Viral encephalitis

Epidemiology
Viral encephalitis are everywhere on the globe, and each form of the disease occurs in areas with special conditions. The main feature of the epidemiology of viral encephalitis is the spread of blood-sucking arthropods: mosquitoes and ticks. For each form of encephalitis is characterized by certain carriers, the boundaries of which are determined focality and endemicity of infection. Some of hydraulic and geographic characteristics of the area (for example, marshes, lakes and other reservoirs), contributing to the emergence mosquito vector, create a favorable environment for the spread of mosquito-encephalitis. The presence in this or that area ticks - carriers and custodians of the virus causes the endemicity of such areas against tick-borne encephalitis. People affected by these diseases when it is in focus. For viral encephalitis is characterized by a strong seasonality. The maximum rise in the incidence follows the period of the most intensive breeding and activity of blood-sucking mosquitoes. Diseases in rural areas and in cities. Usually affects people from rural areas, however, described the epidemic mosquito encephalitis defeat mainly urban residents.
In different epidemic was sick people of different age groups, except for children in the first year of life. Mortality in different forms of encephalitis varies from 5%to 60%. The most severe and high fatality characterized Japanese encephalitis.
Mosquito encephalitis. Japanese encephalitis is distributed mainly in the basin of the Pacific ocean. The greatest number of diseases registered in Japan. The number of diseases in the USSR small.
Encephalitis type St. Louis and horse encephalomyelitis are found mainly in the Americas. Encephalitis valley of the river Murray common in Australia.
The mosquito vectors of the virus encephalitis are certain types of mosquitoes. In the centers of Japanese encephalitis common Culex tritaeniorhynchus, C. pipiens, Aetogoi and other Most important is the first kind. The main carriers of encephalitis type St. Louis and Western equine encephalomyelitis were C. tarsalis, Eastern equine encephalomyelitis - Anopheles crucians, and other human Infection occurs in the attack on him of infected mosquitoes. Mosquitoes are temporary reservoirs of the virus, because they have HIV transmission to the offspring is not installed. The main sources of infection are birds, domestic and wild animals. Preserving agents mosquito encephalitis in majapidamiste period associated with the wintering survival of infected mosquitoes, and long virusencyclo in birds. The virus from overwintered mosquito bite enters the body of animals and people, which in turn infected mosquitoes, begins epidemic outbreak. In endemic foci of proximately mosquito - mammals and birds. Once infected mosquito can transmit the virus only after sufficient accumulation in the body and penetration in the salivary glands.
The main sources of infection in Japanese encephalitis are pigs, horses and poultry. American encephalitis - wild and domestic birds (most studied chickens). Animals and birds can be virus carriers, while remaining quite healthy.
Disease outbreaks - in summer and autumn (August, September).
Encephalitis type Economo. Sources of the infection are sick, convalescents and healthy virus carriers. Assume that the pathogen spreads through airborne droplets. Diseases occur mainly in winter and spring (February-April). Sick mainly people aged up to 40 years. The incidence is higher among men. The case fatality rate of about 30%. In the past experienced major epidemics, currently sporadic cases.