Showing papers on "Bulinus truncatus published in 1966"

The ecology of Bulinus truncatus and Biomphalaria alexandrina and its implications for the control of bilharziasis in the Egypt-49 project area.

Abstract: The respective vectors of the two forms of bilharziasis in Egypt do not have the same ecological distribution. Bulinus truncatus is most abundant in large canals, and decreases in density as the water approaches and flows into drains. Biomphalaria alexandrina is most abundant in drains, and decreases in density upstream from these habitats. Both species are most abundant in the presence of aquatic vegetation, but they differ in their respective associations with the water hyacinth, Eichhornia crassipes. Biomph. alexandrina reaches maximum abundance in the presence of this plant, but Bul. truncatus is as uncommon in the absence of plants as in the presence of E. crassipes.Calculation of life-table parameters from field data shows that, under optimum field conditions, both species can double their populations in 14-16 days. The reproductive rates of both species are greatest in March and the death rates in midsummer. The observed peak densities in May and June give a false impression of optima because of undercollection of young snails, which are most abundant in March and April.Control operations should take advantage of the findings on population parameters. A single area-wide treatment with molluscicide in April is recommended. During the remainder of the year, search for isolated foci of snail breeding and individual treatment of these will effect large savings of chemical and will be effective in controlling the transmission of the parasites.

Host-parasite relationship of Bulinus truncatus and Schistosoma haematobium in Iran: 2. Effect of exposure dosage of miracidia on the biology of the snail host and the development of the parasites

Abstract: Laboratory experiments were carried out to study the development of Bulinus truncatus and the larval stages of Schistosoma haematobium after the snails had been exposed to various numbers of miracidia. The results showed: (1) that in the cercarial-incubation period the growth and survival rate of snails was not influenced by the development of the larval stages of S. haematobium, but that in the cercaria-shedding period the life-span of the infected snails was shorter than that of the non-infected controls; (2) that reduction of oviposition was proportional to the exposure of miracidia; (3) that the length of the cercarial-incubation period in snails was inversely proportional to the exposure number of miracidia; (4) that all the snails exposed to 20 miracidia (the maximum exposure number used) shed cercariae; (5) that snails exposed to one miracidium each shed fewer cercariae than those exposed to two or more miracidia each; and (6) that the peak of cercaria-shedding occurred 40 to 90 days after the shedding had started, varying in different groups.

Host-Parasite Relationship of Bulinus truncatus and Schistosoma haematobium in Iran. 3. Effect of Water Temperature on the Ability of Miracidia to Infect Snails.

Abstract: Laboratory studies were made in Iran to test the effect of water temperature on the ability of the miracidia of S. haematobium to penetrate B. truncatus. Snails three to four weeks old were exposed to two miracidia each for two hours at nine water temperatures ranging from 10°C to 38°C. After exposure, all the snails were kept in aquaria at room temperature. The cercaria-positive rates of these nine groups of snails showed that the optimum exposure temperature was in the range 20°C-30°C. The infection rate was low at temperatures outside this range. It is concluded that the optimum transmission seasons in bilharziasis-endemic areas in Iran are spring and autumn but that transmission still occurs in hot summer and cold winter months although to a much smaller extent.

Host-parasite relationship of Bulinus truncatus and Schistosoma haematobium in Iran. 1. Effect of the age of B. truncatus on the development of S. haematobium.

Abstract: This paper is the first of a series of four on various aspects of the interaction between Bulinus truncatus and the bilharziasis parasite Schistosoma haematobium It describes laboratory studies conducted to determine the effect of the age of B truncatus on the development of S haematobium The results indicated (1) that the young snails could be infected even if they were one day old; (2) that the infection rates were higher in the snails of two to five weeks of age than in those of one week; (3) that the cercarial-incubation period was shorter in the young snails than in the older ones; (4) that the survival rate of the snails in the cercarial-incubation period was lower in the young snails than in the older ones; (5) that the survival rate of the cercaria-shedding snails was also apparently lower in the young ones than in the older ones; (6) that the maximum life-span for a cercaria-positive snail extended to 329 days after the date of exposure to infection

Host-parasite relationship of Bulinus truncatus and Schistosoma haematobium in Iran. 4. Effect of month of infection on cercarial-incubation periods of S. haematobium and S. bovis.

Abstract: Studies were conducted each month for one year to determine the cercarial-incubation periods of Schistosoma haematobium and Schistosoma bovis in Bulinus truncatus for different months of infection. The snails were kept in outdoor aquaria in order to simulate the natural temperature conditions in the endemic bilharziasis areas of Iran. The results showed that the cercarial-incubation periods of these two schistosome species varied with the environmental water temperature. Snails exposed in August had the shortest incubation period, and snails exposed in November the longest. The cercarial-incubation period for S. haematobium was longer than that for S. bovis in all months. The difference between the cercarial-incubation period of these two species varied from three to 18 days, being greater in the winter than in the summer. It has been concluded that the low temperature of the water in the winter retards the development of miracidia into cercariae and that the winter is therefore the poorest season for potential transmission. In summer, in spite of the hot weather, snails may still shed cercariae, but spring and autumn are the optimum seasons for cercariae transmission.