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D H Molyneux

Publications and source records attributed to D H Molyneux.

At least 37 records · Page 2Linked to original sources
PubMed1997

Patterns of change in vector-borne diseases.

The statuses of vector-borne diseases have changed over recent years. How a few such diseases have changed and the primary causes of change (urbanization, increased conflict, changes in water-resource management, ecological and environmental change, and reduced health service resourcing) are the subjects of the present review. The key impacts which these primary causes have on selected vectors and the infections they transmit are tabulated. The success of vector-control programmes against onchocerciasis and Chagas disease is discussed, and the methods used to evaluate the epidemiological impact of such controls are described. Bednet programmes for control of malaria are recognized as a potential future means of reducing morbidity and mortality in children. In contrast to the success achieved in limiting Simulium and Triatoma populations through vertical programmes, control of tsetse, whilst successful in Uganda, has not been utilized to stem recent epidemics of sleeping sickness in resource-stressed settings in Central Africa. Vector-borne diseases will continue to be a problem because of the adaptability of vectors, the potential problems of managing effective vector controls within decentralized health systems, and the influence of activities outside the health sector itself. Changes beyond the health sector can increase the problem posed by a vector and increase the frequency of transmission.

Animals↗
PubMed1997

Variation in cuticular hydrocarbons among strains of Anopheles (Cellia) stephensi Liston possibly related to prior insecticide exposure.

Cuticular lipids were extracted in hexane from the females of four strains of Anopheles stephensi and separated by capillary gas chromatography. When the chromatograms produced were quantified and compared by discriminant analysis, compositional variations in the hydrocarbons indicated that two of the strains, 'Russ' (originally isolated in the former (U.S.S.R.) and 'Iraq' (from Iraq), both of which were susceptible to DDT and malathion, could be confidently separated from 'Beech' from India and 'St Mal' from Pakistan, both of which were resistant to DDT and malathion. A high degree of hydrocarbon segregation between each of the four strains might be associated with geographical variation. It appears that there are significant and real differences in the hydrocarbons of these strains and these may be at least partially related to genetic alterations resulting from prior insecticide exposure. However, far more analysis is required if any relationship with prior exposure is to be confirmed.

Animals↗
PubMed1996

Cytotaxonomic identifications of the Simulium damnosum complex (Diptera:Simuliidae) from Nigeria.

Cytotaxonomic analysis of Simulium damnosum s.l. larvae collected from 23 sites across 4 bioclimatic zones in Nigeria revealed the presence of 5 cytospecies (S. damnosum s.str., S. sirbanum, S. squamosum, S. yahense and S. soubrense (including the Beffa form). The biogeographical distribution of the sibling species was mostly similar to that observed further west in the OCP area, although geographic cytotaxonomic variation was recorded in S. squamosum, S. damnosum s.str. and S. sirbanum. Some aspects of the chemical and physical environment of the breeding habitats were investigated.

Animals↗
PubMed1995

In vitro cultivation of Trypanosoma acomys: production of insect stages and bloodstream forms.

When Trypanosoma acomys bloodstream forms were cultivated at 37 degrees C in Schneider's Drosophila medium supplemented with 20% (v/v) heat-inactivated foetal calf serum (FCS), with Microtus agrestis embryonic fibroblasts in RPMI 1640 medium supplemented with 20% FCS or in Baltz's medium supplemented with 10% FCS, the parasites transformed and largely remained as epimastigotes. Epimastigotes were also usually the commonest stage observed when the parasites were co-cultivated with a mosquito cell line at 27 degrees C. However, if these cultures were initiated with the supernatant suspensions from fibroblast cultures that had been cryopreserved, trypomastigotes, including bloodstream-like forms, were the predominant stage for the first 4 days of culture. It is suggested that the glycerol supplement or the temperature changes stimulated this unusual morphogenesis. At 27 degrees C, T. acomys was incapable of multiplying and died when cultured in fresh Schneider's Drosophila medium supplemented with 20% FCS, but co-cultivation with the mosquito cell lines or cultivation in cell-free supernatants from 1-week-old mosquito cell cultures was successful at this temperature; most of the parasites multiplied as epimastigotes.

Animals↗
PubMed1995

Oral transmission of trypanosomes of the subgenus Herpetosoma from small mammals.

The rodents Microtus agrestis, Clethrionomys glareolus, Apodemus sylvaticus and white BK rats were given either a single intraperitoneal (i.p.) injection, an intragastric (i.g.) inoculation or an oral (p.o.) inoculation of the culture forms, including metacyclic trypomastigotes, of Trypanosoma microti, T. evotomys, T. grosi and T. lewisi, respectively. Similar levels of parasitaemia were produced by each of the three routes of infection, although the prepatent period was 3-5 days shorter in the case of the i.p.-injected animals. The oral inoculation of blood from mice infected with T. musculi into uninfected mice (outbred) and from rats infected with T. lewisi into uninfected BK rats produced parasitaemia after 6-8 days. This is the first report of the oral and i.g. transmission of T. microti, T. evotomys and T. grosi into their specific homologous hosts.

Animals↗
PubMed1995

Theileria parva carrier state in naturally infected and artificially immunised cattle.

Rhipicephalus appendiculatus adult ticks, collected in the field from zebu (Bos indicus) and exotic (Bos tarus) cattle with high antibody titres to Theileria parva schizont antigen, transmitted Theileria parva infection typical of East Coast fever to susceptible cattle. Uninfected R. appendiculatus nymphs applied to naturally recovered zebu and exotic cattle kept under tick-free conditions in the laboratory for 16 and 7 months respectively, transmitted fatal theileriosis to susceptible cattle. Cattle immunised by the infection and treatment method were shown to be carriers of Theileria parva by examination of the salivary glands of ticks applied to them and by tick transmission. Three and 7 months after immunisation, Theileria parva infected lymphocytes were established in vitro from peripheral blood lymphocytes. This was the first demonstration, in vitro, of the existence of schizonts in Theileria parva (East Coast fever) infection carrier status. These studies show that cattle from endemic and epidemic areas of East Coast fever (ECF) become carriers thereby maintaining the T. parva population. The relevance of the findings in this study to the control of ECF by dipping, immunisation and treatment is discussed.

Animals↗
PubMed1995

Effects of haemagglutination (lectin) inhibitory sugars on Theileria parva infection in Rhipicephalus appendiculatus.

We have previously described the presence of haemagglutinins in tissues of the tick, Rhipicephalus appendiculatus and determined their sugar specificities by inhibition experiments. In this study, haemagglutination inhibitory sugars are shown to have an effect in vivo on the abundance of Theileria parva infected salivary gland acini in Rhipicephalus appendiculatus. A significant increase (P < 0.05) was observed in T. parva acinar infection rates in the salivary glands of R. appendiculatus fed on ears of rabbits infused with melibiose and raffinose. In contrast, mannose and turanose (non-haemagglutination inhibitory sugars) did not cause elevation of T. parva acinar infection rates. The effect of melibiose in elevating acinar infections was observed when used only during T. parva maturation in the salivary glands but not during parasite pick-up from an infected bovine host. Stabilates produced from ticks with elevated acinar infections did not differ from control stabilates in infectivity to cattle, by comparison of prepatent periods to pyrexia, or parasitosis, or in the severity of reactions.

Animals↗
PubMed1995

Proposals to unify the genera Grahamella and Bartonella, with descriptions of Bartonella talpae comb. nov., Bartonella peromysci comb. nov., and three new species, Bartonella grahamii sp. nov., Bartonella taylorii sp. nov., and Bartonella doshiae sp. nov.

Polyphasic methods were used to examine the taxonomic positions of three newly identified Grahamella species. A comparison of the 16S rRNA gene sequences of these organisms with the sequences available for other bacteria revealed that these three species form a tight monophyletic cluster with members of the genus Bartonella. This cluster is only remotely related to other members of the order Rickettsiales. Determinations of the levels of DNA relatedness between Grahamella species and Bartonella species (by using a modified hydroxyapatite method) revealed that all of the species belonging to these two genera are distinct but closely related. On the basis of these data and the results of guanine-plus-cytosine content and phenotypic characterization studies, we propose that the genera Grahamella and Bartonella should be unified and that the latter name should be retained. Bartonella talpae and Bartonella peromysci, new combinations for former Grahamella species, are created, and the following three new Bartonella species are described: Bartonella grahamii, Bartonella taylorii, and Bartonella doshiae. A taxonomic analysis of Grahamella species complete the study of all members of the family Bartonellaceae, and the results of this study support the proposal that the family should be transferred out of the order Rickettsiales.

Alphaproteobacteria↗
PubMed1994

Characterization of Theileria parva which infects waterbuck (Kobus defassa).

Theileria-free waterbuck (Kobus defassa) born in captivity were successfully infected with Theileria parva sporozoites derived from ticks infected by feeding on African buffalo (Syncerus caffer). All waterbuck underwent mild infections with the development of sporadic schizont and piroplasm parasitosis when inoculated with sporozoite doses lethal to cattle. A carrier state of T. parva was demonstrated by feeding clean R. appendiculatus nymphs on two of these infected waterbuck. Tick batches from these waterbuck on 2 of 5 occasions transmitted lethal Theileria infections to cattle. In a separate experiment, waterbuck cells were infected and transformed in vitro by T. parva sporozoites derived from buffalo but not by cattle-derived T. parva (Muguga) sporozoites. Waterbuck cells infected in vitro with T. parva isolated from buffalo were inoculated into autologous waterbuck but no infections developed. Theileria parva isolates generated in this study from various sources were characterized using anti-T. parva schizont monoclonal antibodies (MAbs), and it was found that buffalo-derived and waterbuck-passaged isolates had different profiles. Species-specific synthetic oligonucleotide probes, restriction fragment length polymorphism (RFLP) analysis with cloned T. parva DNA probes, and DNA sequence analysis of the p67 sporozoite antigen gene confirmed that the waterbuck-passaged parasite was T. parva. The Tpr repetitive probe hybridization patterns from the waterbuck-passaged parasites were different from the other samples tested. The ribosomal genotype of the waterbuck-passaged T. parva was similar to that of cattle-derived T. parva Muguga. Analyses with both probes and MAbs suggested that a minor parasite population present within the T. parva 7014 buffalo-derived stock had been selected during waterbuck passage.(ABSTRACT TRUNCATED AT 250 WORDS)

Africa, Eastern↗
PubMed1994

Grahamella in small woodland mammals in the U.K.: isolation, prevalence and host specificity.

Bacteria isolated from the blood of small woodland mammals were identified as members of the genus Grahamella. The prevalence of Grahamella infection among the 37 small mammals examined, detected by cultivation of blood samples, was 62%. This figure is somewhat higher than previous reports. Further characterization of the isolates, based on restriction enzyme analysis of the 16S rRNA gene, serological reactivity and DNA hybridization studies, revealed three distinct Grahamella species. One of the species was found in five different species of small mammal (Apodemus sylvaticus, A. flavicollis, Clethrionomys glareolus, Microtus agrestis and Neomys fodiens). All three species were found in M. agrestis, although there was no evidence of concurrent infection of an animal by more than one species of Grahamella. These observations demonstrate that Grahamella spp. are not host-specific, as previously thought, and that it is therefore invalid to name Grahamella spp. solely on the basis of the host in which they are observed.

Animals↗
PubMed1994

Aggregated oviposition in the Simulium damnosum complex is mediated by eggs in a laboratory bioassay.

The phenomenon of aggregated oviposition in blackflies (Diptera: Simuliidae) was investigated under controlled laboratory conditions, using wild-caught females of the Simulium damnosum complex in Sierra Leone. A method was developed for inducing Simulium females to lay eggs, and used as a bioassay to measure the responses of gravid S. damnosum s.l. to freshly laid eggs of the same species complex. In a series of two-choice tests, significantly more ovipositing flies chose substrates already containing eggs over control substrates (P = 0.004). The time from introduction of flies into the oviposition system to the onset of egg-laying was significantly less when eggs were already present (P = 0.049). Flies responded more quickly when more eggs were present and the relationship between egg-batch number and the time of this response was curvilinear (P = 0.012). Ecological advantages and disadvantages of such aggregation behaviour and the possible role of semiochemicals in its mediation are discussed.

Animals↗
PubMed1994

Midgut lectin activity and sugar specificity in teneral and fed tsetse.

Midgut infection rates of Trypanosoma congolense in Glossina palpalis palpalis and of Trypanosoma brucei rhodesiense in Glossina pallidipes are potentiated by the addition of D+ glucosamine to the infective feed, but not to the levels of super-infection reported for G.m.morsitans, G.p.palpalis and G.pallidipes are shown to possess two trypanocidal molecules: a glucosyl lectin which can be inhibited by D+ glucosamine and a galactosyl molecule inhibited by D+ galactose. Addition of both D+ glucosamine and D+ galactose to the teneral infective feed promotes super-infection of the midguts of G.p.palpalis. The glucosyl lectin is specific for rabbit erythrocytes and is present in guts of fed G.m.morsitans and G.p.palpalis, titres of lectin activity do not increase substantially after the second bloodmeal. The galactosyl specific molecule does not show any erythrocyte specificity, although haemolytic activity is observed only in G.p.palpalis and not in G.m.morsitans. The presence of two trypanocidal molecules in some species of tsetse may account for the innate refractoriness of these flies to trypanosome infection. As D+ glucosamine also inhibits the killing of procyclic trypanosomes taken as an infective feed, it is suggested that the midgut lectin is normally responsible for the agglutination of trypanosomes in the fly midgut by binding to the procyclic surface coat, prior to establishment in the ecto-peritrophic space.

Animals↗
PubMed1994

Identification of the larvae of the Simulium damnosum complex from Nigeria by analysis of cuticular hydrocarbons.

The larvae of three sibling species of the Simulium damnosum complex were studied with a view to identification, using a Gas Liquid Chromatograph to analyze the hydrocarbons in the cuticular wax extracts. Multivariate statistics were applied to the chromatographic data to differentiate three sibling species: S. damnosum s.s., S. squamosum and S. yahense. Paired comparisons between the species gave greater than 96% correct classifications in all cases.

Animals↗