Scrub Typhus Emerges as Leading Cause of Encephalitis in Southern India

A recent multicentre study has identified scrub typhus as the most common infectious cause of acute encephalitis syndrome (AES) among children in southern India. Conducted across three states—Karnataka, Andhra Pradesh, and Tamil Nadu—the study involved 587 children and was published in The Lancet Regional Health – Southeast Asia.

The research team, which included experts from NIMHANS, Indira Gandhi Institute of Child Health, and other institutions, sought to investigate the infectious causes of AES, a condition characterized by fever, altered mental status, and seizures. The findings reveal that scrub typhus, caused by the bacterium Orientia tsutsugamushi, accounts for 44% of AES cases, far surpassing the historically dominant Japanese encephalitis virus at 11%.

Scrub typhus has emerged as a significant public health concern, with the incidence of AES in India reported at between 3.5 and 13.8 cases per 100,000 patient-years. Over 10,000 cases of AES are documented annually, according to the National Vector Borne Disease Control Programme (NVBDCP). The study’s lead author, Dr. Tina Damodar, emphasized that the recognition of scrub typhus as a major contributor to AES has been limited by inadequate surveillance efforts.

Dynamic Landscape of AES in India

The research analyzed data from children aged 28 days to 18 years presenting with AES at three tertiary care hospitals in Bengaluru. During the study period from March 2020 to February 2023, 714 children were screened, with 587 ultimately included in the analysis. A microbiological diagnosis was established for 315 cases, revealing that scrub typhus was responsible for 138 infections.

In addition to scrub typhus, the study identified other notable pathogens, including dengue (10%), leptospira (5%), and chikungunya (5%). Dr. Damodar noted that these findings illustrate a diverse and evolving landscape of AES in the region.

Key predictors for both scrub typhus and other doxycycline-treatable infections included age, illness duration, and specific clinical signs such as lymphadenopathy and hepatomegaly. Notably, the study found that over 60% of microbiologically confirmed cases were linked to infections treatable with doxycycline, yet this antibiotic is not routinely included in AES treatment protocols.

Recommendations for Treatment Protocols

In light of these findings, the researchers recommend integrating doxycycline or azithromycin into the initial treatment for children presenting with AES or acute febrile illness in southern India. This recommendation has already been implemented at the participating referral hospitals.

Dr. Reeta S. Mani, head of Neurovirology at NIMHANS, highlighted the urgency of timely treatment, noting that nearly 40% of the children diagnosed with scrub typhus experienced severe outcomes, including death or neurological complications, largely due to delayed diagnosis. To mitigate this, the study advocates for the wider availability of diagnostic tests for scrub typhus, such as IgM ELISA or PCR, at primary and secondary healthcare facilities.

Additionally, the research team developed a clinical prediction model—a simple point-based tool designed to assist frontline clinicians in identifying children who are likely to benefit from doxycycline treatment, even before laboratory confirmation is available.

The emergence of scrub typhus as a key player in AES underscores the need for enhanced surveillance and revised treatment protocols to improve patient outcomes in southern India.