A veterinary discovery with significant implications for animal and public health
In the sun-drenched landscapes of Brazil's northeastern Sergipe state, a quiet discovery has veterinary scientists and public health experts taking notice. For the first time, horses in this region have been diagnosed with leishmaniosis, a parasitic disease that threatens both animal and human health across the Americas. This finding represents more than just a local veterinary concern—it reveals the steady expansion of a serious zoonotic disease into new territories, suggesting that our understanding of how this parasite moves and spreads may need reconsideration.
Horses in Sergipe showing clinical signs of leishmaniosis represent a new frontier in disease surveillance.
The zoonotic nature of leishmaniosis means animal cases can signal increased risk to human populations.
Leishmaniosis is not a single disease but a collection of related conditions caused by protozoan parasites from the Leishmania genus. These microscopic invaders are transmitted through the bites of infected sandflies—tiny insects that serve as the perfect delivery system for the parasite. When an infected sandfly takes a blood meal, it passes the parasites into its host's bloodstream, beginning a complex biological journey that can manifest in different ways depending on the parasite species and the host's immune response.
Affects internal organs and can be fatal if untreated. Primarily caused by L. infantum in Brazil 1 .
Causes skin sores and ulcers that can lead to permanent scarring. Often caused by L. braziliensis.
| Species | Disease Form | Geographic Distribution | Primary Reservoirs |
|---|---|---|---|
| L. infantum | Visceral | Throughout Brazil, Mediterranean basin | Dogs, wild carnivores |
| L. braziliensis | Cutaneous | South and Central America | Rodents, forest mammals |
| L. martiniquensis | Cutaneous | Caribbean, Central Europe, Southeast Asia | Unknown, possibly horses |
What makes leishmaniosis particularly challenging is its complex transmission cycle, which often involves multiple animal species serving as reservoirs where the parasite can maintain a population even without infecting humans.
The journey to discovering leishmaniosis in Sergipe's equine population began with careful observation. Veterinarians noticed horses presenting with subtle but concerning clinical signs: skin lesions, nodules on various body parts, and in some cases, generalized symptoms like weight loss and lethargy. These manifestations align with reports from other regions where equine leishmaniosis has been documented, including cases of mixed infections where horses carried multiple Leishmania species simultaneously 1 .
| Clinical Sign | Frequency | Common Locations | Duration |
|---|---|---|---|
| Skin nodules | Common | Head, neck, legs | Weeks to months |
| Ulcerated lesions | Variable | Muzzle, ears, genital areas | Persistent without treatment |
| Lymphadenopathy | Occasional | Near affected skin areas | Variable |
| Weight loss | Rare in uncomplicated cases | - | Progressive |
| Asymptomatic infection | Very common | - | Indefinite |
Documenting nature and distribution of skin lesions
Detecting antibodies against Leishmania parasites
Using PCR to identify parasite DNA
Uncovering leishmaniosis in a new location requires sophisticated diagnostic tools that can detect the parasite even when infections are subtle or asymptomatic. The field investigation of equine leishmaniosis relies on a combination of field and laboratory techniques that together create a complete picture of disease presence and spread.
| Reagent/Technique | Primary Function | Application in Leishmaniosis Research |
|---|---|---|
| ELISA Test Systems | Detect anti-Leishmania antibodies | Screening of horse populations for exposure |
| PCR Master Mixes | Amplify parasite DNA | Confirm active infection, identify species |
| IFAT Antigen Slides | Visualize antibody binding | Reference test for serological confirmation |
| DNA Extraction Kits | Isolate genetic material | Prepare samples for molecular analysis |
| Culture Media | Grow live parasites | Isolate strains for further characterization |
The diagnostic journey typically begins with serological screening using tests like ELISA (Enzyme-Linked Immunosorbent Assay) or IFAT (Indirect Fluorescent Antibody Test). These methods detect antibodies that the horse's immune system has produced against the Leishmania parasite, indicating exposure. In studies from similar Brazilian regions, seroprevalence in horses has ranged from 14.3% to as high as 47.9% in some populations 4 6 .
For confirmed cases, researchers turn to molecular methods, particularly Polymerase Chain Reaction (PCR) tests that target specific regions of the parasite's DNA. The kinetoplast DNA (kDNA) is a favorite target because it presents in high copy numbers within each parasite, making it exceptionally sensitive.
PCR tests targeting kDNA provide high sensitivity for detecting even low-level infections.
The discovery of leishmaniosis in Sergipe's horses is not an isolated phenomenon but part of a larger pattern of geographic expansion being observed across the globe. While the disease has been recognized in horses in Brazil since the mid-20th century, its detection in new states like Sergipe highlights its ongoing spread into previously unaffected regions.
This expansion isn't limited to South America. In Central Europe, previously considered non-endemic for leishmaniosis, cases of Leishmania martiniquensis have been reported in horses from the Czech Republic and Austria 3 . Similarly, Panama has documented its first cases of L. martiniquensis in horses, indicating a wider distribution of this species than previously recognized 5 9 .
Sergipe state joins the growing list of Brazilian regions reporting equine leishmaniosis cases.
Rising temperatures may expand the suitable habitat for sandfly vectors.
Deforestation and agricultural expansion bring animals and humans into closer contact with wild reservoirs.
Better detection methods may be revealing previously unrecognized infections.
Perhaps most significantly, research increasingly suggests that horses may play a more important role in the transmission cycle than previously appreciated. Studies have detected Leishmania DNA in sandflies that have fed on horses 7 , demonstrating that infected equines can potentially serve as infection sources for vectors that may then transmit the parasite to humans or other animals.
This concept of horses as "silent reservoirs" is particularly concerning from a public health perspective. Since many infected horses show minimal or no symptoms, they can maintain and spread the parasite without detection, complicating control efforts that traditionally focus on dogs as the primary reservoir.
The detection of equine leishmaniosis in Sergipe represents more than just a new pin on the map of disease distribution—it serves as a powerful reminder of the interconnectedness of human, animal, and environmental health. The expansion of this disease into new territories underscores the dynamic nature of infectious diseases in a changing world and highlights the importance of vigilant surveillance.
From a public health perspective, the findings from Sergipe reinforce the need for a "One Health" approach that integrates human, animal, and environmental health monitoring. Since horses often live in close proximity to human settlements and may serve as indicators of parasite circulation, their inclusion in surveillance programs could provide early warning of increased transmission risk to humans.
For horse owners and veterinarians, the key takeaways are practical: leishmaniosis should be considered in the differential diagnosis of skin lesions in horses, particularly in regions where human or canine cases have been reported. Simple protective measures, such as the use of ectoparasiticides approved for sandfly control and stabling animals during peak sandfly activity times (dusk to dawn), may reduce transmission risk 6 .
As research continues, important questions remain about the precise role horses play in the transmission cycle and why some animals develop disease while others remain asymptomatic. What is clear is that the first report of equine leishmaniosis in Sergipe is unlikely to be the last, as this parasitic disease continues its quiet expansion across new territories.
References will be listed here in the final publication.