Scrub Typhus: A Re-Emerging Zoonotic Disease
Sapna Sharma1 Ayashi Sachan2 Apurv Kaushik3
1Teaching Associate, IPVS, DUVASU, Mathura
2Teaching Associate, IPVS, DUVASU, Mathura
3Corresponding author, Teaching Associate, DUVASU, Email: apurvkaushik149@gmail.com
Abstract
Scrub typhus is an infectious disease which is spread to people by the biting of infected larval trombiculid mites, sometimes known as chiggers, and is caused by the bacteria Orientia tsutsugamushi. This zoonotic disease is prevalent in various tropical and subtropical regions, particularly in rural areas with dense vegetation and favorable climatic conditions. Scrub typhus poses a significant public health concern due to its wide geographic distribution, increasing incidence, and potential for outbreaks. Scrub typhus often presents with non-specific symptoms such as fever, headache, myalgia, and rash, leading to frequent misdiagnosis and delayed treatment. Early diagnosis is crucial to prevent severe complications and mortality, but limited access to healthcare facilities and diagnostic resources in remote regions can hinder timely detection. Recent advancements in molecular diagnostic techniques, serological assays, and point- of-care tests have facilitated rapid and accurate identification of scrub typhus cases, enabling prompt treatment initiation and reducing disease burden. Treatment primarily relies on antibiotics, such as doxycycline, which have shown efficacy in resolving clinical symptoms and preventing severe outcomes. Efforts to combat scrub typhus involve integrated vector control strategies, community-based education on preventive measures, and enhancing surveillance systems for early detection and containment of outbreaks. In conclusion, by fostering a comprehensive understanding of the disease’s complex epidemiology and ensuring accessible and accurate diagnostic tools, the global health community can effectively combat this emerging threat and mitigate its devastating consequences on human health.
Key words: Re-emerging, Rickettsia, Scrub typhus, Weil Felix, Mites
Introduction
Scrub typhus is also known as bush typhus, tsutsu fever, mite born typhus, Hatsuka disease, rural typhus and is acute febrile disease which is caused by Orientia tsutsugamushi derived from Japanese word tsutsuga means “dangerous” and mushi means “bug”. It is a zoonotic disease, with humans being accidental hosts and rodents act as reservoir. During the rainy season, infected chiggar are more frequently found in densely vegetated areas, that’s why the condition is also known as river or flood fever. Only some regions of the world are affected by the sickness. Scrub typhus, which has a greater mortality and fatality rate, has recently expanded throughout India, appeared as a prominent cause of severe fever disease. Most of the states in India have reported extensive cases of this disease: in the north-east, Meghalaya, Assam, and Nagaland; in the north, Himachal Pradesh, Uttaranchal, Jammu, and Kashmir; in the south, Tamil Nadu, Andhra Pradesh, Karnataka, and Kerala; in the east, West Bengal and Bihar; and in the west, Maharashtra and Rajasthan. O. tsutsugamushi invades endothelial cells and causes perivascular inflammation and widespread vasculitis, which causes considerable vascular leakage and end-organ damage. It primarily results in eschar at the site of the bite, which later develops into a cigarette-shaped structure and a black crust. Fever, headache, nausea, vomiting, stomach pain, shortness of breath, hepatosplenomegaly, generalized edema, maculopapular rash and lymphadenopathy are the most typical clinical symptoms in children.
Etiology
The disease also known as tsutsugamushi disease is caused by Orientia tsutsugamushi. It is a tiny obligate intracellular, gram-negative bacterium. Orientia tsutsugamushi or Rickettesia tsutsughamushi is spread to people by biting of trombiculid mites (chiggers) (red) belonging to the genus Leptotrombidium.
Outbreaks
Scrub typhus has been endemic in the Asia-Pacific region, bounded by Japan in the east, Pakistan in the west, Russia in the north and Australia in the south. It accounts for up to 19% of patients admitted to hospitals with undifferentiated febrile illnesses. Scrub typhus is endemic in India and about 40 outbreaks of Scrub typhus cases were recorded during 2008–2017, from almost all the states of the country. The diagnostic specificity may be hampered by more than 40 serotypes with significant antigenic variation that have been identified worldwide. Even yet, Tamil Nadu’s scrub typhus epidemic continues to pose a severe public health threat. The highest numbers of Scrub typhus cases were reported, particularly during the cooler months between September to January, every year.
Symptoms
There is an incubation period of 7–10 days before symptoms manifest. The illness begins with fever, headache and generalized body ache. Fever, vomiting, and abdominal pain are the most common symptoms. However, coughing and difficulty in breathing may be seen in some individuals. A primary papular lesion which later crusts to form a flat black eschar, may be present.
This is associated with regional and later generalized lymphadenopathy (enlarged and tender nodes). The symptoms gradually increase in severity and a macular rash may appear on the trunk. Distribution of eschar: it covers the head, neck, face, chest, abdomen, back, lower extermities. A spotted rash on the trunk may be present. The examination may show liver and spleen enlargement in a significant proportion of those infected.
Diagnosis
Eschar is not always present, but the main symptoms of fever and eschar accumulation on the skin aid in the diagnosis of scrub typhus. The major investigation of preference for the diagnosis of scrub typhus is serology.
Weil-Felix Test: The simplest test now in use is the Weil-Felix OX-K agglutination reaction (WF test). The WF test relies on recognizing the many Proteus agglutinins that react with Rickettsia species’ agglutinogen when they cross-react. Indirect immunofluorescence antibody (IFA) is the standard detection technique. IFA is highly pricey, but the outcome is accessible in a matter of hours. Antigens from the three serotypes Karp, Kato, and Gilliam are commonly used in IFA.
Treatment
Tetracycline is the most commonly used drug for scrub typhus, with doxycycline being the treatment of choice. Scrub typhus can be treated with doxycycline (2.2 mg/kg/dose twice PO or IV, maximum 200 mg/day for 7–15 days) and tetracycline (25–50 mg/kg/day divided every six hours PO, maximum two g/day per mouth, for 7–15 days). One dosage of 200 mg of tetracycline may be used for prophylaxis.
Conclusion
Scrub typhus is a growing and re-emerging zoonotic disease which remains as a significant health challenge in tropical regions, demanding concerted efforts from healthcare professionals, researchers, policymakers, and communities to curb its spread and impact. Due to its non-specific clinical presentation, limited awareness and lack of diagnostic facilities, the disease is grossly under-diagnosed in under developed/developing countries. Hence, early diagnosis and treatment are necessary to reduce the mortality and the complications associated with the disease.
