Lab notes: The scrub typhus bacterium may be causing in many of Assam's encephalitis deaths

The bacterium that causes the mite-borne disease scrub typhus could be responsible for a large number of cases of the often fatal Acute Encephalitis Syndrome or AES in Assam, according to a new study from the north east Regional Medical Research Centre in Dibrugarh, a branch of the Indian Council of Medical Research.

Scrub typhus is a disease characterised by fever, headache, muscle pain, cough and gastrointestinal disruptions. More acute attacks involve haemorraging, rashes, pneumonitis and encephalitis among other symptoms. Scrub typhus is caused by the bacterium Orientia tsutsugamushi which is picked up from scrub-like vegetation.

Assam is an endemic zone for AES, especially that caused by the Japanese encephalitis virus of which there has been a severe outbreak this year in Odisha’s Malkangiri district. However, more than 50% of AES cases in Assam are not due to the Japanese encephalitis virus and the causes remain unrecognised.

In the new study published in the journal Emerging Infectious Diseases, researchers enrolled 511 AES patients, of whom 104 showed signs of recent infection with the bacterium O tsutsugamushi. These 104 patients showed symptoms of fever, inabaility to think clearly or concentrate, headache, unconsciousness, and nausea.

Only 13 patients showed signs of infection from the Japanese encephalitis virus. The research team followed up with 53 of the 104 patients and discovered that 26 died after discharge, including four of nine patients in whom the Orientia DNA was detected.

The study attributes the high rates of illness and death from scrub typhus to the fact that because the Japanese encephalitis virus is the predominant agent of AES in the north east, health providers generally look for other sources of the disease. Furthermore, the nonspecific symptoms of scrub typhus makes it difficult to diagnose accurately. The study records the highest numbers of scrub typhus cases in July through to September, the peak season for Japanese encephalitis transmission.

The researchers recommend recording occupation details and ecologic background of patients from those in rural areas as an important source for identifying those with scrub typhus, as well as increasing awareness among clinicians for prompt diagnosis and treatment.