Re-emerging Scrub Typhus in Sub-Himalayan Belt
Dr Raghubir Singh, Dr Keniesezo Kuotsu, Dr Neithono Kuotsu and Dr Shyamananda Mukherjee
College of Veterinary Sciences and Animal Husbandry, Jalukie, Nagaland
The first report of scrub typhus in India has been since World War II from army barracks in Assam and West Bengal with further reports in 1965, during the Indo-Pak war. In 1978, first time, Jammu has been recognized as a scrub typhus prone region. However, later years, the disease virtually gets disappeared, probably because of widespread use of insecticides to control other vector-borne diseases, and has been lost from the radar of the scientific community of the country. The disease in the past has remained widely endemic in different parts of the country including the sub-Himalayan belt.
Scrub typhus is prevalent in the foothills of Himalayas viz. Jammu & Kashmir, Himachal Pradesh, Sikkim, Manipur, Nagaland, Mizoram, Meghalaya, Assam and West Bengal. It seems a resurgence/re-emergence of the disease in this sub-Himalayan belt may be attributed to changes in the human behavior e.g. unplanned urbanization, deforestation and rapid transport leading to displacement of vectors as well rodents from one place to another.
Scrub Typhus is a zoonotic infectious disease. The term “scrub” is used because of the type of vegetation (terrain between woods and clearings) that harbors the vector and the word “typhus”, a Greek word means “fever with stupor” or smoke. The disease is caused by an obligate intracellular pathogen, Orientia (formerly Rickettsia) tsutsugamushi. “Tsutsuga” means small and dangerous and “mushi” means insect or mite.
Scrub typhus is transmitted by the mite Leptotrombidium deliense (“chiggers,” Trombiculid mite). The vector mites inhabit areas where survival conditions prevail (mite islands) viz., the forest clearings, riverbanks, grassy regions, rice fields. However, it has also been identified in sandy beaches, mountain deserts and equatorial rain forests. Human beings are accidental hosts and are infected when they trespass into mite islands where bitten by the mite larvae (chiggers). The mite feeds on the serum of warm blooded animals only once during its cycle of development and adult mites do not feed on man. Scrub typhus occurs more frequently during the rainy season, usually from June to November. Mites are both the vector and the reservoir. Once they are infected in nature by feeding on the body fluid of the rodents particularly wild rats of subgenus Rattus, field mouse, squirrels and bandicoot, maintain the infection throughout their life stages and as adults, pass the infection on to their eggs in a process called transovarial transmission.
Scrub typhus manifests clinically as a non-specific febrile illness often accompanying headache, myalgia, nausea, vomiting, diarrhea, cough or breathlessness. Severity varies from subclinical illness to severe illness with multiple organ system involvement which can be serious unless diagnosed early and treated. “Eschar” at the site of attachment of the larval mite or chiggers the most characteristic feature of scrub typhus. It is a black necrotic lesion resembling a cigarette burn usually found in areas where skin is thin, moist or wrinkled. Cases of scrub typhus most frequently occur among farmers, forestry workers, and others involved in outdoor occupations. Human host in urban areas may get bitten by the disease-causing mite while jogging in parks, doing yoga or any other recreational activities such as camping in the jungles.
Severe complications from the disease include the acute respiratory distress syndrome (ARDS), shock, hepatitis, renal failure, meningoencephalitis, and myocarditis, in varying proportions of patients. Human to human transmission is absence in this zoonotic disease. The gold standard test for the serologic diagnosis of scrub typhus is the immune-fluorescence assay (IFA). However, while sensitive, the IFA is expensive, requires specialized labs and considerable training. Weil-Felix agglutination test are very insensitive and non-specific. Weil Felix test detects IgM antibody which is detectable 5-10 days following the onset of symptoms. The test results may be negative during the early stages of the disease because the agglutinating antibodies are detectable only during the second week of illness. Eschar samples can be used for conducting Polymerase Chain Reaction. ELISA and isolation of the organism are the other tests to diagnose the disease. Isolation is time consuming, tedious and requires a BSL3+ facility.
Scrub typhus is an easily treatable disease and deaths can be averted through use of antimicrobials. The recommended treatment for uncomplicated cases is Doxycycline or Chloramphenicol which is cost effective. In children, dosage of Chloramphenicol is used with caution. If treatment is not initiated, fever and other symptoms may persist for more than three weeks. Azithromycin has been found to be effective in case of resistance to Doxycycline. However, cases must be suspected earlier based on clinical findings and a delay of more than two weeks may lead to severe form of the disease.
Prevention: Avoidance of Mite—Human Contact
- Avoid mite infested areas
- Wear protective clothing
- Personal prophylaxis against the mite vector by impregnating clothes with miticidal chemicals (permethrin and benzyl benzoate) and the application of mite repellants (diethyl toluamide) to exposed skin surfaces.
- Eliminate mites from sites by application of chlorinated hydrocarbons (lindane, dieldrin and chlordane) to the ground and vegetation in camps and other populated zones in endemic areas.
- Chemoprophylaxis: Weekly once dose of 200 mg doxycycline is effective. It should be considered for non-immune people sent to work in endemic areas and in high-risk travelers.
Scrub typhus is a serious acute febrile illness associated with significant morbidity and mortality. A high index of suspicion is needed in patients presenting with fever especially during monsoon and post monsoon season. There is an urgent need for awareness generation among the medical and para-medical professionals especially at the peripheral levels. Due to paucity of resources in sub Himalayan belt, the cases of scrub typhus remain under-reported, especially in rural areas. Hence, it is recommended that standard treatment guidelines for timely diagnosis and treatment of Scrub typhus should be made available in rural areas which should be in accordance with the facilities available at sub-centers, PHCs, and CHCs. Active surveillance is required to be carried out to know exact magnitude and distribution of the disease.
PIC: Eschar; Most characteristic feature of scrub typhus.
