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Saturday, April 2, 2011

TICK-BORNE TYPHUS FEVERS (Rocky mountain spotted fever)

The casual organism, R.rickettsii is transmitted by the bite of hard (Ixodid) ticks which carry the infection to rodents and dogs and on occasion to man. It is widely distributed througout the world but now decreasing in Western and South-eastern states of the USA and also in South America.
 The pathological changes are similar to those in epidemic typhus. The incubation period is about 7 days.
Clinical features
There may be eschar at the site of the bite, with enlargement of the regional lymph nodes. Symptoms closely resemble those of louse-borne typhus. The rash appears about the third or fourth day, at first like measles, but in a few hours the typical maculopapular eruption develops. Each day it becomes more distinct and papular and finally petechial. The rash first appears on the wrists, forearms and ankles, spreads in 24-48 hours to the back, limbs and chest and lastly to the abdomen where it is least pronounced. The fully developed rash often affects also the palms, soles and face. Petechiae may appear in crops. Larger cutaneous and subcutaneous haemorrhage's may appear in severe cases. The liver and spleen becomes palpable. Complications are as in louse-borne typhus, but gangrene is more common. Untreated, the course of the disease may be mild or rapidly fatal.
Diagnosis
There may be a history of a bite by a tick. The character of the rash, appearing first at the periphery, is helpful. Detection of organisms by immunofluorescence in frozen sections of skin biopsies is quick and efficient.
Management
The various fevers due to rickettsiae respond to tetracycline or chloramphenicol. and doxycyxline single dose of 100 mg is effective in Scrub typhus.Nursing care is important, especially in epidemic typhus. Sedation may be required for Delirium and blood transfusion for haemorrhage.

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