(A) Host animals and infectious sources are mainly small rodents, including the genus of gerbils (mainly black-lined gerbils), rats (mainly brown house mice and rats), mice (brown-backed and red-backed), voles (mainly oriental voles), hamsters (mainly black-lined hamsters) and mice (small house mice and mice). More than 30 species of animals have been identified as natural carriers of this virus in China. In addition to rodents, some domestic animals also carry EHFV, including domestic cats, rabbits, dogs, pigs, etc., proving multihostness. These animals are mostly incidental carriers, and only a few rodent species are epidemiologically proven to be the infectious source of this disease, among which the black-line gerbil is the main host and infectious source of wild rodent type hemorrhagic fever in China, the brown house mouse is the main infectious source of urban type (Japan, Korea) and our country rodent type hemorrhagic fever, and the big forest gerbil is the main infectious source of hemorrhagic fever in forest areas in China. As for the role of other rodents carrying this virus in epidemiology, further observation and research are needed. (The virus can be excreted through the blood, saliva, urine and stool of the host animal, and direct transmission from rodents to humans is an important way of human infection. It is believed that the following routes can cause hemorrhagic fever transmission: 1. respiratory tract. Hemorrhagic fever virus containing rodent excrement contaminated with dust formed by aerosol particles through the respiratory tract infection. 2, digestive tract. Ingestion of food and water contaminated with rat excreta containing hemorrhagic fever virus, infected by oral mucosa and gastrointestinal mucosa. 3.Contact transmission. Rat bites, rodent excrement, secretions and direct contact with broken skin, mucous membranes. 4.Mother to child transmission. Pregnant women can infect the fetus through the placenta after the disease. 5.Insect vector transmission. The bite of mites parasitized on the body surface of rats can cause the spread of the disease. (C) population susceptibility It is generally believed that the population is generally susceptible, the rate of recessive infection is low, in the wild rodent type more than 3-4%; but the domestic rodent type epidemic area recessive infection rate is high, some reports for more than 15%, the general incidence of young adults is high, the onset of secondary infection is rare. After the disease in the fever period can be detected in the serum-specific antibodies, 1 – 2 weeks up to a very high level, antibody duration is long. (D) epidemiological characteristics 1, disease type and regional distribution
The disease is mainly distributed in the eastern, northern and central regions of Asia, including Japan (urban type and experimental animal type are caused by rat type EHFV), Korea (urban type, wild rat type, experimental animal type), the Soviet Far East coastal area (wild rat type) and China (wild rat type, domestic rat type, experimental animal type). Rats (mostly brown house rats) in coastal port cities of many countries and regions naturally carry EHFV antigens and/or antibodies, indicating that they have a worldwide distribution and spread and spread especially among rats in coastal cities, and thus have become a global public health problem. In China, 26 provinces, cities and autonomous regions have been confirmed by pathogenesis or serology, and in recent years, along with the emergence of the house mouse type, the infected areas have spread rapidly and become a serious and urgent problem in large and medium-sized cities and coastal ports. In recent years, a type of EHF heavy HFRS similar to the Asian wild rat type has occurred in the Balkan countries of Eastern Europe, with a mortality rate of 19-30%. Heavy HFRS was first found in Bulgaria, and in recent years the occurrence or prevalence of heavy HFRS has been confirmed by serology in Yugoslavia, Albania and Greece. In Europe, experimental animal HFRS caused by rats has also occurred in Belgium, the Netherlands, England and France. The epidemiological typing of HFRS is closely related to the aforementioned pathogenic typing. HFRS is classified into different serotypes due to the different antigenicity of the virus carried by several hosts, and different host rodent species constitute different epidemic types due to different habits. It is divided into wild rat, domestic rat and laboratory animal types. European heavy HFRS is transmitted by yellow-necked gerbils, which is also wild rodent type, and the pathogen is V-type virus. 2. Seasonality
It is distributed throughout the year, and the peak incidence of wild rodent type is mostly in autumn, from October to January, with a small peak in spring and summer in a few areas. Domestic rodent type mainly occurs in the spring and early summer, from March to June. The seasonal manifestations are related to rodent reproduction, activity and contact with human activities.