The prepatent period and cercarial production ofSchistosoma haematobium inBulinus truncatus (Egyptian field strains) at different constant temperatures

Abstract

The developmental time of Schistosoma haematobium in Bulinus truncatus snails (field strains) was determined in the laboratory at different constant temperatures between 18 and 32 degrees C. The basic relationship between the length of the minimum prepatent period (y, in days) and the temperature (x, in degree C) is given by the hyperbolic formula y = 295/(x-15.3), 15.3 being the theoretical "developmental null point" and 295 the constant time-temperature product. The shortest prepatency was 17-19 days at 30, 31 and 32 degrees C; at 18 degrees C, cercarial development required at least 106-113 days. The maturation time frequently exceeded the possible minimum by several weeks. No schistosome matured in our experiments at 17 degrees or 33 degrees C. The cercarial release per snail at weekly exposures showed a maximum at 25 degrees C with a geometric mean of 109 cercariae (95% confidence limits 79-149), decreasing to 8 (2-30) at 18 degrees C and 62 (38-100) at 32 degrees C. The absolute maximum of cercariae shed by one snail during 5 h "stimulation" was 2,150 in a 25 degrees C batch, 48 at 18 degrees C and 529 at 32 degrees C. The epidemiological application, the prognosis of the transmission period and the estimation of the transmission potential in relation to climatic conditions are discussed.

Symptoms of behavioural anapyrexia – Reverse fever as a defence response of snails to fluke invasion

“…According to these authors, an invasion of miracidia and shedding cercariae constitute two critical moments in the snail-trematode interaction, during which, for example, the number of active hemocytes in the host hemolymph increases significantly. Both the increased phagocytic activity of cells in the hemolymph and the behavioural anapyrexia, increase the chances of survival of the host (Pfluger et al, 1984;Blankespoor et al, 1989). This suggestion is supported by the results of research on the survival of infected snails kept at constant temperatures (Table 3).…”

Modeling freshwater snail habitat suitability and areas of potential snail-borne disease transmission in Uganda

“…The temperature regime used to create the S. mansoni temperature mask were 16-35ºC with a developmental null point of 14.2ºC (Pflüger, 1980, Joubert et al, 1986. A temperature regime of 18-32ºC and a developmental null point of 15.3ºC were used to mask out areas unsuitable for S. haematobium transmission (Pflüger et al, 1984). For F. gigantica a base life cycle development temperature of 16°C (Dinnik and Dinnik, 1963) and a thermal tolerance limit of > 36ºC (Dinnik and Dinnik, 1963;Malone, 2005) was used to create the temperature mask.…”

Schistosomiasis Haematobium, Corsica, France

“…Water temperature was recorded at 11:00 am at these 3 sites (range 15°C–16°C). This temperature range is not optimal for the snail intermediate host stage of the parasite life cycle ( 9 , 10 ). Of 148 live snails that were obtained in the Cavu River, none were infected with schistosome cercariae.…”