Canine visceral leishmaniasis (CVL), caused by Leishmania infantum, is a multisystemic disease in which ocular involvement is frequent but often underestimated. This study aimed to comprehensively evaluate the clinical, ophthalmological, parasitological, hematological, biochemical, and histopathological alterations in dogs naturally infected with L. infantum from an endemic area of northeastern Brazil, with special emphasis on the relationship between ocular manifestations and systemic disease. Twenty-five symptomatic dogs were evaluated through clinical and ophthalmological examinations, parasitological culture, PCR, laboratory analyses, and histopathology of ocular and periocular tissues. Ocular alterations were observed in 80% of the animals, predominantly bilateral and frequently associated with multiple concurrent lesions, including ocular discharge, conjunctivitis, blepharitis, uveitis, and corneal opacity. Functional ophthalmological tests revealed keratoconjunctivitis sicca and corneal ulcers in a substantial proportion of dogs. Hematological abnormalities were highly prevalent, particularly anemia and thrombocytopenia. Comparative analysis demonstrated that dogs with ocular involvement exhibited significantly higher leukocyte counts and segmented neutrophils, as well as increased AST levels, indicating an enhanced systemic inflammatory response. Histopathological examination revealed intense plasmacytic inflammatory infiltrates and the presence of amastigote forms in ocular and periocular tissues, indicating that both immune-mediated and parasite-driven mechanisms could be involved in disease pathogenesis. Collectively, these findings underscore ocular involvement as a clinically relevant manifestation of CVL and reinforce the importance of routine ophthalmological evaluation in clinical management.

Toxoplasma gondii is the etiologic agent of toxoplasmosis, a widely distributed zoonosis with relevance in human and veterinary medicine. The aim of this study was to assess the prevalence of T. gondii infection in Brazilian miners working informally in French Guiana. To this end, 480 individuals were recruited from resting places in the municipality of Oiapoque, Amapá, Brazil. Whole blood samples on filter paper were analyzed for IgM and IgG antibodies by ELISA. Nested PCR of the GRA7 gene was used to detect parasite DNA. Sociodemographic information, characteristics of the mining sites, and lifestyle data were collected using epidemiological questionnaires analyzed using univariate and multivariable models. The results showed that 79.3% of the individuals were IgG seropositive, while 0.8% were IgM seropositive. These were also IgG seropositive. In addition, T. gondii DNA was detected in 2% of the samples analyzed by nPCR, all of which were IgG seropositive and none of which were IgM seropositive. The high seropositivity observed, without association with sociodemographic or occupational variables, suggests that T. gondii exposure may be driven by environmental conditions related to Amazonian mining. These findings highlight the need for further investigation of environmental transmission sources and support targeted public health interventions, including improved water safety, sanitation, surveillance, and health education tailored to mining communities.

Chagas disease, caused by Trypanosoma cruzi, remains a neglected tropical disease of public health importance in Latin America, particularly in rural areas. In Floriano, Piauí, Brazil, data on infection prevalence are limited. This cross-sectional population-based study assessed the seroprevalence of T. cruzi infection and analyzed sociodemographic factors associated with seropositivity among residents of 41 rural communities in Floriano. A total of 1212 individuals aged over six years were examined, revealing a seroprevalence of 3.2% (39/1212), with positive cases detected in 17 communities. Infection was significantly associated with older age (≥60 years; p < 0.0001), low educational level (p = 0.0184), retirement status (p < 0.0001), and low income (p = 0.0505). Logistic regression confirmed age as the strongest determinant of infection (OR = 7.647; 95% CI: 3.741–18.61; p < 0.0001), while higher monthly income showed a negative association with infection (OR = 0.17; 95% CI: 0.01–0.82; p = 0.086), indicating a trend toward significance. These findings highlight the persistence of T. cruzi infection in rural Floriano, predominantly among elderly individuals living in poverty. The identification of previously undiagnosed chronic cases reinforces the urgent need for targeted epidemiological surveillance, early diagnosis, and community-based health education to strengthen local control and prevention strategies.