Rocky Mountain Spotted Fever
P K Ghatak, MD
Rocky Mountain spotty fever is a catchy name but unfortunately, this disease is neither that common in the Rocky Mountain area, nor, the only spotty fever. This illness is caused by an unusual bacterium, Rickettsia rickettsii; and transmitted to humans by a dog tick.
Skin rashes of various types are common findings in diseases transmitted by tick bite, flea bite, and bites from lice and mites.
Rickettsia family of organisms has many characteristics similar to viruses and other features like bacteria. Rickettsia lives as a parasite in the arthropods without harming them. Humans and other animals are susceptible to illness and if the treatment is delayed, deaths generally follows. In 1896, a US Army major Dr. Marshall Wood described Rocky Mountain Spotted Fever (RMSF). In 1899, the first description of a RMSF was published in a medical journal. The case came from the Snake River valley of Idaho. In 1906, Dr. Howard Ricketts identified the pathogen in the blood of a patient; also recovered the same organism from a guinea pig, after inoculating it with the eggs of infected ticks.
At risk people:
The majority of RMSF occur in US States east of the Mississippi River, most frequently from the Carolinas and Virginia. Arkansas, Oklahoma, and Tennessee. In Arizona, the brown dog tick is the vector. In recent years, the incidence of RMSF is on the rise in Arizona.
The annual incidence of RMSF in the USA is 2.2 per million people.
Clinical feature:
The incubation period is 2 to 14 days. The initial symptoms are like any other viral illness. The skin rash generally appears on 2nd day onwards and by 5 days the majority will develop red petechia which gave the disease its name. The petechia start on the wrist they appear successively on forearms, ankles, legs and taros. These rashes are tiny flat pink colored macule and nonpruritic. Rashes also appear on palms and soles. The rashes change color to brawn and towards the end of the illness turn to black eschars and finally fall off the body.
If the patient remains untreated just for a few days, the bacteria spread rapidly through the entire body. The patient becomes deadly sick and develops multisystem failure.
Pathology:
Rickettsia rickettsii invade directly the endothelial cells of blood vessels. The organism rapidly multiply and spread. Just in a day or two, all the major organs of the body are inflamed.
Diagnosis:
Blood cultures are difficult to grow in laboratory. Cultures medium must contain nucleated living cells.
Rise of antibody titer 4 times over the base value, is too late for the patients to wait for treatment. The treatment must begin with the suspicion of RMSF. Skin biopsy is very valuable. Identifying the Rickettsia with immuno- histologic staining is relied upon but skin biopsy must be obtained before starting antibiotics. Antibody level does not rise till the 2nd week of the illness, so it is not helpful in clinical situations, PCR test is the other diagnostic test.
Treatment:
Doxycycline is the preferred antibiotic. The treatment must be continued till the patient is febrile. In pregnancy, chloramphenicol or, Rifampin can be used as an alternative.
A report says
RMSF has become increasingly more common in certain areas of Arizona. Between 2003 and 2018, approximately 430 cases were reported, with an associated case-fatality rate of approximately 5%. The mortality rate in untreated cases of RMSF is 20-25%. Mortality rates can be as low as 5% with proper antibiotic therapy and as high as 70% in untreated elderly individuals. Death in 5 days can be expected in fulminant cases. The classic clinical triad of fever, headache, and rash may be present in less than 5% of patients in the first 3 days of illness but increases to 60-70% by the second week after tick exposure. The absence or delayed appearance of a rash increases the difficulty of diagnosis”.
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