High Seroprevalence Rates of Toxoplasma gondii and Neospora caninum in Dogs in the Pantanal Region of Mato Grosso, Brazil

Acta Parasitologica (2026) 71:69 https://doi.org/10.1007/s11686-026-01241-0 RESEARCH High Seroprevalence Rates of Toxoplasma gondii and Neospora caninum in Dogs in the Pantanal Region of Mato Grosso, Brazil Gabriel Lucas Artiaga-Silva1 · Álvaro Felipe de Lima Ruy Dias1 · Matheus Roberto Carvalho1 Kamilla Silva Melo1 · Arleana do Bom Parto Ferreira de Almeida1 · João Luis Garcia2 · Richard de Campos Pacheco1 · Valéria Régia Franco Sousa1 · Received: 28 November 2025 / Accepted: 5 February 2026 / Published online: 17 March 2026 © The Author(s) 2026 Abstract Purpose Toxoplasma gondii and Neospora caninum are protozoan that infect animals worldwide. Dogs act as sentinels of these infections, indicating potential risks to human health, particularly in the case of T. gondii due to its zoonotic nature. Therefore, we aimed to determine the seroprevalence and associated factors for T. gondii and N. caninum infections in dogs living in the Pantanal biome, Brazil. Methods This study evaluated the seroprevalence in 743 serum samples from dogs in Barão de Melgaço and Nossa Senhora do Livramento, municipalities endemic for canine visceral leishmaniasis located in the Pantanal biome of Mato Grosso, Brazil, by Indirect Immunofluorescence Assay. Results Overall, 66.4% (n = 493) were positive for T. gondii and 12.4% (n = 92) for N. caninum. Seropositivity was associated with dogs older than 3 years (T. gondii—p = 0.001; OR = 2.579; N. caninum—p = 0.004; OR = 7.621), living together with other dogs and/or cats (T. gondii—p = 0.04; N. caninum—p = 0.005), and absence of a public sewage system at home (T. gondii—p = 0.044; OR = 4.730; N. caninum—p = 0.035; OR = 1.376). For T. gondii, additional associations were found with street access (p = 0.015; OR = 3.966), contact with rodents (p = 0.025; OR = 1.539), and a diet including leftover food (p = 0.025; OR = 2.405). Infection by N. caninum was more frequent in rural dogs (p = 0.011; OR = 4.857) and in those coinfected with Leishmania infantum (p < 0.001; OR = 6.407). Conclusion The investigated regions are endemic for T. gondii and N. caninum, with increased risk associated with environmental conditions and dog management practices. Furthermore, dogs infected with L. infantum showed a higher likelihood of coinfection with N. caninum. Keywords Coinfection · Risk factors · Leishmania infantum · Prevalence Introduction In the One Health context, parasitic diseases are important research targets because they are directly associated with socioeconomic vulnerability and inadequate living conditions [1]. Examples include toxoplasmosis, neosporosis, Valéria Régia Franco Sousa 1 Faculty of Veterinary Medicine, Federal University of Mato Grosso, Cuiabá, MT, Brazil 2 National Institute for Research on Human and Animal Toxoplasmosis (INCT), State University of Londrina, Londrina, PR, Brazil and visceral leishmaniasis, which can cause severe clinical disorders in dogs [2, 3] and lead to significant economic losses [4–6]. In dogs, toxoplasmosis, caused by the obligate intracellular protozoan Toxoplasma gondii [3], shows high prevalence rates that can reach up to 70% in Brazil. Although felids are the definitive hosts, dogs may contribute to the mechanical dissemination of the parasite [7, 8]. Considering the parasite can infect a wide range of mammals and birds [7, 9] as well as some reptile species [10], dogs have epidemiological importance as sentinels, and the identification of seropositive animals may indicate a potential risk of infection for humans [11]. Neospora caninum, another obligate intracellular protozoan, can infect canids, which serve as definitive hosts, as 13 69 Page 2 of 8 well as various herbivores, which act as intermediate hosts [12]. Infection can cause neurological disease in dogs and is one of the main causes of abortion in cattle herds [9]. Thus, dogs, particularly those living in rural areas, play a key role in the epidemiology of the disease, significantly contributing to the circulation of the parasite in the environment and increasing the risk of infection for intermediate hosts, such as cattle and wildlife [13, 14]. The Pantanal is a biome characterized by high biodiversity and intense interactions among humans, domestic animals, and wildlife [15, 16]. In addition, it is considered an endemic area for canine visceral leishmaniasis due to the distribuition of Lutzomyia longipalpis, the vector of Leishmania infantum [17]. In this context, the aim of this study was to determine the prevalence and associated risk factors for T. gondii and N. caninum infections by assessing the presence of antibodies in dogs living in areas endemic for canine visceral leishmaniasis in the Pantanal biome of Mato Grosso, Brazil. Acta Parasitologica (2026) 71:69 Materials and Methods Study Area and Sample Size Calculation In this study, 743 canine serum samples were analyzed from two municipalities located in the northern Pantanal region of Mato Grosso, Brazil: 402 samples from Barão de Melgaço (16°11′40″S and 55°58′03″W) (Fig. 1) and 341 samples from Nossa Senhora do Livramento (15°46′30″S and 56°20′44″W) (Fig. 1), collected between 2015 and 2018. Sample size calculations were based on an expected prevalence of 50%, a 95% confidence interval, and a 5% margin of error, estimating the canine population using a dog-tohuman ratio of 1:7 [18, 19]. Antibody Detection Antibody detection was performed using the Indirect Immunofluorescence Assay (IFA) employing a canine anti-IgG conjugate obtained from rabbit inoculations and labeled with fluorescein isothiocyanate (FITC–Sigma®). Slides for T. gondii were prepared using RH strains, with a cut off titer of 1:16 [20, 21]. For N. caninum, the cutoff was 1:50 [20], Fig. 1 Boundaries of the municipalities of Nossa Senhora do Livramento (1) and Barão de Melgaço (2) in the Pantanal biome (green) located in the states of Mato Grosso (MT) and Mato Grosso do Sul (MS)—Brazil 13 Page 3 of 8 69 Acta Parasitologica (2026) 71:69 using NC-1 strains as antigens in slide preparation. Each slide included negative and positive serum controls. Reactions were considered positive when tachyzoites exhibited complete peripheral fluorescence [21]. All samples had previously been evaluated for L. infantum seropositivity using a rapid immunochromatographic test (Dual Path Platform– DPP, Biomanguinhos®, Brazil) and enzyme-linked immunosorbent assay (ELISA, Biomanguinhos®, Brazil) [18, 19]. Epidemiological Information The following information was collected for the entire dog population: breed (defined; undefined), sex (male; female), age (puppy—up to 12 months; young—1 to 3 years; adult— over 3 years) [22], type of diet (commercial feed; leftover food; raw meat; mixed), type of household sewage system (public; open-air; septic tank), street access, cohabitation with other dogs and/or cats, property location (rural; urban), and the presence of rodents and/or marsupials in the dog’s accessible environment. Stat (...truncated)