Farm level bio-economic modelling of aquatic animal disease and health interventions.

A farm level bio-economic model, for aquatic animal production, of the relationships between inputs (e.g. purchased animals), outputs (e.g. harvested animals) and gross margin (GM) was developed to assess ex-ante the economics of disease and animal health interventions. Feed costs were calculated from estimates of food conversion ratio (FCR), animals harvested and mortality. The model was applied to a typical grow-out rainbow trout (Oncorhynchus mykiss) farm on Lake Titicaca, Peru and a typical shrimp (Paenus vannamei) farm in the Mekong Delta, Vietnam. The model was used in two analyses. Firstly, an approach to assess the burden of disease developed by the Global Burden of Animal Diseases (GBADs) project was adopted. Output under conditions of 'ideal health' was estimated by reducing mortality to zero and removing health costs. GM in both systems increased by approximately 25% when production was kept constant (and stocking rates reduced) and more than doubled if production was allowed to rise (and initial stocking increased). The increase in GM under conditions of ideal compared with current production provided an estimate of the maximum possible benefit from improved health management. Secondly, break-even analysis was used to assess the economics of vaccination against infectious pancreatic necrosis (IPN) vaccine (rainbow trout - RBT) and probiotics (shrimp). If initial stocking was kept constant, and production allowed to rise, break-even points for the intervention (when GM was the same with and without the intervention) were achieved when mortality was reduced by 16% in RBT fry and juvenile and 28% in shrimp. If production was kept constant and benefit realised by reduced initial stocking, the break-even point was achieved for i) vaccination of RBT when mortality in fry and juveniles was reduced by 39%, and ii) probiotics in shrimp production when there was a 15% reduction in mortality (nursery and grow-out), 10% increase in shrimp weight at harvest and 10% improvement in FCR. The results demonstrate how relatively simple models, parameterised with basic farm production data, can assess the burden of disease and quantify ex-ante the potential benefit of interventions. In the absence of trial data, these analyses support decision-making by farmers. The models can be adapted for many aquaculture systems. Farm level results can be extrapolated to estimate disease burden, and benefits of interventions, at regional or national level and thus support informed decision-making and allocation of resources to health management.

Review of antimicrobial resistance surveillance programmes in livestock and meat in EU with focus on humans.

OBJECTIVES: In this review, we describe surveillance programmes reporting antimicrobial resistance (AMR) and resistance genes in bacterial isolates from livestock and meat and compare them with those relevant for human health. METHODS: Publications on AMR in European countries were assessed. PubMed was reviewed and AMR monitoring programmes were identified from reports retrieved by Internet searches and by contacting national authorities in EU/European Economic Area (EEA) member states. RESULTS: Three types of systems were identified: EU programmes, industry-funded supranational programmes and national surveillance systems. The mandatory EU-financed programme has led to some harmonization in national monitoring and provides relevant information on AMR and extended-spectrum ß-lactamase/AmpC- and carbapenemase-producing bacteria. At the national level, AMR surveillance systems in livestock apply heterogeneous sampling, testing and reporting modalities, resulting in results that cannot be compared. Most reports are not publicly available or are written in a local language. The industry-funded monitoring systems undertaken by the Centre Européen d'Etudes pour la Santé Animale (CEESA) examines AMR in bacteria in food-producing animals. CONCLUSIONS: Characterization of AMR genes in livestock is applied heterogeneously among countries. Most antibiotics of human interest are included in animal surveillance, although results are difficult to compare as a result of lack of representativeness of animal samples. We suggest that EU/EEA countries provide better uniform AMR monitoring and reporting in livestock and link them better to surveillance systems in humans. Reducing the delay between data collection and publication is also important to allow prompt identification of new resistance patterns.

Effects of dietary wheat bran on absorption and accumulation of PCBs in rats.

Polychlorinated biphenyls (PCBs) are toxic environmental contaminants, which tend to accumulate in the food chain. Since dietary intake is the most important exposure route, PCB body burden may be affected by taking proper dietary measures. In the present study, diets were supplemented with either wheat bran or its cellulose based placebo in order to study the effect of bran consumption on the absorption of dietary PCBs and the excretion of initially stored PCBs. During the period of PCB intake, faecal PCB excretion was elevated by consumption of wheat bran as compared to the placebo. Hence, apparent faecal PCB digestibilities as well as PCB retentions in the whole body were lower in the wheat bran consuming rats. After ending PCB consumption, dietary wheat bran had only a minor effect on faecal PCB output while accumulation in the body was not affected. When PCBs were consumed for a longer time, a small but significant reduction of apparent faecal PCB digestibility was found. However, PCB content in the body kept increasing while PCB retention as percent of intake remained almost constant. Furthermore, differences among individual PCB congeners in metabolic susceptibility and hydrophobic characteristics had an impact on their accumulation in the body.

Polychlorinated biphenyl distribution and faecal excretion in rats fed wheat bran.

Polychlorinated biphenyls (PCBs) are abundant and persistent environmental contaminants, which tend to accumulate through the food chain. Because of the toxic potential of these compounds, body burden should be kept as low as possible e.g. by taking dietary measures. In the present report, the effect of wheat bran consumption on absorption of dietary PCBs as well as on excretion of previously absorbed PCBs was investigated in rats. Moreover, the accumulation of 7 reference PCB congeners in liver and abdominal adipose tissue was studied. Faecal excretion of dietary PCBs was significantly higher in rats fed wheat bran compared to its placebo. As a result, apparent PCB digestibility was diminished, but not enough to significantly affect PCB accumulation in liver and abdominal adipose tissue. Furthermore, excretion of previously absorbed PCBs following switching of the rats to a control diet without added PCBs was enhanced by wheat bran fibre intake, although to a much lesser extent than excretion of PCBs originating directly from the diet. Consequently, stimulation of PCB clearance from liver and abdominal adipose tissue due to wheat bran consumption was not detectable. Although no preferential absorption of PCB congeners was observed, PCB patterns in tissues obviously differed from the dietary PCB pattern. This was mainly due to PCBs 52 and 101, which were metabolised in the body. Moreover, reduced levels of PCB 138 were found in liver, while PCB 28 and 138 were predominantly present in adipose tissue. The experiment also demonstrated that PCB redistribution from the liver to the adipose tissue occurs.

Digestibility, retention and incorporation of low-level dietary PCB contents in laying hens.

Polychlorinated biphenyls (PCBs) are persistent and hazardous environmental contaminants, which tend to bioaccumulate in the food chain. In the present report the long-term effect of low-level dietary PCB concentrations was studied on performance, egg quality, apparent PCB digestibility, apparent PCB retention and PCB accumulation in laying hens that were fed experimental diets for 41 weeks. The tested dietary concentrations of supplemented PCBs, based on the sum of seven reference congeners, were 0, 1.5 and 6 ng/g. PCB ingestion did not significantly affect performance or egg quality parameters. The PCB concentration in egg yolk reached a nearly constant level after approximately 40 and 70 days of consumption of the diets containing 1.5 and 6 ng PCBs/g, respectively. Apparent faecal PCB digestibility and apparent retention were not influenced by dietary levels of added fat varying between 1.5% and 4.5%, but were significantly higher in hens fed diets containing added PCBs. Moreover, apparent PCB digestibility and retention increased significantly with age. Among the seven individual PCB congeners, no systematically significant differences with regard to apparent faecal digestibility were observed throughout the experiment. Accumulation of PCBs in the fat fraction of egg yolk, abdominal adipose tissue and thigh and breast muscle greatly depended upon PCB intake, but never exceeded the maximally allowed concentration of 200 ng/g. As PCBs 52 and 101 were hardly found in egg yolks and hen tissues, it was concluded that both congeners were greatly metabolised. Comparison of relative contents of individual PCB congeners revealed that PCBs 118, 138 and 153 were preferentially incorporated in yolk and body tissues.

Genetic diversity and spread of Bovine leukaemia virus isolates in Argentine dairy cattle.

Effective tools for use in control programmes against bovine leukaemia virus (BLV) infections require insight into the relationship between the variant structure of the bovine leukaemia virus and the spatial-temporal interaction of isolates and hosts. Our study showed the presence of two types of BLV isolates - Australian and Argentine - in dairy herds from various parts of Central Argentina; these isolates were characterised by RFLP on PCR amplicons, and some of them were confirmed by sequencing. One genotype (Argentine) was present in all herds, and the Australian genotype was found in two herds. Phylogenetic analysis indicated four clusters. The first cluster was composed of the Argentine isolates and one from Brazil; the second was composed of several isolates found in European countries and one from Brazil; the third cluster was composed of BLV isolates found in Japan and Germany; the fourth cluster included American and Australian isolates and those from other countries. The comparison of a number of synonymous and non-synonymous nucleotide substitutions using various BLV genes revealed purifying selection, suggesting that molecular evolution occurred under some functional constraint.

Accumulation and tissue distribution of selected polychlorinated biphenyl congeners in chickens.

During one to three consecutive periods of 2 weeks, broiler chickens (n = 108) received test dies to which different amount of PCBs (7 congeners) were added. The relationship between exposure time and accumulation of individual congeners in different chicken tissues, such as breast, thigh and abdominal fat tissue, was observed. In all tissues, the vast majority of the PCB accumulation occurred during the first 2 weeks of exposures. After that, PCB concentrations only increased in the abdominal fat tissue of the animals. The individual PCBs were distributed differently in the various tissues. While CBs 28, 118, 138, 153 and 180 accumulated in the chickens, CBs 52 and 101 were metabolized, but no methyl sulphone metabolites of these congeners could be detected. Our results provide information on the absorption, tissue distribution and biotransformation of the individual PCB congeners and confirm the structure-activity relationships for metabolism of PCBs in birds, which are different from those in fish or mammalian species.

Polychlorinated biphenyls in broiler diets: their digestibility and incorporation in body tissues.

The influence of dietary amounts of polychlorinated biphenyls (PCBs) was studied on performance, apparent PCB digestibility and PCB accumulation in broiler chickens that were maintained until 42 days of age. Dietary concentrations of supplemented PCBs, based on the sum of seven reference congeners, ranged from 0 to 12 ng/g, which was below the legal maximum of 200 ng PCBs/g fat in Belgian feeds. PCB ingestion did not significantly affect body weight and feed intake. Apparent PCB digestibility was not influenced by dietary levels of added fat varying between 4% and 8%, but was significantly higher in broilers fed diets containing added PCBs. Accumulation of PCBs in the fat fraction of abdominal adipose tissue and breast and thigh muscle greatly depended upon PCB intake. However, PCB contents in the various body fat fractions within the same animal differed, even within muscle tissues, indicating an unequal PCB distribution in body fats.

Carriers of foot-and-mouth disease virus: a review.

This review describes current knowledge about persistent foot-and-mouth disease virus (FMDV) infections, the available methods to detect carrier animals, the properties of persisting virus, the immunological mechanisms, and the risk of transmission. In particular, knowledge about the carrier state, the period in which virus can be isolated from animals 28 days or longer post infection, is important, because the risk that animals may carry the virus will influence the diagnostic and preventive measures that need to be taken. Although many years of research have led to much knowledge about foot-and mouth disease and its causative agent, there are still numerous aspects of the virus and the disease that are not yet fully understood. Areas for further research on persistence of FMDV are discussed.

[Laboratory findings during the classic swine fever epidemic of 1997-1998]. / Laboratoriumbevindingen van de klassieke-varkenspest-epizoötie 1997-1998.

The results of the laboratory tests carried out by the Institute for Animal Science and Health (ID-Lelystad), the Netherlands, on samples collected during the Classical Swine Fever (CSF) epidemic 1997-1998 are summarized in this article. The relevance of the different laboratory tests and various samples collected on the eradication of CSF during an outbreak is evaluated.

[Foot-and-mouth disease of cattle is not a zoonosis]. / De runderziekte mond- en klauwzeer is geen zoönose.

In 1997 there was an outbreak of foot-and-mouth disease (FMD) among cattle in Turkey. People visiting that country were warned against importing animal products into the Netherlands. This had nothing to do with hazards to human health, as FMD virus is not a zoonotic virus, but with the risk of spread of the disease to livestock in the Netherlands, notably to cattle and pigs. A disease with similar clinical symptoms in pigs is swine vesicular disease (SVD), which is not a zoonosis either. FMD virus is an aphtovirus, SVD virus is an enterovirus. Hand-foot-and-mouth disease in humans is caused by other enteroviruses, i.e. Coxsackie virus and enterovirus 71.

[Immunobiology of bovine respiratory syncytial virus infections]. / Immunobiologie van pinkengriep.

This paper describes recent findings on the immunobiology of bovine respiratory syncytial virus (BRSV) infections. The pathobiology of alveolar macrophages and BRSV, and the immunological reaction of cattle to the virus after natural or experimental infection, or vaccination, were studied. Because in severe cases BRSV infection leads to lower respiratory tract disease, replication of BRSV in alveolar macrophages was studied. Alveolar macrophages, which are important aspecific defense cells in the lower respiratory tract, exhibited a high intrinsic resistance to BRSV. Furthermore, BRSV-infected alveolar macrophages produced significantly less nitric oxide (which has a bacteriocidal effect) than uninfected macrophages. The kinetics of antibody titres against the envelope protein G were different from those of antibody titres against the envelope protein F. For example, many animals that are reinfected do not possess antibodies against the G protein. After vaccination or after natural infection, antibody titres against the F and G protein, and against epitopes on the F protein, differed markedly, and also in animals with different MHC haplotypes. These findings may be related to differences in protection. The strains of BRSV that circulate in the Netherlands belong to the subgroups A and AB. There was no evidence for differences in virulence between these subgroups. BRSV could be detected in 30% of lungs obtained from calves suffering from severe lower respiratory tract disease. Based on cross-protection studies, calves that were infected with a virus from a particular BRSV subgroup were protected against reinfection with a virus from a different subgroup. A recombinant gE-protein negative bovine herpesvirus 1 vaccine carrying a gene encoding the G protein of BRSV, and a DNA vaccine encoding the same protein afforded protection after experimental challenge of calves. This offers the possibility to develop effective multivalent (gE-negative BHV1) marker vaccines in the future.

A bovine respiratory syncytial virus strain with mutations in subgroup-specific antigenic domains of the G protein induces partial heterologous protection in cattle.

Bovine respiratory syncytial virus (BRSV) strains are tentatively divided in subgroups A, AB and B, based on antigenic differences of the G protein. A Dutch BRSV strain (Waiboerhoeve: WBH), could not be assigned to one of the subgroups, because the strain did not react with any monoclonal antibody against the G protein. We describe here that the WBH strain has accumulated critical mutations in subgroup-specific domains of the G protein gene, which also occur but then independently in G protein genes of BRSV subgroup A or B strains. Although the comparison of nucleotide residues 256-792 of the G gene of the WBH strain with those of subgroup A and B strains showed that the G gene of the WBH strain is different from that of BRSV subgroup A and B strains, the sequence divergence was not more than observed within the G genes of human respiratory syncytial virus subgroup A or B strains. The WBH strain did not induce severe disease after experimental infection of calves, and induced partial protection against a heterologous challenge. Despite the dissimilarity of the conserved central regions of the G protein of the WBH strain and that of the challenge strain, a secondary antibody response against this region was induced in WBH-infected calves after challenge. We conclude that complete BRSV virus can partially protect against a BRSV infection with a strain that contains an antigenic dissimilar G protein.

The influence of enzyme-resistant starch on cholesterol metabolism in rats fed on a conventional diet.

Male Wistar rats were fed on a conventional diet containing normal corn starch or 6% enzyme-resistant starch originating from either raw or retrograded high-amylose corn starch. Furthermore, the diets were either cholesterol-free or contained 1% cholesterol and 0.1% cholic acid. The main objective of this study was to investigate whether the addition of enzyme-resistant starch to a rat conventional diet had any effect on cholesterol metabolism. Therefore, plasma and liver cholesterol concentrations, plasma HDL:LDL cholesterol ratios and neutral steroid and bile acid excretion were determined. No significant effect of enzyme-resistant starch feeding on plasma and liver cholesterol concentrations was found. However, consumption of raw or retrograded high-amylose corn starch resulted in a decrease in esterified and total liver cholesterol concentrations of 24 and 22%, respectively. This was accompanied by a reduction in plasma esterified and total cholesterol levels of 4% and a tendency to higher daily faecal coprostanol and total bile acid excretion.

Critical factors affecting the diagnostic reliability of enzyme-linked immunosorbent assay formats.

This paper aims to evaluate different formats of the enzyme-linked immunosorbent assays (ELISAs) for detection of virus-specific antibodies and focuses on factors that may influence the diagnostic reliability of such tests. Newly developed and well-established ELISAs for detection of infections of bovine herpesvirus 1 (BHV1), bovine respiratory syncytial virus (BRSV), classical swine fever virus (CSFV), pseudorabies virus (PRV) and bovine viral diarrhoea virus (BVDV) are used as examples. Differences between competitive and non-competitive ELISAs are described, with special reference to the influence of the antigen, the conjugated antibody and the test sample on the test results. Attention is drawn to interference, which may result in false positive or false negative test results, with special emphasis on the 'bridging' phenomenon. The use of monoclonal antibodies and discriminatory tests are briefly discussed. Diagnostic reliability is described for tests that are used in monitoring or eradication programmes, emphasising the consequences of false negative and false positive test results. Finally, reducing assay-time and functional quality control for such tests are discussed.

Comparison of DNA application methods to reduce BRSV shedding in cattle.

We compared the protection afforded by three different DNA application methods against bovine respiratory syncytial virus (BRSV) infection in cattle. A synthetic gene that codes for the G protein of BRSV was inserted into a eukaryotic vector and was used in the vaccine. Intradermal (i.d.) application with a needleless injector (NI), the Pigjet, reduced BRSV excretion significantly better after BRSV challenge than intramuscular (i.m.) or i.d. vaccination with a needle. Serum antibodies against the G protein were consistently the highest and showed less variation in Calves vaccinated with the NI compared with those in i.m. and i.d. vaccinated calves. After BRSV challenge, secondary serum and mucosal antibody responses were also the highest in NI vaccinated calves. We conclude that DNA application with the needleless injector is substantially better than i.m. or i.d. application, and is capable to prime the immune response at the respiratory mucosa.

Immunization of cattle with a BHV1 vector vaccine or a DNA vaccine both coding for the G protein of BRSV.

A gE-negative bovine herpesvirus 1 (BHV1) vector vaccine carrying a gene coding for the G protein of bovine respiratory syncytial virus (BRSV) (BHV1/BRSV-G) induced the same high degree of protection in calves against BRSV infection and BHV1 infection as a multivalent commercial vaccine. A DNA plasmid vaccine, carrying the same gene as the BHV1/BRSV-G vaccine, significantly reduced BRSV shedding after BRSV infection compared with that in control calves, but less well than the BHV1/BRSV-G vaccine. Flow cytometric analysis showed a significant relative increase of gamma/delta+ T cells in peripheral blood after BRSV challenge-infection of the calves of the control group but not in the vaccinated groups. These results indicate that the G protein of BRSV can induce significant protection against BRSV infection in cattle, and that the BHV1/BRSV-G vaccine protects effectively against a subsequent BRSV and BHV1 infection.

Effect of route and frequency of administration of apomorphine on growth hormone release in African catfish (Clarias gariepinus).

Apomorphine is known to stimulate growth hormone release in African catfish following an intraperitoneal (IP) injection. In the present study the effect of apomorphine (5 or 20 mg/kg body weight) on plasma GH levels was evaluated after gastro-intestinal or parenteral delivery. Apomorphine increased the plasma GH concentration regardless of the route of administration, indicating that apomorphine can be absorbed from the intestinal tract. The effect of repeated administration of apomorphine differed clearly between the tested doses. Although a single IP injection with 20 mg apomorphine/kg body weight resulted in a clear increase in plasma GH levels, a second injection given 12 hours later was ineffective. In contrast the last of 4 consecutive injections with 5 mg apomorphine/kg body weight given at intervals of 12 hours stimulated the plasma GH levels in a similar way to a single IP injection with the same dose.

Antibody responses against epitopes on the F protein of bovine respiratory syncytial virus differ in infected or vaccinated cattle.

The fusion protein F of bovine respiratory syncytial virus (BRSV) is an important target for humoral and cellular immune responses, and antibodies against the F protein have been associated with protection. However, the F protein can induce antibodies with different biological activity, possibly related to distinct antigenic regions on the protein. Therefore, epitopes were mapped on the F protein using monoclonal antibodies. Two epitopes (A and B) were identified that induced neutralizing antibodies, and one epitope (C) that did not elicit neutralizing antibodies. Subsequently, antibody responses were analysed against these epitopes in cattle sera after natural infection, experimental infection or vaccination. After natural infection or reinfection, the antibody titres against epitope A were significantly higher than those against epitope B or C. After experimental infection and after vaccination with an inactivated vaccine, antibody titres against epitope B and C were significantly higher than after natural infection. Conversely, virus neutralizing antibody titres were significantly lower in these animals with higher antibody titres against epitopes B and C than in naturally infected cattle. Because after natural infection the epitope-specific-antibody titres against epitope A, B or C differed markedly between the cattle, the magnitude of the antibody titres against epitope A, B or C in relation to the major histocompatibility complex (MHC) genes of cattle (BoLA) was studied. The magnitude of the antibody responses against epitope A of the F protein, but not against the G protein, appeared to be associated with the bovine lymphocyte antigen (BoLA) haplotype.