Incidence of Human and Free-Ranging Wild Rodent Infections with Leishmania ( Viannia ) braziliensis , Aetiological Agent of Cutaneous Leishmaniasis.

BACKGROUND: Human and wild rodent infection rates with Leishmania ( Viannia ) braziliensis are needed to differentiate transmission pathways in anthropogenically altered habitats.

METHODS: Human participants in northeast Brazil were tested by the leishmanin skin test (LST) and inspected for lesions/scars characteristic of American clinical leishmaniasis (ACL). Molecular (PCR/qPCR) test records of free-ranging rodents were available from a concurrent capture-mark-recapture study. Force of Infection (λ) and recovery (ρ) rates were estimated from cross-sectional and longitudinal datasets.

RESULTS: Cumulative prevalences of human LST+ves and ACL scar+ves were 0.343-0.563 ( n = 503 participants) and 0.122-0.475 ( n = 503), respectively. Active ACL lesions were not detected. Annual rates of LST conversions were λ = 0.03-0.15 and ρ = 0.02-0.07. The probability of infection was independent of sex and associated with increasing age in addition to the period of exposure. Rodents ( n = 596 individuals of 6 species) showed high rates of exclusively asymptomatic infection (λ = 0.222/month) and potential infectiousness to the sand fly vector. Spatially concurrent rodent and household human infection prevalences were correlated.

CONCLUSIONS: Human exposure to L. ( V. ) braziliensis continues to be high despite the substantial drop in reported ACL cases in recent years. Spill-over transmission risk to humans from rodents in peridomestic habitats is likely supported by a rodent infection/transmission corridor linking houses, plantations, and the Atlantic Forest.