Rocky mountain spotted fever is an acute febrile illness caused by Rickettsia rickettsii transmitted to humans by ticks from infected rodents. The disease is mainly prevalent in the Rocky Mountains of America.
The same arthropod vector is responsible for other tick borne disease is India, Africa, Central Asia and Far East. There is seasonal variation to its prevalence and it is seen in the period where there is maximal seasonal activity of ticks (April to Sept.)
The incubation period of Rocky mountain spotted fever disease varies from 4 to 12 days with a mean of 7 days. In humans the disease is acquired by the bite of an infected tick. Transmission is unlikely until the tick remains attached to the skin for a number of hours.
Pathological changes include proliferation of vascular endothelium, petechial hemorrhages in the skin and serous membranes, Splenomegaly and lymph adenopathy. Degenerative changes may take place in the heart, liver and kidneys.
Clinical features of Rocky mountain spotted fever
It is just like in a case of epidemic typhus. There is sudden onset of high body temperature, headache, rigors, malaise generalized myalgia and vomiting, and temperature continues for 2 to 3 weeks in untreated cases and terminates by lysis over a period of days. The tongue is coated and the conjunctive injected.
The rash which appears on the fourth day is characteristic (Faint pink macules which fade on pressure). It first appears on wrists and ankles and then spreads to the rest of body including face. The first lesions are macules (pink, irregularly defined) which become moculopapular after 2 or 3 days and then petechiae appear. It now fails to fade on pressure.
Other manifestations include splenomegaly, Hepatomegaly, rapid pulse, hypotension, restlessness and insomnia. Severe forms of the disease may show circulatory failure, cyanosis of the extremities and neurological manifestations (stiffness of neck, muscular rigidity, altered reflexes, Babinski sign, convulsions coma).
An abortive form of the Rocky mountain spotted fever disease may be present which lasts for 3 to 4 days while in a fulminating case, serious nervous symptoms appear before the rash appears or there is hemorrhagic rash.
Convalescence in Rocky Mountain spotted fever tends to be prolonged. Complications include Broncho Pneumonia, parotitis, femoral thrombosis, hematuria, Iritis, otitis media and gangrene of the extremities.
Generally there is rise in white cell count but leucopenia is not uncommon. Urine shows albuminuria. Positive serological reaction is obtained with OX19 strains Of Proteus. Complement fixation test, micro agglutination (MA), indirect fluorescent antibody (TEA) and haemagglutination tests are more specific.
Treatment and prevention
Chioramphenicol & Tetracycline are specific drugs for treatment. Prevention is primarily directed towards avoidance of tick infested areas and control of it by insecticides spray. Applications of repellants on exposed areas of body and wearing of protective clothing are other measures.
The mortality rate is variable. Serious and fulminating cases carry high degree of mortality ranging up to 10-20%.
Check the below video on Rocky mountain spotted fever: