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Revisiting the largest human leishmaniasis outbreak in Western Europe (Madrid, Spain): a follow-up entomological
José Risueño1, Elena Verdú-Serrano1, Matranga Alessandra1,2
1Facultad de Veterinaria, Departamento de Sanidad Animal, Campus de Espinardo, Regional Campus of International Excellence 'Campus Mare Nostrum', Universidad de Murcia, Espinardo, 30100, Murcia, Spain.
Background:
During the 2010s, Madrid experienced an outbreak of human leishmaniasis by Leishmania infantum, which affected at least 824 people until 2024 and peaked between 2010 and 2012. It was associated with a high density of infected Phlebotomus perniciosus sand fly vectors and, unusually, with rabbits and hares as the primary parasite reservoirs. In 2023 and 2024 we investigated sand fly species distribution, L. infantum infection rates, and bloodmeal sources in the outbreak area and compared the results with a similar study conducted in 2012-2014.
Methods:
The four sand fly surveillance sites used in 2012-2014 were revisited monthly between April and November 2023 and 2024. Sand flies were collected using CDC light traps and morphologically identified. Leishmania spp. infection and bloodmeal sources in female sand flies were molecularly tested.
Results:
In total, 5429 sand flies (2542 in 2023 and 2887 in 2024, 39% female) were collected, peaking in August and September. Overall, 72% of the captures were of P. perniciosus, 28% Sergentomyia minuta, < 1% Phlebotomus ariasi, and < 1% Phlebotomus langeroni. Leishmania infantum was confirmed in P. perniciosus and the estimated infection prevalence (95% CL) was 10% (7-13%). Blood sources of P. perniciosus were 80% (n = 51) rabbits, 11% (n = 7) humans, 6% (n = 4) hares, and 3% (n = 2) cats. Overall, 25%, 20%, and 19% of sand flies containing hare, human, and rabbit blood were Leishmania PCR-positive, respectively. The annual density of P. perniciosus in 2023-2024 was approximately half that observed in 2012 and comparable to levels in 2013 and 2014. In both 2012-2014 and 2023-2024 studies, L. infantum infection rates in P. perniciosus were similar, and lagomorphs accounted for most bloodmeals.
Conclusions:
Although the number of human leishmaniasis cases and the population of hares have been drastically reduced in the outbreak area, P. perniciosus densities and L. infantum infection rates in 2023-2024 in the sampling sites remain like those in 2012-2014; rabbits persist as a major bloodmeal source and probable reservoir of infection, maintaining human exposure to infected vectors. These results underscore the importance of sustained sand fly surveillance in this hotspot to inform public health decision-making and guide targeted control strategies.
