Contaminated water confirmed as source of infection by bioassay in an outbreak of toxoplasmosis in South Brazil

The protozoanToxoplasma gondiiis a causative agent of toxoplasmosis, an important and widespread zoonotic disease. The transmission of this disease in humans includes ingestion of sporulated oocysts present in contaminated water or food.T. gondiioocysts are widely distributed and toxoplasmosis is considered a major food- and waterborne pathogen worldwide, making drinking water containing sporulatedT. gondiioocysts a major source of contamination for people. In the first half of 2018, an unprecedented outbreak of toxoplasmosis was reported in the city of Santa Maria, southern Brazil. The temporal and spatial distribution of the cases strongly suggested a waterborne infection. Thus, the aim of this study was to investigate a possible involvement of treated water as a source of the outbreak. For this, piglets received potentially contaminated water ad libitum for 21 days and the infection was monitored by serology through IFAT and investigation ofT. gondiiDNA in tissues by PCR amplification of a 529 bp followed by mouse bioassays. All piglets receiving test water ad libitum for 21 days as well as positive controls seroconverted toT. gondii.T. gondiiDNA was detected in 62.5% of the piglets that received test water. All mice inoculated with tissues from each positive piglet were PCR-positive. These results strongly indicated the presence of viable oocysts in the test water administered to the animals during the study.