ITS2 ribosomal RNA indicates Schistosoma hippopotami is a distinct species.

The internal transcribed spacer region of the ribosomal RNA, ITS2, was sequenced from a single specimen of S. hippopotami collected from a pulmonary artery of the hippopotamus, Hippopotamus amphibius in South Africa. The nucleotide sequence was aligned with those of S. mansoni, S. rodhaini, S. haematobium, S. intercalatum, S. curassoni, S. bovis and S. japonicum. Both maximum parsimony and genetic distance analyses were performed on these data sets. Using S. japonicum as outgroup to the African schistosomes, a single most-parasmonious tree was obtained of length 64 steps with a consistency index of 1-S. hippopotami was the sister-group to the remaining African species. This species has lateral-spined eggs and its basal position in the tree suggests that this condition is primitive and that terminal-spined eggs developed secondarily. Molecular data clearly show that S. hippopotami cannot be considered synonymous with S. mansoni. Assuming the hippopotamus is the normal host of S. hippopotami, phylogenetic analysis is consistent with an ancient association between schistosomes and ungulates.

Further studies on the susceptibility of Bulinus africanus to infection with Schistosoma haematobium.

Genetic manipulation of the intermediate host snails of schistosomiasis has been proposed as a possible method of reducing the rate at which the parasite is transmitted to the final host. This technique is based on the finding that snail-schistosome compatibility is variable, and that refractory snails could be introduced into natural habitats in an attempt to change existing highly-susceptible populations into non-susceptible ones. In our search for such a refractory snail population, offspring from eight different Bulinus africanus populations were infected with Schistosoma haematobium, isolated from school children in the Nelspruit district. A great variation in minimum prepatent period was recorded (33-55 days), while the infected snails surviving that period ranged from 22-89%. A significant difference was found between the infection rates of B. africanus from Newlands in Natal and those of the other seven populations from the Eastern Transvaal Lowveld. The former population could be regarded as partially refractory, and none of the other populations proved to be completely refractory, to infection.

Variation in the morphology of the dorsal and dorso-lateral tegument of male Schistosoma haematobium from southern Africa.

The teguments of Schistosoma haematobium males from three localities in the Eastern Transvaal and one in the eastern Caprivi were studied by means of scanning electron microscopy. Eastern Transvaal S. haematobium, which occurs sympatrically with S. mattheei, a bovine schistosome also infecting man and which hybridizes with S. haematobium, exhibited certain S. mattheei characteristics. The occurrence of these characteristics were neither related to the prevalence of human S. mattheei infections nor could they be attributed exclusively to phenotypic plasticity. The variation therefore may be geographical and possibly related to the phylogeny of the two species.

Adherence of blood platelets and leucocytes to hybrid schistosomes.

The bovine parasite, Schistosoma mattheei was crossed with the human schistosome, S. haematobium. The F1 hybrids resulting from this cross were viable in both snails and rodents. However, F1 x F1 (F2) crosses were less viable in snails and a proportion of them seemed to be changed structurally when viewed by scanning electron microscopy. Certain of the schistosomes were covered with a dense mass of interconnected blood platelets resembling a temporary haemostatic plug but not a blood clot. Interspersed between the platelets were a small number of leucocytes. We suggest that the platelets may have responded to the presence of an antigen which is masked in normal schistosomes but which is exposed in certain F2 hybrids.

Do all human urinary infections with Schistosoma mattheei represent hybridization between S. haematobium and S. mattheei?

Enzyme electrophoresis indicated that all Schistosoma mattheei eggs passed in the urine of humans derive from S. mattheei females in copula with S. haematobium males. It appears that S. mattheei males do not reach sexual maturity in man; however, S. haematobiumxS. mattheei males possibly do.

Frequency and possible consequences of hybridization between Schistosoma haematobium and S. mattheei in the Eastern Transvaal Lowveld.

A survey was conducted at a locality in the Eastern Transvaal Lowveld where the prevalence of human infection with the bovine parasite, Schistosoma mattheei, is relatively high. It was found that, when compared to the number of S. haematobium eggs released into the environment, the number of S. mattheei eggs, with enclosed hybrid miracidia, is small. The consequences of backcrossing between the hybrids and S. haematobium was considered; a mathematical model indicated that a high percentage of the S. haematobium population should contain a small proportion of S. mattheei genes. The results indicate that it is highly unlikely that the two species will evolve into a single species, neither does it seem that the virulence of the parental species will be influenced.

Scanning electron microscopical observations on the shedding of the tegument of adult Schistosoma mattheei.

In search of indications of membrane turnover the teguments of male Schistosoma mattheei from cattle and laboratory rodents were studied by means of scanning electron microscopy. A number of slightly elevated circular patches of tegument which appeared to peel off on the edges were seen on the outer membrane of a limited number of specimens from both rodents and cattle. It is suggested that this phenomenon may represent limited rapid turnover of the outer layer in response to host immunological action.

Host cellular components adhering to the tegument of schistosomes from cattle, buffalo, hippopotamus and lechwe.

The teguments of adult Schistosoma mattheei from cattle and buffalo, S. hippopotami from hippopotamus and S. margrebowiei from lechwe were examined by means of scanning electron microscopy for cells possibly engaged in immunological action. Leukocytes were observed on the teguments of the schistosomes from all 4 host species. Although certain of these cells seemed to be fused to the surface membrane of the worms, they did not display pseudopodia. The tegument of certain schistosomes from buffalo exhibited cells the size of platelets with dendritic structures connected to the tegument of the parasite. The results seem to indicate that, as with laboratory hosts, naturally infected domestic and wild hosts are unable to mount an effective cellular response against the tegument of live adult shistosomes. The possible role of platelets in immunology against schistosomes is mentioned.

Leukocyte adherence to Schistosoma haematobium eggs from children.

The pattern of leukocyte adherence to voided Schistosoma haematobium eggs was compared in children 7-16 years old. A method enabling the measurement of the intensity of adherence was first developed by means of scanning electron microscopy, after which it was adapted for light microscopy. The intensity of adherence decreased from younger to older age groups. This result was unexpected, and has bearing on contemporary views on immunity to human schistosomiasis, particularly the blocking antibody theory.

Susceptibility of South African Bulinus africanus populations to infection with Schistosoma haematobium.

The use of intermediate host snails of Schistosoma spp. which are insusceptible to infection has been proposed as a possible method of controlling schistosomiasis. The objective of this approach is to change the susceptibility of natural snail populations from being predominantly susceptible to a non-susceptible state, through the release of refractory snails into natural habitats. In an attempt to determine whether or not such refractory Bulinus africanus populations occur in eastern South Africa, F1 generation snails of populations from 8 different areas were exposed to miracidia hatched from eggs excreted in the urine of schoolchildren infected with Schistosoma haematobium in the Nelspruit district. The proportion of snails successfully infected ranged from 27 to 100%, which revealed considerable genetic heterogeneity amongst populations of the same snail species. One population from Natal could be regarded as partially refractory, while a laboratory population from Durban proved to be 100% susceptible. A completely refractory strain of B. africanus has not yet been identified.

Enzyme polymorphism in Schistosoma mattheei from cattle in the Eastern Transvaal Lowveld.

Enzyme electrophoresis was conducted on 10 Schistosoma mattheei adult worm samples, comprising 270 individuals, collected from cattle in the Eastern Transvaal Lowveld. Glucose-6-phosphate dehydrogenase (G6PDH) was studied in all the samples and phosphoglucomutase (PGM) and malate dehydrogenase (MDH) in five populations each. Only one population was polymorphic for G6PDH. In this population, in addition to the allele found in all the other samples, a second allele occurred with a similar Rf value to S. haematobium. The two alleles were in Hardy-Weinberg equilibrium. MDH-1 exhibited two alleles. However, these alleles were not in equilibrium. In certain populations, heterozygotes occurred together with homozygotes of one of the alleles only. PGM was monomorphic in all the populations studied.

The tegument of Schistosoma hippopotami from Hippopotamus amphibius in the Kruger National Park.

Schistosoma hippopotami were collected from the right heart chambers and pulmonary arteries of Hippopotamus amphibius culled in the Kruger National Park. The schistosomes were subjected to scanning electron microscopy as well as optical microscopy. The results indicate that S. hippopotami is not conspecific to S. mansoni as suggested in the literature. On account of the morphology of certain tegumental structures of both male and female parasites, it is suggested that S. hippopotami is adapted to the pulmonary arterial circulation of its host.

Notes on the occurrence of tubercular spines in Schistosoma margrebowiei and Schistosoma mattheei.

Scanning electron microscopical (SEM) studies on the tegument of the bovid schistosomes, Schistosoma margrebowiei and Schistosoma mattheei have yielded conflicting results; certain authors observed the tubercles on the tegument of these species to be spined, while others reported that they are spineless. The present study indicates that the protrusion of tubercular spines is subject to phenotypic plasticity regulated by external factors such as the identity of the host species and whether or not the schistosome is paired.

Scanning electron microscope studies of miracidia suggest introgressive hybridization between Schistosoma haematobium and S. haematobium x S. mattheei in the Eastern Transvaal.

Schistosoma haematobium miracidia were collected from a locality with a high prevalence of human infection with the animal parasite, S. mattheei, which hybridizes with S. haematobium, and from 2 localities with negligible infection rates. The terebratoria of the miracidia from these localities were compared with each other, with laboratory maintained S. haematobium and with four populations of S. mattheei by means of scanning electron microscopy. It was found that the terebratorial membrane of certain of the S. haematobium miracidia from the locality with a high S. mattheei prevalence in humans, resembled the more intricate membrane of S. mattheei. This suggests introgressive hybridization between S. haematobium and S. haematobium x S. mattheei.

Further observations on the electrophoretic characterization of South African Schistosoma mattheei and S. haematobium.

Eleven enzymes, which were used to compare South African S. mattheei and S. haematobium in a former study, were employed to study intraspecific variation within S. mattheei, using starch gel electrophoresis and iso-electric focusing where resolution in starch gel was poor. Acid phosphatase varied intraspecifically within S. mattheei in that the most southern population differed from the northern populations. Malate dehydrogenase also varied intraspecifically. Three populations which occur sympatric with S. haematobium had a MDH-1 allele in common with the human schistosome while an allopatric population did not.

Remote controlled sampling of cattle and buffalo blood.

1. Blood samples were obtained from cattle and buffaloes over extended periods of time by remote controlled methods at 4-hourly intervals. 2. Initial handling of the animals and deliberate exposure to stress at the end of the experimental times resulted in increased plasma concentrations of a number of variables. 3. Between initial handling and applied stress, the concentration of all variables investigated showed little change and no evidence of rhythms. 4. The results obtained reflect true plasma composition of free ranging cattle and buffaloes at rest.

The occurrence of Schistosoma mattheei in the south-western Transvaal.

To determine whether Schistosoma mattheei is present in the south-western Transvaal, sixty habitats were searched for the intermediate host snail, Bulinus africanus. Ten populations of this snail were located, 2 of which were infected with S. mattheei. Eggs of one of these isolates, originating from a spring in the Mooi River, were examined with an optical microscope. Scanning electron micrographs of the teguments of adult male worms and the terebratorial membranes of miracidia are described. These parasites are morphologically similar to some previously described from another habitat in the same geographical area and both populations can be regarded as typical S. mattheei.