Dermacentor variabilis | |
---|---|
Female | |
Male | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Subphylum: | Chelicerata |
Class: | Arachnida |
Order: | Ixodida |
Family: | Ixodidae |
Genus: | Dermacentor |
Species: | D. variabilis |
Binomial name | |
Dermacentor variabilis (Say, 1821) | |
Normal range in red; other reports in blue |
Dermacentor variabilis, also known as the American dog tick or wood tick, is a species of tick that is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever and tularemia (Francisella tularensis). It is one of the best-known hard ticks. Diseases are spread when it sucks blood from the host. It may take several days for the host to experience symptoms.
Though D. variabilis may be exposed to Borrelia burgdorferi , the causative agent of Lyme disease, [1] these ticks are not competent vectors for the transmission of this disease. [2] [3] [4] The primary vectors for B. burgdorferi are the deer ticks Ixodes scapularis in eastern parts of the United States, Ixodes pacificus in California and Oregon, and Ixodes ricinus in Europe. D. variabilis may also carry Anaplasma phagocytophilum , the causative agent of human granulocytic anaplasmosis, and Ehrlichia chaffeensis , the causative agent of human monocytic ehrlichiosis. [1] [5]
Dermacentor ticks may also induce tick paralysis by elaboration of a neurotoxin that induces rapidly progressive flaccid quadriparesis similar to Guillain–Barré syndrome. The neurotoxin prevents presynaptic release of acetylcholine from neuromuscular junctions.
The life cycle of ticks can vary depending on the species. Most ticks go through four stages: egg, six-legged larva, eight-legged nymph, and adult. After hatching from the egg, a tick must obtain a blood meal at every stage to survive. Ticks can feed on mammals, birds, reptiles, and amphibians. Unlike most tick species, D. variabilis prefers the same host during all of its life stages. [6]
Within North America, the normal range is in the eastern part of the continent, with some reports in California. At the northernmost extent of its geographical range, in Nova Scotia and Massachusetts, ticks are active from April to August, with a peak in May to June. [7] In coastal Virginia, the adults are active from April to September or October, with peaks in May and July. [7] Seasonal activity in Ohio is from late April to September, with peaks in May to June and another smaller peak in August to September. [7] In Georgia, adults are active from late March to August, with peaks in early May, late May, and late June. [7] Florida adult activity is from April to July, with activity being restricted by high summer temperatures and low winter humidity. [7]
Feeding ticks transmit pathogens to the host. Depending on the tick species and its stage of life, preparing to feed can take from 10 minutes to 2 hours. [6] When the tick finds a feeding spot, it grasps the skin and cuts into the surface, where it then inserts its feeding tube. [6] Many species also secrete a cement-like substance that keeps them firmly attached during the meal. [6] The feeding tube can have barbs to help keep the tick in place. [6] Ticks also can secrete small amounts of saliva with anesthetic properties so that the animal or person cannot feel that the tick has attached itself. [6] Therefore, unless one feels the tick crawling, noticing the tick is difficult. If the tick is in a sheltered spot, it can go unnoticed and can slowly suck the blood for several days. If the host animal has a blood-borne infection, the tick will ingest the pathogens with the blood. [6] Small amounts of saliva from the tick may also enter the skin of the host animal during the feeding process. [6] If the tick contains a pathogen, the organism may be transmitted to the host animal in this way. [6] After feeding, most ticks drop off and prepare for the next life stage. [6] At its next feeding, it can then transmit an acquired disease to the new host. [6]
Symptoms of Rocky Mountain spotted fever appear within 3-12 days, usually beginning with a sudden onset of fever and headache, and frequently followed 2-4 days later by a rash around the wrists and ankles that moves slowly up to the rest of the body. Other symptoms include nausea, loss of appetite, abdominal pain, or muscle aches. Rocky Mountain spotted fever can be fatal within days of symptoms beginning, if left untreated. [8] In dogs additional symptoms may include lethargy, blood in the urine, irregular heartbeat, discolored spots on the skin (often bruised or purplish in color), inability to walk normally, loss of coordination, swelling or edema in the limbs, sudden bleeding from the nose or in the stools, difficulty with blood clotting, swollen lymph nodes, pain in the eyes, inflammation, hemorrhage, or conjunctivitis in the mucosal membranes. [9]
Symptoms of tularemia usually appear within 3–5 days, but can appear as late as 21 days after transmission. Oftentimes, patients experience chills, swollen lymph nodes, and an ulceration at the site of the bite. [10]
A tick bite does not automatically transfer diseases to the host. Instead, the tick must be attached to the host for a period of time, generally 6–8 hours [10] but sometimes as little as 3–6 hours, [11] before it is capable of transferring disease. The earlier the tick is removed from a host, the less likely it is to contract the illness.
The American dog tick is commonly found in highly wooded, shrubby, and long-grass areas. Tick numbers can be reduced by cutting the grass, which creates a low-humidity environment, which is undesirable to ticks. Pesticides can also be used and are most effective when applied to vegetation that has been cut to a short level. [10] Doxycycline is the medication of choice to treat Rocky Mountain spotted fever in dogs. [12] Doxycycline is given for 7–21 days dependent on the dosage. [12] Tetracycline is effective and administered more frequently, being given for 14–21 days. [12] Other antibiotic choices include enrofloxacin and chloramphenicol. [12] Veterinary-approved flea and tick preparations [13] are recommended, along with other topicals, collars, [14] and shampoos. [15] Regularly checking dogs and oneself for ticks after hiking or playing in grassy areas and removing ticks as soon as possible decrease the chances a dog will contract a secondary illness carried by the tick. [15] Tweezers are the most common removal method, but fine-point tweezers are best to avoid tearing the tick and spreading possible infectious agents in the bite area. [11] Spread the dog’s fur, grasp the tick as close to the skin as possible, and very gently pull straight upward in a slow, steady motion. [11] Another removal method is a tick removal hook: one places the prongs of the device on either side of the tick and twists upward. [11] Tick removal hooks are recommended in areas where ticks are common. [11] Removing the tick with fingers is never a good idea because squeezing to grasp the tick could potentially inject more infectious material. [11] Apply rubbing alcohol to the bite area afterward to thoroughly clean the wound. [11]
Rocky Mountain spotted fever (RMSF) is a bacterial disease spread by ticks. It typically begins with a fever and headache, which is followed a few days later with the development of a rash. The rash is generally made up of small spots of bleeding and starts on the wrists and ankles. Other symptoms may include muscle pains and vomiting. Long-term complications following recovery may include hearing loss or loss of part of an arm or leg.
Ticks are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. The timing of the origin of ticks is uncertain, though the oldest known tick fossils are from the Cretaceous period, around 100 million years old. Ticks are widely distributed around the world, especially in warm, humid climates.
The Ixodidae are the family of hard ticks or scale ticks, one of the three families of ticks, consisting of over 700 species. They are known as 'hard ticks' because they have a scutum or hard shield, which the other major family of ticks, the 'soft ticks' (Argasidae), lack. They are ectoparasites of a wide range of host species, and some are vectors of pathogens that can cause human disease.
Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by Borrelia bacteria, which are spread by ticks in the genus Ixodes. The most common sign of infection is an expanding red rash, known as erythema migrans (EM), which appears at the site of the tick bite about a week afterwards. The rash is typically neither itchy nor painful. Approximately 70–80% of infected people develop a rash. Early diagnosis can be difficult. Other early symptoms may include fever, headaches and tiredness. If untreated, symptoms may include loss of the ability to move one or both sides of the face, joint pains, severe headaches with neck stiffness or heart palpitations. Months to years later, repeated episodes of joint pain and swelling may occur. Occasionally, shooting pains or tingling in the arms and legs may develop. Despite appropriate treatment, about 10 to 20% of those affected develop joint pains, memory problems, and tiredness for at least six months.
Rickettsia rickettsii is a Gram-negative, intracellular, coccobacillus bacterium that was first discovered in 1902. R. rickettsii is the causative agent of Rocky Mountain Spotted Fever and is transferred to its host via a tick bite. It is one of the most pathogenic Rickettsia species and affects a large majority of the Western Hemisphere, most commonly the Americas.
Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. The economic impact of tick-borne diseases is considered to be substantial in humans, and tick-borne diseases are estimated to affect ~80 % of cattle worldwide. Most of these pathogens require passage through vertebrate hosts as part of their life cycle. Tick-borne infections in humans, farm animals, and companion animals are primarily associated with wildlife animal reservoirs. many tick-borne infections in humans involve a complex cycle between wildlife animal reservoirs and tick vectors. The survival and transmission of these tick-borne viruses are closely linked to their interactions with tick vectors and host cells. These viruses are classified into different families, including Asfarviridae, Reoviridae, Rhabdoviridae, Orthomyxoviridae, Bunyaviridae, and Flaviviridae.
Tick paralysis is a type of paralysis caused by specific types of attached ticks. Unlike tick-borne diseases caused by infectious organisms, the illness is caused by a neurotoxin produced in the tick's salivary gland. After prolonged attachment, the engorged tick transmits the toxin to its host. The incidence of tick paralysis is unknown. Patients can experience severe respiratory distress.
Borrelia burgdorferi is a bacterial species of the spirochete class in the genus Borrelia, and is one of the causative agents of Lyme disease in humans. Along with a few similar genospecies, some of which also cause Lyme disease, it makes up the species complex of Borrelia burgdorferi sensu lato. The complex currently comprises 20 accepted and 3 proposed genospecies. B. burgdorferi sensu stricto exists in North America and Eurasia and until 2016 was the only known cause of Lyme disease in North America. Borrelia species are Gram-negative.
Powassan virus (POWV) is a Flavivirus transmitted by ticks, found in North America and in the Russian Far East. It is named after the town of Powassan, Ontario, where it was identified in a young boy who eventually died from it. It can cause encephalitis, inflammation of the brain. No approved vaccine or antiviral drug exists. Prevention of tick bites is the best precaution.
Ixodes scapularis is commonly known as the deer tick or black-legged tick, and in some parts of the US as the bear tick. It was also named Ixodes dammini until it was shown to be the same species in 1993. It is a hard-bodied tick found in the eastern and northern Midwest of the United States as well as in southeastern Canada. It is a vector for several diseases of animals, including humans and is known as the deer tick owing to its habit of parasitizing the white-tailed deer. It is also known to parasitize mice, lizards, migratory birds, etc. especially while the tick is in the larval or nymphal stage.
Ixodes ricinus, the castor bean tick, is a chiefly European species of hard-bodied tick. It may reach a length of 11 mm (0.43 in) when engorged with a blood meal, and can transmit both bacterial and viral pathogens such as the causative agents of Lyme disease and tick-borne encephalitis.
Amblyomma americanum, also known as the lone star tick, the northeastern water tick, or the turkey tick, is a type of tick indigenous to much of the eastern United States and Mexico, that bites painlessly and commonly goes unnoticed, remaining attached to its host for as long as seven days until it is fully engorged with blood. It is a member of the phylum Arthropoda, class Arachnida. The adult lone star tick is sexually dimorphic, named for a silvery-white, star-shaped spot or "lone star" present near the center of the posterior portion of the adult female shield (scutum); adult males conversely have varied white streaks or spots around the margins of their shields.
Human monocytotropic ehrlichiosis is a form of ehrlichiosis associated with Ehrlichia chaffeensis. This bacterium is an obligate intracellular pathogen affecting monocytes and macrophages.
Rhipicephalus sanguineus, commonly called the brown dog tick, kennel tick, or pantropical dog tick, is a species of tick found worldwide, but more commonly in warmer climates. This species is unusual among ticks in that its entire lifecycle can be completed indoors. The brown dog tick is easily recognized by its reddish-brown color, elongated body shape, and hexagonal basis capituli. Adults are 2.28 to 3.18 mm in length and 1.11 to 1.68 mm in width. They do not have ornamentation on their backs.
Ticks are insects known for attaching to and sucking blood from land-dwelling animals. Ticks fall under the category of 'arthropod', and while they are often thought of in the context of disease transmission, they are also known to cause direct harm to hosts through bites, toxin release, and infestation. Infestation can cause symptoms ranging from mild to severe and may even cause death. Hosts can include any number of vertebrates, though humans and livestock are more likely to be the interest of researchers.
Dermacentor is a genus of ticks in the family Ixodidae, the hard ticks. The genus has a cosmopolitan distribution, with native species on all continents except Australia. Most are found in North America.
Ixodes pacificus, the western black-legged tick, is a species of parasitic tick found on the western coast of North America. I. pacificus is a member of the family Ixodidae. It is the principal vector of Lyme disease in that region. I. pacificus typically feeds on lizards and small mammals therefore its rate of transmission of Lyme disease to humans is around 1% of adults. It is an ectoparasite that attaches itself to the outside of its host and feeds on the host's blood. It can have a heteroxenous lifestyle or monoxenous life cycle depending on how many hosts it feeds on in each cycle. I. pacificus has a four stage life cycle that takes around 3 years to complete. These stages include egg, larva, nymph, and adult. They prefer dense woodland habitats or areas of brush and tall grass.
Ticks of domestic animals directly cause poor health and loss of production to their hosts. Ticks also transmit numerous kinds of viruses, bacteria, and protozoa between domestic animals. These microbes cause diseases which can be severely debilitating or fatal to domestic animals, and may also affect humans. Ticks are especially important to domestic animals in tropical and subtropical countries, where the warm climate enables many species to flourish. Also, the large populations of wild animals in warm countries provide a reservoir of ticks and infective microbes that spread to domestic animals. Farmers of livestock animals use many methods to control ticks, and related treatments are used to reduce infestation of companion animals.
Borrelia mayonii is a Gram-negative, host-associated spirochete that is capable of causing Lyme disease. This organism can infect various vertebrate hosts such as humans via the bite of a black legged tick.
Ixodes angustus is a species of parasitic tick, whose range encompasses the majority of Canada and the United States, along with parts of northern Mexico. I. angustus is a member of the Ixodidae (hard-bodied) family of ticks. It is most abundant in cool, moist biomes such as riparian, boreal or montane zones. I. angustus is a host generalist and has been discovered feeding on more than 90 different host species, including humans and domestic dogs. I. angustus has been identified as a potential vector for Lyme disease but is not considered a principal vector due to the relative rarity with which it feeds on humans.