C.A. Wright

Hybrids between Schistosoma haematobium and S. mattheei and their identification by isoelectric focusing of enzymes

Some biological features of F1 hybrids between South African strains of Schistosoma haematobium and S. mattheei are described and compared with those of both parental species. The distinctive patterns of the G6PD and PGM isoenzymes, resolved by isoelectric focusing, of both species and of the hybrid are defined and the results of enzyme analyses of parasites isolated from human infections in the Transvaal are reported. These show that hybridization does occur naturally in man and that the shape of the eggs produced is not necessarily a guide to the genetic constitution of the enclosed larvae. The experimentally produced F1 hybrids exhibit heterosis in their increased infectivity to both snails and hamsters, in their more rapid growth and earlier maturation and in the increased daily egg production per female worm when compared with both of the parental species. The possible practical implications of this are discussed.

Studies on Schistosoma haematobium in the laboratory I. A strain from Durban, Natal, South Africa

Abstract Some of the characteristics of a strain of Schistosoma haematobium from Natal in experimental infections in hamsters are described. Evidence of the effects of the state of maturity of the intra-molluscan phases of the infection on success of the cercariae is presented. Growth curves for the adult worms from the 90th day of infection to the 170th are given, and the retarded growth of unpaired males in the liver is discussed. The quantitative distribution of parasite eggs in the host tissues is described. An approximate figure for the daily egg output of individual female worms has been calculated. The importance of the influence of individual hosts, both on growth rates and egg production of their parasites, is stressed.

Studies on Schistosoma haematobium in the laboratory III. Strains from Iran, Mauritius and Ghana

Abstract Some biological characteristics of 4 strains of Schistosoma haematobium in hamsters are described and discussed. Marked differences in infectivity, growth-rates, maturation times, egg-production and tissue-deposition of eggs in the different strains are recorded. It is concluded that the retention of the name S. capense is not justified but that very great care is needed in defining the precise source of any strain of S. haematobium . The sex of the hamster host does not appear to have any appreciable influence on either the quantitative or qualitative aspects of an infection with S. haematobium .

Studies on Schistosoma haematobium in the laboratory, II. A strain from South Arabia.

Abstract Some of the characteristics of a strain of S. haematobium from South Arabia in experimental infections in hamsters are described. The relationship between the state of maturity of the intra-molluscan phases of the larvae and subsequent success of the cercariae is discussed. Growth curves for the adult worms and changes in uterine egg count with age are illustrated. The quantitative distribution of parasite eggs in the host tissues is described and approximate figures for the daily egg output of individual worms are given. The effects of host sex on worm burden and parasite sex ratio are discussed. The characteristics of this strain are compared with those of a strain from South Africa.

Taxonomic problems in the molluscan genus bulinus

Abstract An attempt has been made to outline the major problems facing the taxonomist working with the intermediate hosts of Schistosoma haematobium and to indicate how some of these problems may have arisen. The subject of variation is discussed and emphasis is laid upon the importance of individual populations of snails, both from the point of view of the taxonomist and the epidemiologist.