Spotted fever in the Rocky Mountains - Causes, symptoms and treatment. MF.

Synonyms: rock fever, tick-borne rickettsiosis of America, Bull fever, black fever, rocky mountain spotted fever. Malignant variant of spotted fever of the Rocky Mountains - Brazilian typhus, typhus São Paulo, typhus Minas Gerais, Tobia fever.

Spotted fever of the Rocky Mountains is an acute rickettsial disease characterized by symptoms of general intoxication and the appearance of a plentiful makulo-papular exanthema, which becomes hemorrhagic during a severe course of the disease.

The causative agent of a fever of rocky mountains

The causative agent is rickettsia. Characterized by the properties inherent in all rickettsia. Has hemolytic and toxic activity, is an intracellular parasite, inhabits both the nucleus and the cytoplasm. On artificial nutrient media it does not grow. Quickly dies when heated( +50 ° C) and under the influence of disinfectants.

Causes of the

Rocky Mountain Fever Observed in the US( 600-650 cases are recorded annually), in Canada, Brazil, Colombia. In the United States, about 15 species of mites - natural carriers of the causative agent of the fever of the Rocky Mountains - have been identified. The main ones are: Dermacentor andersoni, D. variabilis, Amblyomma arnericanum.

Infection occurs when a tick is bitten, often it goes unnoticed, in the US only 54.2% of patients reported tick bites approximately 2 weeks before the disease. In natural foci there is a natural infestation of about 10 species of animals - mite feeders. The transvarial transfer of rickettsia is characteristic. The role of an additional natural reservoir of infection can be played by dogs.

Symptoms of Rock Fever

The portal of infection is the skin at the site of a tick bite. Unlike other tick-borne rickettsiosis, the primary affect at the site of the tick bite is not formed. Rickettsia through the lymphatic channels penetrate the blood, parasitize not only in the vascular endothelium, but also in the mesothelium, in the muscle fibers. The most pronounced changes in blood vessels are observed in the myocardium, brain, adrenal glands, lungs, skin. Affected endothelial cells of the vessels are necrotic, at the site of injury, wall clots are formed with cellular infiltration around them. In severe disease, extensive ischemic foci in various organs and tissues( brain, myocardium, etc.) are noted. Thrombohemorrhagic syndrome develops.

The incubation period lasts from 3 to 14 days( for mild forms it is longer, and for severe forms it is reduced to 3-4 days).The disease begins sharply with chills, the body temperature rises( up to 39-41 ° C), severe headache, weakness, adynamia, pain in the muscles, bones, joints, and sometimes vomiting. In some patients, for 1-2 days there are indistinctly expressed prodromal symptoms( weakness, loss of appetite).In severe forms of the disease, thrombohemorrhagic syndrome is early manifested( nasal bleeding, vomiting "coffee grounds", hemorrhagic rash, bruising at the injection site, etc.).Primary affect is not formed, but in some patients it is possible to detect regional( to the site of tick bite) lymphadenitis, the increase and soreness of the lymph node is moderately expressed. On the 2nd-4th day( rarely on the 5th-6th), there is a profuse maculopapular rash. The rash appears on the limbs, then on the entire body, on the face, on the scalp and almost always on the palms and soles. With the development of thrombohemorrhagic syndrome, the rash undergoes a hemorrhagic transformation. On the spot spots and papules appear petechiae and larger hemorrhages in the skin. In place of extensive hemorrhages, necrotization in the form of gangrene of individual skin areas( scrotum, etc.) and mucous membranes( soft palate, tongue) can be observed. A conjunctive rash and enanthema in the soft palate is revealed. After 4-6 days, the elements of the rash pale and gradually disappear. At the site of hemorrhages, pigmentation of the skin persists for a long time. Skin flaking is possible.

The manifestations of general intoxication resemble its manifestations in epidemic typhus. There is a strong headache, irritability, agitation, impaired consciousness, hallucinations, delirium. There may be paresis, paralysis, hearing and vision impairment, meningeal signs and other signs of central nervous system damage. The duration of an acute period with severe course reaches 2-3 weeks. Recovery is slow and even with modern therapy, the mortality rate is 5-8%.

Clinical manifestations distinguish: outpatient form of the disease( subfebrile body temperature, uneventful rash without hemorrhagic manifestations, total duration 1-2 weeks);abortive with acute onset, high fever, duration of fever about a week, rash quickly disappears;typical with characteristic symptomatology and duration of the disease up to 3 weeks, and lightning, in which death occurs 3-4 days later. The latter form is characteristic of the malignant variant of the fever of the Rocky Mountains( Brazilian typhus).

Complications - thrombophlebitis, nephritis, pneumonia, hemiplegia, neuritis, visual impairment, deafness, in the period of convalescence and in later terms - obliterating endarteritis.

Diagnosis and differential diagnosis of

With severe clinical symptoms and epidemiological data( stay in the endemic area, bites of ticks 5-14 days before the onset of the disease, etc.), a diagnosis is possible before obtaining laboratory data. To confirm the diagnosis, serological reactions are used: the agglutination reaction with OX19 and OX2( Weil-Felix) proteins, RAC with a specific antigen, the indirect immunofluorescence reaction recommended by the WHO( 1993) is more sensitive. It is also used to isolate the pathogen from the blood of patients by infecting guinea pigs. Differentiate with other tick-borne rickettsiosis.

Treatment of spotted fever of the rocky mountains

The most effective etiotropic drug is doxycycline, which is taken 100 mg 2 times a day until the body temperature normalizes, and then 3 more days. Given the frequent appearance of severe thrombohemorrhagic syndrome, it is necessary to administer heparin( 40,000-60,000 units per day), preferably drip in a 5% glucose solution. With an infectious-toxic shock, appropriate therapeutic measures are carried out.

Forecast

For severe forms, the prognosis is serious even with modern therapies. In the US in recent years, lethality was 5.2%, and among patients older than 40 years - 8.2%.Possible persistent residual effects( deafness, etc.).

Prevention of spotted fever of the rocky mountains

Anti-maltreatment activities are carried out in endemic areas and vaccination of contingents at risk of infection.

But even with timely effective treatment, lethality reaches 3-5%.

"A Guide to Infectious Diseases with the Atlas of Infectious Pathology"
Ed. Yu. V. Lobzin, S. S. Kozlova, A.N.Uskova, 2000.