PubMed Health⌕ Search

Biomedical subjects

R H Andrews

Publications and source records attributed to R H Andrews.

At least 19 recordsLinked to original sources
PubMed1992

Apparent lack of genetic variation within Pelecitus roemeri (Nematoda: Filarioidea) from three Australian species of macropodid marsupial.

An electrophoretic study of Pelecitus roemeri from Macropus robustus, M. giganteus and Wallabia bicolor revealed no genetic differences at 23 enzyme loci. The genetic data support the existing morphological evidence that P. roemeri from these three hosts represents a single species. The data show no genetic variation between nematodes from the same or different host species collected in northern and southern Australia. This result is discussed briefly in relation to Price's model of parasite speciation.

Animals↗
PubMed1992

Interspecific differences in the movements of female ticks on reptiles.

Movements of females of two reptile ticks, Amblyomma limbatum and Aponomma hydrosauri were studied to determine whether the behaviour of the species on hosts was similar or different. Experiments were conducted to determine if the movement of females on hosts prior to mating was influenced by the delayed attachment of conspecific males. A field experiment was also undertaken to determine whether data obtained during laboratory experiments reflected the behaviour of females on hosts in the field. Both in laboratory and field experiments, a significantly greater proportion of Ap. hydrosauri females changed their site of attachment prior to mating. Individual Ap. hydrosauri females made significantly more positional changes than Amb. limbatum females. These interspecific differences occurred irrespective of the absence of conspecific males or presence of non-conspecific adults on hosts. These data may have important ecological implications in relation to the success of colonizing females at their parapatric boundary.

Animals↗
PubMed1992

Detection by allozyme electrophoresis of cryptic species of Hypodontus macropi (Nematoda: Strongyloidea) from macropodid marsupials.

Allozyme electrophoresis of 98 Hypodontus macropi from eight different species of hosts using 24 enzymes revealed a complex of at least six sibling species, with 15-50% fixed genetic differences between taxa. Except for the taxon parasitizing Macropus rufus/M. robustus, pairs of parasite taxa were, in each case, sympatric at each locality examined, thus supporting the conclusion that they represent valid species. The existence of a series of host-specific nematode taxa explains many of the inconsistencies noted previously in the host distribution of H. macropi. Comparison of parasite allozyme phenograms with host phylogeny suggests that four of the speciation events could be attributable to cospeciation and two to host switching. A clear case of host switching between M. rufus/M. robustus and M. fuliginosus was found.

Alleles↗
PubMed1992

Changes in allozyme pattern of the protozoan parasite Giardia intestinalis.

The present study compares the allelic profiles of Giardia intestinalis grown in vivo and in vitro. Three clinical isolates of G. intestinalis were established in suckling mice and subsequently adapted to in vitro culture to test the null hypothesis that samples of the same clinical isolate grown in different culture conditions have identical allelic profiles. For each isolate, a mouse-derived and an axenically cultured sample were analysed electrophoretically at 11 enzyme loci. In each case, the axenically cultured sample of each isolate showed marked allelic differences from its corresponding in vivo sample. These data suggest that there may be either regulated expression of alternative genes encoding distinct isozymes (i.e. gene switching) or selection by different growth conditions of specific genotypes from a mixture present within the original clinical isolate. Although these hypotheses are not tested in this study, the data highlight the importance of confirming that allozymes (or isozymes) are stable genetic characters for the identification and characterization of protozoan taxa.

Alleles↗
PubMed1992

The use of suckling mice to isolate and grow Giardia from mammalian faecal specimens for genetic analysis.

A simple technique is described for preparation of Giardia cysts from faecal samples, the growth of trophozoites in suckling mice and the isolation of trophozoites for genetic analysis by allozyme electrophoresis. In total, 125 new isolates of Giardia have been collected from human and animal sources over a wide geographical area of South Australia and the Northern Territory of Australia. A number of long-established axenized isolates of G. intestinalis belonging to Groups I and II also adapted to grow in suckling mice. These findings indicate that suckling mice are permissive hosts for a variety of genetically dissimilar but morphologically similar organisms of the G. duodenalis type and that this in vivo technique may be less selective than isolation by in vitro culture. The use of suckling mice has revealed that infections can be composed of mixed genotypes and that isolation and purification techniques can be selective. Allozymic interpretation is essential to reveal the genetic complexity of such mixtures.

Alleles↗
PubMed1992

Selection of specific genotypes of Giardia intestinalis by growth in vitro and in vivo.

This study examined whether allelic changes observed when clinical isolates of Giardia intestinalis made in suckling mice were adapted to in vitro growth occurred as a result of gene switching (alternate isoenzymes) or through selection of organisms with different genotypes from mixed infections. Samples were compared electrophoretically at 20 enzyme loci. Marked allelic differences were detected between the uncloned clinical isolates grown in mice and the axenic cultures established from them. Furthermore, the allelic profiles of the uncloned isolates changed during the course of in vivo or in vitro growth. In contrast, all clones produced from each isolate retained identical allelic profiles, regardless of whether they were grown in vivo or in vitro. These findings argue against gene switching as an explanation for the observed allozyme changes and support preferential selection of organisms with specific genotypes by growth conditions. The data indicate the presence of at least 2 and possibly up to 4 distinct genotypes within each clinical isolate. The genetic differences detected between clinical isolates in suckling mice were of similar magnitude to those that separate different axenic isolates of G. intestinalis into cryptic species. Conversely, the genetic differences between the isolates were limited when sampled after establishment in vitro. These findings have significant implications for research on Giardia and other medically important parasites and raise the possibility that culture may exert a similar selective bias on the genotypes isolated from infections with other parasitic protozoa.

Alleles↗
PubMed1992

Distinct genetic groups of Giardia intestinalis distinguished by restriction fragment length polymorphisms.

The taxonomic status of the parasitic protozoal species Giardia intestinalis depends on the morphological similarity of all Giardia isolated from humans and the presumption that Giardia are host-specific. On the basis of electrophoretic data derived from examination of 26 enzyme loci in Australian isolates, it has been proposed that G. intestinalis is a species complex comprising three or four genetically distinct (but morphologically cryptic) species. These received the tentative designations of genetic groups I-IV (R. H. Andrews, M. Adams, P. F. L. Boreham, G. Mayrhofer & B. P. Meloni. International Journal for Parasitology 19, 183-190, 1989). In the present study, two unrelated DNA probes (one specific for a gene encoding a trophozoite surface protein, the other detecting a non-coding repetitive sequence within the G. intestinalis genome) were used in Southern hybridization analyses to examine 10 axenic isolates of G. intestinalis, established from diverse geographical regions in Australia, together with the Portland-1 isolate from the USA. Both probes identified every isolate unambiguously as belonging to one or other of two genetic clusters. Electrophoretic analysis of the same samples indicated that these clusters correspond to the previously defined genetic groups I and II. No heterogeneity was apparent within the seven group I isolates using either probe. However, when probed with the repetitive sequence, the four isolates belonging to group II exhibited small differences in banding patterns, suggesting that this group may be less homogeneous than group I.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Apparent absence of genetic differences among species of Teladorsagia (Nematoda: Trichostrongylidae).

The technique of allozyme electrophoresis was applied to three species of Teladorsagia present in sheep to determine the extent of genetic variation among species. Thirty-four enzyme loci were established of which 22 were invariant and 12 were shown to be polymorphic. No fixed allelic differences were detected among the species and the level of polymorphism was within the range found commonly between populations of a single species. Therefore, the genetic data support breeding data and existing morphological evidence that T. circumcincta, T. davtiani and T. trifurcata as currently recognized do in fact belong to a single species.

Alleles↗
PubMed1989

Giardia intestinalis: electrophoretic evidence for a species complex.

The technique of allozyme electrophoresis was applied to 29 Australasian stocks and 48 clones of Giardia intestinalis from humans as a means of increasing the number of genetic markers currently available for identification and classification. Fifty different enzymes were examined and of these 26 loci were found to be suitable for use as genetic markers. The data indicate the presence of four discrete genetic groups within the sample of G. intestinalis examined. The groups had fixed genetic differences at 23-69% of loci established. The evidence suggests that G. intestinalis is a species complex. The results have important implications for the systematics of human isolates of Giardia, as well as for studies on the epidemiology and demography of giardiasis in Australia and elsewhere.

Animals↗
PubMed1989

Genetic characterization of three strains of Hymenolepis diminuta at 39 enzyme loci.

The technique of allozyme electrophoresis was applied to three strains of Hymenolepis diminuta to distinguish between three hypotheses [(1) multiple species, (2) genetically distinct founder stocks and (3) response to differential selection among similar stocks] proposed to account for metabolic differences among strains. There was no evidence from the 39 enzyme loci established that the three strains represented more than one species. In the absence of knowledge of the population structure of H. diminuta in the wild, electrophoretic data herein could not distinguish between the latter hypotheses. Nevertheless, all three strains were distinguishable on electrophoretic profiles and allelic similarities between strains question the view of their proposed origins.

Animals↗
PubMed1989

A genetic approach to species criteria in the amoeba genus Naegleria using allozyme electrophoresis.

The present study employs allozyme electrophoresis to characterize and inter-relate 61 isolates of Naegleria. Diploidy was confirmed, with heterozygotes observed at 29 of the 33 loci established and in all but two isolates. With a single exception, isolates clustered at two levels of similarity, either below 21% or above 52%. It is argued that such a major discontinuity provides a sound biological basis for a species concept in Naegleria. On this basis the present species-level taxonomy does not reflect the genetic diversity of the genus. The study recognized 18 genetic groups of species rank. The subspecies N. australiensis italica deserves specific rank; additional thermophilic species not closely related to N. fowleri and N. lovaniensis are recognized; and N. gruberi as currently conceived is a complex of 10 species, at least five of which are represented in the formal culture collections. Most species are genetically too different for relationships to be elucidated by allozyme electrophoresis, supporting the view that some of the times of divergence within the genus are extremely ancient.

Alleles↗
PubMed1989

Genetic characterization of three species of Onchocerca at 23 enzyme loci.

The technique of allozyme electrophoresis was applied to species of Onchocerca from cattle to increase the number of enzyme loci established and therefore provide a genetic basis for a rational species-level taxonomy. Twenty-three enzyme loci were established and provided unequivocal genetic evidence for the taxonomic validity of Onchocerca gibsoni, O. gutturosa and O. lienalis. Furthermore, the diagnostic enzyme markers detected form the basis for identification of life-cycle stages, individuals and species and population structure analyses.

Animals↗
PubMed1988

Identification of life cycle stages of the nematode Echinocephalus overstreeti by allozyme electrophoresis.

Data presented in this study highlight the potential of allozyme electrophoresis in providing unequivocal genetic evidence for the identification of life cycle stages, particularly where species have complex life cycles. Adults of the nematode Echinocephalus overstreeti parasitize the elasmobranch Heterodontus portusjacksoni. The putative larval form which is morphologically dissimilar is found in two species of marine molluscs, Chlamys bifrons and Pecten albus. Electrophoretic analysis indicated that the adult and larval forms shared alleles at all of the 34 enzyme loci established. Furthermore, there were no fixed allelic differences between larval forms from different mollusc species.

Alleles↗
PubMed1987

Correspondence between MMPI PTSD measures and clinical diagnosis.

Correspondence of the Minnesota Multiphasic Personality Inventory (MMPI) posttraumatic stress disorder (PTSD) subscale and the clinical scale decision rules reported by Keane, Malloy, and Fairbank (1984) with clinical diagnoses of PTSD was measured on a sample of 595 veterans. The measures demonstrated good sensitivity and selectivity, but the false-positive rate was high. It is suggested the MMPI measures be used to rule out, but not to establish, the diagnosis of PTSD. The construct validity of the PTSD subscale was supported by the finding of a higher mean score in combat than noncombat veterans.

Combat Disorders↗
PubMed1984

Effects of temperature and tick weight on expression of autogeny in the argasid tick Ornithodoros parkeri Cooley (acari: Argasidae).

The effects of different temperatures on the expression of autogenic development in unfed/mated Ornithodoros parkeri Cooley females were examined. High temperature (29 C) induced autogeny in lower, middle and higher weight classes (11-20, 21-30, 31-40 mg, respectively) with all females in the highest weight class and most in the middle weight class ovipositing within 51 days post-mate. At a lower temperature (21 C) autogenic development was not expressed by higher and middle weight females, whereas lower weight females exhibited similar degrees of autogeny at both temperatures. Results are discussed in relation to presumptive factors involved in the control and mediation of autogeny.

Animals↗