Study On Spatio-temporal Distribution And Related Geographic And Climatic Factors Of Japanese Encephalitis In Mainland China,1963-1975

Japanese encephalitis (JE) is an acute infectious zoonosis disease caused by infection with Japanese encephalitis virus (JEV) through mosquito bites. Infection results in damage to the central nervous system and the mortality rate can be more than30%. Furthermore,～30%of the survivors may have neurological sequelae, such as severe consciousness disturbance, dementia, aphasia, and limb paralysis. According to a report by the World Health Organization (WHO),～69000JE cases occur annually worldwide and JE is prevalent in24countries and territories in Asia and Oceania.JE is a vaccine-preventable disease, and immunization programs can prevent JEV infection. Historically, Japan, Korea, and China had high incidence of JE. However, with the implementation of JE vaccination programs in the1960s, both Japan and Korea have almost achieved a state of JE "elimination".China began implementing a JE vaccination program in the1980s, and the incidence of JE has since remained low. After2000, with the help of the WHO and Program for Appropriate Technology in Health (PATH), as well as other international organizations, other JE endemic counties in Asia have begun to implement JE vaccination programs. On the other hand, as a natural focal disease transmitted by mosquitoes, the incidence of JE can be affected by several climatic factors, such as temperature and rainfall. The research conducted in Malaysia confirmed that the effects of climatic factors on JE were masked by vaccination programs and cannot be estimated precisely.Therefore, the JE data derived from the period without JE vaccination are of great significance to reveal the authentic epidemiology of JE and influences of climatic factors on JE incidence.China is a highly endemic area of JE. In addition, there was a nationwide JE epidemic in China during the1960s and1970s, and tens of thousands cases were reported in this era of no JE vaccine intervention. As China was experiencing the "Cultural Revolution" at that time, the functions of government were weakened and the public health authorities almost failed to implement any interventions. Thus, China experienced a natural JE epidemic period with no interventions from the1960s to1970s. In this study, we examined the spatial and temporal distribution of JE cases during the period1963to1975in mainland China. By combining with meteorological data, the effects of rainfall and temperature on JE in several geomorphic units are also discussed. The results of this study are as follows:1. Spatial and temporal distribution and related geographic and climatic factors of JE in Mainland China,1963-1975.During the JE epidemic period from1963to1975, more than140million cases were reported nationwide, and the JE incidence ranged from8.32/100,000to20.92/100,000. The JE epidemic peaked in1966and1971and the number of reported cases were as high as150,000and170,000,separately. It is showed that there was a obvious seasonal distribution of JE cases during the study period.The JE cases mainly clustered in July and August and the total number of cases occurred in these two months accounted for more than70percent of JE cases reported between1963-1975. From the perspective of geographical distribution, the reported JE cases during this period were mainly distributed on the eastern China, especially in the southeast coastal areas.The results of LISA analysis indicated that the hot spots were concentrated mainly in Jiangsu, Zhejiang, Anhui, Hunan, and Fujian provinces, which covered most of the Yangtze River Plain geographically. Ningxia and Gansu, located in the Loess Plateau in northwestern China, were identified as cold spots. To further analyze the effects of climatic factors in different geographical environments on the incidence of JE, China was divided into eight geomorphic units. The results showed that over90%of the JE cases were distributed in the plains with low altitude and the JE incidence was markedly higher on the plains than plateaus.In addition, the correlations between rainfall and temperature in summer and JE incidence were shown to vary among geomorphic unitsthrough the Spearman correlation analysis. Both rainfall and temperature showed significant positive correlations with JE incidence in the Loess Plateau and the Northeast China Plain, while significant negative correlations were observed in the Yunnan-Guizhou Plateau. Only rainfall was positively correlated with JE incidence, and no significant correlation was observed between temperature and JE incidence in the North China Plain. In contrast, the temperature was positively correlated with JE incidence and rainfall showed no significant correlation with that in the Yangtze River Plain.2. Other exploratory analysesAlso, this study tried some exploratory analyses in regards to the characteristics of JE epidemic and related factorsduring the1960s and1970s. In order to discover the dynamic changes of the distribution of JE cases nationwide, the JE data from1960to1979were visualized on the map. Unfortunately, the results did not show the existence of any obvious dynamic variation in space. In addition, the relationship between the incidence of JE and meteorological factors such as temperature and rainfall at the provincial level between1963-1975were analyzed using the Geographical detector, one of the useful methods in spatial analysis.The results showed that summer temperature and summer rainfall had a good explanatory power on JE incidenceand can be interpreted as the potential impact factorsincluded into subsequent modeling work. On this basis, a preliminary analysis of the effectof rainfall and temperature on JE incidence in different geomorphic units during1963-1975were conducted by Spatial autoregressive model in this study.Most of the results were consistent with the Spearman rank correlation analysis, but there were still existing some differences between them.Therefore, further studies are needed. SignificanceIn this study, we examined the spatial and temporal distribution of JE cases during the period1963to1975in mainland China and the effects of rainfall and temperature on JE in several geomorphic units are also discussed. These results may provide an novel insight into the epidemiological characteristics of JE in the absence of vaccine interventionsand other mosquito-borne viral diseases as well. They not only provide data supporting the prevention and control of JE in endemic regions that have not widely implemented JE vaccination programs, but are also of practical significance for prevention and control of JE insome new regions with similar natural and social environments for JEV transmission, such as Europe and Americas.