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Biomedical subjects

D Jefferies

Publications and source records attributed to D Jefferies.

27 records · Page 2Linked to original sources
PubMed1991

Transient activity assays of the Trypanosoma brucei variant surface glycoprotein gene promoter: control of gene expression at the posttranscriptional level.

The putative promoter of the variant surface glycoprotein (VSG) gene of Trypanosoma brucei was cloned into a plasmid containing the chloramphenicol acetyltransferase (CAT) gene. After electroporation into trypanosomes, this construct directed the expression of the CAT reporter gene. The essential region for promoter activity was found to reside within 88 bp upstream of the putative transcription start site. Transcription of the CAT construct occurred at approximately the same level in both bloodstream and procyclic forms and was resistant to alpha-amanitin. However, CAT expression appeared to be modulated in the two forms of the parasite. Sequences 3' to the gene seemed to be important in this respect, as CAT activity in bloodstream forms was readily detectable only when the 3' region of a VSG cDNA was placed downstream of the CAT gene. Two separate VSG gene promoter sequences, both cloned from T. brucei AnTat 1.3A, were equally able to direct CAT expression, which suggests that there are a number of potential VSG gene promoters in the genome, although usually only one expression site is fully active at any one time.

Animals↗
PubMed1991

KVP meter errors induced by plastic wrap.

The purpose of this study was to determine whether erroneous kVp meter readings, induced by plastic wrap, affected the actual kVp (output) of a dental X-ray machine. To evaluate the effect of plastic wrap on dental X-ray machine kVp meters, a radiation output device was used to measure output in mR/ma.s. An intraoral dental X-ray unit (S.S. White Model #90W) was used to make the exposures. First, the kVp meter was not covered with plastic wrap and output readings were recorded at various kVp settings with the milliamperage and time held constant. Secondly, the same kVp settings were selected before the plastic wrap was placed. Milliamperage and time were again held to the same constant. The X-ray console was then covered with plastic wrap prior to measuring the output for each kVp. The wrap possessed a static charge. This charge induced erroneous kVp meter readings. Out-put readings at the various induced kVp settings were then recorded. A kVp of 50 with no wrap present resulted in the same output as a kVp of 50 induced to read 40 or 60 kVp by the presence of wrap. Similar results were obtained at other kVp settings. This indicates that the plastic wrap influences only the kVp meter needle and not the actual kilovoltage of the X-ray machine. Dental X-ray machine operators should select kVp meter readings prior to placing plastic wrap and should not adjust initial settings if the meter is deflected later by the presence of wrap. The use of such a procedure will result in proper exposures, fewer retakes, and less patient radiation. If plastic wrap leads to consistent exposure errors, clinicians may wish to use a 0.5% sodium hypochlorite disinfectant as an alternative to the barrier technique.

Communicable Disease Control↗
PubMed1990

Trypanosoma brucei: constitutive activity of the VSG and procyclin gene promoters.

The variant surface glycoprotein (VSG) and procyclin are the major surface proteins of the bloodstream and procyclic stages, respectively, of Trypanosoma brucei. The promoter regions of the VSG and procyclin gene transcription units could be mapped thanks to the specific enrichment of initial transcripts that occurs following UV irradiation. Whereas the VSG gene is 45 kb distant from its promoter, procyclin genes are located immediately downstream. We show, by run-on assays on isolated nuclei and by cDNA analysis, that transcription occurs from both promoters in bloodstream as well as in procyclic forms. It is inferred that the control of the stage-specific expression of VSG and procyclin genes is not effected at the level of transcription initiation, but most probably by interfering with the elongation and stability of the specific transcripts.

Animals↗
PubMed1989

Intradermal hepatitis B vaccine in thalassaemia and sickle cell disease.

Thirty two patients with beta thalassaemia and sickle cell disease who were having regular blood transfusions were selected to test the efficacy and immunogenicity of low dose (2 micrograms or 0.1 ml) intradermal hepatitis B vaccine compared with the standard (20 micrograms or 1 ml) intramuscular dose. There was no significant difference in the rates of seroconversion, seroconversion had occurred in all patients by seven months. There were no significant differences in antibody titres between the intramuscular and intradermal groups at 1, 2, and 6 months. Although the titres were significantly higher in the intramuscular group at seven months and at 12-18 months, the antibody titre in the intradermal group did not fall below 10 IU/l. The results of this study suggest that low dose intradermal hepatitis B vaccination is an effective and economical way of stimulating an immune response in patients with beta thalassaemia and sickle cell disease.

Anemia, Sickle Cell↗
PubMed1987

Cibarial infections of Trypanosoma vivax and T. congolense in Glossina.

In a percentage of laboratory bred Glossina infected with Trypanosoma congolense or T. vivax, trypanosomes colonized the cibarium as well as the midgut and/or the proboscis. Field-caught tsetse flies also had T. congolense and T. vivax cibarial infections. T. congolense cibarial infections occurred in all species of Glossina examined: G. tachinoides, G. palpalis palpalis, G. morsitans morsitans and G. m. submorsitans. T. vivax was only found in the cibarium of G. tachinoides. Trypanosomes were firmly attached in the cibarium, as shown by scanning electron microscopy. Two field-caught G. tachinoides were also discovered to have only cibarial infections, presumably of T. vivax. More information is required on the occurrence of cibarial infections in Glossina, especially in the field. It is suggested that examination of the cibarium should be carried out as part of the routine dissection of tsetse flies in the field.

Animals↗
PubMed1987

The effect of trypanocidal drugs on the transmission of Trypanosoma brucei brucei by Glossina morsitans centralis.

The effects of trypanocidal drugs on Trypanosoma b. brucei infections in Glossina m. centralis have been investigated. Pentamidine and suramin exhibited no significant effects but both berenil and samorin reduced the number of salivary gland infections in comparison with controls. Berenil at concentrations of 10, 1.0 and 0.1 microgram/ml significantly reduced the number of mature infections when fed to flies throughout the whole period of trypanosome development. A similar result was obtained with samorin at 0.1 microgram/ml. Subsequent experiments showed that administration of both drugs at an early stage was more effective in preventing the maturation of infection than a later but more prolonged administration. Reported drug levels in the blood of different experimental host animals are of the same magnitude as those used here. It is suggested that repeated feeding of T. b. brucei infected Glossina on drug-treated hosts may reduce transmission, although alternative bloodmeal sources would reduce this effect. These influences are worthy of investigation in the field.

Animals↗
PubMed1986

Fluid mechanics of bloodmeal uptake by Leishmania-infected sandflies.

The fluid mechanics of blood flow in the pharynx and cibarium of Phlebotomus papatasi are described using a simple static model. The flow is characterized as viscous laminar. The Hagen-Poiseuille equation is used to assess the effects of attached parasites in the foregut of Leishmania-infected sandflies on blood flow. The reductions in flow rate imposed by parasite colonization of the pharynx and cibarium will reduce the ability of an infected fly to take a bloodmeal, thus encouraging further probing, enhancing transmission. Regurgitation of the contents of the foregut is also possible. This will aid the deposition of infective forms from the foregut. Transmission by means of regurgitation of parasites from the midgut is considered unlikely.

Animals↗