Abstract
Visceral Leishmaniasis (VL) is a disseminated protozoan infection caused by Leishmania donovani that affects almost half a million people annually. In Northern Ethiopia, VL is common in migrant agricultural laborers returning from the lowland sesame fields of Metema and Humera. Recent VL foci have emerged in resident rural populations near the town. In the current study, we evaluate multilevel entomological, epidemiological and ecological factors associated with infection and disease through fine-scale eco-epidemiological analyses in three villages. Satellite images showed that villages constructed in or close to vertisols, were likely to become endemic for VL. Vertisols or black-cotton soil, are characterized by high contents of smectitic clay minerals, which swell when hydrated and shrink upon desiccation, causing extensive deep cracking during the dry season. The population densities of Phlebotomus orientalis, the vector, were negatively correlated with distance from vertisols and persons living close to vertisols were more likely to be bitten by sand flies, as evidenced by sero-positivity to Ph. orientalis saliva. Apparent (albeit non-significant) clustering of VL cases and abundant asymptomatic infections close to vertisols, suggest anthroponotic transmission around houses located close to vertisols. Comparable rates of male and female volunteers, mostly under 15 years of age, were infected with L. donovani but a significantly higher proportion of males succumbed to VL indicating a physiological gender-linked male susceptibility. Our data suggest that the abundant infected persons with high parasitemias who remain asymptomatic, may serve as reservoir hosts for anthroponotic transmission inside villages. Only limited insights on the transmission dynamics of L. donovani were gained by the study of environmental factors such as presence of animals, house structure and vegetation cover.
Highlights
Visceral leishmaniasis (VL), known as Kala-Azar, is a vectorborne parasitic disease caused by protozoan parasites of the Leishmania donovani (Kinetoplastida: Trypanosomatidae) species complex and transmitted by blood-sucking phlebotomine sand flies (Diptera, Psychodidae)
We conducted studies in a relatively new focus of VL in the Tahtay Adiyabo district of northern Ethiopia, where VL presumably emerged due to mass influx of agricultural workers returning from the endemic regions of Humera and Metema
The proportion of asymptomatic infections was markedly higher in Salamo compared with Erdwayane and Dedevit (Table 1)
Summary
Visceral leishmaniasis (VL), known as Kala-Azar, is a vectorborne parasitic disease caused by protozoan parasites of the Leishmania donovani (Kinetoplastida: Trypanosomatidae) species complex and transmitted by blood-sucking phlebotomine sand flies (Diptera, Psychodidae). It is a systemic disease of the bone marrow, spleen and liver that primarily affects cells of the reticuloendothelial system (Alvar et al, 2012). VL is endemic in 98 countries with some 200 million people at risk, 200–500 thousand new cases and 20- 40 thousand fatalities annually (Alvar et al, 2012). Over 90% of the cases occur in six countries: India, Bangladesh, Nepal, Sudan, Ethiopia and Brazil (Chappuis et al, 2007)
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