Background Toxoplasmosis is a zoonotic disease that affects humans and warm‐blooded animals. This study describes an outbreak of toxoplasmosis in howler monkeys (Alouatta sp.) and survival of capuchins (Sapajus apella), under the same environmental conditions. Methods Howler monkeys were submitted to post‐mortem examination. Tissue samples were processed to histopathology and immunohistochemistry to detect lesions and tachyzoites of Toxoplasma gondii. Tissue samples were also frozen and submitted to PCR and genotyping of T. gondii. Results Typical lesions were observed in several organs including the liver, lymph node, and brain, with intralesional cysts and tachyzoites of T. gondii demonstrated by immunohistochemistry. T. gondii genomic sequences were amplified by PCR, and genotyping characterized the same T. gondii clone in all howler monkeys. Conclusions Our results support the notion that some species of neotropical primates are highly susceptible to toxoplasmosis and the hypothesis that capuchins (S. apella) may be resistant.

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