Scrub typhus, a bacterial disease endemic to many countries of Asia-Pacific region, including India and China, has now increasingly been reported in Nepal. Transmitted to humans through the bites of Leptotombidium mite larvae (commonly called as ‘chiggers’) infected with a specific type of bacterium Orientia tsutsugamushi (tsutsugamushi translates to dangerous bug in Japanese), is associated with significant healthcare costs in the region. Among the four stages of their life cycle (egg, larva, nymph and adult), the microscopic mite larva (chigger) is epidemiologically important because of its dual role both as the vector and the primary natural reservoir of O. tsutsugamushi. These chigger mites feed on small wild animals, including rats, and mice and often found brilliantly coloured. Thus, more contact with the rodents, higher the chance of getting Scrub typhus. It should be noted that other life stages do not feed on vertebrate mammals and thus do not transmit the disease to humans. According to the WHO, scrub typhus is an occupational disease among rural residents of Asia-Pacific region.

 Endemic in Nepal

Scrub typhus as a cause of acute febrile illness in Nepal was first reported in 1981, as evident from a research published in Royal Society of Tropical Medicine and Hygiene by a group of researchers in British Military Hospital, Dharan, Nepal in association with US Army Medical Research Unit, Institute for Medical Research, Kuala Lumpur, Malaysia. Since then the incidence of the disease has been reported throughout the country at various time periods. In 1999, the World Health Organization (WHO) stated, “Scrub typhus is probably one of the most underdiagnosed and underreported febrile illnesses requiring hospitalisation in the region”. In the context of Nepal, this opinion remains valid even today and could justifiably be adjusted to say that the Scrub typhus is probably the most prevalent, neglected, under-recognised and severe, yet easily treatable disease in Nepal and the region. The disease has now taken hold in most parts of the Tarai, and is considered to be endemic there. After the catastrophic mega-earthquakes of 2015, multiple outbreaks of Scrub typhus were reported in several parts of the country. 

According to the Epidemiology and Disease Control Division (EDCD), a governmental regulatory body under the Ministry of Health based at Teku, Kathmandu, more than 800 cases of Scrub typhus and 14 deaths were reported from 47 districts in 2016. Within the last six months alone, scrub typhus infection has killed 9 people, with 426 confirmed cases form 32 districts. Chitwan district of central Nepal is by far the most affected due to the typhus, where more than two hundred cases were identified. Apart from Chitwan, cases were reported from Makawanpur, Nawalparasi, Kapilwastu, Dang, Pyuthan, Arghakhachi, Gulmi, and Palpa districts as well. Typhus cases were increased after the onset of summer but the risk is not low even in the winter. That’s why the Chief of EDCD, Dr Gunanidhi Sharma, has appealed to everyone to be aware of the risk of Scrub typhus in the winter as well. During the rice harvesting season in Nepal, which is October-November, we may see more cases of typhus because of the high chances that farmers will be in contact with the chiggers in the field.  

In Nepal, the prevailing common clinical practices of not confirming the cause of fever of unknown origin by lab investigation, rather treating most of the fever as typhoid fever (caused by a group of bacteria, unrelated to scrub typhus, called Salmonella Typhi) and prescribing antibiotics accordingly, is leading us nowhere in the prevention and control of febrile illness such as those due to Scrub typhus. In fact, Scrub typhus has remained as undifferentiated treatable fever in Nepal since for long time. 

Sign and symptoms  

According to the US based Centre for Disease Control and Prevention (CDC), the symptoms of scrub typhus usually begin within 10 days of being bitten by the mite. A characteristic dark, scab-like region at the site of the chigger bite (commonly known as black eschar) may often be observed which is useful to the clinicians for making the diagnosis. Other symptoms may include high fever, chills, headache, body aches, muscle pain, enlarged lymph nodes, rash, hearing loss, and neurological complications. An elevated level of liver enzymes has also been reported in many patients. If left untreated, people with severe illness may develop acute respiratory distress, meningoencephalitis, gastrointestinal bleeding, hypotensive shock, and even acute renal failure. 

Diagnosis and Treatment 

Clinical diagnosis of scrub typhus is complicated because of the similarities in symptoms with many other diseases, such as malaria, dengue, typhoid fever, brucellosis, and leptospirosis. Laboratory testing using the gold standard Indirect Immunofluorescence Assay (IFA) is often expensive, and requires trained personnel, making it technically impractical in rural areas.  Additionally, the IFA test, which is considered as confirmatory test for scrub typhus, is not available in all healthcare settings of Nepal. Commercially available rapid diagnostic kits provide reliable and well-accepted preliminary results within an hour, but the availability of these tests is severely limited due to the high cost. Enzyme-linked immunosorbent assay (ELISA) provides more confirmatory result when compared to commercial test kits but this test is available only in some of the clinical settings. 

Scrub typhus represents a major cause of treatable febrile illness throughout the Nepal, but its disease incidence remains elusive. Mortality rate in untreated patients range from nil to 30 percent and tends to vary between different geographical regions. Proper diagnosis and effective antibiotic treatment on time can reduce the disease burden. Several researches showed that antibiotics are most effective if given as soon as possible after the symptoms begin.  According to CDC, scrub typhus in persons of any age can be treated with doxycycline, but evidence of resistance to doxycycline has raised concern. Azithromycin is also used to treat paediatric and pregnant patients. 

Prevention

As of now, there is no vaccine available to prevent scrub typhus. Efforts are being made and still continue to develop a viable vaccine against scrub typhus, but the complexity continues because of the antigenic variation in O. tsutsugamushi strains.  Early case identification and rodent control are major steps to prevent scrub typhus outbreak in particular area. We need to stay away from the contact with infected chiggers. When traveling to scrub typhus endemic area, avoid areas with lots of vegetation, avoid places where chiggers may be found, and should wear full length cloths. Especially farmers who visits land regularly should avoid walking barefoot or wearing sandals, and use a tarp when sitting on ground cover. Measures should be taken to control rodents in and around the residential areas. The use of insect repellents is also recommended while travelling or hiking. As a precautionary measure, health centres and stakeholders should launch Scrub typhus prevention campaign to increase awareness about this preventable and treatable typhus. 

- Thapa is a PhD Scholar in the Department of Microbiology, Immunology and Genetics at the University of North Texas Health Science Center, Fort Worth, Texas, USA; Rayamajhee has a Master’s in Medical Microbiology, Tribhuvan University and is the; Co-Founder of  Kathmandu Research Institute for Biological Sciences