R. J. Knowles

Bio: R. J. Knowles is an academic researcher from British Museum. The author has contributed to research in topics: Malate dehydrogenase & Schistosoma intercalatum. The author has an hindex of 9, co-authored 12 publications receiving 285 citations.

Observations on Schistosoma bovis Sonsino, 1876

Abstract: Summary Some biological characteristics of Schistosoma bovis Morocco, Sardinia and Iran in hamsters are described and discussed. Differences in infectivity, growth rates, maturation times, egg production and tissue deposition of eggs in the different strains are recorded. The egg shape and size of S. bovis Morocco, Sardinia, Iran, Kenya and S. mattheei are compared, as are the acid phosphatase, malate dehydrogenase and glucose 3-phosphate dehydrogenase isoenzymes. The compatibility/incompatibility of the same four strains of S. bovis to various members of the five species complexes of the genus Bulinus are recorded.

The influence of Calicophoron microbothrium on the susceptibility of Bulinus tropicus to Schistosoma bovis.

Abstract: A total of 480 snails were collected from 3 habitats on the Mau Escarpment, Kenya, and were identified asBulinus tropicus. Of the 351 snails examined alive in London, 75 were infected withCalicophoron microbothrium, 39 withC. microbothrium andSchistosoma bovis, 1 withS. bovis. 24 with other species of trematodes and 212 were uninfected. Examination of digestive glands ofB. tropicus either uninfected or infected with bothC. microbothrium andS. bovis demonstrated that it is possible to differentiate between parasite and host enzyme activity using glucose phosphate isomerase. However, malate dehydrogenase enables a much clearer differentiation between the enzyme activity of the schistosome and that of the amphistome. Laboratory snail infection experiments demonstrated that it is possible successfully to infectB. tropicus withS. bovis if the snails have previously been exposed to miracidia ofC. microbothrium.

Mating behaviour in mixed infections of Schistosoma haematobium and S. intercalatum

Abstract: Summary Experiments were designed to examine the mating behaviour of Schistosoma haematobium and S. intercalatum in mixed infections in hamsters. Individual worms were identified by electrophoretic analysis of glucose-6-phosphate dehydrogenase which was characteristic for each isolate, in addition the uterine eggs of individual females were examined. The results showed that a specific mate recognition system does not exist for S. haematobium and S. intercalatum. The application of statistical tests to the results suggests that S. haematobium male worms are better at pairing with female worms of either species than S. intercalatum male worms. The significance of the results is discussed in relation to an occurrence of natural hybridization between these species in Cameroun.

On Schistosoma curassoni, S. haematobium and S. bovis from Senegal: development in Mesocricetus auratus, compatibility with species of Bulinus and their enzymes

Abstract: A comparative study on the development of Senegalese isolates of Schistosoma curassoni, S. haematobium and S. bovis in hamsters is reported, together with the compatibility of these parasites with Bulinus spp. and enzymes of adult worms. The mean worm return from 35 hamsters exposed to 100 cercariae each of S. curassoni was 11·5%, and of these 54% were paired, the remainder were single males. The growth and maturation of the worms were recorded from 40 to 100 days. The cross-over point (when paired females are of the same length as paired males) was reached at 42 days post-infection when the worms averaged 13·7 mm in length. The majority of tissue eggs (84·5%) were recovered from the liver, compared with 11% in the colon, 2·5% in the caecum and 1·6% in the small intestine. Estimates of the fecundity of paired females averaged 167 eggs/day per female worm. Snail-infection experiments showed S. curassoni to be compatible with B. umbilicatus, marginally compatible with B. senegalensis and incompatible with B...

Observations on an isolate of Schistosoma bovis from Tanzania.

Abstract: The eggs ofSchistosoma bovis isolated from Misungwi, Tanzania measure 211.1 μm±18.4 long and 66.7 μm±5.4 wide. The parasite is naturally transmitted byBulinus africanus and is compatible in the laboratory with snails belonging to theB. truncatus, B. forskali, andB. reticulatus groups. The compatibility withB. africanus group snails is shared with isolates from Kenya and Sudan but not withS. bovis from more northern distributions. Enzyme analyses were carried out by isoelectric focusing. In adult worms, phosphoglucomutase (PGM), hexokinase (HK), malate dehydrogenase (MDH), and lactate dehydrogenase (LDH) proved to be monomorphic whereas two types of glucosephosphate isomerase (GPI), three types of glucose-6-phosphate dehydrogenase (G6PDH), and two types of acid phosphatase (AcP) were identified. Differences in the pI values of GPI and MDH of snail digestive glands and of larval parasites allowed the intramolluscan stages to be characterised. The GPI heterogeneity encountered was common both to the larval and adult parasites. The enzyme types identified inS. bovis are discussed both from an intra- and interspecific viewpoint.

A comparison between mitochondrial DNA and the ribosomal internal transcribed regions in prospecting for cryptic species of platyhelminth parasites

Abstract: We examined the relative merits of mitochondrial DNA loci and ribosomal DNA internal transcribed spacers for their use in prospecting for cryptic species of platyhelminth parasites. Sequence divergence at ITS1 and ITS2 was compared with divergence at 2 mtDNA loci (NADH dehydrogenase-1 and cytochrome c oxidase I) between closely related species of trematodes and cestodes. Both spacers accumulated substitutions substantially more slowly than mtDNA, which clearly shows a higher level of divergence among species relative to intra-specific variation. Besides a slow rate of substitution, other caveats that may be encountered when using ITS sequences as a prospecting marker are discussed. In particular, we note recent studies that suggest the existence of substantial levels of intra-individual variation in ITS sequences of flatworms. Because it is likely that closely related species share this phenomenon, it may confound the detection of cryptic species, especially if small sample sizes are studied. Although potential limitations of mtDNA are also recognized, the higher rate of evolution and smaller effective population size of this marker increases the probability of detecting diagnostic characters between cryptic species.

A molecular phylogeny of the genus Echinococcus

Abstract: Three nucleotide data sets, two mitochondrial (COI and ND1) and one nuclear (ribosomal ITS1), have been investigated in order to resolve relationships among species and strains of the genus Echinococcus. The data have some unusual properties in that mitochondrial heteroplasmy was detected in one strain of E. granulosus, and more than one class of ITS1 sequence variant can occur in a single isolate. The data failed to support the hypothesis that E. granulosus, as it is currently viewed, is a single valid species. Rather, the strains of E. granulosus seem to comprise at least three evolutionarily diverse groups, the sheep strain group, bovine strain group and horse strain group. Molecular distances between them are comparable to, or greater than, molecular evolutionary distances observed between recognized species. The affinities of the cervid strain of E. granulosus are unclear because of ambiguous data, but this strain does not appear to be ancestral to others. E. multilocularis may not be distinct from E. granulosus. However, the remaining two species, E. vogeli and E. oligarthrus appear distinct and rather distant from the first two. Based on the results presented here, taxonomic revision of the genus is clearly warranted.

Immune mechanisms in trematode-snail interactions

Abstract: Digenetic trematodes, including several species of medical and veterinary significance, nearly all depend on molluscs (usually gastropods) as hosts for asexual reproduction. The molluscan internal defence system, although lacking many of the familiar features of the vertebrate immune system, may pose a substantial obstacle to digenean development. In this article, Wil van der Knaap and Eric Loker discuss the manner in which this system is mobilized to kill larval trematodes and the real and putative mechanisms of digenean evasion of molluscan immune responses. These two possible outcomes of trematode-snail associations make them intriguing model systems for exploring processes of parasite infectivity and host resistance.

Bidirectional introgressive hybridization between a cattle and human schistosome species.

Abstract: Schistosomiasis is a disease of great medical and veterinary importance in tropical and subtropical regions, caused by parasitic flatworms of the genus Schistosoma (subclass Digenea). Following major water development schemes in the 1980s, schistosomiasis has become an important parasitic disease of children living in the Senegal River Basin (SRB). During molecular parasitological surveys, nuclear and mitochondrial markers revealed unexpected natural interactions between a bovine and human Schistosoma species: S. bovis and S. haematobium, respectively. Hybrid schistosomes recovered from the urine and faeces of children and the intermediate snail hosts of both parental species, Bulinus truncatus and B. globosus, presented a nuclear ITS rRNA sequence identical to S. haematobium, while the partial mitochondrial cox1 sequence was identified as S. bovis. Molecular data suggest that the hybrids are not 1st generation and are a result of parental and/or hybrid backcrosses, indicating a stable hybrid zone. Larval stages with the reverse genetic profile were also found and are suggested to be F1 progeny. The data provide indisputable evidence for the occurrence of bidirectional introgressive hybridization between a bovine and a human Schistosoma species. Hybrid species have been found infecting B. truncatus, a snail species that is now very abundant throughout the SRB. The recent increase in urinary schistosomiasis in the villages along the SRB could therefore be a direct effect of the increased transmission through B. truncatus. Hybridization between schistosomes under laboratory conditions has been shown to result in heterosis (higher fecundity, faster maturation time, wider intermediate host spectrum), having important implications on disease prevalence, pathology and treatment. If this new hybrid exhibits the same hybrid vigour, it could develop into an emerging pathogen, necessitating further control strategies in zones where both parental species overlap.

Introgressive Hybridization of Schistosoma haematobium Group Species in Senegal: Species Barrier Break Down between Ruminant and Human Schistosomes

Abstract: Background Schistosomes are dioecious parasitic flatworms, which live in the vasculature of their mammalian definitive hosts. They are the causative agent of schistosomiasis, a disease of considerable medical and veterinary importance in tropical and subtropical regions. Schistosomes undergo a sexual reproductive stage within their mammalian host enabling interactions between different species, which may result in hybridization if the species involved are phylogenetically close. In Senegal, three closely related species in the Schistosoma haematobium group are endemic: S. haematobium, which causes urogenital schistosomiasis in humans, and S. bovis and S. curassoni, which cause intestinal schistosomiasis in cows, sheep and goats.