Laboratory and field trials of a slow-release copper molluscicide in St. Lucia

Tests of a slow-release molluscicide containing 50 percent copper sulfate were undertaken in laboratory and field situations in St. Lucia. In laboratory trials, a granule form of the molluscicide produced 100 percent mortality of Biomphalaria glabrata down to 4 mg.liter active ingredient (a.i), while the pellet form produced 100 percent mortality down to 8 mg/liter a.i. In field trials, a dose of 100 mg/liter a.i. in granule form caused mortality of B. glabrata in banana drains but had no effect on B. glabrata populations in a marsh habitat. In both habitats, the dose of 100mg/liter produced mortality of other molluscan fauna which caused changes in the molluscan diversity indices. This failure in field trials may have been due to dilution of copper levels caused by flooding and also by uptake of copper by mud and algae (AU)

Further observations from St Lucia on control of Schistosoma mansoni transmission by provision of domestic water supplies

Individual households in five settlements were provided with piped water in a pilot scheme to investigate the effect on transmission of S. mansoni in St Lucia. Nearby comparison settlements, in the same valley, were provided with water through a public standpipe system. The incidence of S. mansoni infection among children decreased in the experimental area, leading to lower prevalence rates and lower intensity of infection in all age groups. Over the study period, indices of infection increased in the comparison settlements, but by the end of the period development was making those settlements less suitable for comparison purposes and some reduction in transmission was occurring. The changes in human infection rates were reflected in the results of studies with sentinel snails. In the experimental area, infection rates gradually fell owing to reduced water contact and consequently less contamination of the river and its banks, and possibly to the intensity of infection. It is suggested that a piped water supply be considered as a method of schistosomiasis control, but that the cost should not be debited only to the control of this disease since clean water supply has other medical and social benefits (AU)

Control of Schistosoma mansoni transmission by chemotherapy in St. Lucia. II. Biological results

Chemotherapy of all persons infected with Schistosoma mansoni was begun in Marquis Valley, St. Lucia, in March 1974. From January 1972 to the start of chemotherapy, the infection rate in field Biomphalaria glabrata collected in the valley was 1.09 percent (117/10,736) and the rate in sentinel B. glabrata was 1.48 percent (56/3,790). From March 1974 through December 1975, no infections were detected in either field snails (11,742 collected) or sentinel snails (3,230 exposed). The accumulation data suggest that, because of differences in topography and average annual rainfall, S. mansoni transmission occurs in this valley during the rainy season, whereas in other St. Lucian valleys under study it occurs during the dry season (AU)

Dispersion of St. Lucian Schistosoma mansoni cercariae in natural standing and running waters determined by cercaria counts and mouse exposure

Experiments were carried out to investigate the dispersion of Schistosoma mansoni cercariae in natural standing waters on St. Lucia using Sandt's method and mouse exposure. In standing-water habitats, cercariae located and infected mice as far as 3.1m. The worm burdens in mice increased in direct proportion to the numbers of cercariae, from 300 worms at the 200 cercariae per mouse level to 942 worms at the 800 cercariae per mouse level. At each cercarial level, more male than female worms were recovered. The sex ratios (male to female) of the worms were 1.8 at the 200 cercariae per mouse level, 1.5 at the 400 cercariae per mouse level and 1.1 at the 800 cercariae per mouse level. Between 1.2 and 6.9 percent of the cercariae succesfully infected mice. In running-water habitits, cercariae were carried down-stream as far as 195.1m, but they infected mice only as far as 97.5m. The mice exposed in water with an average water velocity of39.9cm/sec yielded the highest number of worms, followed by those exposed at 10.4cm/sec and 74.4cm/sec. In each case, more male than female worms were recovered. The sex ratios of the worms were 2.5 at 10.4cm/sec, 9.6 at 39.9cm/sec and 18.0 at 74.4cm/sec. Between 0.100 and 0.185 percent of the cercariae succesfully infected mice. On St. Lucia, cercariae shed by infected snails in standing-water habitats such as marshes and banana drains, probably play little role in transmission owing to the limited ability of cercariae to move very far. These habitats might, however, assume greater importance where they border streams because cercariae could be swept into them. On the other hand, running waters extend significantly the dispersion of cercariae and increase the risk of people becoming infected while washing their clothes and bathing in the streams (Summary)