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Search Results: 1 - 10 of 203725 matches for " Donald P Knowles "
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Expanding Possibilities for Intervention against Small Ruminant Lentiviruses through Genetic Marker-Assisted Selective Breeding
Stephen N. White,Donald P. Knowles
Viruses , 2013, DOI: 10.3390/v5061466
Abstract: Small ruminant lentiviruses include members that infect sheep (ovine lentivirus [OvLV]; also known as ovine progressive pneumonia virus/maedi-visna virus) and goats (caprine arthritis encephalitis virus [CAEV]). Breed differences in seroprevalence and proviral concentration of OvLV had suggested a strong genetic component in susceptibility to infection by OvLV in sheep. A genetic marker test for susceptibility to OvLV has been developed recently based on the TMEM154 gene with validation data from over 2,800 sheep representing nine cohorts. While no single genotype has been shown to have complete resistance to OvLV, consistent association in thousands of sheep from multiple breeds and management conditions highlight a new strategy for intervention by selective breeding. This genetic marker-assisted selection (MAS) has the potential to be a useful addition to existing viral control measures. Further, the discovery of multiple additional genomic regions associated with susceptibility to or control of OvLV suggests that additional genetic marker tests may be developed to extend the reach of MAS in the future. This review will cover the strengths and limitations of existing data from host genetics as an intervention and outline additional questions for future genetic research in sheep, goats, small ruminant lentiviruses, and their host-pathogen interactions.
Silencing of a putative immunophilin gene in the cattle tick Rhipicephalus (Boophilus) microplus increases the infection rate of Babesia bovis in larval progeny
Reginaldo G Bastos, Massaro W Ueti, Felix D Guerrero, Donald P Knowles, Glen A Scoles
Parasites & Vectors , 2009, DOI: 10.1186/1756-3305-2-57
Abstract: In this study, RNA interference was used to silence R. microplus genes that had been previously shown to be up-regulated in response to B. bovis infection. The silencing of a putative immunophilin gene (Imnp) in female ticks fed on a calf acutely infected with B. bovis decreased the hatching rate and survival of larval progeny. Interestingly, Imnp was up-regulated significantly in ovaries of R. microplus in response to B. bovis infection and its silencing in female ticks significantly increased the infection rate of the protozoan in larval progeny. The results also showed that the silencing of a putative Kunitz-type serine protease inhibitor (Spi) gene and a putative lipocalin (Lpc) gene decreased the fitness of R. microplus females, but had no significant effect on the infection rate of B. bovis in larval progeny.The silencing of the Imnp, Spi or Lpc genes decreased the fitness of R. microplus females fed on a calf during acute B. bovis infection. The Imnp gene data suggest that this putative immunophilin gene is involved in the defense system of R. microplus against B. bovis and may play a role in controlling the protozoan infection in tick ovaries and larval progeny.Ticks are obligate hematophagous ectoparasites that can affect human and animal health both directly by blood feeding and indirectly by transmitting pathogens. The cattle tick Rhipicephalus (Boophilus) microplus is an economically important ectoparasite of bovines implicated in the transmission of the apicomplexan protozoan Babesia bovis, the etiological agent of bovine babesiosis (also known as tick fever) [1]. Adult females R. microplus acquire B. bovis merozoites by ingesting blood from an infected bovine and pass the protozoan transovarially to their larvae progeny that can transmit B. bovis sporozoites to cattle during subsequent feeding [1-3]. The control of bovine babesiosis relies on the control of tick populations and the use of live attenuated vaccines in some endemic areas [1,3]. The contro
The Rhipicephalus (Boophilus) microplus Bm86 gene plays a critical role in the fitness of ticks fed on cattle during acute Babesia bovis infection
Reginaldo G Bastos, Massaro W Ueti, Donald P Knowles, Glen A Scoles
Parasites & Vectors , 2010, DOI: 10.1186/1756-3305-3-111
Abstract: Here we describe in two independent experiments that RNA interference-mediated silencing of Bm86 decreased the fitness of R. microplus females fed on cattle during acute B. bovis infection. Notably, Bm86 silencing decreased the number and survival of engorged females, and decreased the weight of egg masses. However, gene silencing had no significant effect on the efficiency of transovarial transmission of B. bovis from surviving female ticks to their larval offspring. The results also show that Bm86 is expressed, in addition to gut cells, in larvae, nymphs, adult males and ovaries of partially engorged adult R. microplus females, and its expression was significantly down-regulated in ovaries of ticks fed on B. bovis-infected cattle.The R. microplus Bm86 gene plays a critical role during tick feeding and after repletion during blood digestion in ticks fed on cattle during acute B. bovis infection. Therefore, the data indirectly support the rationale for using Bm86-based vaccines, perhaps in combination with acaricides, to control tick infestation particularly in B. bovis endemic areas.Ticks are blood-feeding arthropods that affect animals and humans both directly by their feeding activity and indirectly by transmitting a wide variety of pathogens ranging from viruses to more complex protozoan parasites. The one-host tick Rhipicephalus (Boophilus) microplus is an economically important ectoparasite of cattle involved in the transmission of the apicomplexan protozoan Babesia bovis, the etiological agent of bovine babesiosis [1]. Adult females of R. microplus acquire B. bovis merozoites by ingesting blood from an infected bovine and pass the protozoan transovarially to their larval offspring that can transmit B. bovis sporozoites to cattle during subsequent feeding [1-3]. It was recently shown that R. microplus females can acquire B. bovis from both acute and persistently infected cattle, and efficiently transmit the protozoan transovarially to their larval progeny [4,5
Ovine Progressive Pneumonia Virus Is Transmitted More Effectively via Aerosol Nebulization than Oral Administration  [PDF]
Lynn M. Herrmann-Hoesing, Stephen N. White, Liam E. Broughton-Neiswanger, Wendell C. Johnson, Susan M. Noh, David A. Schneider, Hong Li, Naomi S. Taus, James Reynolds, Thomas Truscott, Rohana P. Dassanayake, Donald P. Knowles
Open Journal of Veterinary Medicine (OJVM) , 2012, DOI: 10.4236/ojvm.2012.23019
Abstract: A new method of experimental infection of ovine progressive pneumonia virus (OPPV), aerosol nebulization (Nb), was compared to intravenous (IV) and oral (PO) methods of experimental infection. Seven month old lambs were given 3.5 × 107 TCID50 of Dubois OPPV LMH19 isolate using IV, PO, or Nb methods and were monitored for infection using cELISA and OPPV quantitative (q) PCR for 35 weeks. Four out of four sheep in the IV group, six out of six sheep in the Nb group, but only two out of six sheep in the PO group became infected by OPPV; whereas the uninoculated controls (n = 2) and a sentinel control (n = 1) remained uninfected during the course of the study. The time to a cELISA or OPPV qPCR positive result in the Nb group was quicker and statistically different from the time to a cELISA or OPPV qPCR positive result in the PO group (cELISA P value = 0.0021 and OPPV qPCR P value = 0.0007). When the Nb and IV groups were compared, sheep became cELISA and OPPV qPCR positive at similar times (cELISA P value = 0.6 and OPPV qPCR P value = 0.1). In addition, sheep became OPPV qPCR positive prior to cELISA in both the IV and Nb groups (IV P value = 0.027 and Nb P value = 0.007). Aerosol nebulization is a more natural experimental method of transmitting OPPV and may be valuable for testing potential vaccines or specific host genetics.
Ovine progressive pneumonia provirus levels are unaffected by the prion 171R allele in an Idaho sheep flock
Robert D Harrington, Lynn M Herrmann-Hoesing, Stephen N White, Katherine I O'Rourke, Donald P Knowles
Genetics Selection Evolution , 2009, DOI: 10.1186/1297-9686-41-17
Abstract: Scrapie is the prototypical prion disease and one of several described in animals and humans. Accumulation of disease associated prion protein (PrPSc), an abnormally folded form of normal host prion protein (PrPC), is central to disease and expression of the host prion gene (PRNP) is necessary in pathogenesis [1]. PRNP open reading frame (ORF) variants associate with disease incubation time [2] and relative disease susceptibility in sheep [3-7], goats [8-10], elk [11-13], deer [12,14] and humans [15-18].Polymorphisms in sheep at PRNP codons 136 (Alanine/Valine), 154 (Arginine/Histidine), and 171 (Glutamine/Arginine) are involved in scrapie susceptibility (for review see [19]). Codon 171 is an important element of susceptibility in the United States (US) sheep population [6,7]. Sheep homozygous for glutamine at codon 171 (171QQ) are highly susceptible to Scrapie, whereas sheep heterozygous (171QR) or homozygous (171RR) for arginine are highly resistant to classical strains of US Scrapie.The PRNP 171Q allele predominates in US sheep whereas the 171R allele and 171RR genotype are less common (the latter two occur at a frequency of about 37% and 16%, respectively [20]). Selective breeding for the 171R minor allele to produce animals with the 171QR or 171RR genotypes is sometimes used as a Scrapie control measure, however the functional consequences of 171R selection on other traits is uncertain. Genetic selection may have unexpected positive or negative effects as individual genes may have multiple biological roles (pleiotropy) or may be linked to other genes that impact overall biological functions. Uncertainty regarding PRNP selection effects (beyond Scrapie resistance) has led to investigation of multiple ovine traits related to reproduction, milk, meat, fiber and genetic diversity. However, PRNP selection effects on disease susceptibility (besides Scrapie) has only been studied for Salmonella resistance [21].Ovine progressive pneumonia/Maedi-Visna virus (OPPV) is a
Prevalence of equine Piroplasmosis and its association with tick infestation in the State of S?o Paulo, Brazil
Kerber, Claudia E.;Labruna, Marcelo B.;Ferreira, Fernando;De Waal, Daniel T.;Knowles, Donald P.;Gennari, Solange M.;
Revista Brasileira de Parasitologia Veterinária , 2009, DOI: 10.4322/rbpv.01804001
Abstract: serum samples were collected from 582 horses from 40 stud farms in the state of s?o paulo and tick (acari: ixodidae) infestations were evaluated on them. serum samples were subjected to the complement fixation test (cft) and a competitive inhibition elisa (celisa) for babesia caballi and theileria equi. logistic regression analyses were performed to construct multivariate models that could explain the dependent variable (horses positive for b. caballi or t. equi) as a function of the independent variables (presence or abundance of each one of the tick species found on the farms). a higher overall prevalence of b. caballi (54.1%) than of t. equi (21.6%) was found by the two tests. the ticks dermacentor nitens neumann, 1897, amblyomma cajennense (fabricius, 1787) and rhipicephalus (boophilus) microplus (canestrini, 1887) were present on horses on 38 (95%), 20 (50%), and 4 (10%) farms, respectively. infestations by d. nitens were statistically associated with b. caballi-positive horses on the farms by either the cft or celisa. infestations by a. cajennense were statistically associated with t. equi-positive horses on the farms by either cft or celisa.
Lymphocytes and Macrophages Are Infected by Theileria equi, but T Cells and B Cells Are Not Required to Establish Infection In Vivo
Joshua D. Ramsay, Massaro W. Ueti, Wendell C. Johnson, Glen A. Scoles, Donald P. Knowles, Robert H. Mealey
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0076996
Abstract: Theileria equi has a biphasic life cycle in horses, with a period of intraleukocyte development followed by patent erythrocytic parasitemia that causes acute and sometimes fatal hemolytic disease. Unlike Theileria spp. that infect cattle (Theileria parva and Theileria annulata), the intraleukocyte stage (schizont) of Theileria equi does not cause uncontrolled host cell proliferation or other significant pathology. Nevertheless, schizont-infected leukocytes are of interest because of their potential to alter host cell function and because immune responses directed against this stage could halt infection and prevent disease. Based on cellular morphology, Theileria equi has been reported to infect lymphocytes in vivo and in vitro, but the specific phenotype of schizont-infected cells has yet to be defined. To resolve this knowledge gap in Theileria equi pathogenesis, peripheral blood mononuclear cells were infected in vitro and the phenotype of infected cells determined using flow cytometry and immunofluorescence microscopy. These experiments demonstrated that the host cell range of Theileria equi was broader than initially reported and included B lymphocytes, T lymphocytes and monocyte/macrophages. To determine if B and T lymphocytes were required to establish infection in vivo, horses affected with severe combined immunodeficiency (SCID), which lack functional B and T lymphocytes, were inoculated with Theileria equi sporozoites. SCID horses developed patent erythrocytic parasitemia, indicating that B and T lymphocytes are not necessary to complete the Theileria equi life cycle in vivo. These findings suggest that the factors mediating Theileria equi leukocyte invasion and intracytoplasmic differentiation are common to several leukocyte subsets and are less restricted than for Theileria annulata and Theileria parva. These data will greatly facilitate future investigation into the relationships between Theileria equi leukocyte tropism and pathogenesis, breed susceptibility, and strain virulence.
Differential Expression of Three Members of the Multidomain Adhesion CCp Family in Babesia bigemina, Babesia bovis and Theileria equi
Reginaldo G. Bastos, Carlos E. Suarez, Jacob M. Laughery, Wendell C. Johnson, Massaro W. Ueti, Donald P. Knowles
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0067765
Abstract: Members of the CCp protein family have been previously described to be expressed on gametocytes of apicomplexan Plasmodium parasites. Knocking out Plasmodium CCp genes blocks the development of the parasite in the mosquito vector, making the CCp proteins potential targets for the development of a transmission-blocking vaccine. Apicomplexans Babesia bovis and Babesia bigemina are the causative agents of bovine babesiosis, and apicomplexan Theileria equi causes equine piroplasmosis. Bovine babesiosis and equine piroplasmosis are the most economically important parasite diseases that affect worldwide cattle and equine industries, respectively. The recent sequencing of the B. bovis and T. equi genomes has provided the opportunity to identify novel genes involved in parasite biology. Here we characterize three members of the CCp family, named CCp1, CCp2 and CCp3, in B. bigemina, B. bovis and T. equi. Using B. bigemina as an in vitro model, expression of all three CCp genes and proteins was demonstrated in temperature-induced sexual stages. Transcripts for all three CCp genes were found in vivo in blood stages of T. equi, and transcripts for CCp3 were detected in vivo in blood stages of B. bovis. However, no protein expression was detected in T. equi blood stages or B. bovis blood stages or B. bovis tick stages. Collectively, the data demonstrated a differential pattern of expression of three orthologous genes of the multidomain adhesion CCp family by B. bigemina, B. bovis and T. equi. The novel CCp members represent potential targets for innovative approaches to control bovine babesiosis and equine piroplasmosis.
Targeted Surface Expression of an Exogenous Antigen in Stably Transfected Babesia bovis
Jacob M. Laughery, Donald P. Knowles, David A. Schneider, Reginaldo G. Bastos, Terry F. McElwain, Carlos E. Suarez
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0097890
Abstract: Babesia bovis is a tick-borne intraerythocytic protozoan responsible for acute disease in cattle which can be controlled by vaccination with attenuated B. bovis strains. Emerging B. bovis transfection technologies may increase the usefulness of these live vaccines. One use of transfected B. bovis parasites may be as a vaccine delivery platform. Previous transfection methods for B. bovis were limited by single expression sites and intracellular expression of transfected antigens. This study describes a novel transfection system in which two exogenous genes are expressed: one for selection and the other for a selected antigen designed to be delivered to the surface of the parasites. The strategy for duplicating the number of transfected genes was based on the use of the putative bidirectional promoter of the B. bovis 1.4 Kb ef-1α intergenic region. The ability of this region to regulate two independent expression sites was demonstrated using a luciferase assay on transiently transfected B. bovis parasites and then incorporated into a stable transfection plasmid to control independent expression of the selectable marker GFP-BSD and another gene of interest. A chimeric gene was synthetized using sequences from the protective B-cell epitopes of Rhipicephalus microplus tick antigen Bm86 along with sequences from the surface exposed B. bovis major surface antigen-1. This chimeric gene was then cloned into the additional expression site of the transfection plasmid. Transfection of the B. bovis Mo7 strain with this plasmid resulted in stable insertion into the ef-1α locus and simultaneous expression of both exogenous genes. Expression of the Bm86 epitopes on the surface of transfected merozoites was demonstrated using immunofluorescence analyses. The ability to independently express multiple genes by the inclusion of a bidirectional promoter and the achievement of surface expression of foreign epitopes advances the potential of transfected B. bovis as a future vaccine delivery platform.
Conservation in the face of diversity: multistrain analysis of an intracellular bacterium
Michael J Dark, David R Herndon, Lowell S Kappmeyer, Mikel P Gonzales, Elizabeth Nordeen, Guy H Palmer, Donald P Knowles, Kelly A Brayton
BMC Genomics , 2009, DOI: 10.1186/1471-2164-10-16
Abstract: These comparisons revealed that A. marginale has a closed-core genome with few highly plastic regions, which include the msp2 and msp3 genes, as well as the aaap locus. Comparison of the Florida and St. Maries genome sequences found that SNPs comprise 0.8% of the longer Florida genome, with 33.5% of the total SNPs between all five strains present in at least two strains and 3.0% of SNPs present in all strains except Florida. Comparison of genomes from three strains of Mycobacterium tuberculosis, Bacillus anthracis, and Nessieria meningiditis, as well as four Chlamydophila pneumoniae strains found that 98.8%–100% of SNPs are unique to each strain, suggesting A. marginale, with 76.0%, has an intermediate level of strain-specific SNPs. Comparison of genomes from other organisms revealed variation in diversity that did not segregate with the environmental niche the bacterium occupies, ranging from 0.00% to 8.00% of the larger pairwise-compared genome.Analysis of multiple A. marginale strains suggests intracellular bacteria have more variable SNP retention rates than previously reported, and may have closed-core genomes in response to the host organism environment and/or reductive evolution.While the recent boom in genome sequencing projects has provided a wealth of information about bacterial metabolism and evolution, we know little about interstrain variation. A firm understanding of the rates and sites of variation is useful in determining genotypic differences associated with phenotypic traits and in formulating control strategies for a number of pathogens. Further, knowledge about the pan-genome of organisms will aid in determining the core genomic requirements, as well as shed more light on events that occur in the various environmental niches bacteria occupy.Most studies of bacterial diversity to date have either utilized specific genomic loci [1,2] or have examined metagenomics of specific environmental niches [3,4]. While these types of studies help elucidate th
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