Rocky Mountain spotted fever
Description
Rocky Mountain spotted fever*
is a rickettsial disease that occurs in dogs and
humans. It is caused by Rickettsia rickettsii and spread
by ticks of the genus Dermacentor.
Signs are similar to human disease, including anorexia, fever, and thrombocytopenia.
Signs and symptoms
Rocky Mountain spotted fever can be very difficult to diagnose in its early stages, even among experienced physicians who are familiar with the disease.
People infected with R. rickettsii usually notice symptoms following an incubation period of one to two weeks after a tick bite. The early clinical presentation of Rocky Mountain spotted fever is nonspecific and may resemble a variety of other infectious and non-infectious diseases.
Initial symptoms include:
Later signs and symptoms include:
The classic triad of findings for this disease are fever, rash and history of tick bite. However, this combination is often not identified when the patient initially presents for care. The rash has a centripetal, or "inward" pattern of spread, meaning it begins at the extremities and courses towards the trunk.
The rash first appears 2–5 days after the onset of fever and is often very subtle. Younger patients usually develop the rash earlier than older patients. Most often it begins as small, flat, pink, non-itchy spots (macules) on the wrists, forearms, and ankles. These spots turn pale when pressure is applied and eventually become raised on the skin. The characteristic red, spotted (petechial) rash of Rocky Mountain spotted fever is usually not seen until the sixth day or later after onset of symptoms, but this type of rash occurs in only 35% to 60% of patients with Rocky Mountain spotted fever. The rash involves the palms or soles in as many as 50% to 80% of patients; however, this distribution may not occur until later in the course of the disease. As many as 10% to 15% of patients may never develop a rash.
Abnormal laboratory findings seen in patients with Rocky Mountain spotted fever may include thrombocytopenia, hyponatremia, or elevated liver enzyme levels.
Rocky Mountain spotted fever can be a very severe illness and patients often require hospitalization. Because R. rickettsii infects the cells lining blood vessels throughout the body, severe manifestations of this disease may involve the respiratory system, central nervous system, gastrointestinal system, or renal system. Host factors associated with severe or fatal Rocky Mountain spotted fever include advanced age, male sex, African-American race, chronic alcohol abuse, and glucose-6-phosphate dehydrogenase (G6PD) deficiency. Deficiency of G6PD is a sex-linked genetic condition affecting approximately 12% of the U.S. African-American male population; deficiency of this enzyme is associated with a high proportion of severe cases of Rocky Mountain spotted fever. This is a rare clinical course that is often fatal within 5 days of onset of illness.
Long-term health problems following acute Rocky Mountain spotted fever infection include partial paralysis of the lower extremities, gangrene requiring amputation of fingers, toes, or arms or legs, hearing loss, loss of bowel or bladder control, movement disorders and language disorders. These complications are most frequent in persons recovering from severe, life-threatening disease, often following lengthy hospitalizations.
Treatment
Appropriate antibiotic treatment is initiated immediately when there is a suspicion of Rocky Mountain spotted fever on the basis of clinical and epidemiological findings. Treatment should not be delayed until laboratory confirmation is obtained. In fact, failure to respond to a tetracycline antibiotic argues against a diagnosis of Rocky Mountain spotted fever. Severely ill patients may require longer periods before their fever resolves, especially if they have experienced damage to multiple organ systems. Preventive therapy in non-ill patients who have had recent tick bites is not recommended and may, in fact, only delay the onset of disease.
Doxycycline (For adults, 100 mg every 12 hours. For children under 45 kg [100 lb], 4 mg/kg body weight per day in two divided doses) is the drug of choice for patients with Rocky Mountain spotted fever. Therapy is continued for at least 3 days after fever subsides and until there is unequivocal evidence of clinical improvement, generally for a minimum total course of 5 to 10 days. Severe or complicated disease may require longer treatment courses. Doxycycline is also the preferred drug for patients with ehrlichiosis, another tick-transmitted infection with signs and symptoms that may resemble Rocky Mountain spotted fever.
Chloramphenicol is an alternative drug that can be used to treat Rocky Mountain spotted fever; however, this drug may be associated with a wide range of side effects and may require careful monitoring of blood levels (as it can cause aplastic anemia).
Wikipedia and GNU
The content of this entry is from the Wikipedia article "Rocky Mountain spotted fever" licensed under the GNU Free Documentation License.
