Thiaminases and their effects on animals.
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In trials performed in Brazil, England and Germany, 765 pigs were challenged at one, three to four or 17 weeks after vaccination and their sera were titrated by macrocolour, microcolour or microcytopathic effects neutralization tests. Using O1 virus strains and challenge intervals of three to four weeks, significant correlations (P less than 0.01) were demonstrated between protection and serum neutralizing titres although the titres corresponding to given levels of protection varied with the titration method employed. The protective capacity of antiserum was confirmed by passive antibody transfer experiments. Retrospective analysis of 49 challenge tests showed that when the macrocolour test was employed, a group mean (n = 8) serum titre of 1.74 log10 SN50 corresponded with five out of eight (or more) protected from challenge in 92% of cases. The possibility of using serum titres as an alternative to challenge for oil emulsion vaccine potency tests is discussed.
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Foot-and-mouth disease (FMD) diagnostic methods are reviewed. As the presence of clinical signs alone is inconclusive, laboratory diagnosis should always be carried out. The presence of FMD virus can be demonstrated by cell culture isolation, complement fixation test, ELISA or the more recent polymerase chain reaction (PCR) method. Serological diagnosis is also a valuable tool. The virus neutralization test has been replaced by ELISA and the antibody response to some viral non-structural proteins allows to discriminate between vaccinated and infected animals on a herd basis. More rapid and accurate tests as well as an earlier detection system in preclinical state are still needed.
Although known for many years, foot-and-mouth disease is still able to represent a real threat to many farming economies in the world. The recent 2001 Western European epizootics linked to O PanAsia virus strain can illustrate the fact that many questions are still unanswered in the field of foot-and-mouth epidemiology. It also demonstrates that the increase in international trade, including livestock, animal products and animal food, means an increase in the probability of transmitting, through the same way, some animal diseases, foot-and-mouth included. In our economies, a rapid identification of the virus and a fast elimination of infected, contaminated and even some contact animals are still the key factors to react in front of such a disease.
The foot and mouth disease epidemic commenced in February 2001 when diseased pigs were identified in an abattoir. The infection had become widespread in sheep in England and Wales before this discovery. It was decided to eradicate the disease by slaughter rather than use vaccine. The virus was a Pan-Asia O strain that caused few lesions in sheep and this made the identification of infected flocks very difficult leading to a long drawn-out epidemic. Over four million animals were slaughtered in 2000 herds and flocks. The last outbreak was in September.
Emergency vaccination is one of several measures which may be deployed to control outbreaks of foot-and-mouth disease. It can be a valuable adjunct to the application of the essential zoosanitary controls which must include rapid diagnosis, tracing, movement control and disinfection and which may also include slaughter of infected and in-contact animals and their safe disposal. Criteria which determine the successful application of emergency vaccination include access to vaccine(s) that (i) contain virus strain(s) of sufficient antigenic relatedness to the outbreak strain(s) (ii) are of the required type of vaccine formulation (iii) have acceptable innocuity and potency (iv) have appropriate availability, including quantity and immediacy of supply and (v) meet considerations of cost. Contingency planning should include provision for emergency vaccination and must address the complex decisions of not only when, where, and how to apply vaccine but also its economic consequences. Computer modelling may be a useful aid to cost benefit and decision support systems in this context. Planning must be detailed and regularly reviewed and should ensure, (i) that the legal and financial aspects are catered for (ii) that any contractual supply agreements are in place (iii) that information is collected and its currency maintained on the species, numbers and whereabouts of susceptible livestock (iv) that vaccination teams are formed and trained (v) that the vaccine cold chain is established and maintained (vi) that supplies of vaccination equipment are held in readiness and (vii) that briefing materials are available to inform the various stakeholders on relevant aspects of emergency vaccination. Knowledge concerning the characteristics and performance of emergency vaccines is summarised and areas identified for further research.
The study of the available information, notably after the epizootic of foot-and-mouth disease (FMD) which raged in Western Europe in 2001, shows that, in the current conditions of the international sanitary rules relative to this disease, in a FMD-free country of Western Europe accidentally infected, ring vaccination is a solution which, with regard to preventive slaughter, contains more inconveniences (notably economic) than advantages. The appeal to ring vaccination would be interesting only as far as the international sanitary rules would be modified by taking into account the results expected from the coordinated use of highly purified vaccines and differential research kits (vaccine-linked versus infection-linked antibodies). Propositions are this way made.
Inflammatory mediators that are induced by gram-negative bacteria in the course of intrauterine infections threaten successful pregnancy. To compare the effect of two different routes of cytokine induction, bacterial lipopolysaccharide (LPS) was administered in vivo either into the cord vein or into the amniotic cavity of pig fetuses in the second half of gestation for 20 h and cytokines were detected in the amnion.Tumor necrosis factor-alpha (TNF-alpha) and interleukin-8 (IL-8) were induced in the amniotic epithelium after intra-amniotic but not after intra-venous administration of LPS. The presence of IL-8 was confirmed by RT-PCR. In contrast, transforming growth factor-beta1 (TGF-beta1) was expressed constitutively and was found in all samples of the amniotic epithelium. Amniotic fluid contained only minute levels of TNF-alpha. IL-8 levels in amniotic fluid increased after the treatment with LPS and the highest IL-8 levels were found in dead LPS-treated fetuses.
The dynamics of foot-and-mouth disease epidemics in France was examined through simulations based on an extended state-transition model. Contagion modelling depended on specific parameters: the so-called dissemination rates. Estimation of these parameters relied on a specific discrete-event simulation model. We were able to address the problem of the hidden spread of the epidemic, before the first outbreak is diagnosed. Furthermore, we took into account the silent development of the disease in affected herds before the diagnosis. The effect of control measures such as the active search for secondary outbreaks could thus be studied. We used the model to compare the development of FMD epidemics in two very different French regions and for different control strategies implemented by the animal-health authorities. These strategies gave similar results in a low herd density area, whereas in a high herd density area, the slaughter of contact herds greatly improved the stamping-out strategy. Finally, key parameters of the model were detected through a sensitivity analysis.
Many 'economic' studies of livestock diseases in Great Britain have been carried out over time. Most studies have considered just one or two diseases and used a different methodology and valuation base from other studies, hampering any comparative assessment of the economic impact of diseases. A standardized methodology was applied to the estimation of the direct costs to livestock production of some 30 endemic diseases/conditions of farm animals in Great Britain. This involved identification of the livestock populations at risk, estimation of the annual incidence of each disease in these populations, identification of the range and incidence of physical effects of each disease on production, valuation of the physical effects of each disease and estimation of the financial value of output losses/resource wastage due to a disease and the costs of specific treatment and prevention measures. The wider economic impacts of disease (such as the implications for human health, animal welfare and markets) were not included in the assessments. Using this standardized methodology with common financial values, a simple spreadsheet model was constructed for each disease. Given the paucity of appropriate disease data for economic assessment, 'low' and 'high' values were used to reflect uncertainties surrounding key disease parameters. Preliminary estimates of the value of disease output losses/resource wastage, treatment and prevention costs are presented for each disease. Despite the limitations of the spreadsheet models and of the estimates derived from them, we conclude that the models represent a useful start in developing a system for the comparative economic assessment of livestock diseases in Great Britain.
During a 2-year period from January 1998 to December 1999, intestinal content from 1541 cattle, 665 sheep and 1976 pigs were analysed for Escherichia coli O157:H7 using the immunomagnetic separation procedure. The animals originated from 848, 605 and 832 herds from the southwest part of Norway, respectively. E. coli O157:H7 was present in three samples from cattle from different herds, giving a herd prevalence of 0.35% and an animal prevalence of 0.19%. From pigs, E. coli O157:H7 was isolated from two pigs from different herds, giving a herd prevalence of 0.24% and an animal prevalence of 0.1%. A follow-up study revealed another positive testing pig from one of these herds. E. coli O157:H7 was not found from any of the 665 investigated sheep. By PCR analysis, all six E. coli O157:H7 isolates were shown to contain the genes encoding Shiga toxin 2 (stx2), the intimin protein (eae) and the H7 flagellum (fliC-H7). One of the cattle isolates also harboured the Shiga toxin 1 encoding (stx1) gene. The six isolates were differentiated into three pulse-field gel electrophoresis profiles. The results indicate that the occurrence of E. coli O157:H7 in cattle, sheep and pigs in the southwest part of Norway is low compared to other European countries.
Porcine circovirus type 2 (PCV2) has been associated with a newly identified and described disease in swine called the postweaning multisystemic wasting syndrome (PMWS). An association of PCV2 with various other clinical conditions in pigs are also increasingly being reported. To date molecular studies to determine the extent of genetic variations of this virus have been limited. To more fully understand the extent of genetic diversity we report the sequencing of 34 PCV2 strains from Eastern Canada originating from a variety of clinical conditions spanning years 1990-2001 along with the phylogenetic analysis of these strains and that of 36 PCV2 sequences published in GenBank. Sequence analysis of the complete genome indicated that the Canadian PCV2 strains analyzed in the present study are closely related to each other but also to other PCV2 strains originating from Western Canada, US, Europe and Asia. Sequence analysis of ORF1 and ORF2 genes of the 34 strains revealed that the extent of nucleotide variation was greater for the ORF2 than for the ORF1. The amino acid sequences alignment of the PCV2 capsid protein identified three major regions of amino acid heterogeneity, two of which correspond with dominant immunoreactive areas. No repeatable amino acid motifs for these two regions could be associated with PCV2 strains identified from cases of PMWS or other clinical conditions. Phylogenetic analysis of all 70 strains revealed one large cluster composed of strains from Europe, Taiwan, China and Canada. This large cluster could be divided in several sub clusters, in two of which Canadian strains were found closely related to strains from Germany. The remaining strains from Canada and the US were spread in small groupings along the phylogenetic tree and an association with geographic origin could not be established. The genomic characterizations performed in this study indicate that PCV2 strains associated with PMWS are scattered throughout the phylogenetic tree often in groupings including PCV2 strains identified from cases other that PMWS such as, porcine reproductive and respiratory syndrome (PRRS), generalized tremors, porcine dermatitis and nephropathy syndrome (PDNS), arthritis, nervous signs, erysipelas and even healthy pigs.
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Infections with the larval stages of taeniid cestode parasites cause substantial human morbidity as well as economic losses in domestic livestock species. Despite ongoing efforts around the world, few countries have been able substantially to reduce or eradicate these infections through the use of anthelmintics and lifestyle changes. Vaccines offer an additional potential tool to assist with the control of parasite transmission. Here, Marshall Lightowlers and colleagues review the substantial progress that has been made towards developing practical vaccines against hydatid disease in sheep and cysticercosis in sheep and cattle. Recombinant antigens have been used to induce more than 90% protection against challenge infections. Such success in animals encourages investigation of the potential use of vaccines in humans to prevent hydatid disease arising from infection with Echinococcus granulosus and cysticercosis from infection with Taenia solium.
The potbellied pig was introduced into the United States in 1985 and has since become a desirable pet throughout the country. When seeking medical or husbandry advice, pig owners often seek the counsel of their local small animal practitioner. The practitioner may feel at a loss to adequately respond to requests for veterinary care because they do not remember pig medicine from veterinary school. Large animal practitioners, who have knowledge of the medicine and surgery of commercial pigs, often do not like caring for potbellied pigs because they are pets and not production animals. This article is intended to provide the small animal practitioner with some practical knowledge in the husbandry and medical care of the pet pig, also known as the yuppy puppy.
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