Studies of the immunology and epidemiology of orf

The responses of seven sheep to orf virus infection were examined by cannulating the efferent supramammary lymphatic before infecting the drainage area of the node. All animals developed lesions typical of orf virus infection, and responded after an initial lag period with an increase in total cell output paralleled by an increased proportion of lymphoblast cells. The majority of these lymphoblasts contained immunoglobulin, with a predominance of the IgG class. When efferent lymph cells from four of the sheep were cultured in vitro they were found to produce measurable amounts of virus specific antibody. When assessed in two of the sheep, the proportion of cells which stained with a T-cell-specific monoclonal antibody was found to decrease as the response developed. In contrast, analysis of afferent lymph (derived from efferent prefemoral lymphatics cannulated eight weeks after removal of the node) in four sheep revealed no marked cellular changes following experimental infection.The serological responses of naturally and experimentally infected lambs to orf virus infection was analysed using an enzyme-linked immunosorbent assay (ELISA) together with the Western Blotting technique. The combination of these methods permitted a quantitative and qualitative assessment of humoral responses, which revealed considerable variation between animals. However, all post-exposure sera reacted with a polypeptide which appears to be a component of the surface tubules which are characteristic of the virus. Despite high titres in some animals, there was no apparent association between humoral responses and recovery or protection.The heterogeneity of the orf virus population within the UK was examined using the restriction enzyme EcoRI by digesting viral DNA prepared from scab material derived from various outbreaks, and separating the fragments by electrophoresis in polyacrylamide gels. This technique revealed obvious genomic differences among the isolates which were examined, extending even to those derived from animals undergoing synchronous infections on the same premises.By subjecting orf scab material to various contrived environmental conditions both indoors and outdoors, it was shown that exposure to rainfall can abrogate infectivity of the virus, which questions the significance of virus persisting on pasture as a source of infection.Two rams which were shown to suffer from chronic orf infection suggest that the virus is capable of surviving inter-epizootic periods within the animal population. These animals had high serum antibody titres, but exhibited reduced delayed hypersensitivity responses to intradermal challenge with orf virus when compared with control animals.It was concluded that humoral responses play little or no part in recovery and protection from of virus infection, and that immunity is manifested by an accelerated reaction which is the result of a delayed hypersensitivity response

Novel immunization strategies against protozoan parasites. Proceedings of a workshop

The main aim of this meeting was to review those developments in the fields of immunology and immunoparasitology that have relevance to the development of vaccination strategies for ECF and trypanosomiasis. Of relevance to the control of ECF were recent developments in the elucidation of events that surround the induction of cytotoxic T lymphocytes, and the role of cytokines in the control and pathogenesis of parasitic infections. Chief areas of interest to the trypanosomiasis programme were disease-related perturbations of the immune system, the role of individual T cell subsets in immunity to parasites and the involvement of cytokines in the control and pathogenesis of parasitic diseases. More specific discussions focused on the role of CTL in parasitic infections; antigen processing for class I MHC - restricted responses; novel technologies for identifying antigens that provoke CTL responses; the role of detrimental immune responses in pathogenesis; the role of T cell subsets and their products in the control of parasitic diseases; and immunization strategies for driving immune responses towards favourable rather than detrimental mechanisms

Zoonoses (Project 1): Wildlife/domestic livestock interactions

The objective of this study was to synthesise the best available scientific knowledge about zoonotic disease transmission through livestock and wildlife interaction (direct or indirect), with emphasis on risk factors, drivers and trajectories of transmission, as well as promising interventions for controlling important zoonoses, based on managing the interaction between domestic livestock and wildlife. A multi-disciplinary team from the International Livestock Research Institute, Kenya, and the Royal Veterinary College, United Kingdom, with expertise in zoonoses, epidemiology, socio-economics, and wildlife, undertook the review. A database of important zoonoses was compiled and used to develop a list of priority zoonoses with a livestock-wildlife interface for developing countries. Spatial relationships between important zoonoses and land use and human population density were explored. A systematic review was carried out focussing on: disease transmission routes, risk factors for disease transmission, drivers of wildlife-livestock interactions, pathogens of wildlife capable of recombining with organisms in livestock, wildlife species that are potential sources of zoonotic pathogens, production and socio-economic factors influencing the risk of transmission, and risk management and control interventions

Expression Analysis of the Theileria parva Subtelomere-Encoded Variable Secreted Protein Gene Family

Background The intracellular protozoan parasite Theileria parva transforms bovine lymphocytes inducing uncontrolled proliferation. Proteins released from the parasite are assumed to contribute to phenotypic changes of the host cell and parasite persistence. With 85 members, genes encoding subtelomeric variable secreted proteins (SVSPs) form the largest gene family in T. parva. The majority of SVSPs contain predicted signal peptides, suggesting secretion into the host cell cytoplasm. Methodology/Principal Findings We analysed SVSP expression in T. parva-transformed cell lines established in vitro by infection of T or B lymphocytes with cloned T. parva parasites. Microarray and quantitative real-time PCR analysis revealed mRNA expression for a wide range of SVSP genes. The pattern of mRNA expression was largely defined by the parasite genotype and not by host background or cell type, and found to be relatively stable in vitro over a period of two months. Interestingly, immunofluorescence analysis carried out on cell lines established from a cloned parasite showed that expression of a single SVSP encoded by TP03_0882 is limited to only a small percentage of parasites. Epitope-tagged TP03_0882 expressed in mammalian cells was found to translocate into the nucleus, a process that could be attributed to two different nuclear localisation signals. Conclusions Our analysis reveals a complex pattern of Theileria SVSP mRNA expression, which depends on the parasite genotype. Whereas in cell lines established from a cloned parasite transcripts can be found corresponding to a wide range of SVSP genes, only a minority of parasites appear to express a particular SVSP protein. The fact that a number of SVSPs contain functional nuclear localisation signals suggests that proteins released from the parasite could contribute to phenotypic changes of the host cell. This initial characterisation will facilitate future studies on the regulation of SVSP gene expression and the potential biological role of these enigmatic proteins

Willingness to pay for contagious bovine pleuropneumonia vaccination in Narok South District of Kenya

Contagious bovine pleuropneumonia (CBPP) is an economically important trans-boundary cattle disease which affects food security and livelihoods. A conjoint analysis–contingent valuation was carried out on 190 households in Narok South District of Kenya to measure willingness to pay (WTP) and demand for CBPP vaccine and vaccination as well as factors affecting WTP. The mean WTP was calculated at Kenya Shillings (KSh) 212.48 (USD 3.03) for vaccination using a vaccine with the characteristics that were preferred by the farmers (preferred vaccine and vaccination) and KSh −71.45 (USD −1.02) for the currently used vaccine and vaccination. The proportion of farmers willing to pay an amount greater than zero was 66.7% and 34.4% for the preferred and current vaccine and vaccination respectively. About one third (33.3%) of farmers would need to be compensated an average amount of KSh 1162.62 (USD 13.68) per animal to allow their cattle to be vaccinated against CBPP using the preferred vaccine and vaccination. About two-thirds (65.6%) of farmers would need to be compensated an average amount of KSh 853.72 (USD 12.20) per animal to allow their cattle to be vaccinated against CBPP using the current vaccine and vaccination. The total amount of compensation would be KSh 61.39 million (USD 0.88 million) for the preferred vaccine and vaccination and KSh 90.15 million (USD 1.29 million) for the current vaccine and vaccination. Demand curves drawn from individual WTP demonstrated that only 59% and 27% of cattle owners with a WTP greater than zero were willing to pay a benchmark cost of KSh 34.60 for the preferred and current vaccine respectively. WTP was negatively influenced by the attitude about household economic situation (p = 0.0078), presence of cross breeds in the herd (p < 0.0001) and years since CBPP had been experienced in the herd (p = 0.0375). It was positively influenced by education (p = 0.0251) and the practice of treating against CBPP (p = 0.0432). The benefit cost ratio (BCR) for CBPP vaccination was 2.9–6.1 depending on the vaccination programme. In conclusion, although a proportion of farmers was willing to pay, participation levels may be lower than those required to interrupt transmission of CBPP. Households with characteristics that influence WTP negatively need persuasion to participate in CBPP vaccination. It is economically worthwhile to vaccinate against CBPP. A benefit cost analysis (BCA) using aggregated WTP as benefits can be used as an alternative method to the traditional BCA which uses avoided production losses (new revenue) and costs saved as benefits

Efficacy of two vaccine formulations against contagious bovine pleuropneumonia (CBPP) in Kenyan indigenous cattle

AbstractA live, attenuated vaccine is currently the only viable option to control of CBPP in Africa. It has been suggested that simple modifications to current vaccines and protocols might improve efficacy in the field. In this report we compared the current vaccine formulation with a buffered preparation that maintains Mycoplasma viability at ambient temperature for a longer time. Groups of animals were vaccinated with the two formulations and compared with non vaccinated groups. Half of the animals in each group were challenged 3months post vaccination, the other half after 16months. Protection levels were measured using the pathology index, calculated from post mortem scores of lesions from animals killed during the course of clinical disease. In the challenge at 3months post vaccination, the protection levels were 52% and 77% for the modified and current vaccine preparations, respectively. At 16months post vaccination, the protection levels were 56% and 62% for the modified and current vaccine preparations, respectively. These findings indicate that there are no differences in protection levels between the two vaccines. Because of its longer half life after reconstitution, the modified vaccine might be preferred in field situations where the reconstituted vaccine is likely not to be administered immediately

Trans-Species Polymorphism and Selection in the MHC Class II DRA Genes of Domestic Sheep

Highly polymorphic genes with central roles in lymphocyte mediated immune surveillance are grouped together in the major histocompatibility complex (MHC) in higher vertebrates. Generally, across vertebrate species the class II MHC DRA gene is highly conserved with only limited allelic variation. Here however, we provide evidence of trans-species polymorphism at the DRA locus in domestic sheep (Ovis aries). We describe variation at the Ovar-DRA locus that is far in excess of anything described in other vertebrate species. The divergent DRA allele (Ovar-DRA*0201) differs from the sheep reference sequences by 20 nucleotides, 12 of which appear non-synonymous. Furthermore, DRA*0201 is paired with an equally divergent DRB1 allele (Ovar-DRB1*0901), which is consistent with an independent evolutionary history for the DR sub-region within this MHC haplotype. No recombination was observed between the divergent DRA and B genes in a range of breeds and typical levels of MHC class II DR protein expression were detected at the surface of leukocyte populations obtained from animals homozygous for the DRA*0201, DRB1*0901 haplotype. Bayesian phylogenetic analysis groups Ovar-DRA*0201 with DRA sequences derived from species within the Oryx and Alcelaphus genera rather than clustering with other ovine and caprine DRA alleles. Tests for Darwinian selection identified 10 positively selected sites on the branch leading to Ovar-DRA*0201, three of which are predicted to be associated with the binding of peptide antigen. As the Ovis, Oryx and Alcelaphus genera have not shared a common ancestor for over 30 million years, the DRA*0201 and DRB1*0901 allelic pair is likely to be of ancient origin and present in the founding population from which all contemporary domestic sheep breeds are derived. The conservation of the integrity of this unusual DR allelic pair suggests some selective advantage which is likely to be associated with the presentation of pathogen antigen to T-cells and the induction of protective immunity

Multi-component subunit vaccines against Theileria parva

Cattle that recover from Theileria parva infection are solidly immune to rechallenge with homologous parasites. Most of the ILRAD/ILRI immunological research into the disease has focused on defining the basis of this protection. Over 15 years of basic and applied immunological research at ILRAD/ILRI have demonstrated that protection in T. parva immune cattle is primarily mediated by parasite-specific Cytotoxic T. lymphocytes (CTL). This paper summarises the status of the research and options including antigens, in vivo activation requirements and antigen delivery systems