Scrub typhus infection may affect up to 10 percent of rural populations annually and is a leading yet under-recognized cause of hospitalizations for fever across India, according to a study of over 32,000 people living in Tamil Nadu.
The London School of Hygiene & Tropical Medicine (LSHTM) and Christian Medical College Vellore, India, collaborated on the study, which was published in the New England Journal of Medicine.
Scrub typhus is a potentially life-threatening infection caused by the bacterium Orientia tsutsugamushi, which belongs to the Rickettsia family. Infected larval mites, or chiggers, spread it to humans through their bites. Chiggers live on grass, plant litter, and bare soil in rural areas of Asia, where they usually feed on small mammals like rats and shrews.
Symptoms, such as fever, headache, body aches, and rash, usually begin around 10 days after infection. The tissue around chigger bites will also typically turn black, which can aid doctors with diagnosis.
If left untreated, severe illness from scrub typhus infection can lead to acute respiratory distress syndrome (ARDS), shock, meningitis, and kidney failure, which can be fatal. Cases can be treated using the antibiotics doxycycline and azithromycin, but there is currently no vaccine to prevent infection.
The study enrolled more than 32,000 people living across 37 rural villages in Tamil Nadu, India. Since scrub typhus is common in the area, the sample represented a typical rural Indian population at risk of infection. The team visited households every six to eight weeks from August 2020 to July 2022 to collect blood samples and record any symptoms of illness they may have experienced. Researchers tested blood samples from people who reported fever for scrub typhus infection.
High Incidence of Scrub Typhus Found in Rural Tamil Nadu
The researchers found a high incidence of scrub typhus across the two-year study period, with almost 10% of the population infected annually. Most people with these infections showed no symptoms, but 8% to 15% of those infected developed a fever that often required hospitalization and intensive care due to severe illness. A total of five people died from scrub typhus-associated complications during the study.
The researchers say that under-reporting of fever is an important limitation of the study and that it’s likely more cases of scrub typhus may have occurred over the two-year period. The researchers conducted the study during the COVID-19 pandemic, while quarantine measures were in place in the area.
Study Highlights Asymptomatic Infections and Severe Illness Risks
“Wolf-Peter Schmidt, principal investigator of the study and Clinical Assistant Professor at the London School of Hygiene & Tropical Medicine (LSHTM), said that scrub typhus particularly affects India, with infections typically occurring between August and February.
“Over two years, we observed many cases of both asymptomatic and symptomatic infections, with some people getting infected twice during that period. It is not clear why some infections become severe or even life-threatening. Schmidt said five people in our study died from scrub typhus, while we recorded no deaths from malaria, dengue, or typhoid fever—diseases usually seen as the main causes of severe fever in India.
Call for Improved Scrub Typhus Diagnosis and Community Awareness
Carol Devamani, lead author and MD in Community Medicine based at the Christian Medical College Vellore, said, “After COVID, scrub typhus was the most important cause of fever in our study, accounting for almost 30 percent of fever hospitalizations.
“Doctors often overlook scrub typhus as a possible cause when patients show up with a fever, even though cases are common and treatable. Diagnostic tests are available at major hospitals but not in the community.
“Our study highlights a need to inform communities about the possible dangers of scrub typhus infection, and to improve diagnostic capabilities in the community for timely treatment. Only by doing so will we reduce the number of unnecessary hospitalizations and fatal cases,” Devamani added.