What Makes a Tick, Tick?
So then, what makes a tick do what it does? What does make a tick, tick? Like many arthropods, including insects, such as mosquitoes and bedbugs, and other arachnids, including mites, ticks are referred to as “ectoparasites” or parasites that live on the outside of their hosts. Their ectoparasitic activity is called hematophagia. Don’t you just love these technical medical terms? Broken-down, “hemato” means blood and “phagia” means eating. In the common vernacular, these arthropods are bloodsuckers. They’re vampires on a minor scale. Yet, the consequences of these activities are potentially major.
So, there you have it! It is blood that makes a tick, tick. Whether it is a wood tick, deer tick, dog tick, Lone Star or Gulf Coast tick, it is the need for a blood meal, in order to transform to the next stage of their life cycle, which makes these 8-legged critters do what they do, that is…BITE. Other than being a little unsightly, having one of them latched-onto the skin and ballooning-up, becoming fat and ugly, as it fills-up with one’s blood, the actual bite is painless and would, and often does, go unnoticed. One exception is the occasionally intensely painful reaction that may follow the bite of some ticks.
Yet, that is not the end of the story. Simply knowing that the need for blood causes a tick to bite is just an introduction to tick bites. The bite itself is not the real issue. Ticks are typically not very discriminate with regard to the animals they bite for a meal. As a result, various bacteria and other parasites, which have no ill-effect on the tick itself, can be easily picked-up in the blood meal from a given animal and then transmitted to human beings during a subsequent blood meal. Ticks are second only to mosquitoes in the transmission of human disease. Examples of tick-borne illnesses in North America include Lyme disease, Rocky Mounted Spotted Fever, Ehrlichiosis, Tularemia, Babesiosis, Relapsing fever, Colorado tick fever, Q fever and tick paralysis. A single tick can actually carry more than one of these illnesses at a time. Yet, a very small percentage of tick bites results in the transmission of one of these diseases. Another, rather bizarre disease, noninfectious in nature, has also recently been reported, as a result of tick bites. Some bites have actually caused an allergic reaction to develop with the ingestion of red meats.
The actual identification of various ticks is beyond the scope of this posting but if the reader is interested in investigating an excellent link for this, click here. The chart that follows provides information about the tick-borne illnesses mentioned, including the organism causing the particular disease, which ticks carry the offending parasite, its animal host or hosts, typical geographic distribution and typical symptoms of the disease.
All of these tick-borne illnesses require evaluation and treatment by a physician. Their specific treatments are also beyond the scope of this blog. However, we will cover prevention as well as what to do if one discovers a tick firmly attached to his or her skin. Ticks live in heavy vegetation, brush and trees, where they have the greatest probability of encountering an animal for a blood meal. Hikers, therefore, have an increased risk of picking-up one of these beasties. Ticks do not jump or fly and are not carried by the wind. They have an amazing ability to sense the presence of a potential host from long distances by determining trace amounts of gases like CO2 and select ambush sites based upon their ability to identify paths that are well traveled. They then crawl onto and attach to the host.
Avoidance of areas where tick populations may be high, such as thick, grassy areas, shrubs and low-hanging trees is recommended. However, hikers in such areas should wear lightly-colored clothing, to more easily see ticks and brush them off, long sleeves and pants, with pant cuffs tucked into their hiking boots or socks. Avoid vegetation as much as possible by walking in the center of paths. Apply insect repellents containing DEET, avoiding application to the face and hands and avoiding DEET of concentrations >15% in children. Also, repeated applications of even low concentrations of DEET should be avoided in children. Close inspection of all areas on the skin immediately after exposure to areas likely to have ticks, paying particular attention to body folds. This also includes inspecting the skin of pets likewise exposed.
Removing a tick from the skin once it has attached itself, and especially after it has become imbedded and begun to swell with blood, poses a rather challenging problem. Care should be taken to remove the entire tick and attempt to not leave any of its mouth parts behind. The sooner the removal is undertaken the better. This is best accomplished by using a fine forceps or “tweezers.” After thoroughly cleansing the area with alcohol or other disinfectant, grab the tick as closely as possible to the skin surface with the forceps tips, and pull firmly, steadily and gradually away from the skin. Squeezing the body of the tick during the removal should be avoided since this could inject infectious material into the bite. Although it is best to remove the entire tick, including its mouth parts, leaving small remnants of these behind does not increase the potential for transmitting disease other than a localized skin infection or foreign body reaction. Old home remedies such as burning the tick with a match or the application of gasoline or petroleum to “smother” the tick should all be avoided. Unless one is an expert entomologist, it is recommended that the removed tick be taken to a local health care provider or public health facility to initiate specific identification of the tick.
ILLNESS: Lyme Disease.
ORGANISM: Spirochete (a spiral-shaped bacterium) Borrelia burgdorferi. TICK VECTOR(S) and (GEOGRAPHIC DISTRIBUTION): Deer ticks – Ixodes scapularis (Northeastern, North central and mid-Atlantic U.S.); Ixodes pacificus (Pacific coastal). RESERVOIRS: mice->deer or bear->humans or canine/feline pets.
SYMPTOMS: Early (within days to weeks) – Erythema chronicum migrans (80%), a large, red bulls-eye skin rash; muscle/joint pain; headache; fever; neurologic problemsα (10 – 15%); heart inflammation with irregular heart beat; arthritis; Late (after several months) – Chronic neurologic problemsβ(up to 5%); profound fatigue; chronic arthritis.
ILLNESS: Rocky Mountain Spotted Fever (AKA “Black measles”).
ORGANISM: Bacterium Rickettsia rickettsii. TICK VECTOR(S) and (GEOGRAPHIC DISTRIBUTION): American dog tick or wood tick – Dermacentor variabilis (U.S. east of Rocky Mountains); Rocky Mountain wood tick – Dermacentor andersoni (Rocky Mountain U.S.); Brown dog tick – Rhipicephalus sanguineus (southwestern U.S. and along the U.S-Mexico border); Cayenne tick – Amblyomma cajennense (southern U.S.). RESERVOIRS: Smaller animals (rodents, birds, reptiles, amphibians) -> larger animals (larger rodents, deer, fox, dogs) -> humans.
SYMPTOMS: Early (1 – 2 weeks) – fever, nausea & vomiting, loss of appetite, headache, muscle aches, rarely inflammation of parotid salivary gland; Late (2 – 5 days after early symptoms) – rash (85 - 90%) 1. non-itchy, small, pink bumps starting on extremities then on torso; 2. characteristic, generalized, bright-red flat spots (petechiae) including palms and soles (35 – 60%).
ILLNESS: Ehrlichiosis [2 major types identified: Human Monocytic Ehrlichiosis (HME) & Human Granulocytic Anaplasmosis (HGA)]
ORGANISM: HME – 3 different Ehrlichiae bacteria in U.S.γ; HGA – Anaplasma phagocytophilum. TICK VECTOR(S) and (GEOGRAPHIC DISTRIBUTION): (HME bacteriae) Lone Star tick – Amblyomma americanum (South-central, southeastern, and mid-Atlantic U.S.); (HGA) at least 3 different ticksδ (See distribution of other tick-borne illnesses carried by same ticks); RESERVOIRS: (HME) White-tailed deer -> humans; (HGA) White-footed mouse -> dogs, horses and humans.
SYMPTOMS: HME – Fever, chills, headache, malaise, muscle aches, nausea, vomiting, diar-rhea, confusion, red eyes, rash in 60% of children and <30% of adults. Mortality up to 3%; HGA – Similar symptoms to HME except rash rarely seen or up to 10% and mortality < 1%.
ILLNESS: Tularemia (AKA “Rabbit fever,” “Deerfly fever,” “O’Hara’s fever,” and “Pahvant Valley plague”).
ORGANISM: Two major bacterial subtypes – Francisella tularensis tularensis and F. tularensis palaearctica. TICK VECTOR(S) and (GEOGRAPHIC DISTRIBUTION): American dog tick or wood tick – Dermacentor variabilis; Rocky Mountain wood tick – Dermacentor andersoni; Lone Star tick – Amblyomma americanum (See distribution of other tick-borne illnesses carried by same ticks); ε; RESERVOIRS: (F. tularensis tularensis) Rabbits, hares & pikas -> humans; (F. tularensis palaearctica) Beaver and muskrat -> humans.
SYMPTOMS: Ulceroglandular (most common) – ulcer at site of bite; lymph node swelling in armpit or groin depending upon bite location; Glandular – Swelling of lymph node in armpit or groin but without ulcer; Pneumonic – cough, chest pain, and difficulty breathing - occurs if other forms are left untreated – All forms accompanied by high fever, lethargy, loss of appetite, facial and eye redness. < 1% morality.ζ
ORGANISM: Malaria-like protozoan red blood cell parasite – Babesia microti. TICK VECTOR(S) and (GEOGRAPHIC DISTRIBUTION): Deer tick – Ixodes scapularis (See distribution of Lyme Disease carried by same tick). RESERVOIRS: White-footed mouse -> humans.
SYMPTOMS: Flu-like illness with fever, chills, sweats, headache, body aches, loss of appetite, nausea, fatigue; jaundice, dark urine resulting from the destruction of red blood cells. No skin findings. Complications: Low blood pressure; severe anemia due to destruction of red blood cells; very low platelet count; blood clots and bleeding; malfunction of kidneys, liver, lungs, and heart; death.
ILLNESS: Tick-borne Relapsing fever (Sporadic endemic relapsing fever)η
ORGANISM: 3 Borrelia spirochete bacteria in U.S. – B. hermsii; B. parkerii; B. uricatae. TICK VECTOR(S) and (GEOGRAPHIC DISTRIBUTION): 3 Orthinodoros soft tick vectors, each corresponding to its respective Borrelia spirochete – O. hermsii (higher elevations and coniferous forests of the western/northwestern U.S. and southern British Columbia, Canada); O. parkerii (lower elevations of the western/northwestern U.S and southern British Columbia, Canada); O. turicatae (New Mexico, Texas, Oklahoma, Kansas and Mexico). RESERVOIRS: (O. hermsii) Ground or tree squirrels and chipmunks -> humans; (O. parkerii and O. turicatae) Ground squirrels, prairie dogs and burrowing owls -> humans.
SYMPTOMS: One to 4 recurring episodes of fever often associated with non-specific flulike symptoms, light sensitivity, rash (red spots or scattered petechiae on torso and extremities), neck pain, eye pain, confusion, and dizziness, lasting about 3 days, with intervals without symptoms lasting about a week. Each febrile episode ends in a febrile crisis comprised of 2 phases: 1) a “chill phase,” with very high fever (up to 106.7º F or 41.5ºC) and chills, the victim possibly developing deliriousness, agitation, rapid heart rate and rapid breathing, which last 10 to 30 minutes; followed by 2) a “flush phase,” with drenching sweats, a rapidly decreasing body temperature and possibly a transiently low blood pressure. Uncommonly, liver involvement may occur and rarely, with B. turicatae infection, there may be neurologic involvement. Typically, the illness resolves without treatment.
ILLNESS: Spotted Fever group Rickettsia (SFGR)
ORGANISM: 2 Rickettsial bacteria in U.S. – R. parkeri and Rickettsia species 364D. TICK VECTOR(S) and (GEOGRAPHIC DISTRIBUTION): (R. parkeri) Gulf Coast tick – Amblyomma maculatum (Eastern and southern U.S., particularly along the coast); (Rickettsia species 364D) Pacific Coast tick - Dermacentor occidentalis (Northern California, Pacific Coast) RESERVOIRS: (R. parkeri) Livestock, deer, dogs -> humans; (Rickettsia species 364D) Dogs, raccoons, rabbits, livestock -> humans.
SYMPTOMS: Both Rickettsiae produce signs and symptoms similar to Rocky Mountain Spotted Fever (RMSF). Rickettsia species 364D characterized as a “spotless” (no rash) RMSF. Distinctive eschar (blackened or crusty scab) at site(s) of bite(s) help to distinguish from RMSF.
ILLNESS: Southern Tick-Associated Rash Illness (STARI)
ORGANISM: Unknown. Putative - Borrelia lonestari.TICK VECTOR(S) and (GEOGRAPHIC DISTRIBUTION): Lone Star tick– Amblyomma americanum [See distribution of Ehrlichiosis (HME) carried by same tick]; RESERVOIRS: White-tailed deer -> humans.
SYMPTOMS: Very similar to Lyme Disease,θ with expanding “bull's-eye,” erythema chronicum migrans-like rash that develops around the site of a Lone Star tick bite, appearing within 7 days of tick bite and expanding to a diameter of 8 centimeters (3 inches) or more; frequently associated with fatigue, headache, fever, and muscle pains. However, the serious systemic complications of Lyme Disease have not yet been described with this illness.
* U.S. only.
α These can include Bell’s Palsy (facial paralysis on either side of face); meningitis with headache, fever and stiff neck; peripheral neuritis (numbness and tingling of the arms and legs); encephalitis (brain swelling, with learning difficulties, confusion, memory loss, mood changes and sleeping disturbances).
β Polyneuropathy (shooting pains, numbness, and tingling in the hands or feet); Lyme encephalopathy (subtle difficulties with concentration and short-term memory); chronic encephalomyelitis (cognitive impairment, weakness in the legs, awkward gait, facial palsy, bladder problems, vertigo, and back pain; frank psychosis; panic attacks; anxiety; delusions).
γ Ehrlichia chaffeensis (most common), Ehrlichia ewingii, and Ehrlichia murislike (EML – provisional).
δ Ixodes scapularis, Ixodes pacificus and Dermacentor variabilis.
ε Also, a common non-tick vector is the deerfly, Chrysops discalis.
ζ Two other forms of tularemia, Oculoglandular and Oropharyngeal, can also occur but are not tick-borne or other arthropod-borne illnesses.
η Relapsing fever can also be transmitted via a louse, i.e. louse-borne relapsing fever. The causative organism in LBRF is Borrelia recurrentis.
θ B. hermsii, B. turicatae, and B. parkeri