An evaluation of strategic and threshold control measures against the Karoo paralysis tick,Ixodes rubicundus (Acari: Ixodidae) in South Africa

Paralysis caused by feeding female Ixodes rubicundus ticks is a major problem in large areas of South Africa. As the life cycle of the tick extends over a period of 2 years, it was hypothesized that strategic treatment of sheep with an acaricide over a 2 year period, timed to kill most engorging females, should markedly lower the biotic potential of the tick. Two flocks of sheep grazing in separate paddocks known to be infested with I. rubicundus were treated either strategically or on a threshold basis (i.e. only when tick challenge exceeded a predetermined critical level in terms of paralysis) for a 2 year period. The tick burdens of untreated control sheep running with the two flocks were monitored over a 4 year period and their seasonal dynamics determined. The times at which peak infestations occurred were similar for both flocks of sheep, but significant differences in mean tick burdens between the two flocks were recorded. Tick numbers on sheep in the strategically treated flock did not decrease during the third and fourth years of the trial as was expected. Possible reasons for this were low stocking densities, especially during times of peak abundance of adults and the presence of wild hosts which maintained tick populations.     

A comparison of Ixodes rubicundus (Acari: Ixodidae) infestations on Friesian and Bonsmara cattle in South Africa

This study was conducted to compare the relative resistance of crossbred Bos indicus X B. taurus Bonsmara and B. taurus Friesian cattle to Ixodes rubicundus (Karoo paralysis tick) infestations. During periods of peak abundance of the ticks, Friesian oxen harboured almost twice or more than twice as many ticks as either Bonsmara oxen or cows. During periods of low tick abundance tick burdens on both cattle breeds were closely similar. It is envisaged that cattle can play an important role in an integrated control strategy against the Karro paralysis tick.     

DDT (dicophane) and postmenopausal breast cancer in Europe: case-control study.

OBJECTIVE: To examine any possible links between exposure to DDE (1,1-dichloro-2,2-bis (p-chlorophenyl)ethylene), the persistent metabolite of the pesticide dicophane (DDT), and breast cancer. DESIGN: Multicentre study of exposure to DDE by measurement of adipose tissue aspirated from the buttocks. Laboratory measurements were conducted in a single laboratory. Additional data on risk factors for breast cancer were obtained by standard questionnaires. SETTING: Centres in Germany, the Netherlands, Northern Ireland, Switzerland, and Spain. SUBJECTS: 265 postmenopausal women with breast cancer and 341 controls matched for age and centre. MAIN OUTCOME MEASURE: Adipose DDE concentrations. RESULTS: Women with breast cancer had adipose DDE concentrations 9.2% lower than control women. No increased risk of breast cancer was found at higher concentrations. The odds ratio of breast cancer, adjusted for age and centre, for the highest versus the lowest fourth of DDE distribution was 0.73 (95% confidence interval 0.44 to 1.21) and decreased to 0.48 (0.25 to 0.95; P for trend = 0.02) after adjustment for body mass index, age at first birth, and current alcohol drinking. Adjustment for other risk factors did not materially affect these estimates. CONCLUSIONS: The lower DDE concentrations observed among the women with breast cancer may be secondary to disease inception. This study does not support the hypothesis that DDE increases risk of breast cancer in postmenopausal women in Europe.     

Human immunodeficiency virus type 2 (HIV-2) seroprevalence and characterization of a distinct HIV-2 genetic subtype from the natural range of simian immunodeficiency virus-infected sooty mangabeys.

The extent of zoonotic infections in rural Sierra Leone, where both feral and pet sooty mangabeys harbor divergent members of the human immunodeficiency virus type 2 (HIV-2)-sooty mangabey simian immunodeficiency virus (SIVsm) family, was tested in blood samples collected from 9,309 human subjects in 1993. Using HIV-1- and HIV-2-specific enzyme immunoassays and confirmatory Western blot analysis to test for antibodies to SIVsm-related lentiviruses, we found only nine subjects (0.096%) who tested positive for HIV: seven tested positive for HIV-1 and two tested positive for HIV-2. Compared with other rural West African communities, Sierra Leone displayed the lowest seroprevalence (0.021%) of HIV-2 infection yet reported, much lower than the previously reported seroprevalence in SIVsm-infected feral and household pet sooty mangabeys. Heteroduplex analysis demonstrated that two of the newly found HIV-1 strains belonged to subtype A, the most common HIV-1 subtype in Africa, but this is the first report of subtype A in Sierra Leone. The two HIV-2-infected individuals harbored two distinct HIV-2 strains, designated 93SL1 and 93SL2. Phylogenetic analysis indicated that HIV-2 93SL1 is a member of HIV-2 subtype A, the first strain of this HIV-2 subtype found in Sierra Leone. In contrast, HIV-2 93SL2 belongs to none of the five previously characterized HIV-2 subtypes (A to E) but is a new subtype, herein designated F, having the most divergent transmembrane sequences yet reported for HIV-2. The fact that both of the two most divergent HIV-2 subtypes known, E and F, are rare and found as single occurrences in persons from Sierra Leone may be related to the fact that this small region of West Africa also contains free-living and household pet sooty mangabeys with highly divergent variants of SIVsm. This finding provides support for the hypotheses that new HIV-2 subtypes result from independent cross-species transmission of SIVsm to the human population and that these single-occurrence transmission events had not spread widely into the population by 1993.     

One hundred and one new simple sequence repeat-based markers for the canine genome

One hundred and one new dinucleotide repeat polymorphisms specific for the canine genome have been identified and characterized. Screening of both primary libraries and marker selected libraries enriched for simple sequence repeats led to the isolation of large numbers of genomic clones that contained (CA)_n repeats. Over 200 of these clones were sequenced, and PCR primers that bracket the repeat were developed for those that contained ten or more continuous (CA)_n units. This effort led to the production of 101 polymorphic markers, which were assigned to one of four categories depending on their degree of polymorphism. Fiftyfour markers were found to be highly or very highly polymorphic as they had four or more alleles when tested on a panel of unrelated dogs. This group of markers will be useful for following inheritance of traits in crosses between dogs.The nucleotide sequence data reported in this paper have been submitted to GenBank and have been assigned the accession numbers indicated in Table 1.     

Parasites of Pleurobrachia pileus Muller, 1776 (Ctenophora), from Galway Bay, western Ireland

Specimens of Pleurobrachia pileus Müller from Galway Bay,western Ireland, were found to be parasitised by three trematodes,one isopod and one nematode. Among these, the trematode, Opechonabacillaris Molin and didymozoid larvae were the most abundant,infecting over 17% of the Pleurobrachia population. Peak infectionwas during the summer of each year when >40% of P. - pileuswere parasitised. Serious infection was found to be either accompaniedor followed by a sharp decline in the abundance of the ctenophore.A close, but negative, correlation was established between theabundance of P. pileus and the percentage of parasitic infection.The percentage of infection in larger P. pileus was higher thanin small specimens. No parasites were detected from P. pileus1 mm or less in length.     

Construction of plasmid cloning vectors for lactic streptococci which also replicate in Bacillus subtilis and Escherichia coli

The cryptic Streptococcus cremoris Wg2 plasmid pWV01 (1.5 megadaltons) was genetically marked with the chloramphenicol resistance (Cmr) gene from pC194. The recombinant plasmid (pGK1, 2.4 megadaltons) replicated and expressed Cmr in Bacillus subtilis. From this plasmid an insertion-inactivation vector was constructed by inserting the erythromycin resistance (Emr) gene from pE194 cop-6. This plasmid (pGK12, 2.9 megadaltons) contained a unique BclI site in the Emr gene and unique ClaI and HpaII sites outside both resistance genes. It was stably maintained in B. subtilis at a copy number of approximately 5. pGK12 also transformed Escherichia coli competent cells to Cmr and Emr. The copy number in E. coli was about 60. Moreover, pGK12 transformed protoplasts of Streptococcus lactis. In this host both resistance genes are expressed. pGK12 is stably maintained in S. lactis at a copy number of 3.     

Contrasting modes of photosynthetic enzyme regulation in oxygenic and anoxygenic prokaryotes

Enzymes that are regulated by the ferredoxin/thioredoxin system in chloroplasts — fructose-1,6-bisphosphatase (FBPase), sedoheptulose-1,7-bisphosphatase purified from two different types of photosynthetic prokaryotes (cyanobacteria, purple sulfur bacteria) and tested for a response to thioredoxins. Each of the enzymes from the cyanobacterium Nostoc muscorum, an oxygenic organism known to contain the ferredoxin/thioredoxin system, was activated by thioredoxins that had been reduced either chemically by dithiothreitol or photochemically by reduced ferredoxin and ferredoxin-thioredoxin reductase. Like their chloroplast counterparts, N. muscorum FBPase and SBPase were activated preferentially by reduced thioredoxin f. SBPase was also partially activated by thioredoxin m. PRK, which was present in two regulatory forms in N. muscorum, was activated similarly by thioredoxins f and m. Despite sharing the capacity for regulation by thioredoxins, the cyanobacterial FBPase and SBPase target enzymes differed antigenically from their chloroplast counterparts. The corresponding enzymes from Chromatium vinosum, an anoxygenic photosynthetic purple bacterium found recently to contain the NADP/thioredoxin sytem, differed from both those of cyanobacteria and chloroplasts in showing no response to reduced thioredoxin. Instead, C. vinosum FBPase, SBPase, and PRK activities were regulated by a metabolite effector, 5-AMP. The evidence is in accord with the conclusion that thioredoxins function in regulating the reductive pentose phosphate cycle in oxygenic prokaryotes (cyanobacteria) that contain the ferredoxin/thioredoxin system, but not in anoxygenic prokaryotes (photosynthetic purple bacteria) that contain the NADP/thioredoxin system. In organisms of the latter type, enzyme effectors seem to play a dominant role in regulating photosynthetic carbon dioxide assimilation.     

The growth of Saccharomyces cerevisiae CBS 426 on mixtures of glucose and ethanol: a model

Saccharomyces cerevisiae CBS 426 was grown in continuous culture in a defined medium with a mixture of glucose and ethanol as carbon source. Growth on ethanol as the sole carbon source was only possible after the addition of a small amount of glutamic acid. The flows of glucose, ethanol, oxygen, carbon dioxide and biomass to and from the system were measured and a model for the growth of the yeast on the carbon sources constructed. The model is shown to allow independent estimation of Y_ATP and P/O. Y_ATP is not independent of the substrate used, but the amount of ATP used in the production of biomass from the monomers is approximately the same for growth on ethanol and on glucose.Nomenclature C chemical state vector - C_i component of the chemical state vector (C-mol) - C_x biomass present in the system (C-mol biomass) - H₂ reduction equivalents (NAD(P)H + H⁺ and FADH₂) - k the amount of ATP required in the production of 1 C-mol of biomass from the monomers (mol ATP/C-mol biomass) - m_ATP maintenance requirement for ATP (mol ATP/C-mol biomass·h) - P/O (=), efficiency of the oxidative phosphorylation (mol ATP/atom O) - r vector of reaction rates - r_i component of the vector of reaction rates (C-mol/h) - r_ATP rate of ATP production (mol ATP/h) - r_x rate of biomass production (C-mol biomass/h) - Y_ATP Y_ATP growth yield on ATP (C-mol biomass/mol ATP) - (Y_ATP)_max maximum growth yield on ATP - stoichiometry matrix - P/O - vector of the flows to the system - _s flow of glucose to the system (C-mol glucose/h) - _o flow of oxygen to the system (mol O₂/h) - _c flow of carbon dioxide to the system (mol CO₂/h) - _x flow of biomass to the system (C-mol biomass/h) - _e flow of ethanol to the system (C-mol ethanol/h) - _w flow of water produced during metabolism (mol H₂O/h)