Rickettsial diseases

What are rickettsial diseases?

Rickettsial disease encompasses a group of diseases caused by the microorganisms, rickettsiae.

Rickettsiae are bacteria that can only survive inside cells. Rickettsial diseases vary considerably in severity from self-limiting mild illnesses to severe life-threatening infections, particularly if complications arise. The organisms cause disease by damaging blood vessels in various tissues and organs. In severe cases, multiple tissues and organs are affected.

What are the types of rickettsial diseases?

Rickettsial diseases fall into three groups.

Spotted fever group

• Rocky Mountain spotted fever
• Rickettsialpox
• Boutonneuse fever
• Siberian tick typhus
• Australian tick typhus
• Oriental spotted fever

Typhus group

• Also called rickettsia typhi
• Louse-borne typhus and Brill-Zinsser disease (relapsing louse-borne typhus)
• Murine typhus

Other rickettsial diseases

• Scrub typhus (tsutsugamushi disease)

Ehrlichia, Anaplasma and Coxiella (Q fever) are no longer classified as rickettsial infections.

Who gets rickettsial diseases?

Rickettsial diseases occur all over the world but some types of rickettsial diseases are more prevalent in certain geographic locations. They are rare in New Zealand.

• Rocky mountain spotted fever: primarily continental United States and rarely elsewhere
• Rickettsialpox: large cities in Russia, South Africa, and Korea
• Boutonneuse fever: Mediterranean countries, such as Spain, Italy, and Israel
• Louse-borne typhus: Europe, Asia and Africa, and in the last two decades, African countries, especially Ethiopia and Nigeria
• Murine typhus: large cities around the world with high rat infestations (this includes Auckland)
• Scrub typhus: Japan, Solomon Islands and Pakistan

How do you get rickettsial diseases?

Most rickettsial diseases are spread to humans by arthropods such as ticks, lice, mites, and fleas.

Rocky mountain spotted fever: R rickettsii

• Vector: wood tick, dog tick and Lone Star tick
• Humans become incidental host after being bitten by infected adult tick

Rickettsialpox: R akari

• Vector: house mouse is the natural host of the mouse mite transmitting rickettsialpox

Boutonneuse fever: R conorii

• Vector: various ticks including dog ticks

Louse-borne typhus: R prowazekii

• Vector: lice (Pediculus humanus)

Murine typhus: R typhi and R felis

• Transmitted between rats by a rat flea
• Humans accidentally infected by the faeces of infected fleas

Tsutsugamushi disease: Orientia tsutsugamushi

• Vector: larval trombiculid mites in soil and scrub

What are the signs and symptoms of rickettsial diseases?

Signs and symptoms differ slightly depending on the type of rickettsial disease. However, like other viral or bacterial exanthems, most patients present with fever, headache and malaise (feeling generally unwell) and a widespread rash of some description.

Rocky mountain spotted fever

• Onset gradual or abrupt, starting about 2–8 days after a tick bite
• Fever, headache, confusion, aching muscles, gastrointestinal symptoms
• Rash from day 2–3, consisting of of small red blotches on wrists and ankles that become widespread and sometimes blister
• 20% of cases do not develop rash (spotless rocky mountain spotted fever)

Rickettsialpox

• Irregular fluctuating fever occurs and lasts for < 1 week
• Headache, chills, aching muscles, runny nose, sore throat, nausea and vomiting, abdominal pain
• Red raised spot develops at site of mite bite, later forming a dry scab (eschar)
• Rash distributed on the face, neck, trunk and extremities, and is easily confused with rash of varicella (chickenpox)

Boutonneuse fever

• Fever, headache, malaise, aching muscles
• Rash appears on days 3–5 of illness, spreading from the extremities to the trunk, neck, face, palms and soles within 36 hours
• Rash is spotty and blotchy and may persist for 2–3 weeks
• In half the cases, a dry scab known as a tache noire (black spot) develops

Louse-borne typhus

• Abrupt onset occurring 1–2 weeks after louse bite
• Fever and intractable headache
• On days 4–7 of illness, rash appears, spreading from trunk to extremities (face, palms and soles are usually not affected)
• Rash initially splotchy, developing into raised red spots
• Recurrence (Brill-Zinsser disease) is usually milder

Murine typhus

• Similar to louse-borne typhus but tends to have a milder and shorter course
• Flea bite does not have an eschar

Scrub typhus

• Generalised swelling of the lymph nodes is common
• Fever and headache
• Rash occur 1–3 weeks after a mite bite and is a dry scab-like lesion
• Rash usually only around the trunk and has a short duration

Diagnosis of rickettsial diseases

Serology is the mainstay to confirm diagnosis of rickettsial diseases. This is a blood test that detects the presence of antibodies to rickettsial antigens.

What is the treatment for rickettsial diseases?

All rickettsial diseases should be treated with antibiotic therapy. They should be started early in the first week of illness to be most effective and to produce a good outcome. Doxycycline is the drug of choice. Chloramphenicol may be used as an alternative. Supportive therapy with electrolyte and fluid maintenance are also essential to the management of patients with rickettsial diseases, particularly if there are signs of low blood pressure, electrolyte disturbances, and blood coagulation (clotting) problems (DIC).

Rickettsialpox is a self-limiting disease and occasionally antibiotics may not be necessary, especially if the condition is mild and/or the patient is an infant or young child.

What are the complications from rickettsial diseases?

Complications are uncommon for most rickettsial diseases, especially if diagnosed early and appropriate treatment initiated promptly. Rickettsialpox is a self-limiting disease and has no complications. Complications that may occur in some rickettsial diseases include:

• Bronchopneumonia
• Congestive heart failure
• Multi-organ failure
• Deafness
• Disseminated intravascular coagulopathy (DIC)
• Myocarditis (inflammation of heart muscle)
• Endocarditis (inflammation of heart lining)
• Glomerulonephritis (inflammation of kidney).