET) are generally safe, work well and may be applied directly to the skin. For more protection, permethrin based acaricidal spray such as Permanone applied to clothing will last up to a month and through several washings. Permethrin should not be applied to the skin.
Frequent inspection of the body should be done when in a tick infested area. Although some tick borne diseases require the tick to be attached to the skin for 24 to 48 hours, some can transmit disease within an hour.
Removal of attached ticks should never be done by bare hands. Fine tipped forceps can be used to gently grab the tick as close to the skin as possible and gradually pulling it out in a straight line. There are commercial kits for this but they tend to cost more.
Applying petroleum jelly to the tick, or using a lighted match or cigarette, alcohol or fingernail polish DO NOT ease removal of the tick. In fact these “home remedies” increase the expression of tick saliva and other contents and increase the chance of disease transmission (16,17).
Washing clothing in hot water and drying on high heat after being in tick infested areas generally work to kill ticks. Despite this some ticks may still survive, it is recommended that clothing be placed on high heat in the dryer for at least an hour (18).
Please remember that medical information provided by us must be considered an educational service only. This blog should not be relied upon as medical judgement and does not replace your physician’s independent judgement. This is NOT medical advice. Please seek the advice of your physician.
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13- Ristic M, Healy GR: Babesiosis. In Steele JH (ed): CRC Handbook Series in Zoonoses, Section C: Parasitic Zoonoses, vol I. Boca Raton, Fla, CRC Press, 1981.
14- Ruebush [or as Reubush] TK 2nd, Cassaday PB, Marsh HJ, et al: Human babesiosis on Nantucket Island: Clinical features. Ann Intern Med 86:6–9, 1977.
15- Centers for Disease Control: Clindamycin and quinine treatment for Babesia microti infections. MMWR Morb Mortal Wkly Rep 32:65–66, 72, 1983.
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17- Needham GR: Evaluation of five popular methods for tick removal. Pediatrics 75:997,1985.
18- Carroll JF: A cautionary note: Survival of nymphs of two species of ticks (Acari: Ixodidae) among clothes laundered in an automatic washer. J Med Entomol 40:732– 736, 2003.