Small Ruminants and Leishmaniasis: An Overlooked Potential Reservoir?

Leishmaniasis is a vector-borne zoonosis caused by various species of the genus Leishmania.

In Europe, Leishmania infantum is the most commonly identified species, and its spread occurs through various species of sandflies.

LEISHMANIA LIFE CYCLE: FROM SANDFLY TO MAMMALIAN HOST

Leishmania spp. is a parasite with a biphasic life cycle that develops in two types of hosts:

The phlebotomine vector that harbors the extracellular flagellated form known as promastigote.

The mammalian host is where it transforms into the intracellular form called amastigote.

Known and emerging reservoirs in different animal species

The dog has been recognized and extensively researched as the main domestic reservoir.

In this species, the disease can present with a wide clinical spectrum, from subclinical forms without evident signs to severe cases with fatal outcomes.

Regarding cats, leishmaniasis has been documented in endemic areas and occasionally in non-endemic regions over the last 20 years, suggesting its emergent nature in this species.

With the advancement and improvements in infection confirmation tests, the presence of the infection is being detected in other species, both domestic (ferret) and wild fauna (European mink, white-naped mangabey, among others).

In the case of small ruminants, their possible epidemiological role in relation to Leishmania infantum infection began to be studied in Europe in 2013, with a first study conducted in the region of Thessaly (Greece), where no antibodies against L. infantum were detected in 361 sheep from 34 different farms.

However, years earlier, in 2002, a study was published in a national magazine in Spain in which seropositivity was detected in sheep and goats in Catalonia, specifically in the Priorat area (Tarragona).

In all seropositive small ruminants, low antibody levels were observed, with a seroprevalence of 11.86% in sheep and 18.85% in goats.

FIRST CLINICAL CASE OF LEISHMANIASIS IN SMALL RUMINANTS IN SPAIN

Following the description of a first case of leishmaniasis in a goat from Catalonia attended remotely by the Ruminant Clinical Service (SCRUM) of the University of Zaragoza, the potential role of production animals in the epidemiology of this parasite infection has begun to be assessed.

In this specific case, it was a goat that was kept as a companion animal.

Clinical manifestations and laboratory findings

The animal presented persistent dermal lesions (exfoliative dermatitis) over several months of evolution (Image 1), accompanied by lymphadenomegaly.

From the perspective of clinicopathological alterations, although most analytical values were within reference ranges, the following were detected:

• Increase in total proteins, alanine aminotransferase (ALT), and total bilirubin.
• Hyperglobulinemia.
• Decrease in gamma-glutamyl transferase (GGT) and calcium (Ca).

A serum protein electrophoresis was performed to investigate the nature of the hyperglobulinemia, revealing a polyclonal gammopathy (Graph 1).

Finally, an indirect ELISA serology was performed as a confirmation test for infection by L. infantum, resulting positive with moderate levels of anti-Leishmania antibodies.

Treatment and evolution of the clinical case

Due to all these clinical and laboratory findings and a positive result by serology, a totally empirical anti-Leishmania therapeutic protocol was established based on meglumine antimoniate at a dose of 100 mg/kg every three days subcutaneously for 25 days, due to the owner’s inability to administer the treatment daily.

Before this case described in Spain, another case had been documented in Kenya in a goat that presented cutaneous and visceral lesions, but Leishmania aethiopica was considered the most plausible etiological agent.

From this first clinical case described in Spain, research began in our territory:

If small ruminants are exposed to infection by Leishmania spp. (detection of anti-Leishmania antibodies by serology).

If seropositive animals can be detected.

If infected animals present or not compatible lesions similar to those described in the sick goat or clinical signs produced by the parasite in other animal species for which scientific information is available.

EXPOSURE OF SHEEP AND GOATS TO LEISHMANIA INFANTUM: NEW EPIDEMIOLOGICAL STUDIES

A first study conducted by SCRUM has revealed the presence of antibodies against L. infantum in sheep from different provinces within the area of influence of cases attended by this service. A total of 302 serum samples from the provinces of Zaragoza, Guipúzcoa, Huesca, Lleida, and Guadalajara were analyzed.

The results of the ELISA analysis (Image 3) showed:

• A seroprevalence of 9.27%, indicating previous contact with the parasite.
• Higher seropositivity rate in adult and female sheep, which had not been described before in similar studies.

These new findings suggest that other species, such as sheep, could have a potential role in its epidemiological cycle. Although none of the sheep showed clinical signs compatible with leishmaniasis, the detection of antibodies suggests they may have been exposed.

Subsequently, another epidemiological study conducted in Germany, a country traditionally considered as a non-endemic area for L. infantum infection, was published, using the same serological technique, allowing for a direct comparison of results. In this study, 551 animals (551 sheep and 88 goats) were analyzed in two southern states of Germany, Baden-Württemberg and Bavaria.

Using the ELISA technique, antibodies were detected in eight sheep (1.45%), distributed across several herds. In contrast, all goats tested negative.

Although no significant associations were found between seropositivity and factors such as age, sex, or herd location, the fact that these animals have had contact with L. infantum in regions without confirmed vectors suggests a possible change in the epidemiological scenario.

The results showed a global seroprevalence of 10.8% (93/864), highlighting cattle with a 21.6% (27/125), followed by sheep with a 15.4% (43/280), goats with a 7.3% (22/302) and pigs 0.6% (1/157).

An important aspect to consider in seroepidemiological studies is the possible variability of results between investigations. These differences may be due to:

The diversity of serological techniques employed: each method presents different sensitivities and specificities, which directly influences the ability to detect antibodies.

The type of antigen used in the test: it can capture different immunological profiles in the animals analyzed.

Serum dilution: higher concentrations can hinder the detection of low titers, while lower dilutions increase the risk of false positives.

The established cutoff values to consider a result as positive: are not always uniform across studies, complicating the direct comparison of seroprevalence or exposure rates between different populations or regions.

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