The world's first documented toxoplasmosis outbreak associated with a municipal water supply
was recognized in 1995 in Victoria, British Columbia, Canada. It was hypothesized that
domestic cat (Felis catus) or cougar (Felis concolor) faeces contaminated a surface water
reservoir with Toxoplasma gondii oocysts. An extensive investigation of the Victoria watershed
1 year following the outbreak documented the presence of an endemic T. gondii cycle involving
the animals inhabiting the area. Cats and cougars were observed throughout the watershed.
Serological evidence of T. gondii infection was demonstrated among domestic cats living in the
Victoria area. Cougars were found to shed T. gondii oocysts. Serological evidence of T. gondii
infection in deer mice living in the riparian environments of the watershed suggested that
T. gondii oocysts were being shed near the water edge. Contamination of Victoria's water supply
with T. gondii oocysts potentially occurred during the study period and future waterborne
toxoplasmosis outbreaks in this and other communities are possible.