Japanese encephalitis is an infectious disease that affects not only people but also animals. The virus primarily affects the brain. Endemic outbreaks occur from August to September and last no more than 50 days a year. The appearance of heavy rainfall against the background of hot weather is a beneficial environment for the propagation of pathology carriers - mosquitoes.
A bit of history
Back in 1871, Japanese doctors described a disease with a fatal outcome in 60% of cases. Already in 1933, Khaiashi isolated the virus and accurately established how the disease is transmitted. In Russia, the first mention of the Japanese encephalitis virus appeared in 1938, the disease was discovered in Southern Primorye.
The virus got its name due to an outbreak in Japan. In those terrible times, namely in 1924, more than 7 thousand people were infected with the virus, 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 a virus of the genus Flavivirus, from the family Togaviridae. The virus dies when the temperature is heated to 56 degrees after only 30 minutes. If it is boiled, it will die in 2 minutes. If the virus is dried and frozen, then it will not die and can be stored almost forever. At room temperature, the virus can maintain its vital activity for about 45 days, and in a milk environment up to 30 days.
Possible carriers
In natural conditions, the main carrier are waterfowl. In some rodents, the virus has also been isolated.
In subsidiary farms, pigs and horses may be carriers of Japanese encephalitis. Pigs carry the disease asymptomatically, and the incubation period is not more than 5 days. Very rarely, sick pigs may have spontaneous abortions.
An infected person is dangerous to others. The virus enters the human body with the saliva of infected mosquitoes. In humans, the incubation period is from 4 to 21 days. The accumulation of infection occurs in the nervous tissue of various parts of the brain. Vascular lesions of the lining and brain tissue are possible. At the same time, pathology is most often asymptomatic. Most people who have never had encephalitis have antibodies in the circulatory system. With age, each person's immunity only strengthens.
Where is the most common virus?
Naturally, Japanese encephalitis is not very characteristic of the territory of our country. The virus is found from south to southeast Asia, and this is the northern part of Australia, India, Pakistan, Thailand, Japan and Indonesia. The list of “dangerous” countries includes about 24 states. In total, about 3 billion inhabitants of the planet live under the threat of a disease. On the territory of our country, mosquitoes that can cause the disease are found in abandoned villages, on the outskirts of villages and cities, in areas where it often rains and high humidity.
Pathogenesis
The nature of the course of Japanese encephalitis depends on the general state of health. The healthier the person, the lower the risk of getting sick. Most often, the virus dies already at the injection site.
If, however, the virus "lingers" in the body, then its development depends largely on body temperature: if it rises, then the virus "rages" and develops rapidly. Elevated body temperature contributes to the intensive course of the disease. Once the virus has crossed the blood-brain barrier, it is sent to the brain parenchyma. 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 proceeds in three periods:
1. Beginner. The duration of the period is about 3 days. It is characterized by a spontaneous increase in body temperature to 40 ° C, which can last at this level for about 10 days. A person is disturbed by a headache, chills, pain in the lumbar region, gastrointestinal tract, in the limbs. Some patients experience nausea, up to vomiting. The pressure can increase and the heart rate rises to 140 beats.
2. The acute period. On the 3rd or 4th day, an exacerbation of the pathology occurs, signs that are characteristic of meningitis may appear, the patient's condition is inhibited, up to a coma. Many patients suffer from mental disorders, hallucinations, rave.
Muscle tone rises, and the patient can only be in a supine position, on his side or on his back. The limbs are in a bent state. Muscle cramps are observed on the occipital and chewing muscles. Optic hyperemia of the optic nerve is possible, up to 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. Residual effects of brain damage, muscle weakness, impaired coordination, pressure sores may be observed.
There are patients who tolerate the disease in a mild form, without neurological symptoms.
A severe course of the disease can be fatal.
Features of epidemiology and prognosis
The causative agents of Japanese encephalitis are most often found in poorly settled areas, near ponds and marshes. In tropical countries, epidemics last longer than 50 days. At risk are people who work outdoors or near water bodies. Most often, Japanese encephalitis affects men from 20 to 40 years old.
At risk are also tourists who go on vacation 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 advised to be vaccinated before traveling to hot countries.
The prognosis for recovery is very small, the probability of death reaches 80%. As a rule, the first 7 days are dangerous, the patient may fall into a coma, or he is tormented by an endless convulsive attack.
People who survived all stages of the disease often have residual effects:
- psychoses
- hyperkinesis;
- decreased intellectual ability;
- paralysis;
- asthenic condition.
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, pathology can be determined by a blood test. Over the next two weeks, the disease can be diagnosed by the results of cerebrospinal fluid tests.
2. Serological examination. Diagnosis involves the use of the enzyme immunoassay or the RN, RNGA, RTGA, and RSK tests.
Therapeutic measures
Treatment of patients who have "met" with carriers of Japanese encephalitis cannot be carried out by only one doctor. The treatment includes infectious disease specialists, neurologists and resuscitators. In stationary conditions, the patient is given 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 the prevention of cerebral edema, detoxification, normalization of the activity of all organs and systems.
The main problem is that it is impossible to cure Japanese encephalitis. Therapy can only eliminate the symptoms. Therefore, it is very important to vaccinate in a timely manner.
Morbidity prevention
Actively immunizing the population is very important to prevent epidemics. Japanese encephalitis vaccines are called "formol vaccine." Passive emergency prophylaxis involves the administration of 6 ml of immunoglobulin and 10 ml of hyperimmune horse serum.
In addition, the prevention of morbidity is a series of comprehensive measures to protect against mosquito attacks. In epidemiologically hazardous areas, the use of protective clothing may be recommended. Mandatory to use repellents, from ointments to sprays, the use of all measures to prevent mosquitoes in the living room.
You can get vaccinations against Japanese encephalitis in Moscow at 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 appear. Redness and swelling may occur at the injection site. Headache, diarrhea, pain in the muscles may appear. Some patients complain of dizziness and nausea, chills and a rash.
Immunization is not carried out in the presence of a number of infectious diseases, during the period of gestation and lactation, if it is known for certain that the patient has hypersensitivity to heterologous proteins, severe allergic reactions.
Today, there are 4 main types of Japanese encephalitis vaccines:
- inactivated;
- based on mouse brain cells;
- inactivated, based on Vero cells;
- live recombinant and live attenuated vaccines.
The most popular vaccine SA14-14-2 has passed the WHO re-qualification and is manufactured in China.
For tourists, vaccination is carried out depending on which country they are going to leave, where they will live, on the outskirts of the village or in the city, for how long, 1 week, month or year.
Vaccination can be carried out in two ways:
| full | shortened |
vaccination days | 1, 7, 30 | 1, 7, 14 |
vaccination age | from 1 year of life | from 1 year of life |
revaccination | every 3 years | every 3 years |
Citizens with subsidiary plots should take care of vaccinating the animals they raise. Live pigs are most often used for pigs. In areas classified as risk zones, it is advisable to conduct regular treatment with insecticides.