The impact of mixed species infection on trypanosome virulence and transmission

Animal African trypanosomes are protozoan parasites that cause nagana, a devastating disease of livestock in sub-Saharan Africa. It is well documented that strains of one causative agent, Trypanosoma congolense (subtype: Savannah), exhibits strikingly different virulence profiles in the hosts that they infect – measured in terms of host survival - though the molecular basis of these different phenotypes are not known. This parasite is also known to be found in mixed infections with other African trypanosomes, namely T. brucei and T. vivax. Such mixed infections, or coinfections, affect both the host and parasite, and are modulated by a number of factors, including inter-strain or inter-species competition. Limited work has been done to study how such competition may impact upon parasite virulence, or transmission potential to a new host. To this end, we sought to generate genome and transcriptome data for different T. congolense field strains and identified differences in the predicted protein sequences between these lines. Transcriptome data also revealed differentially expressed transcripts between strains of high virulence and those of low virulence. Next, we utilised field- and laboratory studies to investigate the interaction between coinfecting African trypanosomes. Surveys from the field indicated that T. congolense, T. vivax, and T. brucei indeed infect cattle in the same geographical area. This screen, using two different assays, was capable of detecting trypanosome coinfections, although mixed infections between African trypanosome species were not observed. In vivo experiments in mice highlighted the interactions that occur between T. congolense and T. brucei. First, it was shown that a T. congolense field strain (MF1 CL1) could drive T. brucei EATRO 1125 PFR-Ty to become cell-cycle arrested, and pre-adapted for transmission. Secondly, we observed a dynamic cycling in parasitaemia between the two species within the same host over the course of a chronic infection – only one species peaked at a given time. Furthermore, T. brucei EATRO 1125 PFR-Ty that re-emerged after a peak of T. congolense IL3000 parasitaemia comprised of a high proportion of PAD1+ cells. Taken together, these data indicate competition avoidance between these conspecifics. Thirdly, a line of T. brucei that was retrieved from a chronic coinfection, exhibited enhanced virulence when compared to the original line. Mice infected with this chronic line of parasites showed significant weight-loss, and immunofluorescence assays highlighted a reduced capacity to form stumpy cells in this group. These data suggest selection for more virulent cells, which could enhance transmission. Finally, we generated a luciferin-reporter line of T. brucei (AMLuc 4.2), to investigate competition avoidance between this species, and T. congolense IL3000. This newly-generated line of parasites was then used to establish a model for in vivo imaging of trypanosomes in a live host, and the ex vivo imaging of infected organs

Parasite co-infection: an ecological, molecular and experimental perspective.

Laboratory studies of pathogens aim to limit complexity in order to disentangle the important parameters contributing to an infection. However, pathogens rarely exist in isolation, and hosts may sustain co-infections with multiple disease agents. These interact with each other and with the host immune system dynamically, with disease outcomes affected by the composition of the community of infecting pathogens, their order of colonization, competition for niches and nutrients, and immune modulation. While pathogen-immune interactions have been detailed elsewhere, here we examine the use of ecological and experimental studies of trypanosome and malaria infections to discuss the interactions between pathogens in mammal hosts and arthropod vectors, including recently developed laboratory models for co-infection. The implications of pathogen co-infection for disease therapy are also discussed

Environmental factors affecting wood properties of Eucalyptus spp. grown on the Zululand coastal plain and along the Mpumalanga escarpment of South Africa.

Thesis (M.Sc.)-University of Natal, Durban, 2003.The environmental factors affecting wood property formation of Eucalyptus spp. trees in two distinct geographic areas within South Africa were studied. Wood prop~rty data for trees from 43 sites (26 in Zululand and 17 in Mpumalanga) were collected from work conducted at the Forest and Forest Products Research Centre (FFPRC) at the CSIR (Council for Scientific and Industrial Research) in Durban. The wood properties considered included screened pulp yield, fibre length, wood density and active alkali chemical consumption during pulping. The effect of environmental factors on growth rate (expressed as Site Index at a base age of 5 years) was also measured. A detailed site description for each forest compartment was carried out. Detailed annual and monthly rainfall and minimum and maximum temperature estimates were calculated for each site by interpolating long term means of these variables by splining using the software package Anusplin. These estimates of climatic factors were validated by comparison to the data published in the South African Atlas of Agrohydrology and -Climatology. The outputs of the Anusplin model were used to derive surrogate bioclimatic parameters for each site using the computer program Bioclim. These parameters are considered as better descriptors of the energy-water balance experienced by the plant than normal measures of climate such as mean monthly or annual precipitation. Soil characteristics were measured on samples taken from the individual sites. The effects of these environmental and bioclimatic variables on wood properties were analysed using appropriate statistical techniques. Multiple regression models were used to predict wood properties and it is suggested that this approach could form part of a fibre management system. Wood property prediction models incorporating climate (and bioclimate) alone were preferred to those including soil data as no further site data are required. The effect of edaphic factors was considered to describe any further variation not accounted for by bioclimate alone. Particle size distribution of the soil, as an indication of the water holding capacity of that soil, was not found to effect wood properties or growth significantly. A weak influence of organic matter content in the topsoil on wood density was noted in Mpumalanga. In Zululand, a multiple linear regression using both rainfall of the wettest quarter and mean diurnal temperature range as inputs yielded the best predictive model for growth rate. In this region a combination of precipitation seasonality and mean diurnal temperature range gave the best linear regressi'o,n model describing variation in screened pUlp' yield and fibre length. In Mpumalanga effective rooting depth was found to have a pervasive effect on plant development. Solar radiation (as a measure of energy supply), calculated from a function of latitude, aspect, slope and time of year, was also found to significantly affect the growth rate and SPY of plant material in Mpumalanga. Measures of temperature in both geographic regions were found to significantly affect wood density

African trypanosomes

Abstract African trypanosomes cause human African trypanosomiasis and animal African trypanosomiasis. They are transmitted by tsetse flies in sub-Saharan Africa. Although most famous for their mechanisms of immune evasion by antigenic variation, there have been recent important studies that illuminate important aspects of the biology of these parasites both in their mammalian host and during passage through their tsetse fly vector. This Primer overviews current research themes focused on these parasites and discusses how these biological insights and the development of new technologies to interrogate gene function are being used in the search for new approaches to control the parasite. The new insights into the biology of trypanosomes in their host and vector highlight that we are in a ‘golden age’ of discovery for these fascinating parasites

X-ray and Gamma-ray Emissions from Different Evolutionary Stage of Rotation Powered Millisecond Pulsars

The $Fermi$-LAT has revealed that rotation powered millisecond pulsars (MSPs) are a major contributor to the Galactic $\gamma$-ray source population. Such pulsars may also be important in modeling the quiescent state of several low mass X-ray binaries (LMXBs), where optical observations of the companion star suggest the possible existence of rotation powered MSPs. To understand the observational properties of the different evolutionary stages of MSPs, the X-ray and $\gamma$-ray emission associated with the outer gap model is investigated. For rotation powered MSPs, the size of the outer gap and the properties of the high-energy emission are controlled by either the photon-photon pair-creation process or magnetic pair-creation process near the surface. For these pulsars, we find that the outer gap model controlled by the magnetic pair-creation process is preferable in explaining the possible correlations between the $\gamma$-ray luminosity or non-thermal X-ray luminosity versus the spin down power. For the accreting MSPs in quiescent LMXBs, the thermal X-ray emission at the neutron star surface resulting from deep crustal heating can control the conditions in the outer gap. We argue that the optical modulation observed in the quiescent state of several LMXBs originates from the irradiation of the donor star by $\gamma$-rays from the outer gap. In these systems, the irradiation luminosity required for the optical modulation of the source such as SAX J1808.4-3658 can be achieved for a neutron star of high mass. Finally, we discuss the high-energy emission associated with an intra-binary shock in black widow systems, e.g. PSR B1957+20.Comment: 46page, 10 figures, 3 tables, to Appear in Ap

Three new biological control programmes for South Africa: Brazilian pepper, Tamarix and Tradescantia

Three weed biological control (biocontrol) programmes are described, all of which are considered to be ‘transfer projects’ that were initiated elsewhere, and on which South Africa has piggybacked its biocontrol efforts. Using knowledge and expertise from international collaborators, South African weed researchers are following a long tradition of transfer projects, which has been a largely successful and practical approach to biocontrol. Two Brazilian weeds, the Brazilian pepper tree Schinus terebinthifolia and the spiderwort Tradescantia fluminensis are being targeted, along with the Old-World trees Tamarix ramosissima and T. chinensis. The potential biocontrol agents are described and ranked for the two trees according to what has been discovered elsewhere, while the agent already released against T. fluminensis is rated (as poor), and other potential agents are considered. The addition of molecular techniques, climate matching and remote sensing in transfer projects can increase the chance of successful biocontrol and the inclusion of these techniques in the three new programmes is discussed. Transfer projects are a cost-effective and pragmatic way to pick winning biocontrol programmes

The accuracy of dietary recall of infant feeding and food allergen data.

BACKGROUND: Research investigating the association of infant dietary factors with later health outcomes often relies on maternal recall. It is unclear what the effect of recall bias is on the accuracy of the information obtained. The present study aimed to determine the extent of recall bias on the accuracy of infant feeding and food allergen data collected 10 years later. METHODS: Mothers were recruited from a prospective birth cohort from the Isle of Wight. When their child was 10 years of age (2011/2012), mothers were requested to complete a retrospective infant feeding questionnaire asking the same questions as those solicited in 2001/2002. RESULTS: In total, 125 mothers participated. There was substantial agreement for recollection of any breastfeeding (κ = 0.79) and the duration of breastfeeding from 10 years earlier (r = 0.84). Some 94% of mothers recalled accurately that their child had received formula milk. The exact age at which formula milk was first given was reliably answered (r = 0.63). The brand of formula milk was poorly recalled. Recall of age of introduction of solid food was not reliable (r = 0.16). The age of introduction of peanuts was the only food allergen that was recalled accurately (86%). CONCLUSIONS: The present study highlights the importance of maternal recall bias of infant feeding practices over 10 years. Recall related to breastfeeding and formula feeding were reliable, whereas recalls related to age of introduction of solid or allergenic foods, apart from peanut, were not. Caution should be applied when interpreting studies relying on dietary recall

A trip down memory lane with Retrovirology

Fifteen years ago, Retrovirology was amongst the first open-access journals to be established through Biomed Central, instigated by our late Founding Editor Dr. Kuan-Teh Jeang. Since then, in what seemed like a rather daring move to be paper-free, Retrovirology has witnessed the exponential growth of open access journals that have changed the landscape of scientific publishing and communications. As was pointed out by the staff editors in PLoS Biology [1], the infancy of open access journal was a very different time from our present day, which was before smartphones, prior to most of the digital social media platforms and at a time when we had only begun to learn about the completed DNA sequences from the Human Genome Projec

Fatal neurologic disease and abortion in mare infected with lineage 1 West Nile virus, South Africa

In 2010, lineage 1 West Nile virus was detected in South Africa in the brain of a pregnant mare that succumbed to neurologic disease and in her aborted fetus, suggesting an association with abortion in horses. All West Nile virus strains previously detected in horses and humans in South Africa were lineage 2.This study was funded by the National Research Foundation of South Africa.http://www.cdc.gov/ei

The Kelvin-Helmholtz instability in weakly ionised plasmas: Ambipolar dominated and Hall dominated flows

The Kelvin-Helmholtz instability is well known to be capable of converting well-ordered flows into more disordered, even turbulent, flows. As such it could represent a path by which the energy in, for example, bowshocks from stellar jets could be converted into turbulent energy thereby driving molecular cloud turbulence. We present the results of a suite of fully multifluid magnetohydrodynamic simulations of this instability using the HYDRA code. We investigate the behaviour of the instability in a Hall dominated and an ambipolar diffusion dominated plasma as might be expected in certain regions of accretion disks and molecular clouds respectively. We find that, while the linear growth rates of the instability are unaffected by multifluid effects, the non-linear behaviour is remarkably different with ambipolar diffusion removing large quantities of magnetic energy while the Hall effect, if strong enough, introduces a dynamo effect which leads to continuing strong growth of the magnetic field well into the non-linear regime and a lack of true saturation of the instability.Comment: 12 pages, 20 figures. Accepted for publication in MNRA