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Japanese mosquito encephalitis: causes, symptoms, diagnosis, treatment
Last reviewed: 04.07.2025
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Japanese mosquito-borne encephalitis (synonyms: encephalitis B, Primorsky Krai encephalitis) is widespread in Primorsky Krai, Japan, and Manchuria.
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Causes and Epidemiology of Japanese Mosquito-Borne Encephalitis
Japanese mosquito encephalitis is caused by a filterable neurotropic virus. The reservoir in nature is mosquitoes, capable of transovarial transmission of the virus. Seasonality is characteristic, coinciding with the increase in mosquito breeding. Japanese mosquito encephalitis occurs in the form of epidemic outbreaks: in Japan - in the summer months, in Primorye - only in the fall. The disease is transmitted exclusively through a mosquito bite. The incubation period lasts from 5 to 14 days. In the body, the virus spreads hematogenously.
Symptoms of Japanese mosquito-borne encephalitis
Japanese mosquito encephalitis begins suddenly, with a sharp rise in body temperature to 40 °C, severe headache, vomiting. Occasionally there is a short (1-2 days) prodromal period with malaise and general weakness. Significant expression of general infectious symptoms is noted: bradycardia, tachycardia, hyperemia of the face and conjunctiva, dry tongue, herpetic eruptions, hemorrhagic rash. From the first days of the disease, pronounced meningeal phenomena, disorders of consciousness (stupor and coma) join. In some cases, delirium, hallucinations, psychomotor agitation occur. Plastic muscle hypertonia, tonic and clonic seizures, hemi- or monoparesis with pathological reflexes and clonus are characteristic.
Depending on the prevalence of a particular syndrome, meningeal, convulsive, bulbar, hemiparetic, hyperkinetic and lethargic forms are distinguished. Japanese mosquito encephalitis often occurs as an infectious-toxic syndrome with rapid development of a comatose state and a fatal outcome. Increased protein content (from 0.5 to 2 g / l), lymphocytic pleocytosis (from 50 to 600 cells in 1 μl) are detected in the cerebrospinal fluid. In the blood, from the first days of the disease, pronounced leukocytosis (12-18x10 9 / l) with a neutrophilic shift in the leukocyte formula, lymphopenia, and an increase in ESR are noted.
Course and prognosis of Japanese mosquito-borne encephalitis
The course is severe. The symptoms increase over 3-5 days. High body temperature lasts from 3 to 14 days, falls lytically. Lethal outcome is recorded in 40-70% of cases, usually in the first week of the disease. However, death may also occur at a later date as a result of complications (for example, pulmonary edema). In favorable cases, complete recovery with a long period of asthenia is possible.
Where does it hurt?
Diagnosis of Japanese mosquito-borne encephalitis
Epidemiological data and seasonality of the disease are of diagnostic importance. Acute onset and severe course of the disease with severe intoxication, increased vascular permeability, and cerebral edema are characteristic. Verification of the diagnosis is carried out using complement fixation and neutralization reactions; antibodies appear on the 2nd week of the disease. Immunity is usually stable.
What do need to examine?
What tests are needed?
Prevention
Preventive measures include mosquito control (draining swamps) and individual and collective methods of preventing mosquito bites.