Rickettsial diseases

Rickettsial disease in humans (spotted fevers, typhus or scrub typhus) is caused by a number of related species of intracellular bacteria of the genus Rickettsia that have blood-feeding arthropod vectors. Each species is associated with a different spectrum of clinical features, geographical distribution, insect vector (tick, louse, flea, mite or chigger), seasonal incidence and other epidemiological factors.

Rickettsial diseases caused by the spotted fever group, scrub typhus group and murine typhus group all occur in Australia.

R.typhi is endemic in some parts of New Zealand.

R. felis has been detected in fleas taken from dogs and cats in the central-lower North Island, but no human cases have been reported.

More detailed epidemiological information is available on the Institute of Environmental Science and Research (ESR) surveillance website.

Rickettsial disease characteristically presents with fever, headache and malaise; there is often lymphadenopathy, myalgia and a rash, either macular or haemorrhagic. Some cases may form an inoculation eschar (ulcer or papule often with a black crust). Neutropenia, thrombocytopenia and moderate increases in transaminases are common laboratory abnormalities. There is great variation in the severity of illness, depending on the organism involved, but continuing fever, cough and signs of bronchitis or pneumonia, photophobia, conjunctivitis, delirium, deafness and hepatosplenomegaly may be present.

Consult ESR or LabPlus for appropriate testing.

Although laboratory testing plays an important role, patient history and clinical findings are essential for a diagnosis of rickettsial infection.

Culture is not straight forward and is potentially dangerous, therefore the diagnosis is a serological one in the appropriate clinical context.

Laboratory definitive evidence for rickettsial disease requires at least one of the following:

• seroconversion or significant increase in IgG antibody titres between acute and convalescent sera
• detection of rickettsial nucleic acid.

Laboratory suggestive evidence for rickettsial disease requires at least one of the following:

• single raised IgG titre
• detection of IgM antibodies.

The following serological tests are available at LabPlus:

• Rickettsia typhi for murine typhus
• Orientia tsutsugamushi (formerly R. tsutsugamushi) for scrub typhus group
• Rickettsia conorii for tick typhus group.

The following serological tests are available at Waikato Hospital:

• Rickettsia typhi IgG and IgM
• spotted fever group IgG and IgM.

Note that there is significant cross reactivity between the different Rickettsia species.

• Under investigation: A case that has been notified, but information is not yet available to classify it as probable or confirmed.
• Probable: A clinically compatible illness with laboratory suggestive evidence.
• Confirmed: A clinically compatible illness with laboratory definitive evidence.
• Not a case: A case that has been investigated and subsequently found not to meet the case definition.

Cases can be further classified in Episurv by disease:

1. typhus: caused by R. prowazekii (the agent of classical epidemic typhus)
2. murine typhus: caused by R. typhi (formerly called R. mooseri endemic or ‘shop’ typhus)
3. rickettsial disease: all other diseases caused by organisms of the Rickettsia genus. This includes scrub typhus, caused by Orientia tsutsugamushi. Record species, if laboratory confirmed, in ‘Other lab details’.

• Rickettsial disease: Variable dependent on the disease agent (usually between 1–3 weeks).
• Murine typhus fever: 1–2 weeks.
• Scrub typhus: 10–12 days (6–21 days).
• Tick typhus: 5–7 days.

Rickettsia spp. live harmlessly in the salivary glands or gut of arthropods, especially fleas and ticks, and are perpetuated in the vector by trans-ovarian spread to the young. Transmission to humans occurs when arthropod faeces, regurgitated material or saliva is inoculated into a bite wound.

There have been no known direct transmissions of rickettsial disease between people.

Attending health practitioners or laboratories must immediately notify the local medical officer of health of suspected cases. Notification should not await confirmation.

There is a specific form in EpiSurv for murine typhus (since this is the only Rickettsia species endemic in New Zealand).

• Obtain a history of travel, contact with animals and insect bites. Ensure acute and convalescent serological diagnosis has been attempted.
• When applying for laboratory testing, ensure that the travel history and likely incubation period are recorded on the laboratory form as these details inform the laboratory’s choice of test kit. For infections probably acquired overseas, it may be useful to discuss testing with the laboratory.

Nil.

Consult an infectious diseases physician. Tetracyclines and chloramphenicol are the drugs of choice.

Advise the case and their caregivers of the nature of the infection and its mode of transmission.

Advise anyone exposed to the same potential animal or arthropod source of the incubation period and typical symptoms of the infection. Encourage them to seek medical attention if symptoms develop.

Check for other cases in the community. If the infection may have been acquired in New Zealand, liaise with staff at the Ministry for Primary Industries and/or territorial authority to investigate potential animal reservoirs of infection. See ‘Reporting’ below.

If the infection has been acquired overseas, advise the case to check for retained vectors (for example, embedded ticks on body) and liaise with Ministry for Primary Industries staff to aid with identification and destruction after removal.

Nil.

In the event of a New Zealand-acquired Rickettsia infection, consider direct communication with local parents, schools and health professionals to encourage prompt reporting of symptoms. In communications with doctors, include recommendations for diagnosis and treatment.

In the event of an endemic Rickettsia infection, take steps to eliminate rodents and fleas from affected households.

Ensure complete case information is entered into EpiSurv.

On receiving a notification, medical officers of health should immediately contact 0800GETMOH - CD option. The Ministry will then notify the appropriate staff in the Ministry for Primary Industries so that further investigation of the source can be undertaken.

• Biggs HM, Behravesh CB, Bradley KK et al. 2016. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis — United States: A Practical Guide for Health Care and Public Health Professionals [PDF, 5.5 MB]. MMWR Recomm Rep. 2016; 65 (RR2).
• Cook GC, Zumla AI (eds). 2008. Manson’s Tropical Diseases (22nd edition). London: WB Saunders.
• Department of Health and Human Services, State Government of Victoria. Rickettsial infections (accessed 1 September 2020).
• Heymann DL (ed). 2014. Control of Communicable Diseases Manual (20th edition). Washington: American Public Health Association.