Spotted Fever, Rickettsial Spotted Fever, Queensland Tick Typhus.
Rickettsia australis.
This is an obligate, intracellular bacterial parasite that proliferates within the endothelial cells of small blood vessels, causing a vasculitis.
Ixodes holocyclus (Australian Paralysis Tick).
Australian Spotted Fever was first described in 1946 when 12 soldiers contracted the disease during training exercises in north Queensland - it was at that time known as Queensland Tick Typhus (QTT).
Infections generally arise in rural areas, but 10% of reported cases appear to have been acquired in major cities. It is apparently not uncommonly seen in tick collectors in southern Queensland. It mostly occurs during the winter and spring, but can occur at any time in temperate areas.
One to 14 days (usually 7-10 days) after a tick bite there is fever, headache and muscle aches (myalgia). Stiff neck, nausea, vomiting and mental confusion are also possible. An inoculation lesion (eschar) 2-5 mm in diameter is present in 65% of cases. Usually there is only one eschar (the possible exception being when a simultaneous tick bites occur).
^ A human eschar lesion caused by Ixodes holocyclus-transmitted Rickettsia australis.
One to 12 days (usually 3-5 days) after the onset of symptoms, a red spotted (macular) or raised (papular) or blistering (vesicular) rash may occur on the trunk and later the face, palms and soles. Lymphadenopathy is normally present. Arthralgia, conjunctivitis, pharyngitis, dry cough, abdominal pain, and neurological involvement may be seen. Untreated, the fever lasts one to two weeks. Changes in the regional lymph nodes draining the area of attachment can also lead to the formation of chronically sensitive enlargement within the node lasting for several years, particularly those around the head and neck.
^ Vesicular rash caused by Ixodes holocyclus-transmitted Rickettsia australis (Bernie Hudson, 2002).
One bout of the disease seems to confer solid immunity in nearly all people. In rare instances there may be an apparent repeated infection after recovery - it is not known whether this is caused by another strain. It is also presently unknown if chronic infections occur. It is rarely fatal.
Diagnostic serology is available in the form of IgM and Weil-Felix tests.
The disease runs it's course in two weeks or so but can be cured more quickly with antibiotics. Treatment is with tetracyclines and is usually rapidly effective, although rare fatalities have been recorded.