Leishmaniasis, a neglected tropical disease, is on the decline in South Asia. However, cases of cutaneous leishmaniasis have risen in Sri Lanka since 2001, and the lack of in-depth research on its epidemiologic characteristics hampers control efforts. We analyzed data collected from patients with cutaneous leishmaniasis in Sri Lanka during 2001–2018 to study temporal and geographic trends and identify and monitor disease hotspots. We noted a progression in case rates, including a sharp rise in 2018, showing temporal expansion of disease-prevalent areas and 2 persistent hotspots. The northern hotspot shifted and shrank over time, but the southern hotspot progressively expanded and remained spatially static. In addition, we noted regional incidence differences for age and sex. We provide evidence of temporally progressive and spatially expanding incidence of leishmaniasis in Sri Lanka with distinct geographic patterns and disease hotspots, signaling an urgent need for effective disease control interventions.
SummaryThe visceralizing potential of apparently dermotropic Leishmania donovani in Sri Lanka (L. donovani-SL) was investigated through long-term follow-up of cutaneous leishmaniasis (CL) patients and in vivo and in vitro experimental infection models. CL patients (n = 250) treated effectively with intra-lesional antimony therapy were followed-up six monthly for 4 years. There was no clinical evidence of visceralization of infection (VL) during this period. Infection of BALB/c mice with L. donovani-SL (test) through intra-dermal route led to the development of cutaneous lesions at the site of inoculation with no signs of systemic dissemination, in contrast to the observations made in animals similarly infected with a visceralizing strain of L. donovani-1S (control). Cytokine (IL-10, IFN-γ) release patterns of splenocytes and lymph node cell cultures derived from mice primed with experimental infections (with either test or control parasites) revealed significantly high IFN-γ response associated with test mice with CL, while prominent IL-10 levels were observed in association with control mice with VL. Furthermore, diminished infection efficiency, intracellular growth and survival of L. donovani-SL parasites compared with L. donovani-1S were evident through in vitro macrophage infection experiments. These studies confirm, for the first time, the essential dermotropic nature of L. donovani-SL suggesting natural attenuation of virulence of local parasite strains.
Background Leishmaniasis is a neglected tropical vector-borne disease, which is on the rise in Sri Lanka. Spatiotemporal and risk factor analyses are useful for understanding transmission dynamics, spatial clustering and predicting future disease distribution and trends to facilitate effective infection control. Methods The nationwide clinically confirmed cutaneous leishmaniasis and climatic data were collected from 2001 to 2019. Hierarchical clustering and spatiotemporal cross-correlation analysis were used to measure the region-wide and local (between neighboring districts) synchrony of transmission. A mixed spatiotemporal regression-autoregression model was built to study the effects of climatic, neighboring-district dispersal, and infection carryover variables on leishmaniasis dynamics and spatial distribution. Same model without climatic variables was used to predict the future distribution and trends of leishmaniasis cases in Sri Lanka. Results A total of 19,361 clinically confirmed leishmaniasis cases have been reported in Sri Lanka from 2001–2019. There were three phases identified: low-transmission phase (2001–2010), parasite population buildup phase (2011–2017), and outbreak phase (2018–2019). Spatially, the districts were divided into three groups based on similarity in temporal dynamics. The global mean correlation among district incidence dynamics was 0.30 (95% CI 0.25–0.35), and the localized mean correlation between neighboring districts was 0.58 (95% CI 0.42–0.73). Risk analysis for the seven districts with the highest incidence rates indicated that precipitation, neighboring-district effect, and infection carryover effect exhibited significant correlation with district-level incidence dynamics. Model-predicted incidence dynamics and case distribution matched well with observed results, except for the outbreak in 2018. The model-predicted 2020 case number is about 5,400 cases, with intensified transmission and expansion of high-transmission area. The predicted case number will be 9115 in 2022 and 19212 in 2025. Conclusions The drastic upsurge in leishmaniasis cases in Sri Lanka in the last few year was unprecedented and it was strongly linked to precipitation, high burden of localized infections and inter-district dispersal. Targeted interventions are urgently needed to arrest an uncontrollable disease spread.
Carbonate rocks are highly soluble. Sinkholes are formed by both the failure of solution cavities and the rapid removal of fines from solution cavities in carbonate and metacarbonate rocks. Sri Lankan landmass is composed of Proterozoic high-grade metamorphic rocks such as gneiss and metacarbonates like marble. Large caves in Sri Lanka form in both marble and gneiss. A few land subsidence events have occurred recently in Ella-Wellawaya area, which is a hilly terrain. In addition, some cases of groundwater table lowering, which has caused drying of dug wells have also been recorded within the area, apparently related to a major development project presently under way in the area.The main objective of this paper is to draw the immediate attention of local researchers and authorities whom are working on mitigation and management of disasters, groundwater and climate change, showing the importance of carrying out detail studies on potential landslides and land subsidence of Ella-Wellawaya area for avoiding and minimising loss of humans and properties. Preliminary surveys on some land subsidence cases and speleological studies including geology, hydrogeology and morphological mapping of the underground caves in the area have been actively carried out. According to the results, it is shown that the subsidence is likely to be correlated with the collapsing of cavities and weathered zones in metacarbonates, and disturbances to the groundwater table. Field explorations done during the last two years have discovered several large underground caves in the area some more than 100 m across. Most of the cave roofs have been thinned by the breakdown of bedrock along weak zones such as joints. Since the process of collapse, trigged by weathering is continuing and patches and lenses of carbonate rocks observed in the caves are still being dissolved, the expansion of the cave spaces is unending. Some of the chambers of these caves are aligned parallel to the steep slopes in the Ella-Wellawaya area and some acted as underground water conduits and storages during the rainy seasons. The Ella-Wellawaya area has been undergone a change in vegetation cover since the colonial period and hence the area is more prone to soil erosion which exposes the near surface natural cavities to the underground caves. Present human exposures and interactions within the susceptible slopes have brought lives and properties under threat. Hence future land subsidence and landslide occurrences are highly predictable with the recent conditions in the area and hence threat to human life and properties is high. The tourism industry, unique to the area could particularly be affected. Hence such hazardous should properly be identified and demarcated and the erosion triggered by present vegetation changes must properly be addressed.
Estimation of knockdown time (KT) is useful in determining bio-effectiveness of mosquito repellents. Knockdown or not knockdown is a binary variable thus, analysis is done by fitting generalized linear models, based on binomial distribution. Use of appropriate link function in fitting a generalized linear model is crucial especially when estimating quantities such as KT 50 and KT 95 . This study was done to determine the most appropriate link function in fitting generalized linear models to estimate KT 50 and KT 95 . Knockdown activity of metofluthrin 0.005% (w/w) and d-trans-allethrin 0.12% (w/w) was tested under two different physiological conditions (blood fed and sucrose fed) using wild-caught female Culex tritaeniorhynchus mosquitoes from an agro-farming area of the north-western province of Sri Lanka. Coefficient of variation of the observed KT 50 and KT 95 was less than 5.5%. Both KT 50 and KT 95 values were estimated by fitting altogether 120 binomial distribution-based generalized liner models with three different link functions namely, logit, probit, and complementary log-log. The G2 statistics was used to test the goodness of fit of the models. However, in order to evaluate the accuracy of all estimated KT 50 and KT 95 values obtained using the above three link functions, they were compared against corresponding observed values using ANOVA followed by Dunnett mean separation procedure. The probit and logit link functions were found to be appropriate in the estimation of KT 50 . As the logit link function is commonly used in modeling binary responses, out of the two, logit link function is recommended. Complementary log-log link function was found to be the most appropriate in estimation of KT 95 . Thus, one link function cannot be recommended in estimating both KT parameters.
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