Abstract
BackgroundVisceral leishmaniasis (VL) is a predominantly rural disease, common in the low lands of eastern Nepal. Since 1997 VL cases have also been reported among residents of the city of Dharan. Our main research objective was to find out whether there had been local transmission of VL inside the city.MethodsWe conducted an outbreak investigation including a case–control study; cases were all urban residents treated for VL between 2000 and 2008 at BP Koirala Institute of Health Sciences, a university hospital in the city. For each case, we selected four random controls, with no history of previous VL; frequency-matched for age. Cases and controls were subjected to a structured interview on the main exposures of interest and potential confounders; a binominal multilevel model was used to analyze the data. We also collected entomological data from all neighborhoods of the city.ResultsWe enrolled 115 VL patients and 448 controls. Cases were strongly clustered, 70% residing in 3 out of 19 neighborhoods. We found a strong association with socio-economic status, the poorest being most at risk. Housing was a risk factor independent from socio-economic status, most at risk were those living in thatched houses without windows. ‘Sleeping upstairs’ and ‘sleeping on a bed’ were strongly protective, OR of 0.08 and 0.25 respectively; proximity to a case was a strong risk factor (OR 3.79). Sand flies were captured in all neighborhoods; in collections from several neighborhoods presence of L. donovani could be demonstrated by PCR.ConclusionThe evidence found in this study is consistent with transmission of anthroponotic VL within the city. The vector P. argentipes and the parasite L. donovani have both been identified inside the town. These findings are highly relevant for policy makers; in VL endemic areas appropriate surveillance and disease control measures must be adopted not only in rural areas but in urban areas as well.
Highlights
Visceral leishmaniasis (VL) is a predominantly rural disease, common in the low lands of eastern Nepal
VL is mainly caused by Leishmania donovani and its transmission is assumed anthroponotic through the bite of the sand fly species Phlebotomus argentipes [1]
Those recent immigrants could have been infected with L. donovani outside Dharan town, but there is a definite concern about the possibility of local transmission of L. donovani in the urban/suburban area for several reasons
Summary
Visceral leishmaniasis (VL) is a predominantly rural disease, common in the low lands of eastern Nepal. Since 1997 VL cases have been reported among urban residents in the town of Dharan. The historic town centre is surrounded by suburban residential areas of recent legal settlers as well as slum areas, where displaced people have moved in at high speed over the past ten years - during the civil conflictseeking safety and job opportunities. Those recent immigrants could have been infected with L. donovani outside Dharan town, but there is a definite concern about the possibility of local transmission of L. donovani in the urban/suburban area for several reasons. Sharing of needles by IDUs could shift the mode of transmission of VL [16] and was the basis for previous outbreaks in Europe [17]
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