Karelian fever is an acute natural focal viral infection (the causative agent is the Edsbyn 5/82 virus) with a transmissible transmission mechanism. The clinical course of Karelian fever is characterized by feverish intoxication syndrome, arthralgia, polyarthritis, skin rashes. The diagnosis of Karelian fever is based on the data of epidanamnesis and serological examination, which demonstrates a 4-fold increase in antibody titers. Antiviral drugs, immunostimulants, antihistamines, NSAIDs, glucocorticosteroids are used to treat Karelian fever.
Karelian fever is an arbovirus infection that occurs with the phenomena of moderate fever and intoxication, arthralgia and exanthema. Karelian fever belongs to the group of transmissible mosquito fevers. Epidemic outbreaks of diseases with similar symptoms in 1980-1982 were registered in the Scandinavian countries: in Sweden (Okelbo disease) and Finland (Pogost disease), as well as in Karelia (Karelian fever), which allowed us to talk about their natural focal nature. Residents of rural areas are at the greatest risk of contracting Karelian fever. The infection is registered in the summer season, during a period of high mosquito activity. Despite the not pronounced clinical picture, the practical absence of severe forms and deaths, the susceptibility to infection is high; the spread of the virus with bird migration is possible, as well as the occurrence of joint complications. These circumstances make the problem of the incidence of Karelian fever relevant for infectious diseases and rheumatology.
Karelian fever is caused by the Edsbyn 5/82 RNA genomic virus belonging to the Togaviridae family (togaviruses), the Alphavirus genus (alphaviruses) of group A. The virus is weakly resistant in the external environment, quickly dies when heated, pH changes, exposure to disinfectants and detergents, organic solvents, UV radiation.
The natural reservoir of the viral pathogen is birds, carriers are mosquitoes of the genus Culex. Infection is realized through a transmissible transmission mechanism when a person is bitten by an infected mosquito. The pathogenesis of Karelian fever has not been studied enough. The entrance gate of infection is the skin at the site of the mosquito bite. In the human body, the virus spreads hematogenically, causing joint damage and the development of generalized exanthema. The disease occurs mainly in people aged 30-60 years, children rarely get sick.
Individual clinical manifestations of Karelian fever can persist for up to 2 years, and IgM antibodies are detected for 4 or more years, which indicates a long-term persistence of the virus in the body. After suffering from Karelian fever, a stable immunity is formed; repeated cases of the disease do not develop.
The duration of the incubation period is from 3 to 14 days (on average one week). Karelian fever manifests acutely, with subfebrility (in about 30% of cases with febrile temperature), arthralgia and exanthematous rashes. Feverish intoxication syndrome (weakness, myalgia, headache) is expressed moderately or weakly, but from the first days of the disease, patients complain of joint pain. Often, the clinical picture of migrating polyarthritis develops mainly of large joints (wrist, elbow, ankle, knee, hip, rarely shoulder, fingers and toes). Arthralgia and arthritis are prolonged, often lasting from 3-4 months to 2 years. In most cases, soreness, swelling and limitation of joint mobility are not accompanied by their structural changes.
On the 2-3 day of the course of Karelian fever, the clinical symptoms are supplemented with roseolous papular exanthema – an abundant small polymorphic rash. Initially, individual spots with a diameter of about 1 cm form on the skin, from which papules and partially vesicles are then formed. There is no itching and fusion of the rash. Exanthema is localized on the trunk and limbs, sparing the face. Skin rashes persist for 5-10 days; after their disappearance, no visible traces remain on the skin.
In typical cases, disease occurs in a mild form and ends with recovery after 7-14 days. However, when the infection passes into a chronic course, disabling consequences and loss of working capacity due to impaired joint function are possible.
Diagnosis and treatment
When diagnosing Karelian fever, attention should be paid to epidemiological data (the presence of the patient in an endemic area, the seasonality of the disease, mosquito bites), as well as clinical criteria (joint damage, the presence of exanthema). The validity of the alleged diagnosis is confirmed after a serological examination (blood ELISA), in which a 4-fold increase in the antibody titer is determined.
The question of developing a specific treatment for Karelian fever remains relevant. Antiviral drugs (inosine pranobex, umifenovir), immunostimulants (alpha interferon), immunomodulators (interferon) can be used as etiotropic agents. In addition, symptomatic therapy is carried out, aimed at relieving the leading symptoms, with the use of antipyretic, antihistamine, nonsteroidal anti-inflammatory drugs. With pronounced articular and skin manifestations, the use of glucocorticosteroids is indicated. Patients should be monitored by a general practitioner or rheumatologist.
Due to the lack of development of specific immunoprophylaxis of this disease, in order to prevent morbidity, it is recommended to use personal protective equipment against mosquitoes during your stay in endemic areas.