REVIEW ARTICLES Year : 2022  |  Volume : 59  |  Issue : 4  |  Page : 303-311

Emerging trends of scrub typhus disease in southern Rajasthan, India: A neglected public health problem

Devendra Kumar, Saha Dev Jakhar
Department of Zoology, University College of Science, Mohanlal Sukhadia University, Udaipur, Rajasthan, India

Date of Submission07-Jul-2021Date of Acceptance23-Feb-2022Date of Web Publication07-Feb-2023

Correspondence Address:
Devendra Kumar
Department of Zoology, University College of Science, Mohanlal Sukhadia University, Udaipur 313001, Rajasthan
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/0972-9062.342357

Scrub typhus is the oldest known vector-borne zoonotic infectious disease in the world which is life-threatening for all age groups as it presents acute febrile illness along with multi-organ involvements and spread with the biting of infectious ‘Trombiculid mite’ (chigger mite). The pathogen of this disease is an obligatory coccobacillus gram-negative rickettsial bacteria Orientia tsutsugamushi. Scrub typhus disease was previously confined geographically only to the Asia Pacific region (tsutsugamushi triangle), but in recent years it has crossed its limit and has spread in other countries beyond the tsutsugamushi triangle and has become more hazardous for the community. The objective of this study is to explore the scrub typhus disease outbreak trends with existing information in southern Rajasthan state, India. This study concluded that scrub typhus disease is being re-emerged again and again in various Indian geographical regions with new species of vectors. The disease has been raised in tremendous amounts in Rajasthan within the last five years especially in the hilly zone and has led to major public health problems with other zoonotic diseases.

Keywords: Scrub typhus; Orientia tsutsugamushi; chigger mite; public health; vector; epidemiology

How to cite this article:
Kumar D, Jakhar SD. Emerging trends of scrub typhus disease in southern Rajasthan, India: A neglected public health problem. J Vector Borne Dis 2022;59:303-11
How to cite this URL:
Kumar D, Jakhar SD. Emerging trends of scrub typhus disease in southern Rajasthan, India: A neglected public health problem. J Vector Borne Dis [serial online] 2022 [cited 2023 Feb 9];59:303-11. Available from: http://www.jvbd.org//text.asp?2022/59/4/303/342357   Introduction 

Scrub typhus is a potentially fatal zoonotic infectious disease, caused by the bite of an infected chigger mite[1] that belongs to the Trombiculidae family. This disease is also known as bush typhus or tsutsugamushi disease. The causative agent of this disease is a gram-negative bacterium named Orientia tsutsugamushi[2],[3],[4], which is an obligatory bacterium. Globally it threatens one billion people and also causes illness in one million people each year[5],[6],[7]. The fatality rate of this disease is about 1% to 7% but in untreated conditions it may be raised up to 30% to 70%[8]. According to the current scenario, scrub typhus is the most common second re-emerging rickettsial disease in India[9]. Chigger mites (Leptotrombidium) are parasitic in nature and usually feed on rodents, birds, and other small field animals but humans are accidental hosts for them and due to this feeding habit scrub typhus normally occurs in a wide range of mammals[10]. The chigger mites play a role as a vector as well as reservoir due to the transovarial transmission process of the bacterium and also preserve their infection throughout the life stages and into their next generation[11],[12].

Diversity and abundance of scrub typhus vector (chigger mite)

The Trombiculidae is a superfamily of mites (Acari: Acariformes) with a unique mode of parasitic nature amongst all medically relevant arthropod vectors. The larval stage of mites, conversationally known as chiggers, are of ectoparasitic predominant on vertebrate hosts but occasionally on invertebrate hosts. In divergence, the deuto-nymphs and fully-grown stages have an edaphic existence and free-living predators of arthropods or their eggs[13]. In India, a few species were described earlier by Oudemans (1914) and Hirst (1915) but the major contributions to Indian chigger studies have been made by Domrow (1967). Audy (1954) reported only 63 species of chigger mites from India, after this Prasad (1974) and Kulkarni (1979) proposed their study and preeminent this number to 123 species known from India. In this connection, National Institute of Virology (NIV), Pune has conducted a survey sequentially of chigger mites over the past three decades in different zoogeographical provinces of India, including the Western Himalayas, Sikkim, and the hilly zone districts of West Bengal, Rajasthan, Maharashtra, Goa, Odisha, Gujarat, and Karnataka. Further, the Indian chigger studies in contrast to their diversity and abundance are also carried out by Prasad (1982) and Fernandes (1984). As a result, a total of 205 species are reported from India which compares favorably with the number of species recorded from Afghanistan (14 species), Japan (73 species), Papua New Guinea (149 species), Malaysia (150 species), Thailand (126 species), Nepal (26 species) and Pakistan (38 species). The genus Leptotrombidium of the tribe Trombiculini is well known as scrub typhus vectors but apart from this, Schoengastiella ligula of the tribe Gahrliepiini has been also incriminated or suspected as a vector for scrub typhus in some part of India[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24],[25],[26].

Biology of scrub typhus vector

Generally, Trombiculid mites (chiggers) have 7 developmental stages like egg, deutovum (pre-larval), larval, proto-nymphal, deuto-nymphal, trito-nymphal, and adult[13]; among them only the larval stage is parasitic in nature and feeds on a wide series of the vertebrate host[27], whereas nymphs and adults feed on small arthropods and decaying materials. Their life cycle is directly influenced by environmental factors like humidity, temperature, and availability of food and nutrients[28]. The larvae do not feed on blood as a food; rather it feeds on incomplete digested host tissue, tissue juices and serum exudates of warmblooded animals only single time during its developmental cycle[16].

The chigger mites prefer to attach with the human body on the axilla, groin, neck and trunk region and penetrate the upper dermis of the host with their sharp chelicerae by injecting a histolytic salivary secretion. After feeding, the engorged chigger larvae detach from the host body and drop down to the floor and after few days they metamorphose to a pupa-like stage subsequent to eight-legged nymphal stage and two weeks later the nymphs pass through another second pupa-like stage and further emerge as adults.

Clinical complications of scrub typhus disease

The incubation period of the disease is about 6 to 21 days. After biting of chigger mite, a papule is formed on host skin but with time duration it changes into a black crust due to the process of ulceration and appears like skin burns[29],[30]. A definitive clinical feature of scrub typhus is the presence of necrotic skin lesions known as “skin-eschar” at the site of trombiculid mite bite[31],[32]. Numerous studies have reported the presence of black eschar varying from 7% to 97% in patients suffering from this disease[33],[34],[35]; these symptoms gradually become severe with the presence of maculopapular rashes on the trunk[36]. Lymphadenopathy and skin rashes are common clinical signs along with necrosis of skin-eschar[9],[37]. The scrub typhus disease spreads systemically through the hematogenous and lymphogenous routes[38]. The primary symptoms appear, like cold, malaise, morbilliform cutaneous rash, headache, cough, nausea, vomiting, myalgia and lymphadenopathy[29],[39],[40],[41], and in some cases gastrointestinal pain is also reported in Indian studies[42]. The fever and headache had been recorded in about 90% to 100% of patients[43],[44] and the infection range may differ from mild and self-limiting to lethal. In an inappropriate disease treatment condition, there may be higher risks of serious complications like gastrointestinal bleeding, myocarditis, kidney failure, pneumonia, and meningoencephalitis. For the clinical treatment, tetracycline, doxycycline and chloramphenicol are given to patients and these drugs are characterized as the first therapeutic choice drugs[45],[46]. Due to this, the disease became a major public health problem globally. It is not only an important health-hazardous issue for humans in the endemic region, it has become exclusively challenging during army operations in endemic areas[31],[47],[48],[49].

Scrub typus is typically underdiagnosed in India, especially in Rajasthan state due to its wide-ranging distribution, nonspecific clinical presentation, limited recognizance, low index of suspicion among clinicians and lack of diagnostic facilities[46]. Due to these reasons, it is emerging again and again in different geographical areas. In Rajasthan, few studies were carried out for scrub typhus clinical complications that reported this disease to be expressively higher among females in comparison to males. Maximum positivity of scrub typhus had been found in females of age group 46-60 years[50]. Further clinical investigations revealed that early diagnosis and appropriate treatment is satisfying and preventing morbidity and mortality[51]. One observational study carried out by some clinical experts, concluded that scrub typhus can exist with or without any black eschar, and early clinical diagnosis and rapid intercession may help to reduce mortality.

Extended endemicity of scrub typhus disease

In the emergence of disease, chigger mites inhabit a triangular geographically confined area which is known as the “tsutsugamushi triangle”[52] and it has been reported from miscellaneous ecological sceneries such as mountainous regions, semi-arid deserts, rainforests, seashores, riverbanks, and terrain undergoing subordinate development[49]. Chiggers have a worldwide distribution with prevalent or special activity over a triangular area bound (13 million km[2]) by Japan in the East, through China, the Philippines, tropical Australia in the South, and West through India, Pakistan, possibly to Tibet to Afghanistan, and south parts of the former USSR in the North[37],[53],[54],[55],[56]. Scrub typhus disease is a serious public health problem in the tsutsugamushi triangle bound areas especially over the Asia-Pacific region[57],[58],[59],[60] but nowadays it is not a geographically limited disease due to its expansion from to newer areas of South America and Africa where the disease caused by new vector species Candidatus Orientia chuto and other species [61],[62][Figure 1]. The distribution of trombiculid mites are reported in tropical, subtropical and temperate zones of different regions and it is also observed that they are highly adapted to a slightly warm and humid environment and that is why disease is prominent in Asia-Pacific region. In the South-East Asian region, the most abundant vectors of scrub typhus are L. delience and L. akamushi. These vectors are endemic in some geographical regions of India, Indonesia, Maldives, Myanmar, Nepal, Sri-Lanka, and Thailand[37].

Figure 1: Traditional (tsutsugamushi triangle area) and expanded endemicity of scrub typhus disease.

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In India, scrub typhus cases had been reported from several states including Tamil Nadu, Kerala, Maharashtra, Assam, West Bengal, Rajasthan, Uttarakhand, Himachal Pradesh, Madhya Pradesh, Jammu & Kashmir, and Haryana[63]. However, according to the current scenario, it is not bounded to confined states, it has spread at a broad level in different geographical areas[64]. In case of multifaceted topographical provinces like southern Rajasthan with highlands, hills, waterways, grasslands or plains, lakes, valleys, and flatlands, the trombiculid mites are being favoured. The disconnected mite-distributed areas, where a large amount of mite was habituated, possibly will form a unique scattered distribution pattern, which is known as “mite-islands”.

Scrub typhus outbreaks in India

In India, tsutsugamushi disease came into prominence as a conflict disease particularly in the eastern regions and thereafter, a succession of several outbreaks were reported from the different geographical regions of the country[63],[65],[66],[67],[68],[69],[70]. After the emergence of this disease, there were several outbreaks reported from military forces camps and areas[71],[72],[73],[74],[75],[76]. In India, the first case of scrub typhus was reported from Kerala. Apart from this, epidemics of scrub typhus were also reported from North, East, and South India[77],[78]. Few studies reported that scrub typhus is present in the entire Shivalik hill ranges from Kashmir to Assam, Eastern and the Western Ghats, and the Vindhyachal and Satpura range in the central part of India[37]. The number of outbreaks have increased in recent decades but according to Integrated Disease Surveillance Programme (IDSP), in 2021 there were only 0-1 outbreaks reported from 2005–2010, whereas after 2011 there are 4 to 14 outbreaks occurring every year[79][Figure 2] & [Table 1].

Figure 2: Reported outbreaks of scrub typhus in India (till 11th week of 2021) (Integrated Disease Surveillance Programme (IDSP), India 2021).

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Table 1: Epidemiological data of scrub typhus disease outbreaks in India

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Globally, scientific fraternity have reported that the mite and ticks are one of the primary vectors of zoonotic diseases in human beings, second only to mosquitoes and it is also reported that scrub typhus is the second most virulent disease due to its high morbidity and mortality rate just next to malaria[80]. The occurrence of tsutsugamushi disease has been well documented from southern India, Maharashtra, Himachal Pradesh and the Himalayan belt[16],[56],[81],[82].

Epidemiology in Rajasthan

In Rajasthan, the first case of scrub typhus was reported from Alwar district in 2008, with further several cases were reported from 2008 to 2010 in a continuous manner. Previously it was coined as “Mystery Disease” but in 2010, the laboratory of National Institute of Virology (NIV), Pune, India confirmed it. Further in 2011, it was reported from 11 districts of Rajasthan, subsequently in 2012 it spread in another districts like Ajmer, Bharatpur, Sikar, Karauli, Jaipur, Dholpur, Bhilwara, Dausa, Tonk and Sawai-Madhopur, and covered almost all of Rajasthan [Figure 3]. After this, it continuously emerged again and again in the previous areas and also embedded in new districts of Rajasthan. Recently it has brutally gripped various districts i.e., Udaipur, Kota, Rajsamand, Chittorgarh, and Baran with the high positive rate[83].

According to the National Health Mission, Government of Rajasthan (2019), the cases of scrub typhus constantly increased from the last nine years. In 2011, there were only 09 cases with fatality rate zero, thereafter, the disease has become more violent year by year and in 2019, a total of 2900 cases were found positive with fatality rate of about 10 [Figure 4]. Amongst them, maximum cases were reported from Udaipur with 776 followed by Jaipur, Kota, Alwar, Chittorgarh, Bharatpur, Rajsamand, Dausa, Sikar and fatality was also observed from Bundi, Alwar and Jhalawar[84]. In Rajasthan, some areas like Kota, Udaipur, Rajsamnad, Bhilwara, and Banswara districts are provided with very favorable geographical areas and climatic conditions like humidity, temperature, and shrubby areas to flourish the scrub typhus vector.

Figure 4: Graphical representation of scrub typhus disease infection rate in Rajasthan from 2011 to 2019.

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Most cases have been reported from rural areas and some are from urban areas as well. In rural areas, people are actively involved in the rearing of cows, goats, buffaloes and other domestic animals which are the major carriers of chigger mites and in urban areas the main carriers of chiggers are rodents. Thus, cattles and rats are the potent carrier and transmitters of the infected mites in this region. Lack of diagnosis, lack of knowledge, domestication of animals and infestation by rats in rural and urban areas are the major reasons for the prevalence of this disease. This is the reason for these regions to be facing scrub typhus disease outbreaks again and again.

In 2019, the Health Department of Rajasthan clearly stated that Udaipur district is on the top position in regards to scrub typhus cases due to the hilly zone which provides all the essential requirements from host to chigger mite[83]. In context to scrub typhus disease, Udaipur was safe before 2015 because the first case was reported after 2015 [Figure 5]. Thereafterthe number ofcases continuously increased year by year in a positive manner. According to the office of Chief Medical & Health Officer Udaipur, in 2015 there were zero cases but in 2019 it increased in tremendous amount and reached 776 number of confirmed cases; this depicts that the vectors gripped the area and disease is continuously emerging in this region.

Figure 5: Graphical representation of scrub typhus positive cases in Udaipur district from 2011 to 2019.

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Transmissibility of scrub typhus

Previously, scrub typhus disease was emerged in the traditionally occupied tsutsugamushi-triangle areas but since a couple of years its re-emergence occurs inside and outsides of triangle bound areas and its re-emergence is still underdiagnosed and most neglected[29],[85],[86]. Several studies reported that as the name of the disease its vectors are found in scrubby areas like grasslands and rice fields. In these areas the biting of mites and the risk of getting an infection is high for field workers and farmers[85],[87]. The transmissibility of this disease is more dependent on climatic variations[85]. [88],[89]. The most suitable weather for infectious mites is high temperature and high humidity which increases the possibility of infection. South Rajasthan especially provides the favorable climatic condition for the mite to flourish in these areas because temperature in monsoon and the post-monsoon season remains around above 20°C to 40°C and the humidity around 80% to 90%, and it has been observed that in post-monsoon season the transmissibility rate reaches its peak level. It has been observed that seasonal variability such as environmental conditions, climatic conditions, host activity and vector mobility, all are correlated with each other. The favourable climatic condition influences and increases the activity of host-like rodents and these host activities help in the establishment of “mite island”. Human activities and livelihood also helps in the expansion of mite island and establishment of zoonotic tetrad (trombiculid mites, small vertebrates like field mice and rats, secondary scrub vegetation and wet season) thus enhancing the transmission of scrub typhus disease[90].

Seasonal fluctuation of scrub typhus

Historically, scrub typhus was known to occur in the post-monsoon season, but its outbreaks are also reported in cooler months[66]. During World War II, along the Assam-India-Burma (Myanmar) border region military persons were found positive with scrub typhus disease throughout the year but maximum from October to December[33],[91],[92]. The seasonal occurrence of this disease varies according to the climatic conditions in different countries[66], generally with two peaks: the first peak in June to July and the second in September to October[16]. In India also, scrub typhus fluctuation was observed seasonally from August to October where L. delience was observed as the primary vector[92]. The correlation between the tsutsugamushi disease outbreaks and climatic conditions indicate the behaviour and population density of Trombiculidae family members within various environments[58]. It was also observed that scrub typhus disease occurs commonly in rainy seasons when the humidity is at peak level and temperature is normal whereas some outbreaks have also been reported during the winter season in southern India. In Rajasthan, the disease increases in the monsoon season and post-monsoon season.

  Conclusion 

Scrub typhus persistence is annoying both for armed forces and the civilian populations at the global level. It appears to be an accurately neglected tropical disease primarily affecting rural populations, but increasingly also affecting metropolitan areas. In the current situation, scrub typhus outbreaks are being reported from various endemic areas in spite of the tsutsugamushi triangle bound areas. It re-emerged every year with newer outbreaks in new geographical areas with new strands and trends. Diagnosis of scrub typhus is very difficult because its clinical features are similar to dengue, malaria and chikungunya disease. It is still under-diagnosed in the case of Southern Rajasthan due to lack of awareness, a low index of suspicion among clinicians, paucity of confirmatory diagnostic facilities, and the mimicking of clinical symptoms with other more prevalent diseases. Dramatically positive cases are increasing due to the negligence of severity of scrub typhus. In Rajasthan, especially in the Udaipur region (hilly zone), it is increasing per year with a huge number of confirmed cases which provide suitable humidity, temperature and host animals for scrub typhus vectors. Therefore, the current review article recommends a well-established surveillance program in Rajasthan as well as at the country level.

Ethical statement: Not applicable

Conflict of interest: None

  Acknowledgements 

The authors would like to thank to Department to Zoology, MLSU, Udaipur, Rajasthan, India for providing the required facilites to do the work.

Key message

The cases of scrub typhus disease are increasing every year due to the transmission and introduction of infected chigger mites into new areas. This disease is still neglected by the clinicians and lacking information regarding vectors. Therefore, a sharp attention is required towards research especially about vector biology.

 

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