Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | International measures | Additional sources of information

Victorian statutory requirement

Notification and school exclusion are not required.

Infectious agents

Numerous species of Rickettsiae are of concern to humans. Rickettsiae (and their associated diseases) of particular importance in Australia are R. australis (Queensland tick typhus, Spotted fever), R. tsutsugamushi (Scrub typhus), R. honei (Flinders Island spotted fever) and R. typhi (murine typhus).

Identification

Clinical features
There is great variation in the severity of illness produced by each organism. Infection most commonly begins with a papule forming at the site of the bite where the infection was introduced. This usually becomes necrotic and forms a typical black eschar (scab). Four days to two weeks after the bite symptoms begin with fever and malaise followed by adenitis in the lymph glands draining the bite site. As the organisms spread throughout the body, fever, malaise and headache increase and general lymphadenopathy occurs in most cases. About a week after onset the main features are continuous fever, cough and signs of bronchitis or pneumonia, photophobia, conjunctivitis, generalised adenopathy, delirium, deafness and a maculopapular rash most commonly over the trunk and proximal limb parts. Splenomegaly occurs in some cases.

Fever may persist for 14 days without antibiotic treatment. The fatality rate in untreated cases is 1–40%. This increases with age and depends on the infection site, the type of Rickettsiae involved and previous exposure.

Method of diagnosis
In endemic areas the clinical picture is sufficiently distinctive for a clinical diagnosis. A biopsy of the eschar can be used to demonstrate rickettsiae by immunofluorescence. Specific diagnosis is seldom possible early enough to help in the management.

Definitive diagnosis can be made by isolation of the rickettsia after inoculation of the patient’s blood into mice. Serological methods are also available although these need to be interpreted with caution because of cross-reactivity between strains.

Incubation period

The incubation is from two to 14 days. The variation in incubation may be in part related to the inoculum size.

Public health significance & occurrence

The epidemiology varies in different parts of the world. Disease occurrence is often associated with the modification of natural habitats by humans such as when a forest is felled and replaced by a secondary growth of scrub. R. australis occurs along the eastern side of Australia, R. honei has been recognised on Flinders Island near Tasmania and R. typhi occurs throughout many states of Australia. Scrub typhus occurs in Queensland but its geographic distribution in the rest of Australia is less clear (Odorico, Graves et al 1998). The public health impact on lives or productivity lost is largely unmeasured but it is suspected to be high.

Reservoir

Humans are incidental hosts and are not useful in propagating the organism in nature. Scrub typhus is transmitted by rodent mites. It occurs in a large area from the Indian subcontinent to Australia and in much of Asia including Japan, China, Korea and parts of Russia. The reservoir also includes rats, mice and other small mammals. An exception is louse-borne typhus (R. prowazekii), which does not occur in Australia. Humans are the principal reservoir for louse-borne typhus and the human body louse (pediculosis humanus var humanus) is the vector.

Mode of transmission

The disease is not directly transmitted from person to person. Humans are infected by the bite of an infected larval mite or in the case of scrub typhus, a rat.

Period of communicability

The person is infective for lice during the febrile illness and probably two or three days after the temperature returns to normal. People are at risk of infection for as long as they remain in infected areas.

Susceptibility & resistance

All non immune people are susceptible to infection and according to environmental exposure. Long-lasting immunity probably follows infection.

Control measures

Preventive measures
There is no vaccine available. People who enter infected areas can be protected by impregnating their clothing with dimethyl phthalate and renewing the repellent frequently. Chemoprophylaxis can be successfully used short term and for this a consultation with an infectious diseases specialist is recommended. People camping can also help prevent tick bites by using camp beds for elevation from the floor.

Control of case
Treatment is generally doxycycline or chloramphenicol. Consult the current version of Therapeutic guidelines: antibiotic (Therapeutic Guidelines Limited).

In severe disease, consultation with an infectious diseases specialist is recommended.

Control of contacts
Consider active case finding if other people were exposed to the same setting as the case such as a camping holiday or military exercise.

Control of environment
Not applicable. The mites themselves act as reservoirs so no immediate effect is achieved by rodent control.

Special settings
Not applicable.

Outbreak measures

Except in the case of an epidemic of louse borne typhus, no outbreak measures are necessary.

International measures

In the event of an epidemic of louse borne typhus occurring in Australia, the Department of Human Services will notify the World Health Organization (WHO) and neighbouring countries of this occurrence in an area previously free of the disease.

Additional sources of information

• Bell, D 1995, Tropical Medicine, 4th edn, Blackwell Science.
• Odorico, D, Graves, S, Currie, B, Catmull, J, Zoltan, N, Ellis, S, Wang, L and Miller, D 1998, ‘New Oriental tsutsugamushi Strain from Scrub Typhus in Australia’. Emerging Infectious Diseases, vol. 4, no. 4.