Rickettsial diseases

Case history #1

A 25-year-old woman presents to a hospital emergency department with a 24-hour history of fever (39°C), severe headache, myalgia, arthralgia, abdominal pain, and lethargy. Three days ago she had returned from a holiday to Indonesia where she had travelled rough and slept in very basic accommodation. She thinks she may have been exposed to a variety of ectoparasites and been bitten by mosquitoes. The initial working diagnosis is malaria with differential diagnoses of dengue, typhoid fever, salpingitis, and leptospirosis (all travel-associated). There is also the possibility of a non-travel-associated bacteraemia due to urinary tract infection (UTI) or pneumonia. On examination she is febrile and flushed but no rash is obvious. An eschar (ectoparasite bite site), of which she is initially unaware, is eventually detected in her natal cleft. This latter key finding leads to the possibility of rickettsial infection being considered. There is no abnormality on chest or abdominal examination and no lymphadenopathy. A urine analysis rules out UTI. Full blood count shows a mild lymphocytosis with atypical lymphocytes consistent with a viral infection. The neutrophil count is normal. The C-reactive protein is 150 mg/L. There is a significant thrombocytopenia but no anaemia. The liver function tests show mild transaminitis. Mild hyponatraemia is also present. Blood cultures are taken but the report (48 hours later) is "no growth". Blood tests for malaria are negative. Baseline (acute phase) serum is collected for serology. The laboratory is asked to store the serum untested until a later (convalescent phase) serum can be collected in 5 to 7 days' time. These two sera will then be tested together to look for seroconversion to the antigens of the suspected pathogen. In view of the possible rickettsial infection, the patient is given a trial of doxycycline. She is discharged with advice to see her general practitioner (GP) in 2 days if not improved. She is afebrile within 48 hours and visits her GP 5 days later who finds her well apart from a faint macular rash that has appeared on her trunk, arms, and legs. The eschar is healing. She has follow-up serum taken for convalescence rickettsial serology, which confirms the diagnosis. The subsequent laboratory report states "seroconversion to spotted fever group rickettsiae, consistent with recent infection with a tick-transmitted rickettsia". There are no sequelae and the patient returns to normal good health.

Case history #2

A dishevelled older man is brought to hospital by ambulance having been found almost unrousable under a city bridge, where he normally sleeps. He is homeless and spends his days wandering the streets of the city. He is clearly septic, although not febrile, with a rapid respiratory rate (30 breaths per minute), severe hypotension (90/60 mmHg), and hypoxia (SpO₂ 90%). He is severely malnourished, underweight, smells of alcohol, and has fleas. A chest examination and chest x-ray shows that he has bilateral pneumonia. Blood cultures are taken. Despite coughing he is not producing sputum. A catheter specimen of urine is sent to the laboratory to rule out UTI. An intravenous line is inserted and benzylpenicillin (to cover pneumococcal pneumonia) and ceftriaxone (to cover gram-negative pneumonia and septicaemia) is initiated. He is admitted to the intensive care unit. Over the next 24 hours he does not improve. When seen by the visiting infectious diseases/medical microbiologist consultant the next day he is clearly deteriorating. An unusual cause for his pneumonia and sepsis is then considered. Staphylococcal, legionnaires' disease, and Mycoplasma pneumonia are considered. Initial blood cultures are negative and his intravenous antibiotic cover is broadened to include minocycline and vancomycin. A baseline serum is also collected for subsequent serology. Over the next week he gradually improves and is sent to the respiratory ward. No useful data have come from the microbiology laboratory, however. Given that his living environment is heavily populated with rats, it is thought that this illness may be associated with rats and rat fleas. Plague (Yersinia pestis) is unlikely, except in a developing country. Rat bite fever is also a possibility (although there are no signs of rat bites on his body). Murine typhus (Rickettsia typhi) is acquired by inhaling the infectious faeces of the infected fleas that live on the rodents and which contaminate the environment. The convalescent serum is tested serologically (along with the acute serum) for antibodies to this bacterium. There is a significant (4-fold) increase in antibody levels between the acute and convalescent sera, demonstrating recent, acute infection with R typhi. The diagnosis is now confirmed as sepsis and pneumonia due to murine typhus (R typhi). The lack of initial response was due to this bacterium always being completely resistant to penicillin and cephalosporin antibiotics. Fortunately all rickettsiae are very sensitive to doxycycline and minocycline. The patient eventually recovers fully with no sequelae and is referred to the social workers for placement.

Other presentations

In situations of mass crowding, poverty, famine, and war there is a risk of epidemic typhus (Rickettsia prowazekii). This infection is transmitted by the human body louse bite. This typically presents with a sudden onset of fever, myalgia, headache, and prostration. At 4 to 6 days around one half of people infected develop a macular rash, which starts centrally and spreads peripherally with the exception of the face, palms, and soles. In severe cases, the rash may become petechial and haemorrhagic. Possible complications include encephalitis or pneumonia. The fever lasts approximately 2 weeks. R prowazekii sometimes remains latent and recrudesces years or decades later (Brill-Zinsser disease). Recrudescent typhus is usually mild, with lower mortality rates and a shorter course.[3]The Center for Food Security & Public Health, Iowa State University. Typhus fever - Rickettsia prowazekii. Feb 2017 [internet publication]. https://www.cfsph.iastate.edu/Factsheets/pdfs/typhus_fever.pdf

People living in East Asia, Southeast Asia, the Indian subcontinent, Oceania, and northern, tropical Australia, who are exposed to scrub or bush during their work or hobbies, are at risk of being bitten by the larval form ('chigger') of a particular genus of mites, Leptotrombidium species. A rickettsia (Orientia tsutsugamushi) is transmitted to patients by the bite of this mite. This may be a very severe infection with high mortality if untreated.