Seasonality of Viral Encephalitis and Associated Environmental Risk Factors in Son La and Thai Binh Provinces in Vietnam from 2004 to 2013

Abstract

Abstract. In Vietnam, Japanese encephalitis virus accounts for 12-71% of viral encephalitis (VE) cases followed by enteroviruses and dengue virus among identified pathogens. This study is the first attempt to evaluate the seasonality of VE and associated environmental risk factors in two provinces from 2004 to 2013 using a seasonal trend-decomposition procedure based on loess regression and negative binomial regression models. We found seasonality with a peak of VE in August and June in Son La and Thai Binh, respectively. In Son La, the model showed that for every 1°C increase in average monthly temperature, there was a 4.0% increase in monthly VE incidence. There was a gradual decline in incidence rates as the relative humidity rose to its mean value (80%) and a dramatic rise in incidence rate as the relative humidity rose past 80%. Another model found that a 100 mm rise in precipitation in the preceding and same months corresponded to an increase in VE incidence of 23% and 21%, respectively. In Thai Binh, our model showed that a 1°C increase in temperature corresponded with a 9% increase in VE incidence. Another model found that VE incidence increased as monthly precipitation rose to its mean value of 130 mm but declined gradually as precipitation levels rose beyond that. The last model showed that a monthly increase in duration of sunshine of 1 hour corresponded to a 0.6% increase in VE incidence. The findings may assist clinicians by improving the evidence for diagnosis.

A spatial and temporal analysis of paediatric central nervous system infections from 2005 to 2015 in Ho Chi Minh City, Vietnam

“…This is consistent with the downward trend of bacterial CNSI in the countries where Hib immunization has been implemented [27]. The incidence of viral encephalitis has been reported as being higher in summer-fall (rainy) months in the North of Vietnam [16], while a higher incidence of non-BI in our data was identified in the winter and spring (dry) months. This disparity may be associated with the differing climatic conditions between the North and the South of Vietnam.…”

“…There is evidence to suggest that various spatial, climatic and socio-demographic risk factors may be associated with the incidence of CNSI in low-middle income countries such as those located in the African sub-Saharan meningitis belt and Asia (e.g. vector-born encephalitis is associated with proximity to rice cultivation and pig rearing and bacterial meningitis is associated with seasonality (the winter months) and high population densities) [10][11][12][13][14][15][16][17]. Vietnam faces continuing lack of access to costly vaccines against bacterial and viral etiologies of CNSI.…”

Long-Term Epidemiological Dynamics of Japanese Encephalitis Infection in Gansu Province, China: A Spatial and Temporal Analysis

“…14,37 Hence, further investigation should be conducted in these high-risk areas to discover the role of biological, social, and environmental factors in the transmission of JE. 42,43 Currently, JE seems to have a tendency to break through geographical restrictions. Studies had shown that JEV had been found in mosquitoes and pigs in Tibet, and its neutralizing antibodies had also been detected in human serum.…”

Seroprevalences of multi-pathogen and description of farm movement in pigs in two provinces in Vietnam

“…It is well recognized that JE is endemic in Southeast Asia, which is a major cause of viral encephalitis (VE) in young children [35][36][37]. In Vietnam, national surveillance for VE in humans is ongoing, with the JE virus considered to be a leading cause of VE, accounting for 12-71% of cases [38][39][40]. JE is a virus transmitted by mosquitoes and pigs are well known as a major amplifying host for transmission to humans [41,42].…”