Queensland tick typhus

Did You Know?

• After transmission, Rickettsia australis enters the body via the bloodstream; the first sign is damage to skin microcirculation causing a rash.
• Early treatment includes oral antibiotics such as doxycycline or chloramphenicol; intravenous administration is used if oral intake is not possible.
• The disease was noted during World War II among Australian soldiers training on the Atherton Tableland in Queensland.

Signs and symptoms

The incubation period ranges from 2 to 14 days after a tick bite. Clinical features include fever, headache, an eschar at the bite site, erythematous eruption, and satellite lymphadenopathy. The illness resembles Rocky Mountain spotted fever but is less severe. If untreated for over one to two weeks, recovery may be prolonged and risks include pneumonitis, encephalitis, septic shock, or death. Prolonged lethargy or fatigue can persist after the rash clears.

Causes

Queensland tick typhus is caused by the bacterium Rickettsia australis. The tick life cycle includes egg, larva, nymph, and adult stages. An adult female may lay over a thousand eggs. After hatching, larvae attach to a host, feed, detach, and molt into nymphs. Nymphs attach to a larger host, feed, detach, and molt into adults. Adults feed once more and reproduce. The nymph stage is most capable of transmitting the disease; nymphs are under two millimeters and often go undetected while feeding. Transmission occurs primarily via Ixodes holocyclus and Ixodes tasmani. After attachment, feeding begins within 10 minutes to 2 hours. Ticks remain attached for about 12 to 18 hours before dropping off. A tick must be attached for a prolonged period to transmit bacteria; a flat, small tick likely has not fed.

Diagnosis

Diagnosis is challenging because initial signs are non-specific. Travel history is important. Serological assays, particularly the indirect microimmunofluorescence assay (IFA), are the best diagnostic tools, though rheumatologic or immune-mediated disorders can cause false positives. PCR testing for rickettsial DNA from an eschar or blood sample can sensitively detect infection during the first few days.

Prevention

No vaccine exists. The US CDC recommends personal protective measures in tick-prone areas. Before entering such areas, wear clothing covering arms and legs, closed-toed shoes, and long socks tucked into pants. Use DEET repellent on skin and Permethrin on clothing. Pets should be on preventive medications and a veterinarian consulted. After returning, check clothes and gear for ticks; dry clothes on high heat for 10 minutes (or wash in hot water and dry on high heat if wet). Shower within two hours to remove unattached ticks. Perform a full-body check for attached ticks. Bathe and check pets for ticks as well.