Screening for visceral leishmaniasis in humans and animals in Laos

Visceral leishmaniasis (VL) is a vector-borne protozoan disease with a global distribution, with higher rates of infection associated with HIV. Zoonotic species of Leishmania have also been reported infecting domestic animals. Reports of VL are increasing in Southeast Asia, with over 200 cases reported in Thailand since the first autochthonous case in 1999, and recently the first patients have been reported from Vietnam and Cambodia. However, no cases of VL have been reported from Lao PDR (Laos) and clinical awareness of the disease is limited. This study aimed to investigate whether Leishmania is circulating in Laos by screening people living with HIV, stored samples from unselected patients with fever, and ruminants taken to abattoirs.

People living with HIV from two specialist units in Vientiane Capital had EDTA blood taken and DNA extracted and tested for Leishmania by nested-PCR. Stored serum samples from patients presenting to Mahosot Hospital with fever and without known HIV infection, as well as serum from goats, cows and buffalo taken to abattoirs in four provinces in Laos were tested for Leishmania using the InBios Kalazar Detect Rapid Test.

There were 1015 people living with HIV tested between 2021 and 2024 for Leishmania by nested-PCR, all of whom were negative. Of 511 human serum samples collected between 2005 and 2023, two (0.4%) tested positive by rapid test. These samples were identified as coming from the same patient, with samples taken 10 months apart. There were 5/159 (3.1%) ruminant serum samples positive by rapid test with 3/45 (6.7%) buffalo positive, 2/47 (4.3%) goat positive and 0/67 cows positive.

This study suggests Leishmania may be circulating in Laos with undetected cases. Further investigation is needed to confirm the findings, determine at-risk populations and increase clinical awareness of the disease. This study expands on the current regional knowledge on leishmaniasis and shows the need for further epidemiological studies.