Colorado Tick Fever

What is the Colorado Tick Fever?

Colorado tick-borne fever is an acute arbovirus disease characterized by two-wave fever, general intoxication, in some patients the central nervous system is affected.

The name in 1930 was first used by Becker (F.E.Becker) when describing an acute febrile human disease, most often a two-phase course, caused by a virus transmitted by ixodic ticks.

Causes of Colorado Tick Fever

The causative agent of the Colorado tick fever is an arbovirus belonging to the family of reoviruses (Reoviridae), the genus of orbiviruses (Orbivirus). Antigenically different from other arboviruses. The size of viral particles varies in the range of 10-50 nm. The pathogenic virus for mice, hamsters, can multiply on developing chicken embryos. In the dried state can last up to 4 years, is inactivated when heated.

The disease is endemic to the western states of the United States. Human infection occurs when a forest tick bites (Dermacentor andersoni), in endemic areas, the virus was isolated from 14% of the collected mites of this species. There were isolated reports of virus isolation from another species of tick, Dermacentor variabilis. The incidence is characterized by pronounced seasonality (from April to August with a maximum in June), due to the activity of the tick carrier. In 15% of healthy people who are constantly in endemic foci, antibodies to the Colorado tick-fever virus are detected, which indicates a wide spread of infection, including in the form of mild forms that go unnoticed. The incidence of Colorado tick-borne fever is 20 times higher than the incidence of fever of the Rocky Mountains. The pathogen persists in the body of a sick person (up to 1-3 months). A sick person is not dangerous to others, although there have been cases of infection after a blood transfusion.

Pathogenesis during the Colorado Tick Fever

Gated infection is the site of the bite. Primary affect, as a rule, does not form at the site of the bite, and there is no regional lymphadenitis. The virus enters the bloodstream and hematogenously spreads throughout the body. It has neuro and dermatropic properties. The virus persists for a long time in the body. Within 2 weeks, the virus can be isolated from the blood of patients; in 50% of cases, it is detected within 1 month. In the acute phase of the disease, the virus can be found in the cerebrospinal fluid. It was possible to isolate the virus from washed erythrocytes of convalescents after 120 days from the onset of the disease. After suffering the disease remains resistant immunity.

Symptoms of the Colorado Tick Fever

The incubation period lasts from 1 to 14 days (usually 3-6 days), 90% of patients before the disease. The disease begins to increase in body temperature to 39-40 ° C, sometimes with a mild chill. The back and limbs. Driving, retroorbital pain, photophobia. 25% have abdominal pain, mainly in the epigastric region, vomiting, diarrhea is very rare. The examination of the sclera are injected. The first wave of fever lasts for 2 days, then the body temperature critically drops to normal and even subnormal. Patients at this time noted strong weakness. After 2 days, the body temperature rises again, with the second fever wave, usually higher than the first. After 3 days, body temperature returns to normal. This typical temperature curve is observed in half of the patients. Some patients may have a third wave of fever.

Many authors have described a rash of a macular or maculopapular nature. Exanthema is localized mainly on the body. On extremities hemorrhagic transformations of rash are sometimes noted. However, rash is observed only in 5-23% of patients. For the long term, it depends on the age of the patient. Thus, in 10% of patients older than 30 years, it lasts for 1 week, reconvalescence occurs within 1 week. In the study of peripheral blood marked leukopenia.

Approximately 3% of patients (most often in children) develop severe complications from the central nervous system (meningitis, encephalitis, meningoencephalitis). Signs of damage to the nervous system, severe headache, drowsiness, impaired consciousness, meningeal symptoms. When spinal puncture marked moderate cytosis (up to 200-300 cells in 1 μl) with a predominance of lymphocytes, the protein content is sometimes increased. Any residual effects after transferred encephalitis is not observed. Fatal cases are extremely rare.

Diagnosis of Colorado Tick Fever

Recognition is based on epidemiological data (stay in an endemic area, seasonality, flare bite) and characteristic clinical symptoms. The expressed leukopenia matters. For the laboratory, it is possible to use a sample of the patient. Serological methods are also used (paired sera RSK). From the Rocky Mountains (50% of the patients from the Rocky Mountains), tularemia, encephalitis.