The ongoing risk of Leishmania donovani transmission in eastern Nepal: an entomological investigation during the elimination era.

BACKGROUND: Visceral leishmaniasis (VL), a life-threatening neglected tropical disease, is targeted for elimination from Nepal by the year 2026. The national VL elimination program is still confronted with many challenges including the increasingly widespread distribution of the disease over the country, local resurgence and the questionable efficacy of the key vector control activities. In this study, we assessed the status and risk of Leishmania donovani transmission based on entomological indicators including seasonality, natural Leishmania infection rate and feeding behavior of vector sand flies, Phlebotomus argentipes, in three districts that had received disease control interventions in the past several years in the context of the disease elimination effort. METHODS: We selected two epidemiologically contrasting settings in each survey district, one village with and one without reported VL cases in recent years. Adult sand flies were collected using CDC light traps and mouth aspirators in each village for 12 consecutive months from July 2017 to June 2018. Leishmania infection was assessed in gravid sand flies targeting the small-subunit ribosomal RNA gene of the parasite (SSU-rRNA) and further sequenced for species identification. A segment (~ 350 bp) of the vertebrate cytochrome b (cytb) gene was amplified from blood-fed P. argentipes from dwellings shared by both humans and cattle and sequenced to identify the preferred host. RESULTS: Vector abundance varied among districts and village types and peaks were observed in June, July and September to November. The estimated Leishmania infection rate in vector sand flies was 2.2% (1.1%-3.7% at 95% credible interval) and 0.6% (0.2%-1.3% at 95% credible interval) in VL and non-VL villages respectively. The common source of blood meal was humans in both VL (52.7%) and non-VL (74.2%) villages followed by cattle. CONCLUSIONS: Our findings highlight the risk of ongoing L. donovani transmission not only in villages with VL cases but also in villages not reporting the presence of the disease over the past several years within the districts having disease elimination efforts, emphasize the remaining threats of VL re-emergence and inform the national program for critical evaluation of disease elimination strategies in Nepal.

Transmission of Leishmania donovani in the Hills of Eastern Nepal, an Outbreak Investigation in Okhaldhunga and Bhojpur Districts.

BACKGROUND: In the Indian subcontinent, Visceral leishmaniasis is endemic in a geographical area coinciding with the Lower Gangetic Plain, at low altitude. VL occurring in residents of hill districts is therefore often considered the result of Leishmania donovani infection during travel. Early 2014 we conducted an outbreak investigation in Okhaldhunga and Bhojpur districts in the Nepal hills where increasing number of VL cases have been reported. METHODOLOGY/PRINCIPAL FINDINGS: A house-to-house survey in six villages documented retrospectively 35 cases of Visceral Leishmaniasis (VL). Anti-Leishmania antibodies were found in 22/23 past-VL cases, in 40/416 (9.6%) persons without VL and in 12/155 (7.7%) domestic animals. An age- and sex- matched case-control study showed that exposure to known VL-endemic regions was no risk factor for VL, but having a VL case in the neighbourhood was. SSU-rDNA PCR for Leishmania sp. was positive in 24 (5%) of the human, in 18 (12%) of the animal samples and in 16 (14%) bloodfed female Phlebotomus argentipes sand flies. L. donovani was confirmed in two asymptomatic individuals and in one sand fly through hsp70-based sequencing. CONCLUSIONS/SIGNIFICANCE: This is epidemiological and entomological evidence for ongoing local transmission of L. donovani in villages at an altitude above 600 meters in Nepal, in districts considered hitherto non-endemic for VL. The VL Elimination Initiative in Nepal should therefore consider extending its surveillance and control activities in order to assure VL elimination, and the risk map for VL should be redesigned.

Feasibility of a combined camp approach for vector control together with active case detection of visceral leishmaniasis, post kala-azar dermal leishmaniasis, tuberculosis, leprosy and malaria in Bangladesh, India and Nepal: an exploratory study.

BACKGROUND: We assessed the feasibility and results of active case detection (ACD) of visceral leishmaniasis (VL), post kala-azar dermal leishmaniasis (PKDL) and other febrile diseases as well as of bednet impregnation for vector control. METHODS: Fever camps were organized and analyzed in twelve VL endemic villages in Bangladesh, India, and Nepal. VL, PKDL, tuberculosis, malaria and leprosy were screened among the febrile patients attending the camps, and existing bednets were impregnated with a slow release insecticide. RESULTS: Among the camp attendees one new VL case and two PKDL cases were detected in Bangladesh and one VL case in Nepal. Among suspected tuberculosis cases two were positive in India but none in the other countries. In India, two leprosy cases were found. No malaria cases were detected. Bednet impregnation coverage during fever camps was more than 80% in the three countries. Bednet impregnation led to a reduction of sandfly densities after 2 weeks by 86% and 32%, and after 4 weeks by 95% and 12% in India and Nepal respectively. The additional costs for the control programmes seem to be reasonable. CONCLUSION: It is feasible to combine ACD camps for VL and PKDL along with other febrile diseases, and vector control with bednet impregnation.

Insecticide-treated bed nets in rural Bangladesh: their potential role in the visceral leishmaniasis elimination programme.

OBJECTIVE: To analyse the feasibility, acceptability and effectiveness of insecticide-treated bed nets with slow-release insecticides (KO Tab 123) as an option for kala-azar vector management in Bangladesh. METHODS: Intervention study involving an insecticide dipping programme through village health workers supervised by public health officers covering 6967 households in Mymensingh and 8287 in Rajshahi district. In a subsample of households, sandfly densities at baseline, 1, 12 and 18 months were measured with CDC light traps both in intervention and control areas. Bioassays were performed for determining the bioavailability of the insecticide and tests of chemical residues in the treated bed nets were undertaken. Satisfaction surveys and direct observation of use of treated bed net use were conducted. RESULTS: The dipping programme was feasible with the help of communities and public health staff, was well accepted, reached a coverage of 98.2% and 96.2% in the two study sites within 4 weeks and was effective in terms of a significant reduction in sandfly densities (approximately 60%) for a period of 18 months. Bioassay results were satisfactory (>80% sandfly mortality) and the average chemical content of the treated bed nets was sufficient for killing sand flies at the end of the observation period. CONCLUSION: Bed nets treated with slow-release insecticides can be an important complementary measure for sandfly control in the visceral leishmaniasis elimination programme.

Epidemiology of Leishmania donovani infection in high-transmission foci in Nepal.

OBJECTIVE: Nepal reports a visceral leishmaniasis (VL) incidence of 5 per 10 000 per year on the basis of notification by health facilities, but little community-based epidemiological information exists. We report data on prevalence rates of Leishmania donovani infection in ten communities in East Nepal. METHODS: Ten clusters with highest VL incidence rates were purposefully selected in Nepal. All households were mapped and socio-demographic data and data on past VL incidence were collected. An exhaustive serological survey was performed of individuals aged >2 years, by collecting finger prick blood on filter paper in November-December 2006. The samples were tested by direct agglutination, and a titre >or=1:1600 was taken as marker of infection. A generalized estimating equation (GEE) model was used to assess risk factors for Direct Agglutination Test (DAT) positivity taking into account the clustering at household and village level. RESULTS: The sero-survey (n = 5397) showed an infection prevalence rate of 9%, (range 5-15% per cluster) with higher prevalence in men (9.9%) than in women (8.3%) (P = 0.049). Male gender, increasing age and poverty were significant risk factors in the final GEE model. CONCLUSION: Leishmania infection rate in high-transmission areas in Nepal is associated with gender, age and socio-economic status.

Effect of village-wide use of long-lasting insecticidal nets on visceral Leishmaniasis vectors in India and Nepal: a cluster randomized trial.

BACKGROUND: Visceral leishmaniasis (VL) control in the Indian subcontinent is currently based on case detection and treatment, and on vector control using indoor residual spraying (IRS). The use of long-lasting insecticidal nets (LN) has been postulated as an alternative or complement to IRS. Here we tested the impact of comprehensive distribution of LN on the density of Phlebotomus argentipes in VL-endemic villages. METHODS: A cluster-randomized controlled trial with household P. argentipes density as outcome was designed. Twelve clusters from an ongoing LN clinical trial--three intervention and three control clusters in both India and Nepal--were selected on the basis of accessibility and VL incidence. Ten houses per cluster selected on the basis of high pre-intervention P. argentipes density were monitored monthly for 12 months after distribution of LN using CDC light traps (LT) and mouth aspiration methods. Ten cattle sheds per cluster were also monitored by aspiration. FINDINGS: A random effect linear regression model showed that the cluster-wide distribution of LNs significantly reduced the P. argentipes density/house by 24.9% (95% CI 1.80%-42.5%) as measured by means of LTs. INTERPRETATION: The ongoing clinical trial, designed to measure the impact of LNs on VL incidence, will confirm whether LNs should be adopted as a control strategy in the regional VL elimination programs. The entomological evidence described here provides some evidence that LNs could be usefully deployed as part of the VL control program. TRIAL REGISTRATION: ClinicalTrials.gov CT-2005-015374.

Chemical and environmental vector control as a contribution to the elimination of visceral leishmaniasis on the Indian subcontinent: cluster randomized controlled trials in Bangladesh, India and Nepal.

BACKGROUND: Bangladesh, India and Nepal are working towards the elimination of visceral leishmaniasis (VL) by 2015. In 2005 the World Health Organization/Training in Tropical Diseases launched an implementation research programme to support integrated vector management for the elimination of VL from Bangladesh, India and Nepal. The programme is conducted in different phases, from proof-of-concept to scaling up intervention. This study was designed in order to evaluate the efficacy of the three different interventions for VL vector management: indoor residual spraying (IRS); long-lasting insecticide treated nets (LLIN); and environmental modification (EVM) through plastering of walls with lime or mud. METHODS: Using a cluster randomized controlled trial we compared three vector control interventions with a control arm in 96 clusters (hamlets or neighbourhoods) in each of the 4 study sites: Bangladesh (one), India (one) and Nepal (two). In each site four villages with high reported VL incidences were included. In each village six clusters and in each cluster five households were randomly selected for sand fly collection on two consecutive nights. Control and intervention clusters were matched with average pre-intervention vector densities.In each site six clusters were randomly assigned to each of the following interventions: indoor residual spraying (IRS); long-lasting insecticide treated nets (LLIN); environmental management (EVM) or control. All the houses (50-100) in each intervention cluster underwent the intervention measures. A reduction of intra-domestic sand fly densities measured in the study households by overnight US Centres for Disease Prevention and Control light trap captures (that is the number of sand flies per trap per night) was the main outcome measure. RESULTS: IRS, and to a lesser extent EVM and LLINs, significantly reduced sand fly densities for at least 5 months in the study households irrespective of type of walls or whether or not people shared their house with cattle. IRS was effective in all sites but LLINs were only effective in Bangladesh and India. Mud plastering did not reduce sand fly density (Bangladesh study); lime plastering in India and one Nepali site, resulted in a significant reduction of sand fly density but not in the second Nepali site. CONCLUSION: Sand fly control can contribute to the regional VL elimination programme; IRS should be strengthened in India and Nepal but in Bangladesh, where vector control has largely been abandoned during the last decades, the insecticide treatment of existing bed nets (coverage above 90% in VL endemic districts) could bring about an immediate reduction of vector populations; operational research to inform policy makers about the efficacious options for VL vector control and programme performance should be strengthened in the three countries.

Population preference of net texture prior to bed net trial in Kala-Azar-endemic areas.

Prior to a community-based efficacy trial of long-lasting insecticidal nets (LLINs) in the prevention of visceral leishmaniasis (VL; also called kala-azar), a pilot study on preference of tools was held in endemic areas of India and Nepal in September 2005.LLINs made of polyester and polyethylene were distributed to 60 participants, who used the nets sequentially for 7 d. Acceptability and preference were evaluated via indirect indicators through questionnaires at three defined time points before and after use of the LLINs and through focus group discussions (FGDs). In the latter, preferences for color and size were also assessed. Untreated bed nets were owned by 87% of the households prior to the study. All users liked textures of both LLIN types after 7 d of use, but had a slight preference for those made of polyester if they were to recommend a LLIN to relatives or friends (p<0.05), mainly because of their relatively greater softness in comparison to polyethylene LLINs. Users reported that both net types reduced mosquito bites and number of insects, including sand fly (bhusana; genus Phlebotomus), inside the house. Side effects were minor and disappeared quickly.The large-scale intervention trial considered the preferences of the study population to decide on the best tool of intervention--light-blue, rectangular, polyester LLINs of different sizes.

Prevalence of Shigella species and their antimicrobial resistance patterns in Eastern Nepal.

The study was conducted to determine the prevalence of Shigella species and their antimicrobial resistance patterns in eastern Nepal. Stool samples submitted to the diagnostic laboratory of B.P. Koirala Institute of Health Sciences, Nepal, during August 2000-July 2004, were cultured for Shigella species and were confirmed by biochemical and serological tests. Of 53 Shigella species isolated, Shigella dysenteriae type 1 was the most predominant isolate (73.7%), followed by S. flexneri (23%) and S. boydii (4%). The majority (79%) of Shigella species were isolated from children aged less than five years. An overall high resistance was observed for trimethoprim-sulphamethoxazole, ampicillin, nalidixic acid, mecillinam, and ciprofloxacin. There was a statistically significant (p < 0.001) increasing trend in the prevalence of ciprofloxacin resistance in S. dysenteriae type 1. The results suggest reconsideration of the empiric use of these antimicrobial agents for shigellosis. A further study is required to evaluate additional antimicrobial agents.