Showing papers in "Veterinary Research in 2000"

Aujeszky's disease (pseudorabies) virus: the virus and molecular pathogenesis--state of the art, June 1999.

Abstract: Considerable progress has been made during the last years in understanding the molecular basis of protein function in pseudorabies virus (PrV), the causative agent of Aujeszky's disease (AD). Major topics have been the identification and functional characterisation of viral envelope glycoproteins and cellular virus receptors, elucidation of viral proteins involved in neurovirulence and neuropathogenesis, detection and characterisation of attenuating mutations present in and leading to successful attenuated live vaccines, and the near completion of the genomic sequence of PrV DNA. This review, which follows an article prepared for the 1993 AD symposium in Budapest, Hungary, will briefly summarise those recent developments and update the reader on the current state of the art in PrV research.

Hyperketonemia and the impairment of udder defense: a review.

Abstract: The objective of this study was to review the possible relationships between hyperketonemia and the function of phagocytes with respect to the bovine udder defense mechanism. We hypothesize that an increased incidence of clinical mastitis in high-producing cows is caused by the impairment of the udder defense mechanism during hyperketonemia. First, we review the acute phase of udder defense mechanisms after intramammary infection. The physiological changes of cows in negative energy balance are subsequently discussed. Finally, possible relationships between udder defense and physiological changes during negative energy balance, especially hyperketonemia, are reviewed. The three stages of an acute phase of udder defense are: (1) immediately eliminating invading pathogens by phagocytes, (2) releasing inflammatory substances, especially chemoattractants, and (3) migration of polymorphonuclear leukocytes into the infected udder. Leukocytes from hyperketonemia subjects show a lower capacity of the phagocytic defense mechanism. In addition, the phagocytic and bactericidal capacities of neutrophils are reduced when these cells are acting in the presence of high concentrations of ketone bodies. Lower amounts of cytokine production after bacterial infection are observed in ketotic subjects. The chemotactic capacity of blood leukocytes is impaired in leukocytes obtained from ketotic cows. Lower numbers of blood leukocytes are observed in ketotic cows. In conclusion, the impairment of the udder defense mechanism in negative energy balance cows seems related to hyperketonemia.

Guidelines and recommendations for antimicrobial minimum inhibitory concentration (MIC) testing against veterinary mycoplasma species

Abstract: The absence of standardised procedures for minimum inhibitory concentration (MIC) testing of antimicrobial agents against veterinary mycoplasma and ureaplasma species (Mollicutes) has made it difficult to compare results originating from different laboratories. This report, prepared on behalf of the International Research Programme on Comparative Mycoplasmology (IRPCM), offers guidelines and recommendations for veterinary MIC testing of these organisms in an effort to rectify this problem. The subjects discussed include suitable media for broth and agar MIC assays, storage and preparation of antimicrobial agents, standardisation of mycoplasma inocula for MIC tests, validation of equipment, incubation conditions, and determination of MIC end points. A standard medium for all veterinary mycoplasma MIC tests cannot currently be recommended, owing to the diversity of nutritional requirements of different mycoplasma species. Instead mycoplasma broths or agars giving optimal growth of specific mycoplasmas or ureaplasmas are recommended, as suboptimal growth may lead to falsely low MIC results. The importance of using standardised mycoplasma inocula, for assays using either solid or liquid media is stressed. The growth phase may be less important as lag phase and logarithmic phase cultures of Mycoplasma gallisepticum, M. synoviae, M. bovis and M. hyopneumoniae have given very similar results in liquid MIC assays. The liquid method of Tanner and Wu and the agar method described by Hannan et al. are compared and described in detail. Methods for calculating MIC50s and MIC90s are described and the interpretation of results discussed. Methods for assessing mycoplasmacidal (MMC) activity of antimicrobial agents are also described. Adoption of these guidelines should lead to more consistent MIC results being obtained between laboratories.

PRRSV, the virus.

Abstract: Porcine reproductive and respiratory syndrome virus (PRRSV) is a positive-strand RNA virus that belongs to the Arteriviridae family. PRRSV grows in primary alveolar macrophages and in monkey kidney cell lines. The genomic RNA is approximately 15 kb. The genome encodes the RNA replicase (ORF1a and ORF1b), the glycoproteins GP2 to GP5, the integral membrane protein M, and the nucleocapsid protein N (ORFs 2 to 7). A comparison of nucleotide sequences of different strains indicates that European and North American strains represent two distinct antigenic types. Various PRRSV-specific monoclonal antibodies and recombinant structural proteins have been produced. Well-defined PRRSV mutants can be generated with the recently developed infectious cDNA clone of PRRSV.

Proinflammatory cytokines and viral respiratory disease in pigs.

Abstract: Swine influenza virus (SIV), porcine respiratory coronavirus (PRCV) and porcine reproductive and respiratory syndrome virus (PRRSV) are enzootic viruses causing pulmonary infections in pigs. The first part of this review concentrates on known clinical and pathogenetic features of these infections. SIV is a primary respiratory pathogen; PRCV and PRRSV, on the contrary, tend to cause subclinical infections if uncomplicated but they appear to be important contributors to multifactorial respiratory diseases. The exact mechanisms whereby these viruses cause symptoms and pathology, however, remain unresolved. Classical studies of pathogenesis have revealed different lung cell tropisms and replication kinetics for each of these viruses and they suggest the involvement of different lung inflammatory responses or mediators. The proinflammatory cytokines interferon-alpha (IFN-alpha), tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) have been shown to play key roles in several respiratory disease conditions. The biological effects of these cytokines and their involvement in human viral respiratory disease are discussed in the second part of this review. The third part summarises studies that were recently undertaken in the authors' laboratory to investigate the relationship between respiratory disease in pigs and bioactive lung lavage levels of IFN-alpha, TNF-alpha and IL-1 during single and combined infections with the above viruses. In single SIV infections, typical signs of swine "flu" were tightly correlated with an excessive and coordinate production of the 3 cytokines examined. PRCV or PRRSV infections, in contrast, were subclinical and did not induce production of all 3 cytokines. Combined infections with these 2 subclinical respiratory viruses failed to potentiate disease or cytokine production. After combined inoculation with PRCV followed by bacterial lipopolysaccharide, both clinical respiratory disease and TNF-alpha/IL-1 production were markedly more severe than those associated with the respective single inoculations. Taken together, these data are the first to demonstrate that proinflammatory cytokines can be important mediators of viral respiratory diseases in pigs.

Herd factors associated with the seroprevalences of four major respiratory pathogens in slaughter pigs from farrow-to-finish pig herds.

Abstract: The objective of this study was to investigate sero-epidemiological aspects of Mycoplasma hyopneumoniae (Mh), influenza H1N1 and H3N2 viruses and Aujeszky disease virus (ADV) in fattening pigs from 150 randomly selected farrow-to-finish pig herds. Different herd factors were examined as potential risk indicators for the percentage of pigs with antibodies against the 4 pathogens. The median within-herd seroprevalences of the pathogens were: Mh 76%, H1N1 100%, H3N2 40% and ADV 53%. There was a positive association between the seroprevalences of both influenza viruses, and a negative association between the seroprevalences of ADV and H1N1. The percentage of pigs seropositive for Mh increased with the purchase of gilts and with the season (slaughter date in March-April). The within-herd seroprevalences of both influenza viruses were higher in the case of a higher density of pig herds in the municipality. A higher number of fattening pigs per pen additionally increased the risk of being seropositive for H3N2. The percentage of pigs with anti-gE-antibodies against the wild type ADV increased with higher airspace stocking density in the finishing unit, increasing herd size, increasing number of pig herds in the municipality and slaughter date in March-April. Increased seroprevalences for these 4 respiratory pathogens were mostly associated with pig density in the herd and its vicinity, the winter period, and with the purchase of gilts. Purchase of gilts, number of fattening pigs per pen and airspace stocking density are risk factors that can be managed directly by farmers striving to attain a high respiratory health status of pigs.

Porcine antimicrobial peptides: new prospects for ancient molecules of host defense.

Abstract: Antimicrobial peptides (AMPs) are small, endogenous, polycationic molecules that constitute a ubiquitous and significant component of innate immunity. These natural antibiotics have broad microbicidal activity against various bacteria, fungi, and enveloped viruses. Because most AMPs kill bacteria by physical disruption of cell membranes, which may prevent microorganisms from developing resistance against these agents, they are being explored as possible alternatives to conventional antibiotics. Pigs, like many other mammals, produce an impressive array of AMPs, which are synthesized predominantly by host leukocytic phagocytes or mucosal epithelial cells. Currently, more than a dozen distinct porcine AMPs have been identified and a majority belongs to the cathelicidin family. This review briefly summarizes recent advances in porcine AMP research with an emphasis on the diverse biological functions of each peptide. Mechanisms of action of these AMPs and their role in the resistance to infections are considered. Finally, the current status of pharmaceutical and agricultural uses of AMPs as well as future prospects for their application in the food animal industry is discussed.

A review of evidence for immunosuppression due to Porcine Reproductive and Respiratory Syndrome Virus

Abstract: Accounts of field disease and experimental studies involving porcine reproductive and respiratory syndrome (PRRS) are reviewed for evidence of immunomodulation or immunosuppression by the causative virus. The conclusion is that immunomodulation through infection of alveolar macrophages is likely to occur, but that it is transient and at a local level, in the lung. There is some evidence for more subtle effects via more disseminated replication or induction of apoptosis with some isolates, but more definitive studies are needed. There is some emerging evidence of interaction between PRRSV and different cells of the immune system, but its significance for the course of disease or pig health are unclear. Likewise, the current experimental evidence for any interaction of PRRSV with other pathogens is ambiguous and therefore no firm conclusions can yet be drawn. Strains of PRRSV do vary in pathogenicity, which may be related to their degree of ability to cause overt respiratory disease in the absence of other agents. Experimentally, varying degrees of interstitial pneumonia are a common histological finding. There is, as yet, no firm evidence of general immunosuppression--in fact, some contrary evidence exists in the form of observations of a transient enhancement of humoral response, possibly through polyclonal B cell activation. The basis of pathogenicity of PRRSV and of any interaction with other agents is still unknown and is likely to remain unclear. Virus interaction with the pig's immune system must be addressed before any assessment of virulence of any known or emergent strains of PRRSV can be made.

Production of muraminidase-released protein (MRP), extracellular factor (EF) and suilysin by field isolates of Streptococcus suis capsular types 2, 1/2, 9, 7 and 3 isolated from swine in France.

Abstract: A total of 323 isolates of Streptococcus suis recovered from diseased or healthy pigs in France were serotyped. The presence of virulence-related proteins, Muraminidase-Released Protein (MRP), Extracellular Factor (EF) and Suilysin was also studied in 122 isolates of capsular types 2, 1/2, 9, 7 and 3 to evaluate their implication in virulence of S. suis. Capsular types 2, 1/2, 9, 7 and 3 were the most frequently detected (93%), with 69% for the capsular type 2 alone. Capsular types 2, 1/2, 9, 7, 3, 1, 4, 8, 18, 10 and 12 were isolated from diseased pigs, whereas types 2, 7, 9, 1/2, and 3 originated from the nasal cavities or tonsils of healthy animals. Most of the S. suis type 2 isolates recovered from diseased pigs carried MRP+ EF- Suilysin- (46%) or MRP+ EF+ Suilysin+ (28%) phenotypes. The MRP+ EF- Suilysin- phenotype was also detected in 67% of S. suis type 2 strains isolated from healthy pigs. The production of the virulence-related proteins was less frequently found in S. suis types 1/2, 9, 7 and 3 recovered either from diseased or healthy pigs. In this study, all the capsular type 1/2 strains were MRP+ EF- Suilysin- and all the S. suis type 7 harboured an MRP- EF- Suilysin- phenotype. The MRP- EF- Suilysin- phenotype was found in S. suis types 2, 3, 7 and 9 isolated from septicaemia, meningitis, pneumonia, and pleurisy. These results suggest that the presence of these proteins should not be used as a single condition for classifying the virulence of a field isolate in France.

Clinical response and immunomodulation following experimental challenge of calves with type 2 noncytopathogenic bovine viral diarrhea virus.

Abstract: Huit veaux âges de 16 a 18 semaines, seronegatifs pour le virus de la diarrhee virale bovine (VDVB), le virus de la leucose bovine et le virus de l'immunodeficience bovine, ont ete infectes (jour 0) par voie intranasale avec l'isolat canadien non-cytopathogene 24515 de VDVB de type 2, dans le but d'etudier l'effet de ce virus sur des parametres cliniques, hematologiques et immunologiques. Tous les veaux exposes au virus ont montre une elevation de la temperature corporelle et une diminution significative (P < 0,05, 0,01 ou 0,001) des leucocytes (neutrophiles, lymphocytes et monocytes) du sang a partir du jour 3 ou 5 post-infection (PI) et jusqu'a la fin de l'experience au jour 12 PI. Le VDVB a ete isole a partir des cellules blanches du sang a partir du jour 5 PI, et aussi a partir de nombreux tissus (la rate, le thymus, les ganglions mesenteriques et sous-maxillaires, l'intestin grele, les poumons et la glande thyroide) preleves lors de l'euthanasie des animaux au jour 12 PI. Des diminutions significatives (P < 0,05) dans les pourcentages des cellules mononucleaires (CMN) du sang exprimant a leur surface les molecules B7 ou MHC II ont ete observees dans le groupe de veaux exposes au virus aux jours 7, 10 et/ou 12 PI, comparativement aux pourcentages obtenus chez les veaux temoins (n = 5). Cependant, aucune difference dans les pourcentages des CMN exprimant les molecules B4 ou MHC I ne fut observee entre les deux groupes d'animaux tout au long de l'experience. Finalement, une augmentation significative (P < 0,05 ou 0,01) de la capacite phagocytaire des CMN, analysee par cytometrie de flux, fut observee chez les animaux exposes au virus aux jours 3, 5, 7, 10 et 12 PI. Les resultats de cette etude montrent le caractere virulent de cet isolat viral chez des veaux âges de 4 a 4 mois et demi et suggerent que l'infection des animaux par le VDVB de type 2 est associee a des perturbations de certaines fonctions immunitaires.

The distribution of vitamin A and retinol-binding protein in the blood plasma, urine, liver and kidneys of carnivores.

Abstract: The contents of retinol and retinyl esters as well as retinol-binding protein (RBP) in the plasma, urine, liver and kidneys of dogs, raccoon dogs and silver foxes were investigated. In the plasma and urine of all three species, vitamin A was present as retinol and retinyl esters. Vitamin A levels (1376+/-669 microg x g(-1)) were significantly higher in the livers of dogs than in the kidneys (200+/-217 microg x g(-1), P < 0.001 ). However, vitamin A levels in the kidneys of raccoon dogs (291+/-146 microg x g(-1)) and silver foxes (474+/-200 microg x g(-1)) were significantly higher than in the liver (67+/-58 microg x g(-1) and 4.3+/-2.4 microg x g(-1), respectively, both P < 0.001). RBP was immunologically detected in the blood plasma of all species, but never in the urine. In the liver, immunoreactive RBP was found in hepatocytes. In the kidneys of all species, RBP was observed in the cells of the proximal convoluted tubules. The levels of vitamin A in the livers of raccoon dogs and silver foxes were extremely low, which would be interpreted as a sign of great deficiency in humans. This observation might indicate that the liver status cannot be used as an indicator of vitamin A deficiency in canines. The high levels of vitamin A in the kidneys in all three species may indicate a specific function of the kidney in the vitamin A metabolism of canines.

Development of a complete ELISA using Salmonella lipopolysaccharides of various serogroups allowing to detect all infected pigs

Abstract: Mise au point d'une methode ELISA complete basee sur des lipopolysaccharides de plusieurs serogroupes permettant de detecter tous les porcs infectes par des salmonelles. Bien que la volaille soit la principale source d'intoxication alimentaire par les salmonelles, le porc contribue aussi a la contamination humaine. Cette etude a ete menee pour mettre au point une technique serologique permettant d'evaluer le statut infectieux des porcelets vis-a-vis des salmonelles. Une technique ELISA dite complete a ete elaboree avec des lipopolysaccharides de Salmonella Typhimurium. Anatum, Hadar et Infantis, serovars representatifs des serogroupes isoles dans 30 elevages engraisseurs contamines. S. Enteritidis a ete ajoutee en raison de son importance dans les infections humaines et afin d'inclure l'antigene O: 9. Cette methode permet de depister potentiellement 100 % des pores infectes par des salmonelles. La correlation etait significative entre cette technique serologique et les tests bacteriologiques sur les ganglions mesenteriques (p = 0.01) et la sensibilite ainsi que la specificite etaient elevees (respectivement de 97 % et 94 %). Aussi cet ELISA a ete utilise pour preciser la periode de contamination des pores dans une etude transversale dans 4 elevages: des serologies positives ont ete recensees uniquement sur les pores de 20 semaines. La presence d'anticorps chez les porcelets a ete etudiee: la persistance des anticorps maternels a ete observee jusqu'a 7 semaines et une seroconversion a ete detectee a partir de 8 semaines indiquant une contamination probable par des salmonelles.

Metalloproteinases and tumor necrosis factor-alpha activities in synovial fluids of horses: correlation with articular cartilage alterations.

Abstract: Le depistage precoce des arthropathies reste un defi pour le veterinaire equin. Certains marqueurs biologiques presents dans le liquide synovial pourraient etre des mdicateurs precoces de l'osteoarthrose C'est pourquoi, le liquide synovial de 90 articulations de 14 chevaux devant etre euthanasies a ete recueilli. La dissection des articulations prelevees a ensuite permis de visualiser les surfaces articulaires, Pour chaque echantillon, l'activite des metalloproteinases (MMPs) a ete evaluee par zymographie et la cytotoxicite du tumor necrosis factor alpha (TNF-α) a ete mesuree sur culture cellulaire. La correlation des resultats de l'examen macroscopique et des dosages biochimiques montre une augmentation significative de l'intensite des MMP-9 monomere et dimere dans le liquide synovial des articulations presentant des lesions cartilagineuses graves. En revanche, l'activite du TNF-α n'apparait pas correlee a la gravite de l'atteinte articulaire. Les taux de MMP-9 monomere et dimere dans le liquide synovial de chevaux semblent donc etre de bons temoins de l'alteration du cartilage articulaire.

Aujeszky's disease virus: opportunities and challenges.

Abstract: Since its description in 1902, Aujeszky's disease (AD) has become one of the most thoroughly examined viral diseases of swine. The causative agent, Aujeszky's disease virus (ADV), is a neurotropic alphaherpesvirus that produces fatal encephalitis in newborn pigs and a milder syndrome in older animals. In several instances this virus has been used as a test case to examine novel vaccine concepts in swine, including the honor of being the first genetically modified vaccine used in the field. Furthermore, the examination of the immune response to infection or vaccination with this virus has revealed important information about the function of the porcine immune system, including evidence on the existence of a dichotomy between the humoral and cellular immune response in swine. This review presents a summary of research where ADV has been a valuable tool for the development of novel vaccines and has provided information to better understand the immune response of swine to infectious agents.

The effect of two levels of dietary protein on resistance and resilience of dairy goats experimentally infected with Trichostrongylus colubriformis : Comparison between high and low producers

Abstract: Numerous studies have examined the interactions between protein nutrition and the response to nematode parasitism in sheep, but very few in goats. Compared with other ruminants, goats are less resistant to nematode infection. In addition, in dairy goats, high producing animals have been shown to be less resistant and less resilient to infection compared to low producing ones. The objective of the present study was to examine the consequences of protein supplementation on both resistance and resilience of dairy goats to nematode trickle infection, taking into account the initial level of milk production of the animals. During a 14-week period, 40 milking goats received a high protein (HP) diet supplying 130% of the protein requirements, and 38 goats were fed a intermediate protein (IP) diet (120% of the protein requirements). In addition, half of each group was given a weekly trickle infection with Trichostrongylus colubriformis larvae, the other part of the flock remained non-infected. Faecal egg counts (FEC), eosinophil counts and pathophysiological data (urea, albumin and inorganic phosphate concentrations in the serum) were measured twice a month. Milk production data (milk yield, protein and fat contents) were also recorded every 15 days. The results showed that FECs were lower (p < 0.05) and eosinophil counts higher (p < 0.05) in the animals receiving the HP diet suggesting that resistance was enhanced by protein supplementation. Meanwhile, milk parameters (related to resilience) were not affected by the level of protein in the diet when considering the whole groups. In contrast, in the high producing goats, the milk production and milk composition parameters were improved with the HP diet. To conclude, we have seen that the expression insufficient. Because the milk production is dependent on the protein supply, we suggest that there is a competition in the use of the protein between the development of resistance and the milk production. (Resume d'auteur)

A RT-PCR assay for the rapid recognition of border disease virus.

Abstract: Identification rapide du border disease virus par RT-PCR. Une methode d'amplification en chaine par polymerase apres transcription inverse (RT-PCR) a ete developpee pour la detection specifique du border disease virus (BDV), utilisant les amorces PBD1 et PBD2 flanquant un fragment d'ADN de 225 pb, choisi dans la region 5' non codante du genome des pestivirus. Des tests sur 70 souches de pestivirus ont demontre la specificite de la methode. Une methode de RT-PCR nichee dans un seul tube ferme a egalement permis de detecter specifiquement le BDV, tout en ameliorant la sensibilite. Cette derniere methode utilise des amorces externes generales pour les pestivirus (324 et 326), les amorces internes PBD1 et PBD2 ainsi qu'une sonde fluorogenique TaqMan reconnaissant specifiquement le BDV. Les stocks de virus ont ete testes a la fois par RT-PCR specifique du BDV et RT-PCR specifique du virus de la diarrhee bovine type 2 (BVDV2), afin de determiner s'ils contenaient un melange des deux virus. Il a ainsi ete montre que les souches de pestivirus ovins 175375 et 59386 etaient initialement du BDV, mais ont ete contaminees par du BVDV2 lors de cultures. Ceci explique les differences constatees dans les resultats de precedents typages genetiques de 59386. La RT-PCR peut etre utilisee pour detecter du BDV dans des echantillons cliniques, mais elle est surtout utile pour le typage rapide des souches pestivirales en laboratoire.

A brief review of procedures and potential problems associated with the diagnosis of porcine reproductive and respiratory syndrome

Abstract: Experience has shown that, for a number of reasons, a diagnosis of porcine reproductive and respiratory syndrome (PRRS) is sometimes difficult. In this review we discuss: (1) field observations and laboratory tests that are useful in arriving at a definitive diagnosis; (2) the impact of so-called atypical PRRS on diagnostic procedures in North America; (3) the means by which diagnostic problems can often be circumvented by appropriate sample selection; and (4) methods used for presumptive identification of PRRS virus strains.

Ultrastructural pathogenesis of the PRRS virus

Abstract: Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) was first isolated in swine alveolar macrophages (SAMs) and has subsequently been reported to replicate in other cell lines. Entry of the virus inside the cell takes place by receptor-mediated endocytosis. Following the entry of the virus into the cell, several not completely understood changes take place. PRRSV has been reported to be an apoptotic-inductor virus both in vivo and in vitro. Interestingly, it has been suggested that PRRSV-induced apoptosis occurs in cells other than those in which PRRSV replicates by a bystander mechanism. In this paper the ultrastructural pathogenesis of PRRSV will be reviewed.

Decreased neutrophil bactericidal activity during phagocytosis of a slime-producing Staphylococcus aureus strain.

Abstract: La phagocytose et la destruction intracellulaire sont deux importants mecanismes de defense des leukocytes polymorphonucleaires (PMN) contre la mammite provoquee par Staphylococcus aureus chez les bovins. Nous avons compare la destruction intra- et extracellulaire par les PMN du sang pour un S. aureus non-producteur de « slime » (NSP) et son variant producteur de « slime » (SP), en utilisant une analyse bacteriologique in vitro. Sept vaches saines en moyenne lactation ont ete utilisees a cette fin. Les pourcentages de destruction totale pour le NSP et SP etaient de 34 ± 3 % et 21 ± 4 % (P < 0.05) et les pourcentages de phagocytose etaient de 40 ± 4 % et 31 ± 4 %, respectivement. Une correlation significativement positive (r = 0.79; P < 0.001) entre la phagocytose et la destruction totale etait observe. Ces resultats suggerent que la presence de « slime » pourrait etre responsable d'une ingestion phagocytaire et d'une destruction totale diminuees.

The "colorful" epidemiology of PRRS.

Abstract: The paper describes the specifics of the epidemiology of the Porcine Reproductive and Respiratory Syndrome (PRRS), that is its "behavior" as a communicable disease in porcine populations, and compares them to the general epidemiological characteristics of communicable diseases. This analysis shows that infection with the PRRS virus "behaves" epidemiologically both as an epidemic and as an endemic disease: on the one hand it can spread like an epidemic in naive populations, and on the other it seems to linger on infinitely in an affected population with its clinical expression varying from farm to farm like an endemic disease. The paper tries to draw "epidemiological" conclusions on the general methods for controlling and/or eradicating the disease, and to identify areas of further research.

Apoptosis of polymorphonuclear leukocytes of the juvenile bovine mammary gland during induced influx

Abstract: Afin de determiner le role de l'apoptose dans la resolution des mammites, la dynamique de l'apoptose des leucocytes polymorphonucleaires (PMN) durant l'influx induit dans le systeme des cavites de la glande mammaire juvenile des bovins a ete etudiee. L'application du derive synthetique du muramyl dipeptide dans le sinus du trayon de la glande mammaire a ete suivi de l'influx massif de PMN avec un pic a 24 h et une resolution 96 heures apres la stimulation. Au cours des 24, 48, 72 et 96 h apres la stimulation, les suspensions cellulaires ont ete examinees en microscopie optique pour detecter l'apoptose des PMN. L'identification des PMN apoptotiques a ete realisee a partir des caracteristiques morphologiques. Les PMN apoptotiques ont ete observes des 24 h apres la stimulation et ont atteint un pic a 48 h. La proportion la plus faible de PMN apoptotiques a ete observee au bout de 96 h apres la stimulation, ce qui correspondait aux valeurs obtenues avant stimulation. La presence des macrophages contenant des PMN phagocytes apoptotiques a ete revelee par coloration histochimique a la myeloperoxydase (MPO) et par microscopie electronique. Durant la phase de resolution les macrophages MPO positifs ont atteint un pic 48 h apres la stimulation. L'apoptose des PMN et la phagocytose par les macrophages semble representer un mecanisme de deblaiement important dans la resolution de l'influx induit des PMN dans le systeme des cavites de la glande mammaire juvenile.

Inoculation of lactating ewes by the intramammary route with Mycoplasma agalactiae: comparative pathogenicity of six field strains.

Abstract: L'agalactie contagieuse affecte les chevres et les moutons. Chez la plupart des moutons infectes, l'agent causal, Mycoplasma agalactiae, induit des mammites et/ou de l'agalactie, des keratoconjonctivites et des arthrites. Cependant, quelques souches de M. agalactiae ont ete isolees de lait de tank provenant de troupeaux ne presentant aucun signe clinique d'agalactie. L'etude presente a ete entreprise afin de comparer 4 souches dites « asymptomatiques » a 2 souches virulentes et de mesurer la pathogenicite de ces souches « asymptomatiques ». Six groupes de 4 ou 5 brebis en lactation ont ete inocules par voie intramammaire avec 10 8 bacteries viables de chaque souche. Les signes cliniques ont ete regulierement evalues ainsi que l'excretion des mycoplasmes dans le lait et la reponse serologique. Les brebis ont ete autopsiees 7 semaines apres l'inoculation et le niveau d'infection des noeuds lymphatiques retromammaires a ete mesure. Parmi les 4 souches apparemment asymptomatiques, 2 etaient aussi virulentes que les souches isolees de brebis malades, tandis que les 2 autres ont induit des signes cliniques moins severes. Les autres parametres, en particulier le niveau d'excretion dans le lait et le niveau d'infection des noeuds lymphatiques retromammaires apres autopsie, etaient comparables. La reponse anticorps moyenne etait elle aussi comparable, malgre une grande variabilite individuelle. Cette observation a pour consequence que les troupeaux sans signe clinique desquels des mycoplasmes sont isoles a partir du lait de tank doivent rester sous controle strict car ces mycoplasmes peuvent induire plus tard de l'agalactie contagieuse a la faveur de conditions d'elevage changeantes.

Oral rabies vaccination of foxes with one or two delayed distributions of SAG2 baits during the spring.

Abstract: Lors de la campagne de vaccination orale des renards contre la rage en France au printemps 1997, differents protocoles de distribution des appâts vaccinaux (SAG2) ont ete compares : dans une premiere zone test, une distribution fin avril suivie d'une seconde deux semaines plus tard a la mi-mai et dans une deuxieme zone test, une distribution fin avril suivie d'une seconde, quatre semaines plus tard, fin mai. Dans les zones temoins, une distribution classique et unique a ete realisee a la mi-mai ou fin mai. Aucune difference significative n'a ete notee entre les taux de prise d'appâts, ni entre les taux de seroconversion chez les renards jeunes ou adultes preleves dans les zones tests et temoins. Cependant, les taux de seroconversion obtenus chez les renardeaux dans toutes les zones vaccinees fin mai ont ete significativement (P < 0.01) plus eleves que dans les zones vaccinees a la mi-mai (43 et 56 % contre 24 et 20 % respectivement). Chez les renardeaux egalement, l'efficacite vaccinale des appâts a ete significativement plus elevee (P < 0.05) dans les zones vaccinees fin mai (46 et 57 %) que dans les zones vaccinees a la mi-mai (24 et 25 %). L'amelioration de la reponse immunitaire chez les renardeaux lorsque la date de la campagne est retardee doit etre correlee a leur developpement. Au debut du printemps, les renardeaux sont trop jeunes pour avoir acces aux appâts ou pour se vacciner quand ils les consomment. Dans ce cas une seconde distribution d'appâts ne peut provoquer chez eux un effet rappel. Une campagne de printemps menee tardivement (en mai ou juin) plutot qu'en avril permet aux renardeaux d'acceder en nombre plus important et de facon plus efficace aux appâts vaccinaux.

Les protéases chez les helminthes

Abstract: Proteases in helmintic parasites. Proteases catalyse the cleavage of internal peptide bonds within peptides and proteins. They are classified into four major classes and are involved in a broad range of eukaryotic processes. Proteases have also been found to play a number of critical roles in the virulence of pathogenic agents, particularly of nematode parasites. Parasitic proteases are involved in different aspects of host-parasite interactions. They facilitate the invasion of host tissues and allow nutrition as well as the survival of the parasite in its host. Proteases also participate in the parasite's evasion from the host's immune response. The functional diversity and complexity of these enzymes are described in this review, with a particular focus on the principally identified proteases of four helminths: Schistosoma sp., Fasciola sp., Taenia sp. and Haemonchus sp. Some of these proteases, especially the cysteine proteases secreted by the parasitic trematode Fasciola hepatica, have been successfully tested in experimental immunodiagnosis. Proteases identified in different parasites are currently under study for a use as recombinant vaccines. In this respect, proteases are proposed as major potential targets for immunotherapy and chemotherapy against parasitic diseases.

Immunisation of lambs with excretory secretory products of Oestrus ovis third instar larvae and subsequent experimental challenge.

Abstract: Les produits d'excretion-secretion des larves de Dipteres myiasigenes interviennent dans la nutrition et le developpement de ces larves et sont tres souvent immunogenes. Dans le cas de l'œstrose ovine, leurs proprietes antigeniques et immunogeniques n'ont pas encore ete etudiees. De plus, le role exact de la reponse immune du mouton vis-a-vis des produits d'excretion-secretion n'est pas connu et c'est ce qui a motive ce travail. Vingt quatre agnelles âgees de six a huit mois ont ete reparties de facon aleatoire en deux groupes de douze individus. Le premier groupe a recu deux injections a quatre semaines d'intervalle d'un melange de produits d'excretion-secretion de larves de troisieme stade d'Oestrus ovis et d'adjuvant compler puis incomplet de Freund. Le deuxieme groupe a servi de temoin et a recu seulement deux injections de PBS avec adjuvant complet puis incomplet de Freund. Quinze et trente jours apres la deuxieme immunisation, les animaux des deux groupes ont ete infestes experimentalement par des larves de premier stade d'Oestrus ovis. Douze jours apres la seconde infestation experimentale, tous les agneaux ont ete abattus. Le nombre total de larves d'Oestrus ovis, leur stade de developpement, leur taille ainsi que leur poids ont ete compares entre les deux groupes. Les taux d'installation des larves etaient tres comparables dans les deux groupes (39 % chez les temoins et 35 % chez les immunises) mais le pourcentage de stades larvaires en developpement etait significativement plus important chez les temoins (13 %) que chez les immunises (6 %). L'immunisation avec des produits d'excretion-secretion de larves de troisieme stade, bien que n'ayant pas protege les agneaux de l'installation des larves, a conduit a une inhibition partielle du developpement larvaire.

Onchocerca ochengi transmission dynamics and the correlation of O. ochengi microfilaria density in cattle with the transmission potential.

Abstract: The intensity of natural transmission of Onchocerca ochengi and Onchocerco volvulus by anthropo-boophilic Simulium damnosum s.l. was studied longitudinally in two cattle watering sites of a cattle ranch within a predominantly cattle populated area of the Guinea savanna of Cameroon and related to cattle O. ochengi skin microfilaria abundance. During the 12 months study period, a total of 4696 flies was individually dissected to examine the monthly transmission potential (MTP) of O. ochengi and O. volvulus. The estimated Simulium damnosum s.l. annual biting rates (ABR) on human baits were 47529 flies at the bank of the Vina "du sud" river. The ABR at the lake, which was situated at about 2 km upland from the perennial river, was 8579. The monthly parous rate was highly correlated with monthly biting rate. The annual transmission potentials (ATP) of O. ochengi were calculated to be 7732 and 1669 at the riverbank and the lake, respectively. Transmission occurred mainly in the dry season, peaking in the months of January to mid-March when dermal microfilaria density in the animals was also the highest. The O. ochengi microfilaria uptake by the fly vectors was host microfilaria density-dependent. The MTP of O. ochengi was positively correlated with dermal microfilaria density. The mean number of microfilariae per fly taken up during a blood meal was high during the dry season as was the mean number of infective larvae per fly but declined significantly with the onset of the early rains. A similar seasonality of transmission was also observed for O. volvulus that was concurrently transmitted by the same vector flies, but its ATP was comparatively much lower: 1332 infective larvae per man per year at the riverbank and 107 around the lake. The population dynamics of cattle microfilariae therefore plays an important role in the regulation of O. ochengi transmission.

Enhanced protective response and immuno-adjuvant effects of porcine GM-CSF on DNA vaccination of pigs against Aujeszky's disease virus

Abstract: This study was conducted to investigate whether the co-delivery of DNA encoding porcine cytokines would enhance a protective immune response in pigs to a Pseudorabies virus (PRV; or Aujeszky's disease virus) DNA vaccine. Aujeszky's disease in pigs results in respiratory and nervous symptoms with important economic losses. To evaluate cytokine effects, eukaryotic expression vectors were constructed for porcine GM-CSF, IL-2 and IFN-gamma. cDNA for each of these cytokines was inserted under the control of a CMV promoter in the pcDNA3 plasmid and cytokine expression was confirmed after DNA transfection in various mammalian cell cultures by bioassays (GM-CSF and IL2) and ELISA (IFN-gamma). Pigs were vaccinated by single intramuscular injection with plasmid DNA encoding PRV gB and gD along with various combinations of cytokine plasmid constructs. Pig serum was tested for the production of antibody by isotype specific anti-PRV ELISA. Pigs were then challenged with the highly virulent PRV strain NIA3 on day 21 after vaccination. The survival and growth rate of pigs were monitored for seven days after the viral challenge. The co-administration of GM-CSF plasmid increased the immune response induced by gB and gD PRV DNA vaccine. This immune response was characterized by an earlier appearance of anti-PRV IgG2, a significantly enhanced anti-PRV IgG1 and IgG2 antibody response, a significantly decreased and shortened viral excretion in nasal swabs and an improved protection to the viral challenge. In contrast, the co-administration of porcine IL-2 or IFN-gamma had no adjuvant effects. Our results thus demonstrate for the first time that the application of porcine GM-CSF gene in a DNA vaccine formulation can exert immuno-adjuvant and protective effects with single vaccination in the natural host pig against Aujeszky's disease.