Japanese Encephalitis Transmission Research Articles

Past, present, and future of Japanese encephalitis.

Japanese encephalitis (JE), a vector-borne viral disease, is endemic to large parts of Asia and the Pacific. An estimated 3 billion people are at risk, and JE has recently spread to new territories. Vaccination programs, increased living standards, and mechanization of agriculture are key factors in the decline in the incidence of this disease in Japan and South Korea. However, transmission of JE is likely to increase in Bangladesh, Cambodia, Indonesia, Laos, Myanmar, North Korea, and Pakistan because of population growth, intensified rice farming, pig rearing, and the lack of vaccination programs and surveillance. On a global scale, however, the incidence of JE may decline as a result of large-scale vaccination programs implemented in China and India.

Spatial Delimitation, Forecasting and Control of Japanese Encephalitis: India - A Case Study

Japanese encephalitis (JE) is the leading cause of viral encephalitis through large parts of Asia with temperate and subtropical or tropical climate. In the present communication environmental determinants that influence the occur- rence of JE have been enlisted, and based on which a conceptual frame for JE transmission was developed. The concept of endemic and epidemic has been defined using cluster analysis on JE occurrences in 175 districts over a period of 53 years in India. The average number (±standard deviation) of occurrences in endemic (7.4±3.5) and epidemic districts (3.4±2.9) was statistically significant ('t'=8.3; P=0.000). In the epidemic areas, JE immunization of target population in the risk area may be an effective preventive measure. In the endemic areas regular monitoring of vector population and viral activity, and implementing appropriate integrated methods of vector control are likely to reduce the transmission, besides the selec- tive immunization of children.

Weather variables and Japanese encephalitis in the metropolitan area of Jinan city, China

To identify weather-related risk factors and their roles in Japanese encephalitis transmission and to provide policy implications for local health authorities and communities. Data on notified cases of Japanese encephalitis and weather variables over the period 1959-1979 were collected from Jinan city, a temperate city in China. Due to seasonality of the disease, the data analysis was restricted to five months from June to October each year. Spearman correlation analysis and time-series adjusted Poisson regression analysis were performed to quantify the relationship between weather and the number of cases. The Hockey Stick model was used to detect potential threshold temperatures. Monthly mean maximum and minimum temperatures, monthly total rainfall and monthly mean relative humidity were positively correlated to monthly notification of Japanese encephalitis, while monthly mean air pressure was inversely correlated. Lag times varied from one to two months. All these weather variables were significant in the adjusted Poisson regression model. Thresholds of 25.2 degrees C for maximum temperature and 21.0 degrees C for minimum temperature were also detected. Weather variables could have affected the transmission of Japanese encephalitis in this urban area of China. Public health interventions should be developed at this stage to reduce future risks related to climate change.

Laboratory Transmission of Japanese Encephalitis, West Nile, and Getah Viruses by Mosquitoes (Diptera: Culicidae) Collected near Camp Greaves, Gyeonggi Province, Republic of Korea, 2003

Laboratory Transmission of Japanese Encephalitis, West Nile, and Getah Viruses by Mosquitoes (Diptera: Culicidae) Collected near Camp Greaves, Gyeonggi Province, Republic of Korea, 2003

Laboratory Transmission of Japanese Encephalitis, West Nile, and Getah Viruses by Mosquitoes (Diptera: Culicidae) Collected near Camp Greaves, Gyeonggi Province, Republic of Korea, 2003

We conducted experimental studies to evaluate mosquitoes captured in Paju County, Gyeonggi Province, Republic of Korea, for their ability to transmit West Nile virus (family Flaviviridae, genus Flavivirus, WNV), Japanese encephalitis virus (family Flaviviridae, genus Flavivirus, JEV), and Getah virus (family Togaviridae, genus Alphavirus, GETV) under laboratory conditions. Both Culex pipiens pallens Coquillett and Culex tritaeniorhynchus Giles were highly susceptible to infection with WNV, with infection rates > 65% when allowed to feed on chickens with viremias of approximately 10(7) plaque-forming units (PFU) of virus/ml blood. In contrast, Cx. tritaeniorhynchus were significantly more susceptible to JEV or GETV (infection rate 100%) than were the Cx. p. pallens (infection rate 3% for JEV and 0% for GETV) captured in the same area when allowed to feed on chickens with viremias of approximately 10(5) PFU of virus/ml blood. The detection of JEV in field-collected Cx. tritaeniorhynchus in Gyeonggi Province in 2000 and the demonstrated ability of this species to transmit this virus support the importance of the continued vaccination of Koreans against JEV and indicate a risk of infection for nonvaccinated individuals.

Laboratory Transmission of Japanese Encephalitis and West Nile Viruses by Molestus Form of Culex pipiens (Diptera: Culicidae) Collected in Uzbekistan in 2004

Abstract We evaluated the molestus form of Culex pipiens pipiens (L.) (hereafter referred to as "molestus") captured near Tashkent, Uzbekistan, for their ability to transmit Japanese encephalitis (family Flaviviridae, genus Flavivirus, JEV) and West Nile (family Flaviviridae, genus Flavivirus, WNV) viruses under laboratory conditions. These molestus were highly competent laboratory vectors of WNV, with infection and dissemination rates of 96 and 81%, respectively. Approximately 75% of female molestus that fed after development of a disseminated infection transmitted virus by bite. Therefore, ≈60% of those molestus taking a second bloodmeal between 16 and 25 d after an infectious bloodmeal would be expected to transmit WNV by bite. In contrast, these molestus were less efficient vectors of JEV, with infection and dissemination rates of 51 and 25%, respectively. In addition, only 33% of individuals with a disseminated infection transmitted JEV by bite, indicating a significant salivary gland barrier. Therefore, only ≈8% of orally exposed individuals would be expected to transmit JEV by bite if they took a second bloodmeal 16–25 d later. These data indicate that the molestus form of Cx. p. pipiens should be considered a potentially important vector of WNV in Uzbekistan and may become involved in the transmission of JEV, should this virus be introduced into Uzbekistan.

Laboratory Transmission of Japanese Encephalitis and West Nile Viruses by Molestus Form of <I>Culex pipiens</I> (Diptera: Culicidae) Collected in Uzbekistan in 2004

We evaluated the molestus form of Culex pipiens pipiens (L.) (hereafter referred to as "molestus") captured near Tashkent, Uzbekistan, for their ability to transmit Japanese encephalitis (family Flaviviridae, genus Flavivirus, JEV) and West Nile (family Flaviviridae, genus Flavivirus, WNV) viruses under laboratory conditions. These molestus were highly competent laboratory vectors of WNV, with infection and dissemination rates of 96 and 81%, respectively. Approximately 75% of female molestus that fed after development of a disseminated infection transmitted virus by bite. Therefore, approximately 60% of those molestus taking a second bloodmeal between 16 and 25 d after an infectious bloodmeal would be expected to transmit WNV by bite. In contrast, these molestus were less efficient vectors of JEV, with infection and dissemination rates of 51 and 25%, respectively. In addition, only 33% of individuals with a disseminated infection transmitted JEV by bite, indicating a significant salivary gland barrier. Therefore, only approximately 8% of orally exposed individuals would be expected to transmit JEV by bite if they took a second bloodmeal 16-25 d later. These data indicate that the molestus form of Cx. p. pipiens should be considered a potentially important vector of WNV in Uzbekistan and may become involved in the transmission of JEV, should this virus be introduced into Uzbekistan.

Climate variability and transmission of Japanese encephalitis in eastern China.

A time-series analysis was conducted to study the impact of climate variability on the transmission of Japanese encephalitis in eastern China. Correlation and regression analyses were used to examine the relationship between monthly climatic variables and monthly incidence of Japanese encephalitis in Jieshou County, China over the period 1980-96. Spearman's correlation analysis showed that maximum and minimum temperatures and rainfall were all associated with the transmission of Japanese encephalitis in the county. Regression analysis suggested that monthly mean minimum temperature and monthly precipitation had a significant relationship with the transmission of Japanese encephalitis, with a 1-month lag effect. The results indicated that these climatic variables might be treated as possible predictors for regions with similar geographic, climatic, and socio-economic conditions to Jieshou County.

Field Evaluation of a Sentinel Mosquito (Diptera: Culicidae) Trap System to Detect Japanese Encephalitis in Remote Australia

Incursions of Japanese encephalitis (JE) virus into northern Queensland are currently monitored using sentinel pigs. However, the maintenance of these pigs is expensive, and because pigs are the major amplifying hosts of the virus, they may contribute to JE transmission. Therefore, we evaluated a mosquito-based detection system to potentially replace the sentinel pigs. Single, inactivated JE-infected Culex annulirostris Skuse and C. sitiens Wiedemann were placed into pools of uninfected mosquitoes that were housed in a MosquitoMagnet Pro (MM) trap set under wet season field conditions in Cairns, Queensland for 0, 7, or 14 d. JE viral RNA was detected (cycling threshold [CT] = 40) in 11/12, 10/14, and 2/5 pools containing 200, 1,000, and 5,000 mosquitoes, respectively, using a TaqMan real-time reverse transcription-polymerase chain reaction (RT-PCR). The ability to detect virus was not affected by the length of time pools were maintained under field conditions, although the CT score tended to increase with field exposure time. Furthermore, JE viral RNA was detected in three pools of 1,000 mosquitoes collected from Badu Island using a MM trap. These results indicated that a mosquito trap system employing self-powered traps, such as the MosquitoMagnet, and a real-time PCR system, could be used to monitor for JE in remote areas.

Dynamics of Japanese encephalitis - A study in mathematical epidemiology

An S-->I-->R-->S (susceptible-infective-recovered-susceptible) epidemiological model coupling the dynamics of the spread of Japanese encephalitis (JE) in two populations, human and reservoir animals (pigs, cattle, equines, birds, etc.) through a vector population (a particular species of mosquitos, Culex vishnui, Culex tritaeniorhynchus, etc.) is discussed. We assume that there is a constant recruitment rate of the susceptibles into both the populations, whereas the death rates are proportional to the population sizes, which are hence variables. We also assume that the human population is regulated by the disease. Conditions for the existence of a unique endemic equilibrium were found, and the endemicity of the disease is discussed. The threshold values determine whether the disease dies out or approaches an endemic equilibrium. The persistence of disease and disease-related death can lead to a new equilibrium population size. The criteria for eradication of the disease have been worked out. The analytical results corresponding to the solutions of our system are verified by numerical analysis and computer simulation. The dynamics of disease transmission of JE during 1948-1956 in Japan were also investigated with the help of available data.

Transmission of Japanese Encephalitis in a 3-population model

The model considered for the spread of Japanese Encephalitis (JE) in a human population of varying size from a reservoir population (pigs, cattle, equines, birds, etc.) through a vector population (particular species of mosquitos) is of SIRS (susceptible-infective-recovered-susceptible) type for the human and reservoir populations and SIS (susceptible-infective-susceptible) type for the vector population. We have considered the logistic differential equation with density-dependent birth rate for the vector population whereas the reservoir population is of constant size. We assume that the human population is regulated by the disease. We also assume that there is a constant recruitment rate of susceptibles into the human population. We perform an equilibrium and stability analysis to find a threshold condition. If the threshold is exceeded, then there is a unique equilibrium with disease present which is locally stable to small perturbations and global stability depends on death rates and the ratio of the equilibrium population sizes of the infected vector and total human populations.

Numerical analysis for spread of the infection with Japanese encephalitis virus

A seroepidemiological survey on hemagglutination-inhibition (HI) antibody titer to Japanese encephalitis (JE) virus in herds of swine in Tokyo metropolitan area during the past 21 years has disclosed a recent trend to dalay in period of antibody acquisition and decline in peak seropositivity rate.Untill 1967 where human infections of JE virus were reported in the capital suburban areas, the HI antibody positivity rate of swine in those areas usually rose sharply late in July to early in August and remained thereafter virtually at a 100% level till October.Over the ensuing years, however, the sharp rise of HI antibody titer became delayed 1-2 months as compared to those before 1968 and the peak seropositivity rate lowered to as low as 20-40%.This paper represents an attempt to numerically analyze the process of spread of an epidemic of JE virus infection with a view to theoretical delineation of the recent changes in mode of JE virus infiltration in herds of swine.We postulated that it might be possible to proceed with the numerical analysis by a model set up on the following presumption. The incidence of swine that may newly contract JE virus infection in an arbitrary unit length of period (Yi) can be expressed in terms of product of three factors;the rate of swine which may serve a potential source of infection in a given swine population (Yi-1), that of susceptible swine in that population {100-(Y0+Y1+…+Yi-1)} and the constant (K) representing the coefficient of swine JE transmission. Thus, we considered the following model for estimation of spread of JE virus infection:Yi=Yi-1 ×{100-(Y0+Yi+…+Yi-1)}× K. The cumulative incidence of swine estimated to newly contract the infection (Yi) during consecutive unit lenghts of period being defined as “infection rate”. this theoretical value was found closely approximately to seropositivity rate determined for HI antibody to JE virus in swine populations studied.Analysis of data with this model has revealed (1) that the rate of swine serving as a potential source of JE virus infection at the ontset of an epidemic of JE has diminished with a consequent delay in sharp rising of HI antibody seropositivity rate, and (2) that the recent decline in transmission coefficient relevant to spread of JE epidemics has led to depression of peak seropositivity rate for HI antibody to JE virus. Thus, these changes in epidemiologic features of outbreaks of JE observed in recent years in the Tokyo metropolitan area are explicable from those which have occurred in respect of the two factors, i. e. decreased subpopulation of swine that would serve as the source of infection and depressed coefficient of transmission of the infection.

Observations on the experimental transmission of Japanese encephalitis by mosquitoes.

Summary 1. The results demonstrate that mice infected by the bite of Culex quinquefasciatus develop a sufficient concentration of virus in the blood to produce a transmissible infection in mosquitoes which feed upon them. 2. Mice 3–5 days old when infected developed blood titers which ranged from 3.6 to 5.2 while those 7–12 days old had titers of 2.8–3.8. The mosquitoes transmitted the virus when infected by blood having titers of 2.8, 3.2, 4.5, and 5.2, respectively. The titer is expressed as the exponent of the reciprocal of the LD50 dilution.