Botulism type C outbreak in free-ranging wild birds in a public urban park in Ribeirão Preto, São Paulo state, Brazil

Botulism is a neurological disease caused by the ingestion of the toxin produced by Clostridium botulinum. This bacterium is globally distributed, infects mainly mammals and birds, and is present in both the intestinal microbiota and the environment. The most frequently observed clinical manifestation is flaccid paralysis of the skeletal muscles, which can rapidly progress to death due to cardiorespiratory failure. Diagnosis is performed through clinical, environmental, and laboratory findings, mainly by mouse bioassay seroneutralization, which serves as the gold standard.

During the seasonal period, approximately 30-60 dead or sick animals were found in an urban park in Ribeirão Preto, São Paulo, Brazil, between late 2020 and 2021. However, only four wild ducks (Cairina moschata) and one great egret (Ardea alba) were evaluated. All five animals presented with neurological signs of limb paralysis, dyspnea, and neck flaccidity and were unable to fly. After clinical evaluation, the animals were euthanized, and necropsies were performed. Although we observed discrete hemorrhagic enteritis in the three evaluated ducks, no other relevant lesions were found. Samples were sent to the laboratory, where type C botulinum toxin was detected.

The presence of botulism in urban areas, especially in leisure areas, raises public health concerns. To the best of our knowledge, this is the first report of type C botulism in a public urban park in São Paulo, Brazil. Although this toxin does not pose a direct risk to human health, it is a strong indicator of environmental health, affecting wild free-ranging birds.