Anne Kaukas

Some molecular insights into schistosome evolution

Robust phylogenies based on molecular data for species within the genus Schistosoma have been generated in recent years. The considerable progress made in understanding the relationships between many of the 19 recognised species of Schistosoma is reviewed with particular attention being given to the detection and analysis of parasite variation as shown by studies on ribosomal RNA genes, mitochondrial DNA and RAPDs. For the most part, molecular phylogenies agree with observations based on morphological or life-history characteristics. It is clear that the parasites of man do not form a monophyletic group and that close relationships exist between parasites within species groups, especially in the S. haematobium group of species. The S. japonicum group appears to be the most divergent of the species groups and yet little DNA sequence variation has been observed between various isolates of S: japonicum. Some of the less studied schistosomes have yet to be examined at the molecular level and may prove to be interesting links between the species groups as has recently been shown with S. hippopotami. The power of molecular approaches for the analysis of schistosomes at the population and individual level is now apparent, especially for S. mansoni. Important questions remain concerning the maintenance of parasite diversity and how schistosomes respond to selection pressures imposed either during natural progression through the life-cycle or through drug treatment or vaccination. Gene discovery and gene mapping projects are leading to a better understanding of the schistosome genome and can be expected to contribute significantly to future comparative evolutionary studies.

A phylogenetic analysis of schistosoma haematobium group species based on randomly amplified polymorphic dna

Randomly amplified polymorphic DNA (RAPD) profiles were produced using four oligonucleotide primers with genomic DNA from 15 isolates of schistosome. Both inter- and intraspecific variation were noted. Intraspecific variation was greater for two species of the S. haematobium group (S. haematobium and S. intercalatum) than for S. mansoni. The inferred phylogeny placed S. curassoni and S. bovis as sister groups to S. mansoni-S. rodhaini group. S. mattheei and S. leiperi formed a separate lineage. The results confirm that RAPD profiles may be used for both strain and species differentiation and for the generation of phylogenetic trees.

Schistosomiasis in Dogon country, Mali: identification and prevalence of the species responsible for infection in the local community

The prevalence of schistosomiasis amongst the Dogon people in 4 villages and one school of the Bankass district of Mali was determined during 2 surveys in 1992; 1398 urine and 1199 stool samples were examined. The most common schistosome was Schistosoma haematobium, with an overall prevalence of 51.3%; S. mansoni had a prevalence of 12%. No S. intercalatum egg was seen in the stools. Biomphalaria pfeifferi and Bulinus truncatus were found in pools at the base of the Dogon cliffs; Bulinus forskalii was found in smaller numbers in brick pits. Two isolates from urine samples of children were identified as S. haematobium in the laboratory using an alpha-glycerophosphate marker, restriction enzyme analysis of ribosomal deoxyribonucleic acid (rDNA) and random amplification of polymorphic DNA. The isolates did not develop in Bulinus forskalii or B. crystallinus of the B. forskalii group. Some evidence for past hybridization of S. haematobium and S. intercalatum is provided by the enzyme and rDNA results as well as the positive Ziehl-Neelsen staining of polymorphic eggs in urine samples. The findings are discussed in relation to the published observations concerning schistosomiasis in travellers returning from this region of Mali.

Cattle schistosomiasis in Zambia

A total of 358 cattle was examined for schistosome infection in Zambian slaughterhouses. A total of 542 worms collected from 104 infected individuals was examined for glucose-6-phosphate dehydrogenase and phosphoglucomutase using isoelectric focusing. The overall prevalence of infection was 51%. Ninety three percent of the infected animals had less than 100 worm pairs in the mesenteric veins. Schistosoma mattheei was the predominant species (75%); S. leiperi (12%) and S. margrebowiei (2%) were also identified. The remaining 11% of the worms showed one of two distinct heterozygote patterns. Pattern A is identical to that of a laboratory-produced F1 S. mattheei x S. haematobium hybrid, but could also represent a S. mattheei x S. leiperi hybrid. Further studies are required to elucidate the origins of pattern B.

Schistosomiasis in the Republic of São Tomé and Principe: characterization of Schistosoma intercalatum.

This paper reports the morphological and biochemical characterization of the species of Schistosoma infecting humans in the Republic of São Tomé and Principe. The eggs are typical in shape and size of S. intercalatum, measuring on average between 174.5 microns and 189.1 microns. The eggs are voided in the faeces and not the urine of infected people. The parasite experimentally develops in several different species of Bulinus belonging to the B. forskalii group, including B. forskalii, with a minimum prepatent period of 25 d, and also in snails of the B. reticulatus group (B. wrighti); it is incompatible with snails of the B. africanus and B. truncatus/B. tropicus complex. A survey of 5 different habitats at intervals of 2 weeks over a period of one year showed that populations of B. forskalii increased during the dry period of June, July and August in 1988, and in 3 of the habitats snails were present throughout the year. Hence transmission may take place in these habitats throughout the year. Preliminary evidence suggests that water velocity is a limiting factor confining Bulinus to the north-east of the island where the terrain is less mountainous. Development of schistosomes from São Tomé was followed in experimentally infected hamsters. The cross-over point (the point at which the paired male and female worms are of the same average length) occurred at about 49 d after infection: eggs were first seen in the uteri of the female worms 48 d after infection. The parasite from São Tomé developed in sheep and produced viable eggs.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidemiological and genetic observations on human schistosomiasis in Kinshasa, Zaire

A survey for Schistosoma intercalatum conducted in Kinshasa, Zaire, in September 1994 revealed a prevalence of 3.6% (n = 167). Three isolates of schistosomes were made by exposing Bulinus wrighti to miracidia hatched from eggs collected from 2 infected children. Characterization of the isolates by biochemical (isoenzymes of phosphoglucomutase), molecular (restriction fragment length polymorphism and randomly amplified polymorphic deoxyribonucleic acid analysis) and morphological (egg measurements) techniques confirmed the existence of an autochthonous transmission focus of S. intercalatum in Kinshasa. The study also provided evidence of the occurrence of natural hybridization between S. intercalatum and S. haematobium. No potential snail host for either species was found in the 2 rivers examined. Apart from Bu. globosus from Zambia and Bu. wrighti, snail infection experiments showed an incompatible relationship between the parasite isolates and snails belonging to the Bu. forskalii group, the Bu. iruncatus/Bu. tropicus complex, and the Bu. africanus group.

Hybridisation between the digeneans Schistosoma haematobium and S. mattheei : viability of hybrids and their development in sheep

The F1 and F2 hybrids of Schistosoma haematobium male × S. mattheei female were studied with regard to infectivity to intermediate and definitive hosts, isoenzymes (phosphoglucomutase) of individual male worms, randomly amplified polymorphic DNAs of individual adult worms and scanning electron micrographs of the tubercles of male worms. The infection rate of the F1 hybrid miracidia in Bulinus globosus (41.7%) was greater than that achieved in B. wrighti (16.3%); the infection rate of the F2 in B. wrighti was 15.4%. In the definitive hosts: in sheep only male F1 hybrids (i.e. no females and no F2 worms)were recovered; but in hamsters both paired F1 worms and unpaired F1 males were recovered, as were one pair of worms and unpaired males of the F2 generation. The S. mattheei and S. haematobium male worms showed very distinctive PGM patterns, and the F1 hybrids showed additive patterns and a polymorphism with two distinct types of band patterns which are the result of polymorphism in the S. haematobium. The RAPD profiles of the F1 hybrids were also composite of the two parental species. Scanning electron micrographs of the tubercles of male S. haematobium showed them to be heavily spined, whereas those of S. mattheei males were devoid of spines. The F1 hybrids did show variation ranging from non-spined, some with partial spination, to those with heavily spined tubercles. Male worms of the F2 generation possessed tubercles either with or without spines. The potential significance of hybridisation in areas of sympatry between S. haematobium and S. mattheei is discussed.

Restriction enzyme mapping of ribosomal DNA ofSchistosoma spindale andS. leiperi (Digenea) and its application to interspecific differentiation

Restriction maps were determined for the ribosomal RNA gene complex ofSchistosoma spindale andS. leiperi. The restriction map of theS. spindale rRNA gene complex was found to differ from those of other schistosomes previously described by the presence of an additionalEcoRI site in the non transcribed spacer region. In common withS. mattheei andS. margrebowiei, bothS. leiperi andS. spindale appear to have insertions in the transcribed spacer region, relative toS. mansoni.EcoRI digests of genomic DNA, probed with pSM 889, enabled differentiation ofS. spindale andS. leiperi from four other species of schistosome.