Rocky mountain spotted fever RMSF (spotted fever, tick fever, tick typhus)
Rocky mountain spotted fever is caused by rickettsia rickettsii and transmitted by ixodid ticks. Symptoms are high fever,cough and rash.
Epidemiology and Pathophysiology.
Rocky mountain spotted fever (RMSF) is limited to the Western Hemisphere. Initially recognized in the Rocky Mountain States, it occurs in practically the Atlantic states and throughout Central and Southern America.
In humans rock mountain spotted fever infection occurs mainly from May to September, when adult ticks are active and people are most likely to be in tick-infested area.
In southern states, sporadic cases occur throughout the year.
The incidence is highest in children under 15 years and in others who frequent tick-infested areas for work or recreation.
Hard shelled ticks (family Ixodidae) harmbor R. rickettsii and infected females transmit the agent to their progeny. These ticks are the natural reservoirs. Dermacentor andersoni (wood tick) is principal vector in the western US.
D. variabilis (dog tick) is the vector in the eastern and southern US.RMSF is probably not transmitted directly from person to person.
Small blood vessels are the sites of the characteristic pathologic lesions.Rickettsiae propagate within damaged endothelial cells,and vessel may become blocked by thrombi,producing vasculitis in the skin,subcutaneous tissues,CNS, lungs,heart,kidneys,liver, and spleen.
Disseminated intravascular coagulation often occurs in severely ill patients
Symptoms and signs
A history of tick bite is elicited in about 70% of patients. The incubation period averages 7 days but varies from 3 to 12 days, but the shorter the incubation period the more severe the infection. Onset is abrupt, with severe headache, chills, prostration, and muscular pains.
Fever reaches 39.5 to 40°C within several days and remains high for 15 to 20 days in severe cases , although morning remissions may occur.
Between the first and sixth day of fever most patients develop rash on the wrists, ankles, pals, soles and forearms that rapidly extends to neck, face, axillae, buttocks and trunk.
Initially macular and pink, it becomes maculapapular and darker.
In about 4 days the lesion become petechial and may coalesce to form large hemorrhagic areas that later ulcerate.
Neurologic symptoms include headaches, restlessness, insomnia, delirium, and coma, all indicative of encephalitis.
Hyportension develops in severe cases. Hepatomegaly may be present but jaundice is infrequent.
Nausea and vomiting are common. Localized pneumonitis may occur .
Untreated patients may develop pneumonia, tissue necrosis, and circulatory failure, sometimes with brain and heart damage.
Cardiac arrest with sudden death occasionally occurs in fulminate cases.
Diagnosis and treatment
Any serious ill patient who lives in or near a wooden area in western hemisphere and has unexplained fever, headache and prostration, with or without a history of tick contact should be suspected of having RMSF.
Starting antibiotics early significantly reduces mortality from about 20 to 7% and prevents most complications.
When a tick bite occurs in a known endemic area but clinical signs are absent, antibiotics should not be given immediately. If a fever, headache and malaise occur with or without a rash, antibiotics should be started promptly. No effective vaccine is available. Measures can be taken to prevent tick bites
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