Imagine a parasite circulating actively in a community, infecting dogs, spreading through insect vectors, moving between multiple species—and no one notices. Not because people aren’t looking, but because traditional disease surveillance only watches clinical cases in humans, missing the invisible circulation happening all around them. Research on emerging zoonotic diseases confirms this dynamic is not unique to Honduras, it reflects a global risk intensified by urbanization and climate change. Read more about this in our Promega Connections blog (2).
What parasite is Leishmania?
Leishmania is a parasite transmitted by female sand flies, endemic in 90 countries across Asia, Africa, the Americas and Southern Europe. The parasite causes both visceral (systemic, potentially fatal) and cutaneous leishmaniasis (characterized by ulcerative or non-ulcerative skin lesions). More than 20 species of the genus Leishmania can cause infection, including L. infantum (3).
In the Americas alone, there are an estimated 4,500–6,800 cases annually of leishmaniasis. The disease disproportionately affects impoverished communities in tropical regions where earthen walls, outdoor sleeping, and limited vector control create ideal conditions for transmission (3).
While Leishmania is primarily transmitted to humans through sand fly bites, dogs are widely considered the primary domestic reservoir for the parasite. However, evidence regarding their exact role in transmission remains inconsistent. Some studies suggest asymptomatic dogs act as secondary vectors, while others demonstrate they efficiently transmit the infection. This knowledge gap is precisely why understanding which animals harbor the infection and how they contribute to ongoing transmission is critical for designing effective control strategies (1).
What happens when disease surveillance only looks for clinical cases in humans?
Here is the paradox: Ojos de Agua, Honduras, a rural community of 1,100 inhabitants with a documented history of leishmaniasis, had zero active clinical cases when researchers arrived in 2023. No humans with symptoms. No visible lesions. But the absence of clinical cases does not mean the absence of risk.
In Latin America, leishmaniasis is a well-known occupational hazard for military personnel deployed in endemic areas. A Peruvian military training outbreak in the Amazon basin resulted in a 25% attack rate (1). The question for Honduras: was the parasite still circulating, undetected?
How does a research team design a study to detect what traditional surveillance would never find?
The answer lies in a One Health approach, an integrated methodology that recognizes human, animal, and vector health are interdependent. Rather than monitoring each separately, they implemented integrated surveillance capturing the full transmission cycle—humans, animals, and vectors—all at once.
In August 2023, researchers deployed CDC light traps in intradomestic and peridomestic areas (where animals sleep, near latrines), collecting 644 sand flies over five nights. Simultaneously, they evaluated 43 dogs clinically and extracted blood samples. Critically: they searched for the parasite in three places at once—human blood samples, dogs, and sand flies—while traditional surveillance waits for a clinical case.
Using Wizard® Genomic DNA Purification Kit for high-quality DNA extraction from complex samples, PCR amplification with Promega Master Mix 2X enabled detection of Leishmania in clinical samples and sand flies, and revealed the blood meal sources in sand flies. DNA sequencing subsequently confirmed the species as L. infantum.
What do the numbers mean?
Among 644 sand fly specimens, Lutzomyia longipalpis predominated, and L. infantum DNA was detected in two species: Lu. longipalpis and Pintomyia evansi. Of 64 blood-fed females screened by PCR, 14.1% (9/64) had detectable L. infantum DNA. Of 43 dogs, 23.2% (10/43) tested PCR-positive for L. infantum, and 18.6% (8/43) were seropositive for Leishmania spp.
But here’s what matters: of the 10 PCR-positive dogs, only two showed clinical signs consistent with canine leishmaniasis. The remaining eight showed no apparent clinical manifestations, and clinical examination alone would have missed them. And the humans: zero active cases. Yet human blood was identified in both vector species, and in every Pi. evansi specimen analyzed. Together, these findings point to the potential establishment of a peridomestic transmission cycle.
Why does this matter?
In zoonotic transmission cycles, canine infections frequently precede human cases. Canine leishmaniasis hadn’t been widely documented in central Honduras, so finding 23% PCR-positive dogs suggests canine infection may occur even in areas not previously recognized as endemic. Dogs are widely considered the primary domestic reservoir of L. infantum, although their exact role in transmission is still debated. In this study, no dog blood was detected in the sand flies analyzed. That’s precisely why monitoring parasites where humans, animals, and vectors overlap matters: it can detect cross-species transmission before human disease becomes clinically apparent.
The Honduras study proved it’s possible. The question is: who will implement it next?
How Promega Supports One Health – The One Health approach recognizes that human, animal, and environmental health are deeply connected. At Promega, we support this integrated perspective by providing sensitive, reliable technologies that enable early detection, tracking, and mitigation of zoonotic diseases. From sample prep to detection, our tools are designed to help scientists, veterinarians, and public health professionals work across disciplines to protect communities.
Explore how Promega enables One Health Solutions >>
Summary
This study detected Leishmania infantum DNA in sand flies and dogs in Ojos de Agua, Honduras. The findings indicate active circulation of the parasite and support the potential establishment of a peridomestic transmission cycle. PCR screening identified L. infantum DNA in 14.1% (9/64) of blood-fed female sand flies and 23.2% (10/43) of dogs. Eight of the ten PCR-positive dogs showed no apparent clinical signs. These findings demonstrate why One Health surveillance, integrating molecular diagnostics across species, is critical for early detection of emerging zoonotic disease patterns before they reach human populations.
Additional Resources
For more information consider viewing our webinar (on-demand): Unmasking Emerging Parasites: Diagnostics for One Health Surveillance.
Citations
- Alcántara-Henríquez E. et al. (2026) Detection of Leishmania infantum DNA in Sand Flies and Assessment of Zoonotic Transmission Risk in Central Honduras: A One Health Approach. Tropical Medicine and Infectious Disease. 11, 219. DOI:10.3390/tropicalmed11080219
- Arduengo M. (2025) What Shelter Dogs Can Tell Us About Emerging Zoonotic Diseases. Promega Connections. https://www.promegaconnections.com/what-shelter-dogs-can-tell-us-about-emerging-zoonotic-diseases/
- Pareyn M, Alves F, Burza S, Chakravarty J, Alvar J, Diro E, Kaye PM, van Griensven J. (2025) Leishmaniasis. Nat Rev Dis Primers. Nov 20;11(1):81. doi: 10.1038/s41572-025-00663-w.
Teresa Simon
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