Amblyomma, Rhipicephalus and Ornithodoros

At a glance

Shape

Oval body without segments; hard ticks have a dorsal shield (scutum) and forward mouthparts; soft ticks are leathery with mouthparts underneath

Family

Ixodidae (hard ticks: Amblyomma, Rhipicephalus, Dermacentor, Ixodes); Argasidae (soft ticks: Ornithodoros)

Type

Arachnids (Acari), obligate blood-feeding ectoparasites and vectors

Size

Larvae under 1 mm; engorged adult females up to about 1 cm or more

Morphology

• Larvae have 6 legs; nymphs and adults have 8, as in all arachnids.
• The hypostome has backward teeth and is cemented into the skin, so hard ticks stay attached for days.
• Soft ticks feed for minutes to an hour, usually at night, and hide in nests, cracks and burrows.

Transmission

• Hard ticks climb vegetation and wait for a passing host (questing), then attach in protected skin folds.
• Pathogens pass in saliva during feeding; the longer the attachment, the higher the risk for many infections.
• Some ticks pass pathogens to their eggs, so even larvae can be infected.
• Soft ticks bite briefly at night inside houses, caves or animal shelters; bites are often painless and unnoticed.

Reservoir: Wild and domestic mammals: rodents, dogs, cattle, horses, capybaras; Ticks themselves, which can stay infected through their stages and to their eggs

Vector: Amblyomma and Rhipicephalus carry spotted fever rickettsiae; Ixodes carries Borrelia burgdorferi, Babesia and Anaplasma; Ornithodoros soft ticks carry tick-borne relapsing fever Borrelia.

Isolation precautions

What the care team adds to standard precautions.

• Standard

Life cycle

1. The engorged female drops to the ground and lays thousands of eggs, then dies.
2. Six-legged larvae hatch, climb vegetation and take a first blood meal.
3. The larva drops off, moults into an eight-legged nymph and feeds again.
4. The nymph moults into an adult; females take a large final meal and mate.
5. Many hard ticks use a different host for each stage (three-host ticks); Rhipicephalus sanguineus may complete it on dogs indoors.
6. Soft ticks go through several nymph stages and feed many times, briefly, living for years.

Virulence factors

• Saliva contains anaesthetic, anticoagulant and immune-dampening substances, so the bite is often unnoticed.
• Cement and toothed mouthparts keep the tick attached for days, which gives time for transmission.
• A neurotoxin in the saliva of some attached ticks causes tick paralysis.
• Mouthparts left in the skin can cause a granuloma that lasts months.

Diseases it causes

• Spotted fever rickettsioses, including Rocky Mountain (Colombian) spotted fever by Rickettsia rickettsii Rickettsial infections (spotted fever) →
• Lyme disease (Borrelia burgdorferi, Ixodes ticks) Lyme disease →
• Tick-borne relapsing fever (Ornithodoros soft ticks) Relapsing fever (tick-borne and louse-borne borreliosis) →
• Babesiosis Babesiosis →
• Tularaemia Tularaemia →
• Ehrlichiosis and anaplasmosis
• Tick paralysis: ascending flaccid weakness from a toxin in the saliva of an attached tick

Clinical picture

• Painless bite; a red papule or small eschar at the site; in children, look on the scalp, behind ears and in folds.
• Fever, headache and rash within two weeks of a tick bite: think of rickettsiosis and treat early.
• Tick paralysis: ascending weakness over hours to days that mimics Guillain-Barré syndrome or botulism; it resolves soon after the tick is removed.
• Relapsing fever: recurring fever episodes separated by days without fever.

Diagnosis

• Identify the tick (genus) if it was kept; testing the tick is not used to decide treatment.
• Search the whole body, including the scalp, for an attached tick in any child with ascending paralysis.
• Spotted fever: diagnosis is clinical first; paired serology or PCR confirm later.
• Relapsing fever: spirochaetes seen in blood smears taken during fever.

Treatment

Remove the tick at once with fine-tipped tweezers: grasp it close to the skin, pull straight out with steady pressure, then clean the area; do not use heat, petroleum jelly or nail polish. Doxycycline is the drug of choice for suspected rickettsial disease at any age; tick paralysis improves after removal.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

• Doxycycline

Prevention

• Long, light-coloured clothes tucked into socks in pasture and forest; repellents on skin and permethrin-treated clothing.
• Daily full-body tick checks after field work, including children's scalp and skin folds.
• Tick control on dogs, cattle and horses, and in kennels and houses.
• Seal cracks and rodent nests in houses to keep out soft ticks.

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Connections

← Back to the group: Arthropod vectors

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: About Ticks and Tickborne Disease | Ticks | CDC (CDC, 2025); What to Do After a Tick Bite | Ticks | CDC (CDC, 2025); About Rocky Mountain Spotted Fever | Rocky Mountain Spotted Fever (RMSF) | CDC (CDC, 2025); Rickettsia rickettsii in Amblyomma patinoi Ticks, Colombia (Emerging Infectious Diseases (CDC), 2015).

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Representative model, for educational purposes only.