Scrub Typhus Risk Higher Inside Villages Than Fields, New Study Challenges Long-Held Beliefs

Contrary to the long-standing belief that scrub typhus—a potentially life-threatening illness caused by the bacterium Orientia tsutsugamushi—primarily affects agricultural workers and army men exposed to fields and forests, new research suggests that the infection risk may be significantly higher within village environments themselves.

The findings challenge traditional assumptions about transmission patterns and highlight the need to rethink public health strategies in rural India.

The study was conducted through a collaboration between the London School of Hygiene & Tropical Medicine (LSHTM) and the Christian Medical College (CMC), Vellore. Published in the journal Emerging Infectious Diseases, the research indicates that most human scrub typhus infections may occur inside villages rather than during agricultural or forest activities.

Scrub typhus spreads to humans through the bite of infected larval mites, known as chiggers, which are commonly found in grassy areas, plant litter, and bare soil in rural parts of Asia. Historically, farmers, forest workers, and military personnel have been considered the most vulnerable groups because chiggers were believed to thrive mainly in agricultural fields and forest fringes.

To better understand where infection risk is highest, researchers carried out extensive fieldwork across 25 villages in two districts of Tamil Nadu. They captured more than 800 small mammals in both village settlements and surrounding lands. Each animal was carefully examined for chiggers, which are typically attached to the ears or legs. Over 10,000 chigger samples were tested to determine whether they carried the scrub typhus–causing bacterium.

The results were revealing. Small mammals were four to five times more likely to be trapped within human settlements than in agricultural or forested areas. The majority of animals captured included the greater bandicoot rat, black rat, and Asian house shrew—species that commonly live in close proximity to humans.

Importantly, chigger loads on animals captured inside villages were far higher than on those caught outside. Approximately 4% of the chigger samples tested positive for Orientia. More concerning was the finding that chiggers collected from mammals within villages were more than twice as likely to be infected compared to those from animals outside village limits.

These findings build upon earlier work by the same team, published in Epidemiology and Infection, which followed over 2,000 residents from the same Tamil Nadu villages over two years. That study found no significant increase in scrub typhus risk linked to agricultural tasks, such as grazing livestock or collecting firewood. Additionally, people living on the edges of villages near fields were not at higher risk than those residing in central areas.

Taken together, the studies suggest that transmission may be driven largely by conditions within villages, including rodent infestations and environmental contamination around homes. However, researchers caution that measuring chigger density in different environments is challenging due to their extremely small size—just 0.3 mm. Since chiggers were collected from animals rather than directly from soil, seasonal rodent movement between homes and fields could influence results.

Scrub typhus remains a major yet under-recognized cause of fever-related hospitalization in rural India, potentially affecting up to 10% of rural populations annually. Symptoms—including fever, headache, body aches, and rash—typically appear about 10 days after infection. A characteristic black scab at the bite site can aid diagnosis. If untreated, severe complications such as acute respiratory distress syndrome, meningitis, kidney failure, and shock may occur. Although treatable with antibiotics like doxycycline and azithromycin, there is currently no vaccine.

The researchers recommend strengthening village-level interventions such as solid waste management, safe food storage, and rodent control. Paving courtyards and pathways may also help reduce contact with contaminated soil. Early diagnosis and improved access to testing within communities are essential to reducing the burden of this neglected tropical disease.

Scrub typhus can present with symptoms such as persistent headache, cough, breathlessness, confusion, and disorientation. While many patients recover with timely treatment, about 6% may die despite diagnosis and therapy. Nearly one-third of those infected develop severe disease involving multiple organs, often leading to dangerously low blood pressure. If left untreated, mortality in severe cases can be as high as 70%; even with treatment, death rates may reach 24%.

The disease has been reported across several regions of India. In the South, cases have emerged from Kerala, Karnataka, Andhra Pradesh, and Tamil Nadu. In North India, it has been documented in Bihar, Maharashtra, Jammu & Kashmir, Himachal Pradesh, Uttarakhand, and Rajasthan. In the Northeast, Meghalaya, Sikkim, and West Bengal have also reported infections, indicating its wide geographic spread.

Despite its significant burden, the World Health Organization (WHO) classifies scrub typhus as one of the most underdiagnosed and underreported causes of hospitalized fever. Given its relatively high fatality rate—reaching up to 30% in untreated patients—WHO stresses the urgent need for stronger surveillance and early detection systems.

Scientists from the Indian Council of Medical Research (ICMR), in a study published in Frontiers in Public Health titled “Development and implementation of a strategy for early diagnosis and management of scrub typhus: an emerging public health threat” in 2024, noted that global deaths from scrub typhus may surpass those from dengue. However, dengue continues to receive far greater public attention and professional focus, while scrub typhus remains largely overlooked.

An editorial in the New England Journal of Medicine in 2024 also described scrub typhus as “probably the single most prevalent, under-recognized, neglected, and severe but easily treatable disease in the world,” underscoring the urgent need for awareness, timely diagnosis, and prompt treatment.