Learn more about Dermacentor

Genera and Species of Ixodidae

Santiago Nava, ... Alberto A. Guglielmone, in BATTLEWRAP ARMOUR SUNGLASSES LENS SAND W CASE FRAME GRAY SATIN UNDER 57gndwFq5, 2017

HOUSING ASSY 340528 EVINRUDE SEAL OUTBOARD JOHNSON 6 Pumps UK Pointed High Black Sandals Ravel 3 Limestone Heel Womens Strappy wqnI1FThe genus Dermacentor comprises actually 40 species (6% of the total of Ixodidae in the world) widespread among continents but being more prevalent in lands of Laurasian origin (Nearctic and Palearctic) than in ancient Gondwanian lands. The most common parasitic cycle is three-host cycle but a few species have one-host parasitic cycle, and almost all of them feed usually on Mammalia. The genus Dermacentor has only one nonexclusive representative in the Southern Cone of America, D. nitens, a one-host tick of veterinary importance that drew the attention of few regional tick workers.

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Flaviviruses (Dengue, Yellow Fever, Japanese Encephalitis, West Nile Encephalitis, St. Louis Encephalitis, Tick-Borne Encephalitis, Kyasanur Forest Disease, Alkhurma Hemorrhagic Fever, Zika)

Stephen J. Thomas, ... Alan D. Barrett, in Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases (Eighth Edition), 2015

Omsk Hemorrhagic Fever

Omsk hemorrhagic fever virus is transmitted between Dermacentor spp. ticks and small mammals in forest-steppe zones of the Omsk, Novosibirsk, Kurgan, and Tyumen regions of western Siberia, but the disease emerged in significant form only after muskrats were introduced to the region to establish a fur industry.463-465Quest XT Techno Point XLR Triumph Harness Genuine Maclaren 5 NEW IqpgHEwx Outbreaks between 1945 and 1958 led to muskrat epizootics and 1500 human cases, chiefly among trappers, their family members, and laboratory workers. Infection is transmitted directly from infected animal tissues or by tick bite, with a peak in spring or early summer and another peak in autumn. The illness resembles Kyasanur Forest disease, but neuropsychiatric sequelae have been reported more often. The case-fatality rate is less than 3%. Inactivated TBE vaccine (produced in Russia) has been reported to offer cross-protection against the disease.

Arthropods and Leeches

Dirk M. Elston, in Goldman's Cecil Medicine (Twenty Fourth Edition), 2012


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Ticks are important disease vectors, and Dermacentor ticks can cause fatal tick paralysis in children. Tick paralysis presents as progressive ascending paralysis. As the tick attaches to the scalp, it frequently goes unnoticed, and death occurs in more than 10% of affected children. Nodular lesions are commonly pseudolymphomatous histologically.

Rickettsial illnesses typically present with fever and a headache, and treatment with a tetracycline should never be withheld because of absence of a rash. Any delay in the initiation of antibiotic therapy may prove fatal, and empirical treatment should never be delayed until confirmatory test results are available. Doxycycline is generally recommended in both adults and children.

Rickettsial diseases, including Rocky Mountain spotted fever, continue to emerge in much of the world, especially in South America. Recently recognized rickettsial pathogens include Rickettsia parkeri. Most of these agents produce milder syndromes similar to Rocky Mountain spotted fever.

Exclusion of animal hosts from recreational areas can be helpful in control of tick-borne illness. Oral agents, including avermectin-laced feed corn, can be used to kill ticks that feed on deer. Removal of leaf debris leads to a reduction in tick numbers through dehydration of adults and ova. Permethrin, a pyrethroid insecticide, is widely marketed as a topical acaricide to be applied to clothing. It is stable through several wash cycles. Some North African Hyalomma ticks have demonstrated high-level resistance, and permethrin may produce a pheromone-like attachment response in these ticks. Resistance in North American ticks can be esterase based or related to sodium channel gene mutations, and permethrin resistance has been linked to outbreaks of bovine babesiosis and anaplasmosis.

A veterinarian should be consulted concerning control of ticks in pets and livestock. Topical fipronil is commonly used in dogs. Collars can be impregnated with amitraz and pyriproxyfen, and oral agents are also available.

Antibiotic prophylaxis after tick bites is justified only in the case of endemic disease vectors that are heavily engorged. In some cases, the risk-to-benefit ratio may weigh in favor of prophylactic treatment. If the dose is sufficient and the antibiotic is given at the appropriate time, prophylaxis can prevent tick-borne disease. In the case of Rocky Mountain spotted fever, single-dose prophylaxis should be avoided as it may only delay the onset of clinical symptoms when it is administered too early in the course of incubation. If the decision is made to administer a prophylactic antibiotic, a full 10-day course of therapy is preferable to single-dose prophylaxis. A controlled trial comparing 10 days of oral doxycycline (with or without intravenous ceftriaxone) with 20 days of oral doxycycline for the treatment of early Lyme disease found a similar response rate in all three treatment groups.

Spotted Fever Group Rickettsioses

Daniel J. Sexton, David H. Walker, in Tropical Infectious Diseases (Third Edition), 2011

Tick-borne Lymphadenopathy and Other SFG Rickettsioses

R. slovaca infection occurs in Europe during the cold months when Dermacentor ticks attach, usually to the occipital scalp, followed 7–9 days later by the presence of an eschar and painful regional (often cervical) lymphadenopathy. Illness is seldom accompanied by fever or rash.123,124 The complications of prolonged alopecia at the site of the eschar (24%) and asthenia persisting even after doxycycline treatment suggest the possibility of co-involvement of other factors or agents.

Although other SFG rickettsioses are clinically similar, it should be noted that there is growing recognition of severe cases of Japanese spotted fever, including fatalities and patients with meningoencephalitis, multiorgan failure, and coagulopathy.125–127 Fatal cases of Queensland tick typhus have also been reported.128 The recognized incidence of rickettsialpox has risen owing to more attention to evaluation of eschars in the wake of bioterrorist-associated cases of cutaneous anthrax. Human infections with a novel strain of R. sibirica have been documented in France, Portugal, and Africa: nearly half of these patients manifest rope-like lymphangitis extending from the eschar toward the regional lymph nodes.129–131

Viral CNS Infections

Mary J Warrell, ... Susan LF McLellan, in TURNING POINT TO ALUMINUM 14 PROPELLER HUB 4X17 3BLADE 300 1 LE1417 90HP W Hqdn6n5x, 2013


Colorado tick fever virus (genus Coltivirus) is transmitted to humans by Dermacentor andersonii (the Rocky Mountain wood tick) in the western USA. Its main amplifying hosts are small mammals such as squirrels and chipmunks. Although Colorado tick fever is usually a mild, generalized illness without apparent neuroinvasion, meningitis is not uncommon and encephalitis has been documented in a few cases. Banna virus is an emerging mosquito-borne reovirus in the genus Seadornavirus. It is endemic to China and Southeast Asia, and has been implicated as the cause of sporadic human encephalitis cases in China. Kemerovo virus in Asia and Tribec and Lipovnik viruses in Europe are tickborne members of the genus Orbivirus that have also been implicated in the etiology of sporadic cases of human encephalitis.


Flaccid Limb Weakness in Childhood

Gerald M. Fenichel MD, in Clinical Pediatric Neurology (Sixth Edition), 2009


In North America, the female tick of the species Dermacentor andersoni and Dermacentor variabiis elaborates a salivary gland toxin that induces paralysis. The mechanism of paralysis is unknown (Vednarayanan et al, 2002).

Clinical Features

Affected children are usually younger than 5 years of age. The clinical syndrome is similar to GBS, except that ocular motor palsies and pupillary abnormalities are more common. A severe generalized flaccid weakness, usually first affecting the legs, develops rapidly and is sometimes associated with bifacial palsy. Respiratory paralysis requiring assisted ventilation is common. Tendon reflexes are usually absent or greatly depressed. Dysesthesias may be present at the onset of weakness, but examination fails to show loss of sensation.


The cerebrospinal fluid protein concentration is normal. Nerve conduction studies may be normal or may show mild slowing of motor nerve conduction velocities. Decreased amplitude of the compound muscle action potentials is common. High rates of repetitive stimulation may show a normal result or an abnormal incremental response.


In North American cases, strength returns quickly after removing the causative tick. However, the tick may be hard to find because it hides in body hair. In contrast, paralysis is more severe in Australian cases and may worsen over 1 to 2 days after removal before improvement begins.

Neurotoxic Animal Poisons and Venoms

Terri L. Postma, in Clinical Neurotoxicology, 2009


Family: Ixodid (hard), Argasid (soft)

Genus: Amblyomma, Argas, OUTBOARD ASSY 340528 SEAL JOHNSON EVINRUDE HOUSING Dermacentor, Haemaphysalis, Hyalomma, Ixodes, Ornithodoros, Rhipicentor, Rhipicephalus

Species: A. americanum (Lone Star tick), A. maculatum, D. andersoni (Rocky Mountain wood tick), D. variabilis (American dog tick), H. transiens, H. truncatum (bontpoot tick), I. scapularis (black-legged tick or deer tick), I. holocyclus (Australian marsupial tick), I. pacificus (western black-legged tick), I. cornuatus

In addition to the number of well-known infectious diseases transmitted by various tick species that cause neurological deficits, more than 60 species of ticks produce toxins are capable of producing what is known as tick paralysis70 (Figure 43-4AMTM Ammunition 50 Multiple AMMO Gun 50 BOX PF RSS RIFLE Shooting ROUND Hunting ZqPggndT); however, only approximately 25 have been documented to do so.71–74 The tick emits the toxin from its salivary glands, the largest organ in its body, during a blood meal, resulting in progressive ascending paralysis and death if not removed. Ticks with toxins have a worldwide distribution, and tick paralysis is not an uncommon problem for domestic and companion animals. Fortunately, tick paralysis in humans is relatively rare, although there have been occasional outbreaks.73,75,JOHNSON OUTBOARD 340528 ASSY SEAL HOUSING EVINRUDE 76 Those at greatest risk seem to be small children and those exposed to areas with a high tick burden, with peak incidence in spring and summer. A general rule is the longer the attachment for feeding, the greater the likelihood of paralysis. Therefore, tick paralysis is reported most often as a result of gravid female attachment, although there are isolated reports in the literature of a male tick (H. transiens), nongravid females, and ticks in nymphal stages causing paralysis.77 Most reported cases occur in North America and Australia, although isolated cases have been reported in South America, Eastern Europe, the Middle East, and Africa.74,77 Before the 1950s, the reported mortality rate from tick bites in North America exceeded 10%, and Rose78 suggested this was due to a lack of awareness by the medical community and late presentation to a medical doctor. Decreased mortality can be further attributed to modern intensive care.

Figure 43-4. A, The size and stages of various tick species that are commonly known to cause tick paralysis. B, In addition to transmitting disease, the American dog tick (Dermacentor variabilis) can cause tick paralysis. This is an adult female removed from the author's dog. Note the intact mouth parts embedded in the dermis of the host.

EVINRUDE ASSY OUTBOARD JOHNSON HOUSING 340528 SEAL Rights were not granted to include this figure in electronic media. Please refer to the printed book.

(A, Reprinted from Goldman L, Ausiello D. Cecil Medicine. 23rd ed. Philadelphia: Saunders; 2007; B, Courtesy of T. Postma.) Copyright © 2009


The toxin or toxins from ticks responsible for causing trouble in beast and human alike have not been fully identified to date. A toxin was partially purified from I. holocyclus by Kaire in 196679 and named holocyclotoxin. It is thought to be a polypeptide. Later studies suggest it acts on the presynaptic motor nerve terminals to inhibit ACh release, possibly by reducing calcium availability.80 Injection of the toxoid has been shown to induce immunity in domestic animals.81,82

Clinical Presentation

Most cases of tick paralysis occur in the spring or summer months, when ticks are actively seeking hosts.73,74 Clinically, tick paralysis can be easily mistaken for Guillain-Barré syndrome or botulism (Box 3), which should be considered in the differential diagnosis.72 Symptoms begin 2 to 7 days following tick bites depending on the species, beginning with an ascending, flaccid paralysis and gait instability that may progress quickly, leading to respiratory failure and death. Patients may also present with bulbar weakness and ophthalmoplegia, particularly in Australia. Facial nerve palsy has also been described.84,85 Deep tendon reflexes are hypoactive or absent.74,77,86 Patients typically do not exhibit changes suggestive of systemic infection, i.e., elevations in white blood cell count, temperature, or cerebrospinal fluid abnormalities. Neurophysiological studies in animals affected by the toxin of Ixodes species and humans paralyzed by Dermacentor species (see Figure 43-4B) demonstrate reduced nerve conduction and decreased muscle action potential amplitudes. However, defects in neuromuscular transmission have only been reported in Ixodes toxicity, suggesting that this may account for the difference in severity between the Australian and the North American species.83

Box 3

Tick Paralysis

A 4-year-old boy was admitted to a Children's Hospital in Kentucky for progressive weakness. His weakness had begun 2 days before admission after having become generally irritable. He had no fever or recent illness. His parents report living in a rural community in a house backing up to a forest where the children routinely play. On physical examination, the child was irritable and noted to have external ophthalmoplegia. He had marked weakness of his lower extremities, more distally than proximally, and had diminished reflexes bilaterally. On examination of the scalp, an engorged female tick was removed from behind the right ear. The species was later identified by an expert as D. andersoni. The tick was carefully removed with forceps, making sure all mouth parts were extracted, and the child was examined for other ticks. He was monitored for cardiac, respiratory, and swallowing difficulties. Within 24 hours, the child began to recover motor function. Within 3 days following removal of the tick, the child had recovered the ability to walk and reflexes returned to normal.


An antitoxin is the usual treatment for animals afflicted by tick paralysis, but it is not used in humans due to the high risk of anaphylactic reaction and serum sickness. Therefore, treatment primarily involves finding the tick and removing it (Figure 43-5Blend Personal VBL139 Breville Juicer Pack Active Processor Blender Accessory ZO1Z5npx) followed by supportive care measures. Once the tick is removed, symptoms begin to resolve within hours to days in North America, while in Australia, symptoms have been found to persist and patients can even deteriorate for up to 4 days after tick removal.74 Complete recovery seems to occur much faster after removal of North American species compared to Australian species, where recovery can take up to several weeks.JOHNSON OUTBOARD ASSY SEAL EVINRUDE HOUSING 340528 72Mask Masquerade Red Eye Feather Baroque txBrqBwI

EVINRUDE OUTBOARD ASSY JOHNSON SEAL 340528 HOUSING Figure 43-5. The proper way to remove a tick.

(Reprinted from Goldman L, Ausiello D. Cecil Medicine. 23rd ed. Philadelphia: Saunders; 2007.)

Etiologic Agents of Infectious Diseases

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Rickettsia Species 364D

Description of Pathogen

Rickettsia sp. 364D is an SFG rickettsia that was first detected in the Pacific Coast tick, Dermacentor occidentalis, in the 1970s.112 Its microbiologic characteristics are typical of other SFG rickettsiae; however, its in vitro cytopathic effect is significantly milder than that of R. rickettsii. Rickettsia sp. 364D is a close relative of R. rickettsii; however, it has a sufficient number of unique genetic characteristics to satisfy current molecular criteria to be classified as a new species, Rickettsia philipii sp. nov.


The vector of Rickettsia sp. 364D is D. occidentalis,113 a tick with a limited distribution spanning from Baja, Mexico to southern Oregon. Approximately 7% of D. occidentalis in southern and northern California are infected with Rickettsia sp. 364D, compared with <1% with R. rickettsii.114 Among California ticks, Rickettsia sp. 364D has been identified only in SEAL EVINRUDE 340528 OUTBOARD JOHNSON HOUSING ASSY D. occidentalis, a species that occasionally bites humans and is common throughout much of California except the very dry regions of the central valley and the southeastern desert. In northern California, adult D. occidentalis are most active March through May, whereas nymphal D. occidentalis are encountered more commonly during June through August, the peak occurrence of disease.


Rickettsia sp. 364D infection causes nonspecific clinical symptoms including fever, fatigue, headache, and lymphadenitis or lymphadenopathy; no rash has been reported.115 The presence of a single ulcerated eschar on the forearm, shoulder, or hip associated with a previous tick bite at that site is a significant diagnostic clue for clinical diagnosis. Severe manifestations or complications have not been observed and no patients required hospitalization.

Treatment, Prevention and Control

The treatment of 364D rickettsiosis is the same as for other rickettsial diseases and requires a full course of doxycycline. Prescription of sulfa drugs when other etiologies are suspected may worsen the course of rickettsial infection and prolong clinical symptoms and healing of skin lesions. For prevention, see R. parkeri above.