By Dr Barilin Dkhar and Dr Meban Aibor Kharkongor
Common ailments such as cold, cough, diarrhea, and fever are frequently brought up in general discussions about health and disease. Known to be generally harmless, these symptoms and illnesses are generally attributed to seasonal change, dietary changes or allergies prompting us to either wait till the illness resolves on its own or turn to self-medication. However, if such illnesses are due to serious infections, the prolonged period of waiting and self-treatment can be dangerous and deplete our resources in terms of time, money and energy.
In this context, let’s focus on one of these diseases which has become very common in Meghalaya but has received less attention due to lack of surveillance and limited knowledge among the tribal community. Scrub typhus (ST), also known as Ñiang-soh-ot or Niang-soh-stap in different areas of the State, is very common in Meghalaya and other parts of the world such as the Asia-Pacific region, known as the ‘tsutsugamushi triangle’ which covers South and Southeast Asia, Northern Australia, and the islands of the Indian and Pacific Ocean. It is one of the commonest cause of “fever of unknown origin (FUO)” globally, with an estimated one million new cases annually and more than a billion people at risk of infection. Reports show that around 6% of ST cases may die if left untreated. In India, about one-in-four patients with FUO has ST, although the disease is grossly underdiagnosed due to its non‑specific clinical presentations, low index of suspicion amongst clinicians, limited awareness and limited diagnostic facilities. It is common in young adults, more among males, occurring year-round, but peaking during August-November.
The disease is caused by the bacterium called Orientia tsutsugamushi and is transmitted by the bite of the larval mites (close cousins of spiders and ticks). The female mites lay fertilised eggs in the soil, from which 5–7 days later, the 6-legged larvae or chiggers hatch. These chiggers usually form clusters on leaves, grasses and twigs above soil surface, and can survive in outdoor environments for weeks to months waiting to attach to small animals such as rodents or to humans. The bite of the chiggers is usually painless and goes unnoticed by the person. Subsequently, non-specific symptoms such as chills, headache, coughing, nausea, diarrhoea, and vomiting may be experienced by the infected person. In many cases, an Eschar, which is a dark lesion resembling a cigarette burn develops at the bite site which often helps the physician in identifying the disease. In severe cases, the disease can progress to multi-organ failure involving lungs, kidneys, liver, and brain.
Chiggers commonly feed on small animals such as rodents (rats and mice) and shrews (mole-like animals) whereas humans are accidentally infected when they encroach into the habitats where chiggers are found such as agricultural land, scrubland, forests, river-banks and deforested areas. Vegetation type, humidity, temperature and rainfall affect the survival and multiplication of both rodents and mites, and ultimately the risk of infection.
North-east India is geographically and ecologically distinct from rest of the country. The dense forests, mountains and valleys, and high biodiversity in the region is correlated with high incidence of zoonotic diseases. In this context, existing literature also suggests the recent re-emergence of ST in north-eastern states such as Assam, Arunachal Pradesh, Meghalaya, Mizoram and Nagaland and Sikkim. Meghalaya in particular, has witnessed reports of ST cases from both urban and rural areas in recent years. The disease is commonly associated with ripening of the chestnut and hence the name Ñiangsohot among the Khasi community.
Scientific evidence has also identified various occupational and behavioral risk factors associated with ST acquisition. These include being a farmer, working in vegetable fields, orchards and shrub areas and living at the edge of a village. Factors such as household with poor sanitation/conditions, always observing rodents around home, presence of scrub vegetation, wood piles and cattle around the house have been also been shown to be prominent factors for the acquisition of ST. Although the disease has traditionally been considered as a problem limited to rural areas, changes in the behaviour of urban residents have made their contact with chiggers more likely. For example, in Meghalaya urban dwellers are often fond of making time for recreational activities such as trekking, camping and fishing which often pose them at the risk of infection. During such adventures, one is likely to either rest on the grass which could lead to contact with chiggers and subsequent infection, particularly if one does not change their clothes once they return home.
The lack of awareness regarding ST among people in general and medical personnel in particular is the sole reason for the high mortality associated with this disease, which in reality is easily treatable, provided diagnosis is done before the onset of multi-organ failure, which is approximately within the first 5 days of symptoms.
A preliminary hospital-based study conducted by the Indian Institute of Public Health Shillong (IIPHS) in collaboration with Dr. H. Gordon Roberts Hospital documented 408 ST cases in Meghalaya, with 5% mortality during 2017-2020. Such cases were more common in rural areas, among those involved in farming and agricultural activities. These findings, however, represent only the “tip of the iceberg” for ST burden in Meghalaya and more research work is necessary to understand the true burden and the context-specific key drivers of ST transmission in Meghalaya.
The main preventive steps that can be taken are:
(i) Taking a bath, changing and washing all clothes after outdoor activities in areas with lots of vegetation and bushes.
(ii) Areas in and around the houses should also be kept clean and free from bushes to avoid rodents.
(iii) Avoid sleeping on ground in mite infested areas such as forest clearings, riverbanks, grassy and bushy regions which provide optimal conditions for infected mites to thrive
(iv) Wearing protective clothing (with long sleeves) and boots while venturing into the mite infested areas.
(v) Applying a miticide (e.g. benzyl benzoate) on clothing and bedding and a mite repellent (diethyltoluamide) to exposed skin while visiting or working outdoors.
(vi) Avoiding the drying of clothes on bushes and scrubs – especially when clothes are washed in rivers and streams as is the common practice across the state.
Moreover, active search for the eschar should be done on all patients with fever. The fact that this eschar is often found in areas like under the folds of breasts, axilla, scrotum, groin etc., makes discovery of the lesion even more difficult. Rapid serology test kits available are also not adequately sensitive especially during the first few days of fever. Despite these difficulties in diagnosis, widespread public education regarding this important disease will help prevent deaths to a great extent by early reporting to a healthcare facility.
Globally, there has been growing reports of several zoonotic diseases such as scrub typhus, which are infections that normally circulate in animals, but “spill -over” to humans. Zoonoses have also been linked to recent outbreaks that have threatened global health and economies, including Ebola, Severe Acute Respiratory Syndrome (SARS), and more recently Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the virus causing COVID-19. Some of these zoonoses usually involve a vector (mosquitoes, ticks, mites etc.) in the transmission and are called vector-borne diseases. According to scientific evidence, an estimated 60% of all infectious diseases and about 75% of the emerging infectious diseases are zoonotic in nature. The spread of zoonotic and vector-borne diseases (ZVBD), is associated with environmental factors, climate change, animal health as well as other human activities including urbanization, globalization and associated travel.
The Indian Institute of Public Health (IIPH) Shillong in collaboration with the Indian Council for Agricultural Research – NEH Research Complex, Umiam, Christian Medical College, Vellore and Grassroots NGO through the DBT/Wellcome Trust India Alliance funded Zoonotic and Vector-Borne Disease (ZVBD) Research and Training Centre is currently involved in conducting collaborative, trans-disciplinary research to improve our understanding of the transmission of ZVBDs in Meghalaya. Additionally, the centre will enhance ZVBD research capacity in the region by training an interdisciplinary group of clinical, public health, veterinary and social-science researchers. As part of the study, stakeholder and public engagement plan for ZVBDs will also be prepared to generate awareness among local communities about the risks and prevention of ZVBDs.
(Dr Barilin Dkhar is the Laboratory Research Scientist at the IIPH Shillong and Dr Meban Aibor Kharkongor is a medical consultant at the Dr H. Gordon Roberts Hospital, Shillong)