Japanese encephalitis: symptoms, vector, vaccination

Japanese encephalitis is an infectious disease that affects not only humans, but also animals. The virus mainly affects the brain. Endemic outbreaks are observed from August to September and last no more than 50 days a year. The appearance of heavy rainfall amidst hot weather is a beneficial environment for the propagation of pathogens - mosquitoes.

A bit of history

As early as 1871, Japanese physicians described a disease with a fatal outcome in 60% of cases. Already in 1933, Hayashi isolated the virus and accurately established how the disease is transmitted. On the territory of Russia, the first mention of the virus of Japanese encephalitis appeared in 1938, the disease was discovered in the Southern Primorye.

The virus got its name because of an outbreak in Japan. In those terrible times, namely in 1924, the virus was affected more than 7 thousand people, 80% of all patients died.

In our country, the disease is also called encephalitis B, mosquito or summer-autumn encephalitis.

Etiology and microbiology of Japanese encephalitis

The causative agent of the disease is the virus of the genus Flavivirus, from the family Togaviridae. The virus dies when the temperature is heated to 56 degrees in only 30 minutes. If it is boiled, it will die in 2 minutes. If the virus is dried and frozen, it will not die and can be stored almost forever. At room temperature, the virus can maintain its vital functions for about 45 days, and in a dairy environment up to 30 days.

Possible vectors

In natural conditions, the main vector is waterfowl. In some rodents, the virus was also isolated.

In the subsidiary farms, the carriers of Japanese encephalitis can be pigs and horses. Pigs carry the disease asymptomatically, and the incubation period does not exceed 5 days. Very rarely, pig patients may have spontaneous abortions.

An infected person is dangerous to others. In the human body, the virus enters the saliva of infected mosquitoes. In humans, the incubation period is from 4 to 21 days. Accumulation of infection occurs in the nervous tissue of various parts of the brain. Vascular lesions of the membrane and brain tissue are possible. At the same time, most pathology is asymptomatic. Most people who have never had encephalitis, have antibodies in the circulatory system. With age, each person's immunity is only strengthened.

Where is the most common virus?

Naturally, for the territory of our country Japanese encephalitis is not very typical. The virus is found from south to southeast Asia, this is the northern part of Australia, India, Pakistan, Thailand, Japan and Indonesia. The list of "dangerous" countries includes about 24 states. In general, under the threat of disease occurrence live about 3 billion inhabitants of the planet. On the territory of our country, mosquitoes that can cause disease are found in abandoned villages, on the outskirts of villages and cities, in areas where rains and high humidity often occur.

Pathogenesis

The nature of the course of Japanese encephalitis depends on the general state of health. The healthier the person, the less the risk of getting sick. Most often the virus dies already at the place of introduction of the vaccine.

If the virus is "delayed" in the body, then its development depends largely on the body temperature: if it rises, then the virus "rages" and quickly develops. Increased body temperature contributes to an intensive course of the disease. Once the virus has crossed the blood-brain barrier, it is sent to the parenchyma of the brain. It is in this place that the active development of the virus begins. In severe cases, reproduction can begin already in the nervous system.

Japanese encephalitis: symptoms

In humans, the disease occurs in three periods:

1. Initial. Duration of the period is about 3 days. It is characterized by a spontaneous increase in body temperature to 40 ° C, which can hold at this level for about 10 days. The person is worried about headache, chills, pain in the lumbar region, the gastrointestinal tract, in the extremities. Some patients experience nausea and vomiting. It can increase blood pressure and pulse rate to 140 beats.

2. Acute period. On the 3rd or 4th day there is an exacerbation of the pathology, there may appear signs characteristic of meningitis, the patient's condition is depressed, down to coma. Many patients suffer from mental disorders, hallucinations, raving.

The muscle tone rises, and the patient can be only in a lying position, on the side or on the back. The extremities are in a bent state. Muscle spasms are observed on the occipital and masticatory muscles. Possible hyperaemia of the optic nerve, right up to the edema. Some patients have pneumonia or bronchitis.

3. Period Convalescence. Japanese encephalitis at this stage can progress to 7 weeks. Body temperature usually stabilizes and returns to normal. There may be residual effects of brain damage, weakness in the muscles, impaired coordination, pressure sores.

There are patients who carry the disease in a mild form, without neurologic symptoms.

Severe course of the disease can lead to death.

Features of epidemiology and prognosis

The causative agents of Japanese encephalitis are most often found in poorly situated areas, near water bodies and marshes. In tropical countries, epidemics last longer than 50 days. People who work in the open air or near water bodies are at risk. Most often Japanese encephalitis is sick men from 20 to 40 years.

In the risk group are also tourists who go on holiday to countries with a tropical climate, where there are monsoons and high humidity. These are the Philippines, Thailand, especially the northern part of the state, India, Indonesia and other countries. Therefore, tourists are strongly encouraged to vaccinate before going to hot countries.

The prognosis for recovery is very small, the probability of death is 80%. As a rule, the first 7 days are dangerous, the patient can fall into a coma, or he suffers from an endless convulsive attack.

People who have experienced all stages of the disease often experience residual effects:

• Psychoses;
• Hyperkinesis;
• Decreased intellectual capacity;
• paralysis;
• Asthenic state.

Diagnostic measures

Diagnosis of the disease is a whole complex of clinical and laboratory studies. When choosing a method, doctors focus primarily on the patient's condition. Diagnostics includes:

1. Laboratory research. In the first week after infection, the pathology can be determined by blood analysis. Over the next two weeks, diagnose the disease can be based on the results of cerebrospinal fluid.

2. Serological examination. Diagnosis involves the use of an enzyme immunoassay, or RN-, RNGA-, RTGA-, and RCC-tests.

Healing measures

Treatment of patients who "met" with the vectors of Japanese encephalitis, can not be conducted only by one doctor. Infectious diseases, neurologists and resuscitators are included in the therapy. In stationary conditions, the patient is administered a specific immunoglobulin or serum, about 3 times a day for 1 week of treatment. Along with this, symptomatic and pathogenetic therapy is carried out. These measures are aimed at preventing cerebral edema, detoxification, normalization of activity of all organs and systems.

The main problem is that it is impossible to cure Japanese encephalitis. Therapy can only eliminate symptoms. Therefore, it is very important to vaccinate in a timely manner.

Prevention of morbidity

To prevent epidemics, active immunization of the population is very important. Vaccinations from Japanese encephalitis are called "formulvaccine". Passive emergency prophylaxis involves the administration of 6 ml of immunoglobulin and 10 ml of hyperimmune horse serum.

In addition, preventing morbidity is a series of comprehensive measures to protect against mosquito attack. In epidemiologically dangerous areas, the use of protective clothing may be recommended. Obligatory to use repellents, from ointments to sprays, use of all measures to prevent mosquitoes in a dwelling.

You can get vaccinated against Japanese encephalitis in Moscow in municipal and private medical institutions.

Most often, a person is vaccinated with a "killed" vaccine, so there are no complications after vaccination. At the same time it is recommended to consult a doctor if allergic reactions occur. Perhaps the appearance of redness and swelling at the injection site. There may be a headache, diarrhea, pain in the muscles. Some patients complain of dizziness and nausea, chills and rashes.

Immunization is not performed in the presence of a number of infectious diseases, in the period of fetal and lactation, if it is accurately known that the patient has a hypersensitivity to heterologous proteins, severe allergic reactions.

To date, there are 4 main types of vaccines from Japanese encephalitis:

• Inactivated;
• Based on brain cells in mice;
• Inactivated, based on Vero cells;
• Live recombinant and live attenuated vaccines.

The most popular vaccine SA14-14-2 has been retrained by WHO and is produced in China.

For tourists, vaccination is carried out depending on the country they are going to go to, where they live, on the outskirts of the village or in the city, for how long, for 1 week, a month or a year.

Vaccination can be carried out according to two schemes:

Citizens with a subsidiary farm should take care of vaccinating the animals they grow. For pigs, "live" vaccines are most often used. In areas classified as hazardous, it is advisable to carry out regular treatment with insecticides.