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A Kaukas

Publications and source records attributed to A Kaukas.

15 recordsLinked to original sources
PubMed1997

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.

Animals↗
PubMed1994

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.

Animals↗
PubMed1994

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.

Animals↗
PubMed1988

The effect of growth-promoting antibiotics on the faecal enterococci of healthy young chickens.

Small groups of chickens were given feed containing either avoparcin, nitrovin, virginiamycin or zinc bacitracin from the day of their purchase as day-olds. Differences between the birds receiving growth promoters and the untreated controls were observed during the last third of the 23 d survey period. The enterococcal population of the 'dosed' birds contained a greater proportion of Enterococcus faecium than did that of the control birds while the converse was true for Ent. gallinarum. This apparent selection of Ent. faecium by the growth-promoting antibiotics had an influence on the incidence of resistance to therapeutic antibiotics among the enterococcal population as a whole. This was because this species was generally more resistant than Ent. gallinarum to cephalothin, the MLS antibiotics (erythromycin, lincomycin and tylosin) and tetracycline.

Animal Feed↗
PubMed1987

The effect of ampicillin and tylosin on the faecal enterococci of healthy young chickens.

Enterococcal isolates from young chickens were differentiated into one of three species, namely Enterococcus faecalis, Ent. faecium and Ent. gallinarum. The proportion of each species among the enterococcal population changed with time in birds not dosed with antibiotics. This pattern of change was modified in birds dosed with either tylosin or ampicillin even though ampicillin did not select for ampicillin resistance among the enterococcal population. A gradual increase in tylosin resistance was recorded with time among the enterococci of the 'undosed' control birds. This was associated with an increase in the proportion of Ent. faecium, a species commonly resistant to tylosin, among the enterococci of the birds as they grew older.

Ampicillin↗
PubMed1986

Preliminary observations on the influence of antibiotics on the ecology of Escherichia coli and the enterococci in the faecal flora of healthy young chickens.

Two separate replicated experiments are described. In the first the influence of oxytetracycline on the Escherichia coli flora was assessed, while in the second the effect of tylosin on the enterococci was investigated. In both experiments the administration of the antibiotic was associated with an increase in the average proportion of isolates resistant to the agent although in experiment 1 the agent had no apparent influence on either the total number of E. coli strains, differentiated by biotype and resistance pattern, or the number of 'new' strains per sampling. On the other hand significant differences were noted between the two replicates and also in relation to the age of the birds. In the second experiment fewer enterococcal strains were isolated from the birds dosed with tylosin but since fewer strains on average were isolated from the samples collected prior to dosing it is probable that this difference was due to factors other than the influence of the antibiotic. The enterococci were speciated and the two most commonly isolated were Streptococcus faecalis and S. faecium. The isolation rate of each was expressed as a proportion of the total number of enterococcal isolates per sample and when considered in relation to both dosing and the age of the bird the interaction dosing X age was statistically significant for both species. However, the differences did not appear particularly great and it was possible that the differences were of no practical importance from an ecological point of view.

Animals↗
PubMedDate not supplied

A new method for isolating Trypanosoma brucei gambiense from sleeping sickness patients.

Low infectivity to laboratory mammals and low virulence make Trypanosoma brucei gambiense difficult to isolate and grow in amounts sufficient for biochemical characterization. We report the isolation of T.b. gambiense by feeding cryopreserved primary isolates to laboratory-reared Glossina morsitans morsitans, followed by rapid cultivation in vitro of procyclic forms dissected from infected tsetse fly midguts. This technique allows the characterization of hitherto unsampled populations and avoids selection due to long-term subpassage. Of 16 primary isolates from trypanosomiasis patients of the Fontem focus in Cameroon, 12 (75%) produced infections in tsetse whereas only 4 (25%) infected rats. Ten isolates were subsequently cultivated as procyclic forms in vitro; 2 failed to grow owing to bacterial contamination. In addition, 2 primary isolates from Côte d'Ivoire patients and a stock of low virulence from the Congo Republic were similarly grown. Only one primary isolate produced tsetse salivary gland infections, an observation consistent with the hypothesis that some populations of T.b. gambiense are intrinsically incompatible with G.m. morsitans.

Animals↗
PubMedDate not supplied

The substitution of procyclic for bloodstream form Trypanosoma brucei gambiense in isoenzyme studies.

Examination of 10 enzymes from 8 stocks of Trypanosoma brucei showed that procyclic forms could be substituted for bloodstream forms in isoenzyme studies. T. b. gambiense procyclic forms cultured in vitro offer a better source of material for genetic investigations because this species is usually of low infectivity and virulence to laboratory rodents. Using 6 stocks of T. b. gambiense and 2 stocks of T. b. brucei, enzyme patterns of bloodstream and procyclic forms were identical for isocitrate dehydrogenase, malic enzyme, two nucleoside hydrolases (utilizing inosine and deoxyinosine respectively), phosphoglucomutase and superoxide dismutase. Procyclic forms appeared to have greater threonine dehydrogenase activity than bloodstream forms. Consistent differences between bloodstream and culture forms were observed for alanine aminotransferase, aspartate aminotransferase and malate dehydrogenase. These agreed with known differences in the metabolism of procyclic and bloodstream forms.

Animals↗
PubMedDate not supplied

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.

Adolescent↗
PubMedDate not supplied

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)

Africa, Western↗
PubMedDate not supplied

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.

Adolescent↗
PubMedDate not supplied

Proceedings of the schistosome genome project.

"The host-parasite relationship" is a vast and diverse research field which, despite huge human and financial input over many years, remains largely shrouded in mystery. Clearly, the adaptation of parasites to their different host species, and to the different environmental stresses that they represent, depends on interactions with, and responses to, various molecules of host and/or parasite origin. The schistosome genome project is a primary strategy to reach the goal; this systematic research project has successfully developed novel technologies for qualitative and quantitative characterization of schistosome genes and genome organization by extensive international collaboration between top quality laboratories. Schistosomes are a family of parasitic blood flukes (Phylum Platyhelminthes), which have seven pairs of autosomal chromosomes and one pair of sex chromosomes (ZZ for a male worm and ZW for a female), of a haploid genome size of 2.7 x 10(8) base pairs (Simpson et al. 1982). Schistosomes are ideal model organisms for the development of genome mapping strategies since they have a small genome size comparable to that of well-characterized model organisms such as Caenorhabditis elegans (100 Mb) and Drosophila (165 Mb), and contain functional genes with a high level of homology to the host mammalian genes. Here we summarize the current progress in the schistosome genome project, the information of 3,047 transcribed genes (Expressed Sequence Tags; EST), complete sets of cDNA and genomic DNA libraries (including YAC and cosmid libraries) with a mapping technique to the well defined schistosome chromosomes. The schistosome genome project will further identify and characterize the key molecules that are responsible for host-parasite adaptation, i.e., successful growth, development, maturation and reproduction of the parasite within its host in the near future.

Animals↗