One Health investigation of a human visceral leishmaniasis case in western Portugal

Problem

Visceral leishmaniasis (VL) is a rare but potentially fatal zoonosis endemic in southern Europe. It is transmitted by phlebotomine sand flies, with dogs as primary reservoir. Although human VL is a notifiable disease in Portugal, canine VL is not, which limits baseline surveillance.

Description of the problem

In July 2024 a middle-age male outdoor worker presented at a clinic with 10 weeks of fever, weight loss, splenomegaly and hepatomegaly. He was referred to urgent care and subsequently hospitalized and diagnosed with VL. Following notification of the case, the Public Health Unit of West Local Health Unit in Portugal initiated a multidisciplinary epidemiological investigation which covered the period between November 2023 and August 2024. It followed a One Health approach and included patient interview, occupational and environmental field assessment, veterinary inquiry, entomological trapping and laboratory confirmation of the human case at the National Reference Laboratory.

Results

The case was laboratory-confirmed. Appropriate treatment resulted in clinical improvement. Probable site of infection was the patient’s rural residential area, characterized by free-roaming dogs and nearby livestock farming. Sand fly traps (REVIVE program) yielded 13 phlebotomine sand flies, all of which tested negative for Leishmania. A local veterinary clinic reported a perceived increase in canine VL cases. No secondary human cases were identified. Risk was assessed as low (ECDC/UKHSA frameworks).

Lessons

Multi-agency One Health coordination enabled a comprehensive and proportionate response. The absence of mandatory canine VL notification is a surveillance gap shared across Southern Europe, although its endemic state might partly explain this. Diagnostic delay is common in low-incidence diseases but highlights the need for improved clinician awareness in endemic-adjacent settings. Existing REVIVE infrastructure can be rapidly activated for entomological investigation.

Key messages

• A structured One Health investigation of the first confirmed human visceral leishmaniasis case in the West region of Portugal since 2020 showed low community risk but critical surveillance gaps.

• Integrating human, animal, and entomological data into a single response enables proportionate risk assessment for vector-borne diseases in low-incidence settings.