Mosquito-borne viral encephalitis in children

Mosquito, or Japanese (autumn), encephalitis is an acute seasonal neuroinfection with general infectious manifestations and severe damage to the brain tissue.

ICD-10 code

• A83.0 Japanese encephalitis.
• A83.1 Western equine encephalitis.
• A83.2 Eastern equine encephalitis.
• A83.3 St. Louis encephalitis.
• A83.4 Australian encephalitis (disease caused by Quinjin virus).
• A83.5 California encephalitis (California meningoencephalitis, La Crosse encephalitis.)
• A83.6 Disease caused by Rozio virus.
• A83.8 Other mosquito-borne viral encephalitides.
• A83.9 Mosquito-borne viral encephalitis, unspecified.

Epidemiology

Mosquito (Japanese) encephalitis is a typical natural focal infection. The reservoir of the virus is many wild animals and especially birds, the carriers are mosquitoes Sikh tritaeniorhynonus and others. Infected mosquitoes transmit the virus to humans during a bite with saliva. The disease has a strict summer-autumn seasonality with a maximum incidence in August-September. Usually, an epidemic outbreak is preceded by hot weather, which contributes to the mass breeding of mosquitoes.

All people are susceptible to mosquito encephalitis. Agricultural workers and older children are more likely to become ill. Group illnesses of children in holiday camps located near natural foci of infection, near small bodies of water or in swampy areas are possible.

Classification

Cases with CNS damage are considered typical, which, depending on the severity of general cerebral and focal symptoms, can be mild, moderate, or severe.

Atypical forms of mosquito-borne encephalitis include latent and subclinical forms with an abortive course without damage to the central nervous system.

Causes of mosquito-borne encephalitis

The causative agent of mosquito encephalitis, as well as the causative agent of tick-borne encephalitis, belongs to arboviruses (genus flaviviruses) and represents one of the four antigenic varieties of this genus. Among animals, monkeys, white mice, hamsters, rats, etc. are most sensitive to the virus.

Pathogenesis of mosquito-borne encephalitis

After a bite from an infected mosquito, the virus enters the CNS via the hematogenous route and, due to its pronounced neurotropism, rapidly multiplies in nerve cells. Upon reaching its maximum concentration, the virus re-enters the blood and acts as a general toxicant, which corresponds to the end of the incubation period and the onset of clinical manifestations.

The greatest morphological changes are found in the central nervous system. Macroscopically, the meninges are edematous, hyperemic, with pinpoint hemorrhages. The brain matter is swollen, flabby, with local hemorrhages and foci of softening. Pronounced changes are noted in the area of the optic thalamus and striate formations.

Symptoms of mosquito-borne encephalitis

The incubation period is 5-14 days. The disease begins acutely, with a rise in body temperature to 39-40 °C, chills, headache, nausea and vomiting. The patient's face quickly becomes hyperemic, scleritis and catarrhal conjunctivitis are expressed. On the 2nd-3rd day of the disease, meningeal symptoms appear, and from the 3rd-4th day - symptoms of focal or diffuse encephalitis. Patients are stunned, indifferent, do not react to examination and the environment. Less often, excitement with delirium, hallucinations and loss of consciousness are noted. Due to muscle hypertension, the patient lies with his head thrown back and limbs brought to the stomach. With damage to the pyramidal system, spastic mono- and hemiparesis occur. With damage to the spinal cord, flaccid paralysis appears. With the spread of damage to the boulevard centers, breathing and swallowing disorders, a drop in cardiovascular tone, and damage to the motor sphere are possible. Clinically, this is manifested by various hyperkinesis of the muscles of the face and upper limbs.

In severe cases, tonic or clonic seizures occur.

Symptoms of mosquito-borne encephalitis also include increased sweating, cardiovascular instability, muffled heart sounds, and decreased arterial pressure.

In the blood, leukocytosis, neutrophilia with a shift to band and juvenile forms, lymphopenia, eosinopenia, and an increase in ESR are determined.

During lumbar puncture, clear fluid flows out under pressure. Moderate (up to 100-300 cells in 1 μl) lymphocytic cytosis and a slight increase in protein content are detected.

Diagnosis of mosquito-borne encephalitis

The diagnosis is based on the clinical picture of encephalitis or meningoencephalitis that has developed acutely against the background of general infectious symptoms in a child living in an endemic focus of mosquito encephalitis in the summer or fall. To confirm the diagnosis, PCR and ELISA are used, as well as the isolation of the virus from blood and cerebrospinal fluid in tissue culture or by infecting newborn mice in the brain with subsequent identification of the virus using serological reactions. Of diagnostic value is the detection of an increase in specific antibodies in paired sera of patients in RN, RSK, RTGA, etc.

Treatment of mosquito encephalitis

In the early stages of mosquito encephalitis, it is recommended to administer specific immunoglobulin at a rate of 0.5-1 ml/kg per day in 2-3 doses. Pathogenetic and symptomatic therapy is the same as for tick-borne encephalitis.

Forecast

The prognosis for mosquito encephalitis is serious. Mortality reaches 25-50%. With a favorable outcome, persistent residual effects are possible in the form of decreased intelligence, psychosis, psychasthenia. However, unlike tick-borne encephalitis, there is no long-term progressive course with the formation of persistent hyperkinesis or epileptiform seizures in mosquito encephalitis. The recovery period, as a rule, proceeds relatively well. With the disappearance of symptoms of general infectious toxicosis, the consciousness of patients clears up and focal symptoms gradually decrease. The recovery period is 0.5-2 months; during this time, mental deviations, hemiparesis, autonomic disorders, muscle weakness, gait instability and other manifestations of the disease are possible.

Prevention of mosquito-borne encephalitis

Control of mosquitoes - carriers of the pathogen and creation of active immunity in the population living in endemic areas. Immunization is carried out with a killed vaccine. For emergency prevention, specific immunoglobulin is administered once at a dose of 0.2 ml/kg.

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