Scrub typhus, also known as bush typhus because the mites (Leptotrombidium deliense, commonly known as trombiculid mite) that cause it reside in vegetation predominantly comprising small shrubs, is an infectious disease with symptoms similar to any viral fever. However, it is not caused by a virus, but by a parasite called Orientia tsutsugamushi, which is transmitted by the bite of infected mite larvae in soil containing scrub vegetation. The disease is more common during the wet season when the mites lay eggs.
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The disease has an incubation period of 6-21 days, and lasts for 2-3 weeks. At onset there is fever, headache, bodyache, cough and gastrointestinal symptoms. Patients with a mild infection may recover without any other symptoms. However, roughly every second patient develops a visible black scab at the point of the bite, with a swelling of the lymph nodes. In about a third of cases, a delayed onset of rashes occurs 4-6 days into the disease. Severe cases typically include encephalitis and interstitial pneumonia due to vascular injury. The fatality rate is 7%.
Sores caused by the mite’s bites are usually one of the distinguishing features of the disease, crucial for clinical diagnosis. Similarities in presentation with chikungunya often confounds the diagnosis, doctors say. Like in dengue and chikungunya, the commonest — and cheaper — diagnostic tests involve looking for the antibodies to the parasite rather than the parasite itself in the bloodstream. An indirect immunoperoxidase test or a dot immunoassay or tests for detection of IgM and IgG fall under this category. The failsafe test is the expensive polymerase chain reaction (PCR) test.
Outbreak in Himachal
While dengue and chikungunya have remained the focus, scrub typhus has killed some 24 people in Himachal Pradesh, and affected about 855 others so far this year. The Union Health Ministry promised support to the state on Tuesday. In Delhi, the All India Institute of Medical Sciences has reported more than 30 cases. Himachal Pradesh is one of the endemic areas for the disease — it is also endemic in Pakistan, Afghanistan, Thailand, northern Australia, the Arabian peninsula and Japan. It is an occupational disease frequently found in people who work in the fields and are in the habit of gardening.
In Himachal Pradesh, the disease spreads most commonly during grass cutting operations in the orchards, and is alleged to have taken a serious turn this year due to laxity in controlling the mite. The Health Department has reportedly been asking the Horticulture Department to ask its university for advice on measures to eradicate the mite, and to incorporate these pesticides in spraying schedules, but no response has been forthcoming, however, allege officials. State health officials also say that including an advice to wear socks to the fields in the Information, Education and Communication (IEC) campaign would have helped check the disease.
Antibiotics like Doxycycline or Azithromycin are commonly used to treat the disease. Most cases are self-limiting, and hospitalisation is not required. In fact, in endemic areas, treatment is often started without the final confirmatory diagnostic test. Any fluctuation in blood pressure, pulse rate or respiratory rate (hyperventilation) in a patient with undiagnosed fever, rashes, etc. though should immediately be reported to the nearest hospital. The outcome is often complicated by a reliance merely on clinical diagnosis, with doctors tending to prescribe the ineffective betalactam (ß-lactam) antibiotics. In such cases, the patient often reaches the hospital too late, and succumbs commonly to encephalitis and pneumonia.