Natural infection with Trypanosoma cruzi in a litter of dogs (Canis lupus familiaris) from Floridablanca, Colombia, suggests congenital transmission and a potential zoonotic risk.

Chagas disease (CD) remains a major public health challenge in endemic regions of Colombia, where both domestic and sylvatic host sustain transmission. This study reports the first natural infection with Trypanosoma cruzi in a litter of dogs from Floridablanca, in the Metropolitan Area of Bucaramanga (MAB), Santander, most likely associated with congenital transmission. Eight puppies and their dam were clinically evaluated, and blood samples were analyzed through hematology, quantitative real-time PCR (qPCR), multiplex PCR for discrete typing units (DTUs) identification, and hemoculture. Serological surveillance was also performed in the owners' nuclear family. All puppies and the dam tested positive for T. cruzi DNA by qPCR, with high parasitemia levels (751.8-977.3 parasite equivalents/mL in puppies and 526.2 parasite equivalents/mL in the dam), corresponding to DTU I (TcI). Hematological findings in puppies indicated regenerative anemia, thrombocytopenia, and lymphocytosis. Despite supportive treatment, seven puppies died (mortality rate = 87.5 %), and one was euthanized after three months of disease progression. Postmortem examination revealed multisystemic lesions, including interstitial pneumonia, necrotizing hepatitis, myocardial lymphocytic infiltrates with amastigote cysts, and meningoencephalitis, consistent with acute trypanosomiasis. Hemoculture was positive in this case. None of the family members tested positive for T. cruzi antibodies. To our knowledge, this is the first description of natural infection with T. cruzi DTU I (TcI) in a litter of dogs from Colombia. The marked parasitemia observed, together with hemoculture positivity, highlights the potential of these hosts to infect triatomine vectors and increase the risk of CD transmission in endemic areas.