Visceral leishmaniasis (VL) is the most severe form of leishmaniasis caused by Leishmania infantum-synonymous with L. chagasi-and is transmitted through the bite of sandflies, particularly L. longipalpis, infected with the promastigote forms of this protozoan (Jericó; Andrade Neto; Kogika, 2023; Ivănescu et al., 2023).

With the adaptation of sandflies to domestic environments, dogs have become the primary source of infection for humans in urban areas (Ayres et al., 2022). Infected dogs may remain asymptomatic, develop protective immunity, or present severe clinical manifestations, including ulcerative, scaling, and alopecic skin lesions associated with lymphadenomegaly, anorexia, muscle atrophy, lethargy, splenomegaly, onychogryphosis, vomiting, and diarrhea (Ayres et al., 2022). Even in the absence of clinical signs, dogs may harbor the parasite in the skin, maintaining the potential to infect sandflies and perpetuate the transmission cycle to other dogs and humans (Ivănescu et al., 2023; Ayres et al., 2022; Saout et al., 2024).

In advanced stages, canine visceral leishmaniasis may lead to glomerulonephritis and interstitial nephritis, frequently resulting in renal failure, a poorer prognosis, and, often, death (Jericó; Andrade Neto; Kogika, 2023).

Laboratory tests are essential for the diagnosis of leishmaniasis, as it may mimic other hemoparasitic diseases-such as babesiosis and ehrlichiosis-and may also predispose to secondary infections due to immunosuppression, further complicating diagnosis (Larsson; Lucas, 2022).

The present study aims to report an allochthonous case of canine visceral leishmaniasis treated at a veterinary hospital in the city of São Paulo.

A female canine patient of mixed breed, seven years old, was attended at a veterinary hospital in São Paulo. The animal presented with a history of pruritus, apathy, and hyporexia, which began two years after traveling to the state of Goiás, in the Central-West region of Brazil.

On physical examination, muscle atrophy in the temporal region was observed, along with vasculopathic cutaneous lesions characterized by alopecic, ulcerative, and exudative lesions on the nasal planum (Figure 1A), tail tip (Figure 1B), and bony prominence regions-ischial and carpal areas (Figures 1C and 1D). Additionally, a dyskeratotic condition was noted, characterized by whitish, micaceous scales distributed over the entire dorsal region and on the external surface of the auricular pinnae (Figure 1E).

Figure 1

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The diagnosis of canine visceral leishmaniasis (CVL) was initially suspected based on clinical, cutaneous, and systemic manifestations, combined with a history of travel to an endemic region-Goiás, in the Central-West of Brazil-and was confirmed through complementary diagnostic tests. The visualization of amastigote forms within macrophages in the cutaneous cytopathological examination, along with an ELISA titer three times higher than the cut-off value, was sufficient for definitive diagnosis, as cytology has 100% specificity and ELISA titers at least three times above the cut-off are considered diagnostic (Hernandez-Bures et al., 2021; Larsson; Lucas, 2022). Clinical signs such as pruritus, ulcerative lesions, onychogryphosis, whitish scales, temporal muscle atrophy, and lameness are described in CVL, although they are nonspecific (Larsson; Lucas, 2022). Although the IFA result was reactive, it was interpreted in conjunction with other complementary test results to ensure proper diagnostic correlation, since positive CVL results may also occur in infections caused by T. cruzi, E. canis, T. gondii, N. caninum, and B. canis (Zanette et al., 2014).

Additional complementary tests-including complete blood count, renal and hepatic biochemical profiles, serum proteins, and urinalysis-were essential for disease staging, treatment planning, and prognosis (Brasileish, 2018). According to Brasileish (2018), the patient described in this report fits stage IV of CVL, with a guarded to poor prognosis, based on parasitological findings, hypergammaglobulinemia, and clinical signs indicative of immune complex deposition, such as vasculopathic lesions and suspected arthritis.

The treatment aimed to reduce the parasitic load, as parasitological cure cannot be achieved in cases of CVL (Ayres et al., 2022). Miltefosine (Milteforan®) was used in combination with allopurinol due to their leishmanicidal and leishmaniostatic effects, respectively, along with domperidone for its immunomodulatory action favoring a Th1 response (Larsson; Lucas, 2022).

The response to treatment is correlated with the type of immune response developed by the patient in response to infection, which may be classified as Th1 or Th2. Macrophages infected with amastigote forms act as antigen-presenting cells for CD4+ T lymphocytes, leading to the production of interleukins that promote the differentiation of Th1 and Th2 lymphocytes. Infected dogs with a predominance of the Th1 response produce pro-inflammatory cytokines, playing a key role in controlling the infection. Conversely, those with a predominance of the Th2 response are more prone to antibody production, particularly of the IgG class, which is responsible for the formation of immune complexes. These complexes may deposit in various tissues, leading to different clinical manifestations such as arthritis, glomerulonephritis, uveitis, and vasculopathic cutaneous lesions, thereby contributing to disease progression-even in the presence of appropriate treatment (Larsson; Lucas, 2022; Brasileish, 2018). Given the clinical manifestations suggestive of immune complex deposition-namely vasculopathic skin lesions and suspected arthritis-a possible explanation for the refractoriness to the instituted therapy, and consequently the disease progression observed in the dog described in this report, would be the presumed predominance of a Th2 response and/or the possibility of Leishmania spp. resistance to miltefosine, as previously reported by some authors (Carvalho et al., 2022).

Another cause of refractoriness in the treatment of CVL is coinfection-such as babesiosis and ehrlichiosis-which contributes to immunosuppression, favoring disease progression and worsening prognosis (Beasley et al., 2021). The inability to perform complementary diagnostic tests during the course of treatment prevented the assessment of potential comorbidities that might have been associated with treatment failure, as well as the systemic progression of leishmaniasis that ultimately led to the patient’s death.

The CVL is a zoonosis of significant public health importance. Its treatment is challenging due to high costs, the need for frequent laboratory monitoring, and dependence on the animal’s immunological profile, which directly influences therapeutic success and infection control.