Temperature and the development and survival of infective Toxocara canis larvae

The influence of temperature on the development and survival of Toxocara canis larvae was investigated under laboratory conditions, in water at 15, 20, 25, 30 and 35A degrees C and at room temperature 22A degrees C A +/- 1A degrees C. T. canis eggs were able to develop to the larvated stage at all the tested temperatures. Development rate increased with temperature. Linear regression of development rate against temperature predicted a lower development threshold of 11.8A degrees C. Eggs survived cooling to 1 and -2A degrees C for 6 weeks, and could develop to the infective, larvated stage when transferred to higher temperatures, but their development rates were then retarded compared with non-chilled eggs. Larvated eggs remained viable after 7 weeks of incubation across the tested temperature range, with the highest percentage viability (47%) obtained at 25A degrees C. Development of eggs to the infective larval stage required, on average, 121 degree days between 20A degrees C and 30A degrees C. Results provide a basis for predicting variation in the infectivity of eggs in the environment over time in different climates.