Scrub typhus, an infection caused by a bacterium that is spread by the bite of infected larval mites (chiggers), can be an important but under-appreciated reason for fever-related hospitalizations in India, especially in rural areas. A study by Christian Medical College (CMC), Vellore, and the London School of Hygiene and Tropical Medicine (LSHTM) revealed that almost 10% of the population in rural Tamil Nadu develops the infection each year. The results appeared in the New England Journal of Medicine.
The study enrolled over 32,000 people from 37 rural villages in Tamil Nadu, with data gathered for two years between August 2020 and July 2022. Chiggers, which live in grass, plant debris, and open ground, feed mostly on small mammals such as rats and shrews. It is caused by Orientia tsutsugamushi, a rickettsia family member bacterium, and may cause serious health consequences, such as acute respiratory distress syndrome (ARDS), shock, meningitis, and renal failure.
Dr. Wolf-Peter Schmidt, the principal investigator of the study and a clinical assistant professor at LSHTM, noted that infections are most common between August and February. Symptoms typically develop between 10 days from exposure and can be fever, headache, body pains, and rash. A blackened spot around the biting area can help in diagnosis.
Senior author Carol Devamani of CMC Vellore pointed out that scrub typhus came in as the second most important reason for fever-related hospitalizations following COVID-19 in their research, with almost 30% of such hospitalizations. Even though it is a treatable disease, it tends to go unnoticed because there are no community-level diagnostic centers, and testing is mainly done in large hospitals.
Throughout the study, researchers took blood samples from the participants every six to eight weeks and tested for scrub typhus. What they found was a high rate of symptomatic and asymptomatic infections, with some people getting the disease more than once in two years. Of those infected, 8-15% had severe symptoms that needed hospitalization and intensive care.
"Over the course of two years, we observed numerous cases of both mild and severe infections. It is not known why some of these cases become life-threatening," Schmidt said. Although five of the study participants died from scrub typhus complications, no deaths from malaria, dengue, or typhoid fever, the other causes traditionally blamed for severe fever in India, were reported.
The scientists highlighted raising awareness of scrub typhus and enhancing community-level diagnostic proficiency. Devamani underscored that early diagnosis and treatment may help avoid hospitalization unnecessarily and avert death.
Scrub typhus, while treated with antibiotics including doxycycline and azithromycin, currently has no preventive vaccine. There were also admitted limitations to the study, like possible underreporting of fevers and possible effects of restrictions due to COVID-19.
References:
1. Devamani, Carol. et. al., "Incidence of Scrub Typhus in Rural South India." New England Journal of Medicine. Accessed March 12, 2025. https://www.nejm.org/doi/full/10.1056/NEJMoa2408645.
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(Rehash/Sai Sindhuja K/MSM)