Rocky Mountain spotted fever
Rocky Mountain spotted fever: Excerpt from Professional Guide to Diseases (Eighth Edition)
Rocky Mountain spotted fever (RMSF) is a febrile, rash-producing illness caused by Rickettsia rickettsii. The disease is transmitted to humans by a tick bite.
RMSF is fatal in about 5% of patients. Mortality rises when treatment is delayed and in older patients.
Causes and incidence
R. rickettsii is transmitted to a human or small animal by the prolonged bite (4 to 6 hours) of an adult tick — the wood tick (Dermacentor andersoni) in the west and by the dog tick (Dermacentor variabilis) in the east. Occasionally, it's acquired through inhalation (it can occur in laboratory settings where aerosolization of blood and specimens may occur) or through the contact of abraded skin with tick excreta or tissue juices. (This explains why people should'nt crush ticks between their fingers when removing them from other people and animals.) In most tick-infested areas, 1% to 5% of the ticks harbor R. rickettsii.
Endemic throughout the continental United States, RMSF is particularly prevalent in the southeast and southwest. Because RMSF is associated with outdoor activities, such as camping and backpacking, the incidence of this illness is usually higher in the spring and summer. Epidemiologic surveillance reports for RMSF indicate that the incidence is also higher in children ages 5 to 9, men and boys, and whites.
Signs and symptoms
The incubation period is usually about 7 days, but it can range from 2 to 14 days. Generally, the shorter the incubation time, the more severe the infection. Signs and symptoms, which usually begin abruptly, include a persistent temperature of 102° to 104° F (38.9° to 40° C); a generalized, excruciating headache; nausea and vomiting; and aching in the bones, muscles, joints, and back. In addition, the tongue is covered with a thick white coating that gradually turns brown as the fever persists and rises.
Initially, the skin may simply appear flushed. Between days 2 and 5, eruptions begin around the wrists, ankles, or forehead; within 2 days, they cover the entire body, including the scalp, palms, and soles. The rash consists of erythematous macules 1 to 5 mm in diameter that blanch on pressure; if untreated, the rash may become petechial and maculopapular. By the third week, the skin peels off and may become gangrenous over the elbows, fingers, and toes.
The pulse is strong initially, but it gradually becomes rapid (possibly reaching 150 beats/minute) and thready.
Alert A rapid pulse rate and hypotension (systolic pressure less than 90 mm Hg) herald imminent death from complete vascular collapse.
Other signs and symptoms include a bronchial cough, a rapid respiratory rate (as high as 60 breaths/minute), anorexia, constipation, abdominal pain, hepatomegaly, splenomegaly, insomnia, restlessness and, in extreme cases, delirium. Urine output falls to half of the normal level or less, is dark in color, and contains albumin. Complications, although uncommon, include lobar pneumonia, otitis media, pa-rotitis, disseminated intravascular coagulation (DIC) and, possibly, renal failure. In rare cases, RMSF leads to death.
Diagnosis
CONFIRMING DIAGNOSIS Diagnosis is usually based on a history of tick bite or travel to a tick-infested area and a positive complement fixation test (which shows a fourfold increase in convalescent antibody titer compared with acute titers). Blood cultures or skin biopsy at the rash site should be performed to isolate the organism and confirm the diagnosis.
Another common but less reliable antibody test is the Weil-Felix reaction, which also shows a fourfold increase between the acute and convalescent sera titer levels. Increased titers usually develop after 10 to 14 days and persist for several months.
Additional recommended laboratory tests consist of a platelet count for thrombocytopenia (12,000 to 150,000/µl) and a white blood cell count (elevated to 11,000 to 33,000/µl) during the second week of illness.
Treatment
Treatment requires careful removal of the tick and administration of antibiotics, such as chloramphenicol or tetracycline (preferably doxycycline), until 3 days after the fever subsides. Treatment also includes symptomatic measures and, in DIC, heparin and platelet transfusion.
Special considerations
❑Carefully monitor the patient's intake and output. Watch closely for decreased urine output — a possible indicator of renal failure.
❑Be alert for signs of dehydration, such as poor skin turgor and dry mouth.
❑Administer antipyretics as ordered, and provide tepid sponge baths to reduce fever.
❑Monitor vital signs, and watch for profound hypotension and shock.
❑Be prepared to administer oxygen therapy and assisted ventilation if pulmonary complications develop.
❑Turn the patient frequently to prevent complications of immobility, such as pressure ulcers and pneumonia.
❑Pay attention to the patient's nutritional needs; vomiting may indicate a need for parenteral nutrition or for scheduling frequent small meals.
❑Instruct the patient to report any recurrent symptoms to the physician at once so that treatment measures may resume immediately.
❑Advise the patient to avoid tick-infested areas (woods, meadows, streams, and canyons) in the future if possible.
❑Teach the patient ways to reduce his risk of becoming infected with Rocky Mountain spotted fever:
– Encourage him to inspect his entire body (including his scalp) every 3 to 4 hours for attached ticks.
– Remind him to wear protective clothing, such as a long-sleeved shirt, pants securely tucked into laced boots, and a protective head covering such as a cap.
– Advise him to apply insect repellant to exposed skin as well as to clothing.
❑Offer printed and illustrated instructions, if available, to teach the patient and his family members or other caregivers how to correctly and safely remove a tick. Demonstrate how to use tweezers or forceps and apply steady traction to release the entire tick without leaving its mouth parts in the skin.
❑After the patient removes the tick, caution him not to handle it or its fragments.
❑Finally, instruct the patient to clean his skin with alcohol at the point of attachment.
❑Report all cases to the appropriate health department.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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