Showing papers on "Bulinus truncatus published in 1968"

Location of Bulinus (Physopsis) globosus by miracidia of Schistosoma haematobium.

Abstract: Young Bulinus (Physopsis) globosus snails were exposed to miracidia of Schistosoma haematobium under various conditions of mutual dispersion to investigate host location mechanisms. There is little variation in infectivity of miracidia taken from different human hosts on different days. Exposure of one snail to one miracidium in cylindrical vessels with diameters ranging from 2.3 to 29.0 cm filled to 0.5 cm depth resulted in infection of about 42% of snails; this percentage did not increase if three snails were used in each exposure. With the snails confined under small perspex cages, the percentage infected by single miracidia rose significantly. It is suggested that this was the result of a chemotaxis, and experiments using a simple Y-maze demonstrated an initial response some distance from the snail. In a long trough miracidia were found to range over 294 cm in still water; in water flowing at 15 cm/sec 10 miracidia per snail produced no infections. At 7.5 cm/sec 6.7% of snails became infected. The introduction of a weir to cause turbulence increased infection. It is suggested that miracidia of S. haematobium are unable to infect snails in moderately fast-flowing water unless turbulence occurs near the snails. The success of the free swimming miracidium in finding its host is an important feature in the bionomics of schistosomes. Selective pressures must have evolved the most efficient means of finding and infecting the appropriate snail. It is therefore reasonable to presume that in the miracidium specific mechanisms exist adapted to the behavior and physiology of the appropriate intermediate host. Faust (1924) pointed out a distinct difference between the behavior of miracidia of Schistosoma japonicum (Mollendorf) and those of S. haematobium (Weinland) derived from the northern African snail Bulinus truncatus (Audouin), and suggested that this was an adaptation to the habits of the different intermediate host snails. Wright (1959a) in discussing host location by trematode miracidia has presented arguments suggesting the presence of a chemical attraction between the host snail Biomphalaria (= Australorbis) glabrata (Say) and the miracidia of S. mansoni Sambon. Recently, Maclnnis (1965) showed that miracidia of S. mansoni react positively to chemostimulation in the form of either the appropriate host snails, or extracts of these snails, or to small agar pyramids impregnated with chemicals such as butyric, glutamic, or sialic acids. He reports Gottschalk (1960) as stating that sialic acids are known to be components of mucopolysaccharides, substances which may be present in the mucus of snails Received for publication 16 February 1968. (Wright, 1959b); similarly, Etges and Decker (1963), using a four-arm maze, concluded that S. mansoni miracidia were attracted to B. glabrata. However, Chernin and Dunavan (1962), investigating infection of B. glabrata by miracidia of S. mansoni in various sized vessels, concluded that attraction between the miracidium and the snail had not been demonstrated unequivocally. Host location in running water has been investigated by Webbe (1966) using a trough and the miracidia of S. mansoni with Biomphalaria sudanica tanganyicensis (Smith). He concluded that water flow may enhance the scanning capacity of miracidia because he obtained high infection rates in caged snails exposed to miracidia in water flowing at velocities of 0.5 to 3.5 ft/sec (15 to 105 cm/sec). The work reported here concerns the ability of S. haematobium miracidia to infect Bulinus (Physopsis) globosus (Morelet) under different conditions of mutual dispersion in still and flowing water. Many of Chernin and Dunavan's experiments have been repeated and acknowledgment for these is duly tendered. MATERIALS AND METHODS Snails were laboratory-bred B. globosus. They were exposed when the shell height was between 3.5 to 5.0 mm; i.e., between 4 and 8 weeks old. Parent colonies and young snails were maintained at room temperature in the laboratory. Unless otherwise stated, all exposures of snails to miracidia were carried out in the dark and in constant temperature cabinets regulated to 22 ? 0.5 C. In this way extraneous stimuli were elim-

Distribution and ecology of Bulinus truncatus in Khuzestan, Iran.

Abstract: The results of a 5-year study on the distribution and ecology of Bulinus truncatus in Khuzestan, south-western Iran, are described. Live snails were found in 4 foci, namely, the main focus, the upper Karun River, the lower Karkheh River, and the Bala Rud watershed; in addition, dead snails were found in 3 other foci. The patchy distribution of snails was related to the presence of surface waters and to their chemical composition.Monthly observations on the population dynamics of the snails and on the role of the snails in the transmission of Schistosoma haematobium and S. bovis were carried out in 14 ponds, 9 canals, 5 swamps, 2 field drains, 1 spring and 1 stream-pool. In standing waters, the peak of snail population could potentially occur in 2 seasons-May-July and November-January-but the main seasons for the transmission of mammalian schistosome cercariae were April-May and October-November. In flowing waters, a higher number of snails might be found in summer in some canals and in winter in another group of canals. Canals were found to be more important sites of transmission of human schistosomes than were village ponds. Transmission took place mainly in hot months when man-water contacts were greatest. Village ponds accessible to livestock were found to be important in the transmission of bovine schistosomiasis. As new irrigation systems have been expanding in this area of Khuzestan, more attention should be paid to flowing waters than to standing waters in future schistosomiasis control programmes.

Observations on the infection of bulinid snails with Schistosoma mattheei. I. The susceptibility of Bulinus africanus and Bulinus truncatus.

Abstract: (1968). Observations on the infection of bulinid snails with Schistosoma mattheei. Annals of Tropical Medicine & Parasitology: Vol. 62, No. 3, pp. 382-392.