The Effect of Vaccination Coverage and Climate on Japanese Encephalitis in Sarawak,Malaysia

Background

Japanese encephalitis (JE) is the leading cause of viral encephalitis across Asia with approximately 70,000 cases a year and 10,000 to 15,000 deaths. Because JE incidence varies widely over time, partly due to inter-annual climate variability effects on mosquito vector abundance, it becomes more complex to assess the effects of a vaccination programme since more or less climatically favourable years could also contribute to a change in incidence post-vaccination. Therefore, the objective of this study was to quantify vaccination effect on confirmed Japanese encephalitis (JE) cases in Sarawak, Malaysia after controlling for climate variability to better understand temporal dynamics of JE virus transmission and control.

Methodology/principal findings

Monthly data on serologically confirmed JE cases were acquired from Sibu Hospital in Sarawak from 1997 to 2006. JE vaccine coverage (non-vaccine years vs. vaccine years) and meteorological predictor variables, including temperature, rainfall and the Southern Oscillation index (SOI) were tested for their association with JE cases using Poisson time series analysis and controlling for seasonality and long-term trend. Over the 10-years surveillance period, 133 confirmed JE cases were identified. There was an estimated 61% reduction in JE risk after the introduction of vaccination, when no account is taken of the effects of climate. This reduction is only approximately 45% when the effects of inter-annual variability in climate are controlled for in the model. The Poisson model indicated that rainfall (lag 1-month), minimum temperature (lag 6-months) and SOI (lag 6-months) were positively associated with JE cases.

Conclusions/significance

This study provides the first improved estimate of JE reduction through vaccination by taking account of climate inter-annual variability. Our analysis confirms that vaccination has substantially reduced JE risk in Sarawak but this benefit may be overestimated if climate effects are ignored.     

New baseline environmental assessment of mosquito ecology in northern Haiti during increased urbanization

The catastrophic 2010 earthquake in Port‐au‐Prince, Haiti, led to the large‐scale displacement of over 2.3 million people, resulting in rapid and unplanned urbanization in northern Haiti. This study evaluated the impact of this unplanned urbanization on mosquito ecology and vector‐borne diseases by assessing land use and change patterns. Land‐use classification and change detection were carried out on remotely sensed images of the area for 2010 and 2013. Change detection identified areas that went from agricultural, forest, or bare‐land pre‐earthquake to newly developed and urbanized areas post‐earthquake. Areas to be sampled for mosquito larvae were subsequently identified. Mosquito collections comprised five genera and ten species, with the most abundant species being Culex quinquefasciatus 35% (304/876), Aedes albopictus 27% (238/876), and Aedes aegypti 20% (174/876). All three species were more prevalent in urbanized and newly urbanized areas. Anopheles albimanus, the predominate malaria vector, accounted for less than 1% (8/876) of the collection. A set of spectral indices derived from the recently launched Landsat 8 satellite was used as covariates in a species distribution model. The indices were used to produce probability surfaces maps depicting the likelihood of presence of the three most abundant species within 30 m pixels. Our findings suggest that the rapid urbanization following the 2010 earthquake has increased the amount of area with suitable habitats for urban mosquitoes, likely influencing mosquito ecology and posing a major risk of introducing and establishing emerging vector‐borne diseases.     

The association between distance to water pipes and water bodies positive for anopheline mosquitoes (Diptera: Culicidae) in the urban community of Malindi, Kenya.

The increasing risk of mosquito-borne diseases in African urban environments has been partly attributed to failed planning and resource underdevelopment. Though engineered systems may reduce mosquito proliferation, there are few studies describing this relationship. This study investigates how engineered systems such as roads and piped water systems affect the odds of anopheline immatures (i.e., larvae and pupae) occurring in water bodies located in Malindi, Kenya. Anopheles gambiae s.s. (Giles), An. arabiensis (Patton), and An. merus (Dointz) were identified in urban Malindi, with Anopheles gambiae s.s. being the predominant species identified. The Breslow-Day test was used to explore interactions among independent variables. Logistic regression was used to test whether water bodies positive for anopheline immatures are associated with engineered systems, while controlling for potential confounding and interaction effects associated with urban water body characteristics. Water bodies more than 100 m from water pipes were 13 times more likely to have anopheline immatures present, compared to water bodies that were less than 100 m from water pipes (OR = 13.54, 95% CI: 3.15-58.23). Roads were not significantly associated with water bodies positive for anopheline immatures. Statistical interaction was detected between water body substrate type and distance to water pipes. This study provides insight into how water pipes influence the distribution of water bodies positive with immature anophelines in urban environments.     

Enrichment of a single clone from a high diversity library of phage-displayed antibodies by panning with Anopheles gambiae (Diptera: Culicidae) midgut homogenate

A high diversity library of recombinant human antibodies was selected on complex antigen mixtures from midguts of female Anopheles gambiae Giles. The library of phage-displayed single chain variable region fragment constructs, derived from beta-lymphocyte mRNA of na?ve human donors, was repeatedly selected and reamplified on the insoluble fraction of midgut homogenates. Five rounds of panning yielded only one midgut-specific clone, which predominated the resulting antibody panel. In A. gambiae, the epitope was found throughout the tissues of females but was absent from the midgut of males. The cognate antigen proved to be detergent soluble but very sensitive to denaturation and could not be isolated or identified by Western blot of native electrophoresis gels or by immunoprecipitation. Nevertheless, immunohistology revealed that this sex-specific epitope is associated with the lumenal side of the midgut. Severe bottlenecking may limit the utility of phage display selection from na?ve libraries for generating diverse panels of antibodies against complex mixtures of antigens from insect tissues. These results suggest that the selection of sufficiently diverse antibody panels, from which mosquitocidal or malaria transmission-blocking antibodies can be isolated, may require improved selection methods or specifically enriched pre-immunized libraries.     

The spatial heterogeneity between Japanese encephalitis incidence distribution and environmental variables in Nepal

Background

To identify potential environmental drivers of Japanese Encephalitis virus (JE) transmission in Nepal, we conducted an ecological study to determine the spatial association between 2005 Nepal JE incidence, and climate, agricultural, and land-cover variables at district level.

Methods

District-level data on JE cases were examined using Local Indicators of Spatial Association (LISA) analysis to identify spatial clusters from 2004 to 2008 and 2005 data was used to fit a spatial lag regression model with climate, agriculture and land-cover variables.

Results

Prior to 2006, there was a single large cluster of JE cases located in the Far-West and Mid-West terai regions of Nepal. After 2005, the distribution of JE cases in Nepal shifted with clusters found in the central hill areas. JE incidence during the 2005 epidemic had a stronger association with May mean monthly temperature and April mean monthly total precipitation compared to mean annual temperature and precipitation. A parsimonious spatial lag regression model revealed, 1) a significant negative relationship between JE incidence and April precipitation, 2) a significant positive relationship between JE incidence and percentage of irrigated land 3) a non-significant negative relationship between JE incidence and percentage of grassland cover, and 4) a unimodal non-significant relationship between JE Incidence and pig-to-human ratio.

Conclusion

JE cases clustered in the terai prior to 2006 where it seemed to shift to the Kathmandu region in subsequent years. The spatial pattern of JE cases during the 2005 epidemic in Nepal was significantly associated with low precipitation and the percentage of irrigated land. Despite the availability of an effective vaccine, it is still important to understand environmental drivers of JEV transmission since the enzootic cycle of JEV transmission is not likely to be totally interrupted. Understanding the spatial dynamics of JE risk factors may be useful in providing important information to the Nepal immunization program.     

Abundance of immature Anopheles and culicines (Diptera: Culicidae) in different water body types in the urban environment of Malindi, Kenya

In this study we 1) describe the abundance of Anopheles and culicine immatures in different water body types in urban Malindi, Kenya, 2) compare Anopheles immature density in relation to culicine immature density, and 3) identify characteristics that influence the likelihood of water bodies being co-colonized by Anopheles and culicines. Entomological and environmental cross-sectional surveys conducted in 2001 and 2002 were used in the analysis. A total of 889 Anopheles and 7,217 culicine immatures were found in diverse water body types in 2001 and 2002. Car-track pools (n = 45) and unused swimming pools (n = 25) comprised 61% (70 of 115) of all water bodies found and served as the main habitats for Anopheles immatures. Of the 38 water bodies found containing Anopheles immature mosquitoes, 63% (24 of 38) were car-track pools and unused swimming pools. Culicine immatures utilized several water body types as habitats. We found that Anopheles and culicine immatures had higher density when occurring individually compared to when they occurred simultaneously. We determined that season, permanency, and water body area size influenced the likelihood of water bodies being simultaneously positive for Anopheles and culicines. Though Anopheles immatures were found in diverse water body types, their numbers were low compared to culicine immatures. The low density of Anopheles immatures suggests that Anopheles larval control is an achievable goal in Malindi.     

Feeding and survival of the malaria vector Anopheles gambiae on plants growing in Kenya

The propensity of the malaria vector mosquito Anopheles gambiae Giles (Diptera: Culicidae) to ingest sugars from various plants, and subsequent survival rates, were assessed with laboratory-reared males and females offered eight species of plants commonly cultivated and/or growing wild in western Kenya. In cages (no-choice bioassay), mosquitoes given the opportunity to feed on castorbean (Ricinus communis L.) had the longest survival times (mean and median survival time of 6.99 +/- 0.23 and 5.67 +/- 0.17 days, respectively), comparable to mosquitoes given 6% glucose (mean and median survival time of 8.70 +/- 0.23 and 6.67 +/- 0.33 days, respectively). Survival rates of An. gambiae were low on the other plants, comparable to mosquitoes given only water. Three plants: sweet potato (Ipomoea batatas L.), wild sage (Lantana camara L.) and castorbean provided levels of sugar ingestion by both sexes of An. gambiae detectable using the cold anthrone method, showing a positive correlation between median survival and sugar consumption (Spearman rank correlation coefficient = 0.905, P < 0.0001). Equal numbers of males and females were released in an enclosed semi-field screenhouse system containing a range of local plants, but no host for blood, and allowed to feed ad libitum: 6.7 +/- 0.5% (11/64) of those recaptured were found to contain detectable fructose (all females). Common plants are clearly a viable source of nutrition for adult female An. gambiae, as well as males, and may constitute and important resource for this important malaria vector.