Common Tick Species

Ticks are parasitic arthropods that feed on the blood of vertebrates like mammals (including humans), birds, reptiles, and amphibians. Ticks can transfer various illnesses from animals to humans, including parasitic worms, viruses, and bacteria. The bacteria that cause Lyme disease and Rocky Mountain spotted fever are the most common in Pennsylvania.

Ticks are of more than 900 different species, with at least 25 of them found in Pennsylvania. The blacklegged tick (Ixodes scapularis) and the American dog tick (Ixodes canis and Dermacentor variabilis) account for more than 90% of identification requests sent to Penn State. The lone star tick (Amblyomma americanum), Asian longhorn tick (Haemaphysalis longicornis), and winter tick (Haemaphysalis longicornis) are three more species that may be encountered.

Common tick species

Common tick species that cause diseases in humans include:

Ixodes scapularis (Blacklegged tick)

I. scapularis is found in wooded, brushy areas and grassy edge habitats. Despite being less common in the past, this species' distribution has been growing in recent years. This tick is commonly referred to as a "deer tick." However, blacklegged tick is the preferred common name because deer have historically been regarded as the primary host only during the adult stage.

Small mammals such as mice and chipmunks, as well as birds, are preferred hosts for blacklegged tick larvae; nymphs feed on small mammals and birds, as well as on various media and large mammals such as raccoons, deer, and black bears. Adult blacklegged ticks prefer to feed on larger mammals, especially white-tailed deer. Ticks at any stage, however, can feed on humans, cattle, and companion animals.

Adult ticks can be found in the fall, winter, and early spring, depending on the activity phase. Adult ticks can be active and seek hosts on any day when temperatures are above freezing during the winter. Tick larvae can be found in the late summer, and nymphs can be found in the late spring and summer.

Blacklegged ticks are well known for carrying the pathogens that cause Lyme disease, but they also carry other bacteria such as Anaplasma spp. and Babesia spp., which can cause anaplasmosis and babesiosis, respectively. While there is still some disagreement, blacklegged ticks must adhere to the skin for at least 24 hours before transmitting Borrelia burgdorferi, which causes Lyme disease. Only nymphs and adult ticks spread the infection because they need to feed on a pathogen-infected host to transmit the pathogen to people or other animals. Depending on the area, 20%-40% of blacklegged ticks test positive for B. burgdorferi.

Dermacentor variabilis (American dog tick)

D. variabilis likes open areas with few or no trees, such as grassy fields and scrublands. American dog ticks are substantially larger than blacklegged ticks, with engorged female ticks as large as a grape.

Larvae are most active in the spring and fall, but nymphs and adults can be found throughout the summer. Unfed ticks of all life stages, however, can live for more than a year between hosts (larvae: 15 months; nymphs: 20 months; adults: 30 months); therefore, all life stages may be encountered throughout the year.

Larvae and nymphs prefer to eat tiny rodent hosts. Adults feed on squirrels, raccoons, rabbits, groundhogs, foxes, deer, domestic livestock, and humans, as well as other media and large mammals like squirrels, raccoons, rabbits, groundhogs, foxes, deer, domestic livestock, and humans. They have a reputation for being vicious biters.

Diseases: American dog ticks are the primary vectors of the bacteria that cause Rocky Mountain spotted fever, a less common but possibly more deadly infection than Lyme disease. They've also been linked to tularemia transmission and canine tick paralysis. D. variabilis cannot transmit Lyme disease.

Amblyomma Americanum (Lone star tick)

During the late summer and fall, larval lone star ticks are active, whereas nymphs and adults are active in the spring and summer. The larvae of the lone star tick are frequently observed in huge numbers.

This tick has a wide range of hosts. The larvae consume a wide range of small- to medium-sized animals, and the nymphs consume a wide range of medium- and large-size species. Adults prefer larger creatures to feed on. All stages are aggressive biters who will happily feed on humans, livestock, and pets.

Rocky Mountain spotted fever, ehrlichiosis, tularemia, and STARI (southern tick-associated rash sickness), as well as Heartland virus and Bourbon virus, can all be transmitted by lone star ticks. A. americanum bites have also been linked to an allergy to alpha-gal (red meat).

Adult females are easily distinguished by a single white dot in the center of their reddish-brown bodies.

Groundhog (Woodchuck) tick (Ixodes cookei)

I. cookei can be found in the east of the Rocky Mountains, from Texas to South Dakota and northeastward to Maine.

Groundhog ticks are only found on groundhogs, as well as on birds, small animals, and humans.

Powassan virus encephalitis is caused by the Powassan virus, which is transmitted by groundhog ticks. Because they prefer to eat only groundhogs that do not carry the infection, they are not a significant vector of the pathogen that causes Lyme disease.

Haemaphysalis longicornis (Asian longhorned tick)

The invasive tick H. longicornis is native to East and Central Asia. In early 2010, it spread throughout Oceania and the United States.

Because the Asian longhorned tick is new to North America, its preferred hosts are unknown. Larvae and nymphs prefer small mammals and birds in other parts of the world, and adults prefer large animals, including cattle, horses, deer, and sheep. In the United States, only one case of H. longicornis has been reported.

Diseases: In North America, the Asian longhorned tick is not known to transmit any infections. However, it is known to vector Anaplasma spp., Ehrlichia spp., and Powassan virus in its native region; thus, it may be a vector for infections in the United States as well.

Common tick-borne diseases:

Lyme disease

Lyme disease, also known as Lyme borreliosis, is a bacterial spirochete infection spread by ixodid ticks and caused by the bacterial spirochete Borrelia burgdorferi. It is the most common tick-borne disease affecting humans. The virus is most dangerous to humans, pets, and horses. It's a multisystem sickness marked by erythema migrans (bull’s-eye rash) and a slew of nonspecific complaints and symptoms such as headache, fever, sore throat, and nausea. If left untreated, it can lead to late-stage symptoms such as debilitating rheumatologic, cardiac, and neurologic disorders, as well as mortality in rare cases.

After being bitten by an infected tick, 70%-80% of people who have Lyme disease develop a skin lesion. The lesion begins as a small red macule or papule and grows larger over days or weeks to develop a huge spherical lesion. The center of this lesion frequently clears with time, forming a "bull’s-eye." This condition is known as erythema migrans, and the lesion must be 5 cm (2 inches) in diameter for CDC surveillance purposes. There may be associated or secondary lesions. Intermittent fatigue, fever, headache, stiff neck, arthralgias, or myalgias are commonly associated with this symptom.

Later, the musculoskeletal, neurological, and cardiovascular systems show more severe symptoms. After weeks or months of the initial erythema migrans, recurrent swelling of the joints may develop into a chronic disease at one or more sites. Lymphocytic meningitis, cranial neuritis, bilateral facial palsy (Bell's palsy), radiculoneuropathy, and encephalomyelitis can occur simultaneously or at different times. Myocarditis can develop as a result of atrioventricular conduction abnormalities. Additional symptoms such as arthralgia, myalgia, fibromyalgia, headache, weariness, stiff neck, palpitations, and bundle branch block may be present, although they do not necessarily indicate Lyme disease.

Rocky Mountain spotted fever (RMSF)

Rickettsia rickettsii is the bacterium that causes RMSF.

RMSF causes fever and a red, purple, or black rash, which appears on the wrists and ankles 2-4 days after the fever starts. Headaches, malaise, nausea, and vomiting are among the early symptoms, whereas later signs and symptoms include stomach and joint discomfort, conjunctivitis, and amnesia.

Because typical serologic tests can't tell the difference between RMSF and other spotted fever-group rickettsiae (e.g., Rickettsia parkeri Rickettsiosis, Pacific Coast tick fever, and rickettsialpox), RMSF is frequently reported alongside other spotted fever-group rickettsiae (SFR).

Tularemia

The bacterium Francisella tularensis causes tularemia, also known as rabbit fever. Lone star ticks, American dog ticks, Rocky Mountain wood ticks, rabbit ticks (Haemaphysalis leporispalustris), and deer flies can all carry the bacterium, as well as rabbit blood (e.g., butchering a rabbit without gloves and other protection or via aerosolized blood after a rabbit is struck by a lawnmower).

Fever, chills, loss of appetite, general body aches, and swollen lymph nodes are all symptoms of tularemia. An ulcer occurs at the site of a tick or fly bite when the disease is contracted. Antibiotics are used to treat tularemia, and they can reduce the fatality rate from more than 60% to less than 4%.

Babesiosis

The causative agent of babesiosis, Babesia microti, is a protozoan parasite transmitted by the blacklegged tick (Ixodes scapularis), although it is also rarely transmitted via blood transfusions (as there are no known screenings for the pathogen) and congenitally from a mother to her baby during pregnancy or birth. Babesiosis is most common in the northeastern United States, but cases have been found all around the country. Between 2011 and 2014, 900 to 180 cases per year were reported across the country.

Fatigue and loss of appetite are signs and symptoms of babesiosis, which are followed by a fever with chills, muscle pains, and headaches. Blood may occur in the urine in more severe situations. In otherwise healthy patients, the condition is usually self-limiting, and symptoms go away on their own. Babesiosis, on the other hand, is more severe in specific categories, such as the elderly, those without a spleen, and those who are immunocompromised. Additional consequences, such as low and unstable blood pressure, severe anemia, low platelet count, organ malfunction, and death, can develop in these high-risk patients.

Babesiosis is treated with the same medications used to treat malaria, another protozoan disease.

Erlichiosis

Three species of rickettsia bacteria of the genus Erlichia cause erlichiosis (E. chaffeensis, E. ewingii, and E. muris eauclairensis). It's most frequent in the south, although it's been reported in nearly every state in the east of the Rocky Mountains. The majority of cases occur during the summer, when tick activity is at its peak, but instances have been observed throughout the year. Erlichiosis has only been reportable to the CDC since 2000, and the number of cases has continuously increased from 250 per year to 1500-1700 per year across the country since then.

Symptoms include chills, headaches, body pains, and fever, which are similar to those of Rocky Mountain spotted fever or the flu. Up to 30% of people infected with RMSF develop a rash similar to that of RMSF 5 days after their fevers start. Symptoms are usually moderate, but if antibiotic therapy is delayed, they might become severe. Meningoencephalitis can cause brain or nervous system damage in late stages, as well as respiratory failure, uncontrolled bleeding, organ failure, and death. The extremely young and elderly, as well as those with weakened immune systems, are at greater risk of contracting a serious infection.

Powassan viral encephalitis

Powassan viral encephalitis is caused by an RNA virus that is similar to West Nile and St. Louis encephalitis. Ticks that carry the disease include blacklegged ticks, groundhog ticks, and squirrel ticks (Ixodes marxi). It is likely underreported because many people who contract the virus do not show symptoms.

Symptoms of Powassan virus encephalitis include fever, headache, vomiting, weakness, confusion, lack of coordination, and seizures, which appear 1-4 weeks following a tick bite. Around 10% of Powassan virus encephalitis cases are deadly, and half of those who survive acquire long-term neurological problems.

Powassan virus encephalitis is not treatable with vaccines or drugs; however, supportive care such as respiratory support, intravenous fluids, and medications to lower brain swelling can help.

Tick paralysis

Tick paralysis is caused by poisons injected by ticks into their hosts while feeding. Most animals can be affected, including pets and cattle, but smaller and younger mammals are more vulnerable. Human cases are not common and are usually seen in children under the age of 10.

Tick paralysis is caused by ticks that are adhered to the head, especially toward the base of the skull. Symptoms appear after 1-7 days of a tick bite, and they start with limb weakness. Within a few hours, the weakness advances to paralysis, which affects the trunk, arms, and head. When the ascending paralysis of tick paralysis reaches the lungs, it can cause respiratory failure and death. If the tick(s) are identified and removed, recovery begins immediately, and the symptoms fade away within a day.

The Rocky Mountain wood tick, the lone star tick, and the American dog tick have all been linked to tick paralysis in the United States. Tick paralysis is not caused by all members of a species. The toxin that causes this illness is injected into the tick's salivary fluid. Because the issue is linked to ticks adhering to the head and because recovery is swift when the tick is removed, it's thought that the toxin acts locally and is quickly broken down in the body. Tick paralysis happens infrequently. It is important to be aware that it does happen and to try to locate and remove the tick when symptoms appear.

Allergy to alpha-gal

All mammals, with the exception of Old World monkeys and apes, have the chemical alpha-gal (galactose-alpha-1,3-galactose, including humans). Alpha-gal allergy, also known as meat allergy or mammalian meat allergy, is a food allergy that occurs when a lone star tick bites a human after feeding on a non-human mammal. A tick may inject alpha-gal from its intestines into a person along with saliva during a bite. The body responds by generating a flood of IgE antibodies in an attempt to combat the alien alpha-gal.

Whole-body itching, hives, gastrointestinal discomfort, and anaphylaxis are all signs of IgE-mediated allergies. People with asthma may experience very severe respiratory distress. Unlike most food allergies, which usually emerge immediately or quickly, an allergic reaction to alpha-gal usually takes 3-8 hours to manifest. Some people with alpha-gal allergies report being able to consume certain lean meats (e.g., venison), and the allergy may spontaneously subside with time, ranging from 8 months to 5 years, as reported by patients.

Heartland virus and Bourbon virus

The Heartland virus and Bourbon virus are two newly discovered tick-borne illnesses about which little is known.

Fever, lethargy, headache, nausea, and muscle or joint pain have been reported by the majority of patients infected with the Heartland virus or the Bourbon virus. Because of their comparable symptoms, these diseases may be mistaken for ehrlichiosis or anaplasmosis. The majority of patients will need to be admitted to the hospital. The Heartland virus and Bourbon virus have no vaccinations or drugs to treat them; however, supportive care to manage symptoms may help with recovery.

References

https://pubmed.ncbi.nlm.nih.gov/30736991/

https://pubmed.ncbi.nlm.nih.gov/15938502/

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