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Rocky Mountain spotted fever: causes, symptoms, diagnosis, treatment
Last reviewed: 05.07.2025
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Rocky Mountain spotted fever (synonyms:Tick-borne rickettsiosis of America, Texas fever, Brazilian typhus, etc.) is an acute natural focal zoonotic rickettsiosis transmitted by ixodid ticks and characterized by remittent fever, severe intoxication, damage to the nervous and vascular systems, and abundant maculopapular rash.
The disease "Rocky Mountain spotted fever" was first described by Maxsu in 1899. Ricketts's studies (1906) proved the transmission of the infection through ixodid ticks. Somewhat later, the pathogen was found in the blood of patients (Ricketts, 1909), and isolated and studied in detail by Wolbach in 1919.
Epidemiology of Rocky Mountain Spotted Fever
The sources and reservoir of the infection are wild rodents (voles, gophers, chipmunks, squirrels, rabbits), some domestic animals (cattle, dogs, sheep) and various species of ixodid ticks. In warm-blooded animals, the infection is asymptomatic in the form of temporary carriage. The main and more stable reservoir is formed by 15 species of ixodid ticks, which are specific carriers of rickettsia. Of greatest epidemiological significance are Dermacentor andersoni (forest tick) and D. variabilis, which attack humans. Ticks have transovarial and transphase transmission of the pathogen, which explains the possibility of long-term, lifelong carriage of rickettsia.
The mechanism of infection transmission is realized through tick bites, less often - through crushing them and rubbing tick tissue into the skin during scratching.
The natural susceptibility of people is high. In countries with a moderate climate, the disease has a spring-summer seasonality (the period of maximum activity of ixodid ticks), in the tropics, the infection is transmitted year-round. Rural residents and people of certain professions (foresters, hunters, geologists, etc.) are most often infected when working in the forest or on pastures. The incidence is mainly sporadic. Post-infection immunity is intense.
Rocky Mountain spotted fever is endemic throughout much of the United States, Canada, and Central and South America.
What causes Rocky Mountain spotted fever?
Rocky Mountain spotted fever is caused bysmall polymorphic gram-negative rod Rickettsia rickettsi, which belongs to the genus Rickettsia. It parasitizes in the cytoplasm and nuclei of sensitive cells. It is well cultivated in the body of ticks of various species, in transplantable cell lines, in the yolk sacs of chicken embryos and in the body of guinea pigs, in which it causes the development of toxicosis. The pathogen has hemolytic properties, stains according to Ramanovsky-Giemsa and Gimenez.
Pathogenesis of Rocky Mountain spotted fever
Rickettsia enter the body through the bite of infected ticks without the formation of a primary affect, enter the systemic bloodstream and affect mainly small and medium blood vessels of the skin, subcutaneous tissue, central nervous system, lungs, heart, adrenal glands, liver and spleen. Fixation and reproduction of rickettsia occurs in the vascular endothelium, necrosis of endothelial cells develops with subsequent accumulation of biologically active substances and increased toxicosis. In severe cases of infection, necrotic changes even affect the smooth muscle fibers of the mesothelium, which underlies the possible development of microinfarctions in the brain, DIC syndrome, specific glomerulonephritis, and exanthema. Pathohistological changes in the vessels are similar to those in epidemic typhus.
Symptoms of Rocky Mountain Spotted Fever
The incubation period of Rocky Mountain spotted fever lasts from 2 to 14 days, on average - 7 days. Sometimes at the beginning of the disease there may be short prodromal phenomena in the form of malaise, mild chills and moderate headache. In most cases, the onset of the disease is acute, sudden. The following symptoms are characteristic of Rocky Mountain spotted fever: severe headache, chills, severe weakness, arthralgia and myalgia, rapid increase in body temperature to 39-41 ° C. In severe cases, vomiting, prostration, nosebleeds occur.
Later, the fever becomes remittent, with fluctuations between morning and evening readings of up to 1-1.5 °C.
When examining patients at the onset of the disease, the following symptoms of Rocky Mountain spotted fever are found: hemorrhagic enanthem on the oral mucosa, bradycardia, muffled heart sounds, decreased blood pressure. On the 2nd-5th day of the disease, exanthema usually occurs, although in exceptional cases, the rash may be absent. The spotted elements of the rash quickly turn into maculopapular ones, spreading throughout the body, including the face, scalp, palms and soles. Over the next few days, the rash becomes more distinct, sometimes confluent, hemorrhagic, with a necrotic component. In severe cases, necrosis of the fingertips, auricles, and genitals occurs. The exanthema persists for 4-6 days (sometimes more than a week) and disappears after the temperature drops, leaving peeling and pigmentation for a long time.
Intoxication syndrome is manifested by an increase in symptoms of encephalopathy, including excruciating headache, insomnia, irritability, agitation, impaired consciousness, hallucinations, delirium, delirium and even coma, which indicates the development of encephalitis. In severe cases of the disease, paresis and paralysis, hearing and vision impairment, pathological reflexes and other signs of damage to the central nervous system may be observed, persisting for weeks and even months.
Cardiovascular disorders at the height of the disease are manifested by hypotension, bradycardia, enlargement of the heart borders, muffled heart sounds. Sudden collapses are possible. The occurrence of tachycardia in this period indicates a poor prognosis for the disease. There are no significant disorders in the respiratory system, urinary system, and gastrointestinal tract. Hepatosplenic syndrome develops inconstantly, sometimes with manifestations of jaundice.
The acute period of the disease lasts 2-3 weeks. The severity of the disease and the severity of its individual symptoms can vary widely. There are mild, moderate, severe and fulminant forms of the disease with the development of coma and death in the first days of the disease.
The convalescence period is characterized by its duration and slow reverse development of the impaired functions of the body.
Complications of Rocky Mountain Spotted Fever
The most common complications of Rocky Mountain spotted fever are thrombophlebitis and pneumonia. Acute vascular insufficiency, skin necrosis, gangrene, nephritis, neuritis, visual and hearing impairment are possible. Obliterating endarteritis sometimes develops during the convalescence period.
Rocky Mountain spotted fever has a fairly serious prognosis; in severe cases, in various foci, mortality ranges from 20 to 80%; early administration of antibiotics reduces it to 7%.
Diagnosis of Rocky Mountain Spotted Fever
The disease should be differentiated from other tick-borne rickettsioses, hemorrhagic vasculitis, infectious erythema, leptospirosis, secondary syphilis, yersiniosis. Diagnostics of Rocky Mountain spotted fever takes into account epidemiological anamnesis data (recent visit or stay in an endemic zone), acute cyclic development of the disease with intermittent fever, severe toxicosis, hemorrhagic enanthem, maculopapular and hemorrhagic exanthema, symptoms of CNS damage.
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Laboratory diagnosis of Rocky Mountain spotted fever
The hemogram has no characteristic changes. Proteinuria is typical. The methods for confirming the diagnosis are the immunofluorescence reaction and the RSC with rickettsial antigens. Bioassays with laboratory animals (guinea pigs) can be used to isolate the pathogen.
Treatment for Rocky Mountain Spotted Fever
Etiotropic treatment of Rocky Mountain spotted fever involves the use of drugs with antirickettsial activity: tetracyclines (doxycycline 0.2 g per day), rifampicin (0.3 g 3 times per day), fluoroquinolones (400-500 mg 2 times per day), macrolides in average therapeutic doses. Antibacterial treatment continues throughout the febrile period and the first 2-3 days of apyrexia. Detoxification treatment is carried out, calcium preparations, vikasol, sedatives, and glucocorticosteroids are prescribed.
How is Rocky Mountain Spotted Fever prevented?
For the purpose of non-specific prevention of Rocky Mountain spotted fever in endemic areas, rodents and ticks are exterminated, protective clothing and repellents are used. According to epidemiological indications, preventive vaccination of persons from risk groups is carried out.