|Year : 2014 | Volume
| Issue : 2 | Page : 133-136
Scrub typhus: An under diagnosed re-emerging zoonotic disease
Ruchi Sachdeva1, Sandeep Sachdeva2
1 Department of Respiratory Medicine, North Delhi Municipal Corporation Medical College and Hindu Rao Hospital, New Delhi, India
2 Department of Community Medicine, Post Graduate Institute of Medical Education and Research and Ram Manohar Lohia Hospital, New Delhi, India
|Date of Web Publication||9-Sep-2014|
A 63-year-old male presented with chief complaints of dry cough since 20 days, breathlessness since 20 days, rash since 19 days, high-grade fever with chills and rigors since seven days, and myalgia and joint pain since seven days. On the basis of high clinical suspicion and skin lesion, a diagnosis of scrub typhus was made that was later confirmed by serology. In the context of changing epidemiological, geographical, environmental, human migration, and access to diagnostic laboratories, a differential of scrub typhus should be borne in mind among patients with similar presentations. We report a case of scrub typhus in an urban setting along with a review of literature.
Keywords: Emerging disease, eschar, fever, infection, mite, outbreak, tropical, urban, vector
|How to cite this article:|
Sachdeva R, Sachdeva S. Scrub typhus: An under diagnosed re-emerging zoonotic disease. Trop J Med Res 2014;17:133-6
| Introduction|| |
Scrub typhus is an acute febrile illness caused by gram-negative, obligate, intracellular bacteria, Orientia (formerly, Rickettsia) tsutsugamushi. It is grossly under-diagnosed in India due to its non-specific clinical presentations, limited awareness, and low index of suspicion among physicians. The incubation period is six to twenty-one days and is characterized by focal or disseminated vasculitis and perivasculitis, which may involve the lungs, heart, liver, spleen, and central nervous system, with mortality in the range of 7-30%. The natural reservoir of Rickettsial infections is adult mite from which the organism passes into the larva by transovarial transmission. ,, The mite feeds on the serum of warm blooded animals only once during its cycle of development and an adult mite does not feed on man. Disease is transmitted to humans by the bite of a larval-stage trombiculid mite or chigger.  [Figure 1] shows a chigger that can be seen only with a magnifying glass. Humans are accidental hosts in this re-emerging zoonotic disease. Person-to-person transmission of infection has not been reported.  Physicians should be aware of this condition during the outbreak of fevers such as dengue, malaria, chikungunya, leptospirosis, and other viral fevers for clinching the definitive diagnosis. We report a case of scrub typhus from an urban area.
| Case Report|| |
A 63-year-old male presented with chief complaints of dry cough since 20 days, breathlessness since 20 days, rash since 19 days, high-grade fever with chills and rigors since seven days, and myalgia and joint pain since seven days. When first noticed, the rash was initially localized over the left lumbar area, non-itchy, and scaly, and was later associated with generalized rashes that were small, pin-point, and blanchable, which lasted for few days and then disappeared suddenly. The patient was a non-smoker, non-alcoholic, with no past history of diabetes, coronary artery disease, tuberculosis, or any other chronic illness. There was no history of travel. On general physical examination, there was a localized skin lesion over the left lumbar region, which began as small papules, enlarged, and underwent central necrosis and acquired a blackened crust [Figure 2]. There was no pallor, icterus, cyanosis, pedal edema or lymphadenopathy. Chest examination had bilateral normal vesicular breath sounds and an abdominal examination had mild splenomegaly. On the basis of clinical suspicion, the patient was probed for insect bite and he could vaguely recollect that he was bitten at the site by something when he was strolling in the park. Blood investigation showed Hb - 11.8 g/dl, TLC - 4300/mm 3 , DLC-N - 55%, L - 35%, E - 4%, M - 6%, MCV - 95.7 (80-96), MCH - 31.7 (27.5-33.2), MCHC - 34.1 (33.4-35.5), PCV - 36.6%, platelet - 22 10 9 /L, Na + 139, K + 4.3, Cl 114, Ca ++1.11, PT - 15.2 sec, INR - 1.15, aptt - 59.6, ESR - 40, Monteux-negative, ABG - normal range, CRP - positive; Widal for typhoid was negative; p/s for MP was negative; investigations for leptospirosis and swine-flu were negative; and urine culture examination was sterile. Chest-x-ray showed hilar prominence [Figure 3], and ultrasonography of the abdomen revealed mild splenomegaly. Echocardiography showed that all valves/chambers were normal, trace tricuspid regurgitation (TR), mild left ventricular hypertrophy (LVH), mild diastolic dysfunction grade-1, frequent ectopics, and an ejection fraction of 71%. Contrast-enhanced computed tomography (CECT) chest revealed bilateral minimal pleural effusion [Figure 4], few mediastinal lymphadenopathies, and nodular calcification in the right hilar region. The serology was positive for scrub typhus.
| Discussion|| |
Burden of disease
Scrub typhus is widespread in the so called 'tsutsugamushi triangle', which includes Japan, Taiwan, China and South Korea on the north, India and Nepal on the west, and Australia and Indonesia on the south.  It was first described in Japan, during 1899, where it was found to be transmitted by mites. The disease was, therefore, called tsutsugamushi (from 'tsutsuga' meaning 'dangerous' and 'mushi' meaning 'insect or mite'). More than one-million cases occur annually. Most travel-acquired cases of scrub typhus occur during visits to rural areas in endemic countries, during activities such as camping, hiking, or rafting, but urban cases have also been described. [Figure 5] shows the scrub typhus-affected countries in the Asian region.  In India, epidemics of scrub typhus have been reported from north, east, and south India. ,, Although the disease is endemic in our country, it is grossly under-diagnosed owing to the non-specific clinical presentation, lack of access to the specific diagnostic facilities, and a low index of suspicion by physicians. During the months of August to October, farmers are involved in harvesting activity in the fields, where they are exposed to the bites of larval mites. Furthermore, in the immediate post-monsoon period (September to early months of the next year), there is growth of a secondary scrub vegetation, which is the habitat for trombiculid mites (mite islands).  In recent years, there has been sudden reporting of isolated and clustering of cases across the nation.
Clinical features of scrub typhus are typically non-specific. A high-grade fever starts abruptly and is associated with severe headache, apathy, pain in skin, and myalgia. Characteristically generalized lymphadenopathy and hepatosplenomegaly are seen in the patients. The painless chigger bite can occur on any part of the body, but it is often located in areas that are hard to examine, such as, the genital region or axilla.  An eschar forms at the bite site in about half of the primary infections, which begins as small papules that enlarge, undergo central necrosis, and acquire a blackened crust to form lesions resembling a cigarette burn. The typical rash and eschar may not always be present. However, an eschar is reported in only up to 50% of the cases.  On the basis of a high index of clinical suspicion and diagnostic workup, our patient was diagnosed early and put on doxycycline (100 mg BD) for 14 days. The patient improved clinically, his fever subsided, breathlessness relieved, and was discharged after five days.
Most patients recover without any complications. However, severity may vary from sub-clinical illness to severe illness with multi-organ system involvement, which can be serious enough to be fatal, unless diagnosed early and treated. The various risk factors for the severity of infection include older age, male gender, and potentially hemolytic conditions, such as, glucose-6-phosphate dehydrogenase deficiency and treatment with a sulfonamide-containing antimicrobial drug. The complications of scrub typhus usually develop after the first week of untreated illness. The target cells for Orientia tsutsugamushi are endothelial cells and macrophages, and the virulent strains are associated with hemorrhagic and intravascular coagulation, purpura fulminans, atypical pneumonia, acute respiratory distress syndrome, myocarditis, jaundice, and meningoencephalitis, in addition to a skin rash. ,,,
The confirmation of diagnosis is usually by serological tests such as Weil Felix, with a high specificity, but low sensitivity. A four-fold rise in the agglutinin titer in paired sera or a single titer of ≥1:160 is considered diagnostic of a recent infection. The gold standard diagnostic tests include an immunofluorescent assay and immunoperoxidase assay based on the cell culture-derived O. tsutsugamushi antigen. Molecular methods like polymerase chain reaction (PCR) for detection of 47 kDa and 56 kDa protein gene of O. tsutsugamushi are reliable and quantitative. Rapid diagnostic tests include anti-O. tsutsugamushi IgG and IgM antibody detection, with commercially available enzyme-linked immunosorbent assay (ELISA) kits. The limitations include poor availability and cost. The differential diagnosis includes fever of unknown origin; enteric fever; typhoid; dengue hemorrhagic fever; other rickettsioses; tularemia; anthrax; leptospirosis; malaria; other hemorrhagic fevers; and infectious mononucleosis. The headache may mimic trigeminal neuralgia. ,
Management includes early and prompt use of antibiotics on clinical suspicion of scrub typhus. Unless contraindicated, Doxycycline is the drug of choice while chloramphenicol, tetracycline, azithromycin or rifampicin, are also useful. The mite vector of scrub typhus are typically found in distinct areas and can be eliminated by treating the ground and vegetation with residual insecticides, reducing rodent populations and destroying the limited amount of local vegetation. The Chigger Index (average number of chiggers infesting a single host) of ≥0.69 (critical value) is an indicator of vector control measures.  At present, there is no vaccine available for scrub typhus.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]