Urban schistosomiasis in Lusaka, Zambia: a preliminary study.

A preliminary survey was conducted in Lusaka, Zambia to determine the extent of schistosomiasis transmission in the city. Stool and urine samples were collected from 240 children from seven schools selected to give a cross-sectional representation of the various socio-economic neighbourhoods of the city. In addition to the parasitological examination, students were questioned with respect to their knowledge of the disease and other epidemiological factors. In addition, water bodies near the schools were examined for the presence of snail hosts. Results of the survey suggest that schistosomiasis is actively transmitted within Greater Lusaka. An overall prevalence of 20.9% for S. haematobium was observed, but only one case of S. mansoni was detected. Prevalence rates for S. haematobium in individual schools ranged from 7.5 to 37.5%.

PIP: A retrospective survey of 18 urban clinics, a survey for snail hosts, and a parasitological survey of 240 sixth and seventh grade children attending seven schools were conducted to learn the spread of schistosomiasis transmission in Lusaka, Zambia. During January 1988-April 1989, staff at the 18 urban clinics treated 5703 patients for schistosomiasis (0.43% of total case load). The schistosomiasis cases/1000/month ranged from 0 (Makeni clinic) to 137.2 (Chelstone clinic). The stream in Chainama township, the Kalikiliki dam, and the open drainage canals of the George residential area harbored infected snails. The prevalence of Schistosoma haematobium ranged from 7.5% (Matero and St. Monica schools) to 37.5% (Tunduya school). Overall prevalence was 20.9%, which is larger than the national prevalence rate reported earlier (16%). Boys were more likely to be infected than girls (p = 0.05). The greatest number of S. haematobium eggs in a urine sample was 3880/10 ml in a boy from the Mtendere School. Many urine samples had only one egg. None of the stool specimens harbored schistosome eggs. One child was infected with S. mansoni. Schools in the poorer townships had higher prevalence rates for schistosomiasis than those in the richer townships. 52% of the children knew what schistosomiasis is. 17% had observed blood in their urine. 10% had been treated for schistosomiasis. These findings indicate that transmission of schistosomiasis is active in metropolitan Lusaka.

Adam's rib awry? Women and schistosomiasis.

The present paper reviews the literature to determine whether there are predisposing factors which influence the transmission, prevalence, intensity of infection and morbidity of schistosomiasis in women. The review suggests that: (1) the higher prevalence rates observed in males, in most endemic areas, are not due to sex per se, but to the greater opportunities afforded to males for exposure; (2) cultural and social practices often determine occupational roles and, in some circumstances, these practices may protect women from exposure; (3) when women assume typical 'male' roles, their risk and prevalence of infection increases; (4) in Muslim societies, women's exposure to water is restricted and infection rates are usually lower; (5) morbidity does not appear to be influenced by sex; and (6) the most important impact of schistosomiasis on women is its possible disruption of maternal functions, such as pregnancy, and its role in maternal, infant and child mortality and fetal wastage. Suggestions are also made for expanding existing research and for new studies concerning factors which may influence infection and disease in women.

Schistosomiasis in Zambia: an historical overview and review of the literature.

An historical overview and review of the literature on schistosomiasis in Zambia is presented. The review covers a period of approximately 130 years, from Livingstone's exploratory incursion in 1855 to present-day studies. Five species of mammalian schistosomes occur in Zambia and they are reviewed with respect to their distribution, snail hosts, human prevalence, and their role in producing morbidity and disease in man. The present status of infection and disease in Zambia, as well as considerations of transmission and control in the future, are discussed. The references cited represent 90-95% of the published literature on schistosomiasis in Zambia, excluding case reports.

Application of biotechnology to the study of molluscan hosts of animal parasites.

The intimate and complex relationship that exists between man and mollusc makes the group an ideal target for the application of biotechnology. The paper discusses and reviews the application of both the conventional and new molecular techniques to the study of the molluscan hosts of animal parasites. The remarkable advances in molluscan biology which have occurred during the past two decades as a consequence of conventional technological methods are noted and applications pertinent to problems in Southeast Asia are cited. Applications of new biotechniques, including those of molecular biology, to problems of the host-parasite interaction are discussed. Examples of how the new biotechnology may resolve present and future problems in applied malacology are presented.

The intermediate snail-host: an agenda for future study.

The strategy for the control of schistosomiasis has shifted from one directed towards the interruption of transmission to one of reducing morbidity. As a consequence of this change, it appears prudent to reassess the role of the malacologist and malacology and identify the future direction to be taken by the discipline. The present paper addresses these concerns; first, by reviewing the role of the snail-hosts in the epidemiology and control of schistosomiasis, and, secondly, by suggesting areas for future study. The possible application of newer methods in biotechnology for the resolution of malacological problems are discussed.

Differentiation of the sibling species Biomphalaria occidentalis and Biomphalaria tenagophila by the electrophoretic patterns of their hemoglobin.

A simple and rapid method for differentiating the sibling species Biomphalaria tenagophila and Biomphalaria occidentalis by agarose gel electrophoresis (AGE) is described. Snail hemolymph is used as the test sample and the red coloration of the hemoglobin fraction permits visualization of the migration patterns without resorting to specific stains. Moreover, hemolymph samples may be obtained without killing the snail, thus permitting its use for other studies or for breeding.

Preliminary observations on a hemolymph factor influencing the infectivity of Schistosoma mansoni miracidia.

It has been demonstrated that the infectivity of Schistosoma mansoni miracidia for a highly susceptible strain of Biomphalaria glabrata was reduced markedly when the miracidia were pretreated with hemolymph from the snail Helisoma caribaeum. Although the Helisoma hemolymph factor(s) responsible for this phenomenon has not been identified with certainty, it appears to be a snail lectin associated with binding sites for n-acetyl-D-glucosamine on the surface of the miracidium. Hemolymph from uninfected and infected B. glabrata and from a resistant strain of B. glabrata did not reduce the infectivity of miracidia, nor did pretreatment with bovine plasma albumin. Likewise, we demonstrated that reduction of miracidial infectivity was not due to the presence of a miracidial immobilizing factor found in the hemolymph of many snail species. Differences in the infectivity between pretreated miracidia and controls were statistically significant (P = 0.001).

Schistosoma mansoni: immunofluorescent detection of its antigen reacting with Biomphalaria glabrata amoebocytes.

The reaction of amoebocytes in the hemolymph of the infected intermediate host, Biomphalaria glabrata, to Schistosoma mansoni antigens has been investigated using the indirect immunofluorescence antibody test. Monolayers of amoebocytes, prepared from hemolymph of infected and normal snails, were first fixed and then reacted with antisera obtained from mice infected for 7 to 9 weeks. Nonspecific and cross-reactions between the antisera and monolayers of amoebocytes were eliminated by absorbing the antisera with tissues from uninfected snails. The liberation of detectable schistosomal antigens in the hemolymph in soluble and particulate forms coincided with completion of the infection cycle 3 to 4 weeks after exposure to miracidia. The schistosomal antigens were demonstrable in the cytoplasm of amoebocytes and in the center of amoebocyte aggregates.

Malacological observations bearing on the epidemiology of schistosomiasis in a rural Bahian community.

Observacoes malacologicas relacionadas a epidemiologia e transmissao de esquistossomose foram feitas na comunidade rural de Castro Alves, Estado da Bahia. Sao apresentados os tipos e natureza dos habitats aquaticos os lugares de contacto com agua da populacao,assim como a distribuicao, bionomica e nivel de infeccao de planorbideos hospedeiros. Ambos B. glabrata e B. straminea foram encontrados na area, apesar de que somente o primeiro tenha sido encontrado infectado com proporcoes de ate 22,8%. A reproducao de planorbideos parece ocorrer durante todo o ano,porem o periodo de maior fecundidade ocorreu em outubro continuando ate janeiro ou fevereiro. Foi observado que B. glabrata e capaz de resistir a periodos ocasionais de seca que ocorrem na area e refazer rapidamente a populacao original de seus habitats apos esses periodos. Essas observacoes podem ser uteis para o planejamento de programas de controle da esquistossomose nessa area

An isoenzyme marker possibly associated with the susceptibility of Biomphalaria glabrata populations to Schistosoma mansoni.

Nine laboratory populations and one field population of the snail host Biomphalaria glabrata were compared with respect to their electrophoretic patterns for acid phosphatase (AcP) and with their susceptibility to Schistosoma mansoni infection. A strong correlation (r = 0.98) was noted between the frequency of the isoenzymes AcP2-S and Acp2-F observed in the populations and the level of snail susceptibility as determined by bioassay. The isoenzyme AcP2-S was associated with susceptibility, AcP2-F with the refractory state. Breeding experiments between refractory and susceptible snails demonstrated that the refractory state was dominant and all F1 snails exhibited the AcP2-F isoenzyme and proved refractory to infection.

Susceptibility of Bahian population of Biomphalaria glabrata to an allopatric strain of Schistosoma mansoni.

Seventeen populations of snails (Biomphalaria glabrata) from the state of Bahia, Brazil were studied with respect to their susceptibility to infection with an allopatric strain of Schistosoma mansoni. Two of the populations were from the city of Salvador, 3 from other sites in Bahia, and 12 from habitats in the municipio Castro Alves. Our data show that the Bahian snail populations are extremely variable in their susceptibility to an allopatric strain of S. mansoni and that the phenomenon is not associated solely with distantly separated strains, but is present, as well, in adjacent populations situated in a restricted geographic region. Of the 6 populations found to be completely refractory to infection when exposed at a size of 5--7 mm, only 2 were refractory when exposed at 5--12 days of age. It is suggested that the variability to infection displayed by populations in a restricted geographic area may be explained by assuming that the Founder Principle was operative.

Agglutinins and lysins in the molluscan family Planorbidae: a survey of hemolymph, egg-masses, and albumen-gland extracts.

1. Thirty-one strains representing eight species and four genera of the molluscan family Planorbidae were surveyed for the presence of hemagglutinins and hemolysins. Extracts prepared from albumen-glands and egg-masses, as well as hemolymph, were assayed by a micro-hemagglutination technique in which human erythrocytes were used as receptors. 2. Hemagglutinins and hemolysins for human erythrocytes were not uniformly present in all members of the family and detection of these substances depended, in part, on the material tested. 3. Neither heating to 56 degrees C, dialysis, storage at -20 degrees C for up to a year, nor repeated freezing and thawing appeared to effect the agglutinating activity of egg or albumen-gland extracts. 4. Inhibition of the agglutinating activity of Helisoma hemolymph could be accomplished with N-Acetyl-D-Galactosamine, but this sugar had no effect on the activity of Biomphalaria agglutinins. 5. There is evidence to suggest that the source and nature of agglutinins from Helisoma and Biomphalaria species are different. 6. Lectins may be of some value in characterizing snail populations and as an aid in the taxonomic discrimination of species.

Schistosomiasis in the Gorgol Valley of Mauritania.

Schistosomiasis may be increasing in West Africa due to the development of water-resource projects which were given a strong impetus by the disastrous Sahelian drought. This report concerns the existing epidemiology of schistosomiasis in West Africa for the Fourth Region of Mauritania, along the Gorgol River. In this area two reservoirs are proposed, to supply a new rice irrigation system. During May and November 1974, field surveys were made to determine the prevalence and intensity of schistosomiasis, and the relevant species of snails. The surveys were made as a basis for designing the irrigation systems to minimize transmission. The only snails found in the area were two species of Bulinus; therefore, the human population was tested for Schistosoma haematobium. A high prevalence of schistosomiasis was found in M'Bout, the town nearest the proposed reservoir at Foum Gleita. Prevalence rates were lowest in Kaedi near the confluence of the Gorgol and Senegal rivers. During the period between the first and second survey the incidence rate among children in M'Bout became very high (68%), probably because of increased water contact related to the rains that broke the long drought in August 1974.

Intraspecific variations in the hemolymph of Biomphalaria glabrata, a snail host of Schistosoma mansoni.

An attempt was made to characterize the hemolymph of Biomphalaria glabrata with reference to "normal" intra-specific variation, i.e., both inter- and intra-strain differences. Total protein concentration, per cent hemoglobin, pH, and osmolarity were studied. Seven geographic strains of B, glabrata were examined. In addition, observations were made on the hemolymph of Biomphalaria straminea, several strains of Helisoma caribaeum, and on B. glabrata subjected to infection with Schistosoma mansoni or to periods of starvation. Intra-strain differences in total protein concentration and total hemoglobin concentration in B. glabrata appeared to be more closely related with snail size than with absolute age. Inter-strain variation in B. glabrata was also noted, but the differences were of the same magnitude as those from intra-strain samples. Significant differences in total protein concentration were observed, however, between the means of similar size B. glabrata, B. straminea and H. caribaeum. The osmolatity of the hemolymph from different size B. glabrata was similar as were the osmolalities of the hemolymph from similar size snails of different strains. However, all B. glabrata strains exhibited hemolymph osmolalities lower than observed in strains of H. caribaeum. Infection with S. mansoni reduced the protein concentration of B. glabrata hemolymph. Differences were noted as early as 1.5-24 hr post-infection, with significant alterations occurring at about 11 days post-infection. To a lesser extent, starvation also depleted the protein content of the hemolymph.