Scrub typhus: symptoms, causes, diagnosis and treatment

Scrub typhus is one of the typhus group of illnesses, although it is caused by a different organism from the lice-borne and flea-borne forms. The NHS describes typhus in general as an infection spread by lice, fleas or mites that is very rare in the UK, serious but with most people making a full recovery if treated quickly. Scrub typhus is the mite-borne form.

DermNet explains that the bacterium Orientia tsutsugamushi is transmitted by infected trombiculid mites. Patient.info adds that the bacterium is classified in its own genus because it differs from other rickettsial organisms in its genes and cell wall structure, and that the name scrub typhus came from the discovery that the disease was more frequent in scrub or wasteland areas.

The mites themselves are tiny. Only the larval stage, the chigger, bites humans, and DermNet notes that humans are likely to be accidental hosts, because the mites feed mainly on small mammals, particularly rodents. Mite habitats include forest, plantations, beaches and gardens, and are patchily distributed, so anyone exposed to suitable habitat could be at risk.

Patient.info says infection is greatest near riverbanks, especially where forest has been cleared close by, and in the rainy season, which helps explain why it is so closely tied to place and season.

Patient.info describes scrub typhus as endemic in eastern and southern Asia and northern Australia, with other regions including India, Thailand, Tibet, Japan, Russia and the mountainous regions of Nepal, and says that people visiting endemic areas may also be infected. DermNet notes increasing reports from elsewhere in the world, including recently in Chile.

In the UK, cases are almost always imported by people who have travelled. Anyone who has been in rural or scrubland areas of an endemic region, for example while walking, camping or working outdoors, and who becomes unwell with fever after returning is at risk. Because many other travel-related illnesses cause fever, headache and aching, it is important to tell the clinician where you have been and what you did.

DermNet describes the classic features as fever, myalgia and headache. Symptoms usually start within 6 to 14 days of being bitten; Patient.info gives the incubation period as up to ten days. A cutaneous eschar develops at the site of the bite in most cases, according to DermNet, though Patient.info says only in about half. Patient.info lists a papule followed by an eschar, fever, headache, muscle pain, cough, abdominal pain with nausea and vomiting, swollen regional lymph glands and a flat or raised rash.

• Fever, headache and muscle aches.

• A dark scab (eschar) where the mite fed, found in most cases according to DermNet.

• Swollen lymph glands near the bite.

• A rash on the trunk, which may spread.

• Cough, abdominal pain, nausea or vomiting.

The NHS advises, for typhus in general, getting medical advice if you have symptoms and have recently returned from abroad or are travelling abroad: in England, see a GP, call 111 or get help from NHS 111 online. It stresses that early diagnosis matters and that if typhus is not treated quickly it can sometimes be life-threatening.

If you become severely unwell, seek emergency help through 999 or A&E. Patient.info says severe cases can develop encephalitis and interstitial pneumonia, and that the illness can occasionally be fatal. Tell the clinician about your travel, including the dates and the places you went.

Diagnosis depends on suspecting the disease from the travel history and findings. DermNet states that laboratory diagnosis is difficult, and lists antibody-based rapid tests, serology, polymerase chain reaction (PCR) and cell culture. Patient.info adds that PCR on blood from feverish patients, and sometimes on a small sample of the eschar, can be used, and that a chest X-ray may show lung infiltrates when pneumonia is present.

Because other infections cause fever, muscle pain and headache, DermNet lists typhoid, malaria, melioidosis, dengue, leptospirosis and other rickettsial diseases in the differential diagnosis. The NHS says for typhus that antibiotics are usually started before the test result comes back, because results can take up to a week.

DermNet says scrub typhus is usually responsive to tetracycline antibiotics, especially doxycycline, and that a 7-day course is usually adequate unless the disease is severe. Chloramphenicol is described as the second-line option. Patient.info says that azithromycin has been used in resistant cases and may be better than doxycycline, especially in children and pregnant women, and notes possible antibiotic resistance in some areas.

The outlook is good with timely treatment. DermNet says symptoms should start to improve within 48 hours and the patient should be completely recovered in 7 to 10 days, whereas mortality in untreated cases may be as high as 60%. Patient.info gives a lower figure of 5 to 10% for untreated cases, and the difference reflects variation between studies and populations. Either way, early treatment is clearly better. Severe illness may involve pneumonia, kidney failure, low blood pressure or inflammation of the brain, and requires hospital care.

DermNet says immunity seems to be short-lived and strain-specific, so previous infection does not protect against future infection.

There is no vaccine. DermNet advises avoiding bites by larval mites: applying effective insect repellent such as DEET, and wearing long trousers, shoes and socks in and around mite habitats. The NHS gives similar general advice for typhus, recommending insect repellent containing DEET, long-sleeved shirts and trousers, and regular washing and changing of clothes.

Patient.info says that vector control and acaricides have been used at a public health level, and that no vaccine or chemoprophylaxis is available.