Showing papers in "Veterinary Microbiology in 1997"

Epidemiology of porcine reproductive and respiratory syndrome (PRRS): an overview.

Abstract: PRRS disease was first recognised in the USA in 1987 and in Europe in 1990 and since then the disease has spread widely throughout many pig-producing countries. After a severe epidemic phase, the infection has become endemic. The prevalence of infection is generally high in infected countries. However, in areas with a low density of pigs, infection may spread slowly and if infected animal movements are not significant, farm-to-farm spread can be controlled and prevalence of infection maintained at a low level. The PRRS virus (PRRSV) was completely unknown before 1986, and the question of its origin remains unanswered. The exact epidemiologic relationship between American and European strains of PRRSV is difficult to establish because different isolates appear to belong to two distinct sub-populations which are only distantly antigenically related. In the environment, virus survival is optimal when temperature is cold and when ultra-violet light exposure is low (little sunshine). These conditions are easily attained in winter and that may explain why virus spread increases during this period. Pigs of any age (including wild boars) are the only animals known to be naturally infected with PRRSV. Relatively close contact between pigs is the primary factor in virus transmission. Aerial transmission is a second mechanism of spread, particularly in winter and particularly over distances of less than 3 km. A third route of transmission is via semen. The role of fomites is not clearly documented, however since the virus is excreted in faeces and urine, slurry should be considered as a potential source of contamination. Within herds, the virus spreads rapidly with up to 85 to 95% of pigs in a herd becoming sero-positive within two to three months. Thereafter, virus activity persists for extended periods (several month to years). Nevertheless, some authors have reported spontaneous elimination of PRRSV from infected farms. For the future, there remain questions concerning the possible evolution of the disease (in terms of its sanitary and economic impacts), and the possible influence of vaccines on the epidemiological features of PRRS.

Virus quantification and identification of cellular targets in the lungs and lymphoid tissues of pigs at different time intervals after inoculation with porcine reproductive and respiratory syndrome virus (PRRSV).

Abstract: Sixteen 6 week old conventional pigs were inoculated by aerosol with a European strain of porcine reproductive and respiratory syndrome virus (PRRSV). Virus replication was followed by virus titration and immunofluorescence in the lungs and in associated and distant lymphoid tissues at 3, 14, 21, 35, 42 and 82 days post-inoculation (DPI). PRRSV replication was detected in alveolar macrophages, lungs, tonsils, spleen, retropharyngeal lymph nodes, bronchial lymph nodes and thoracic aortic lymph nodes at 3 DPI. The same tissues, except retropharyngeal and thoracic aortic lymph nodes, were PRRSV positive at 14 DPI. Lungs and alveolar macrophages were PRRSV positive until 35 DPI. PRRSV was not detected in heart, peripheral blood mononuclear cells and bone marrow cells. Viremia was detected from 3 to 28 DPI. Not more than 2% of alveolar macrophages were PRRSV positive even during the acute stage of infection. 80 to 94% of the PRRSV infected cells in the lungs and in lung lavaged cells were identified as macrophages using a porcine macrophage specific monoclonal antibodies. In the lymph nodes and spleen, 100% of the infected cells were macrophages. Anti-PRRSV antibodies were detected by a blocking ELISA as early as 7 DPI. the antibody titre gradually increased to reach a geometric mean titre (GMT) of 160 at 35 DPI. It remained at that level until the end of the study. These findings clearly demonstrate that PRRSV has a tropism for macrophages. PRRSV mainly replicates in macrophages of the lymphoid tissues and lungs in the acute phase of infection and persists in the lung macrophages.

Porcine reproductive and respiratory syndrome virus: a persistent infection.

Abstract: Persistent infection with porcine reproductive and respiratory syndrome virus (PRRSV) was shown in experimentally infected pigs by isolation of virus from oropharyngeal samples for up to 157 days after challenge. Four 4 week old, conventional, PRRSV antibody-negative pigs were intranasally inoculated with PRRSV (ATCC VR-2402). Serum samples were collected every 2 to 3 days until day 42 post inoculation (PI), then approximately every 14 days until day 213 PI. Fecal samples were collected at the time of serum collection through day 35 PI. Oropharyngeal samples were collected at the time of serum collection from 56 to 213 days PI by scraping the oropharyngeal area with a sterile spoon, especially targeting the palatine tonsil. Turbinate, tonsil, lung, parotid salivary gland, spleen, lymph nodes and serum were collected postmortem on day 220 PI. Virus isolation (VI) on porcine alveolar macrophage cultures was attempted on all serum, fecal and oropharyngeal samples, as well as tissues collected postmortem. Postmortem tonsil tissues and selected fecal samples were also assayed for the presence of PRRSV RNA by the polymerase chain reaction (PCR). Serum antibody titers were determined by IFA, ELISA and SVN. Virus was isolated from all serum samples collected on days 2 to 11 PI and intermittently for up to 23 days in two pigs. No PRRSV was isolated from fecal samples, but 3 of 24 samples were PCR positive, suggesting the presence of inactivated virus. Oropharyngeal samples from each pig were VI positive 1 or more times between 56 and 157 days PI. Oropharyngeal samples from 3 of 4 pigs were VI positive on days 56, 70 and 84 PI. Virus was isolated from one pig on day 157 PI, 134 days after the last isolation of virus from serum from this animal. Virus was isolated from oropharyngeal samples for several weeks after the maximum serum antibody response, as measured by IFA, ELISA and SVN tests. All tissues collected postmortem were VI negative and postmortem tonsil samples were also negative by PCR. An important element in the transmission of PRRSV is the duration of virus shedding. The results of this study provided direct evidence of persistent PRRSV infection and explain field observations of long-term herd infection and transmission via purchase of clinically normal, but PRRSV infected, animals. Effective prevention and control strategies will need to be developed in the context of these results.

Epidemiology of Rhodococcus equi infections: a review.

Abstract: An overview of epidemiology of R. equi infection in foals is presented, emphasizing the importance of the virulence-associated antigens and plasmids as epidemiological markers. The monoclonal antibody-based colony blot test has been developed to identify rapidly and accurately virulent R. equi. Epidemiological studies conducted during the recent 5 years have revealed that: (1) avirulent R. equi are widespread in the feces of horses and their environment on every farm; (2) the feces of horses and the environment of the horse farms having endemic R. equi infections demonstrated heavy contamination with virulent R. equi, but the farms without the problem did not, thus suggesting that foals bred on a farm with endemic disease are exposed more frequently to virulent R. equi in their environment than those of a farm without the problem; (3) only virulent R. equi are isolated from lesions of naturally infected foals, showing that natural infections in foals are principally by virulent R. equi, but not avirulent organisms; (4) infected foals which constantly shed large quantities of virulent R. equi in their feces are the major source of virulent R. equi, which this may be the mechanism of progressive development of infection on farms with a history of the disease. At present, farms with a potential for endemic infection can be distinguished on the basis of the contamination with virulent R. equi, so regular examination of foals and their environment by virulence markers might be the most practical approach to control R. equi infection on endemic farms.

Clinical manifestations, diagnosis, treatment, and prevention of Rhodococcus equi infections in foals.

Abstract: Since the 1986 Rhodococcus equi workshop, there have been major breakthroughs in understanding the epidemiology of, the virulence of, and the immune response to, this intriguing pathogen. However, with the exception of the use of hyperimmune plasma for the prevention of the disease (Martens et al., 1989; Madigan et al., 1991) the clinical aspects of R. equi infections have essentially remained unchanged. This article reviews the various clinical manifestations and summarizes recent advances in diagnosis, treatment and prevention of R. equi infections in foals.

General overview of PRRSV: a perspective from the United States.

Abstract: Four years after the report of its discovery, porcine reproductive and respiratory syndrome virus (PRRSV) continues to challenge swine producers, veterinary practitioners, and animal health researchers in the United States. The prevalence of infection is high--60% to 80% of herds is a reasonable estimate--but the clinical effects of infection vary widely among farms. In many herds, infection is unapparent and productivity seemingly unaffected. Some infected herds report occasional respiratory disease outbreaks in young pigs, or periodic outbreaks of reproductive disease, and a few herds experience severe, chronic disease problems, particularly in young pigs. In these herds, secondary infections with viral or bacterial pathogens, particularly Salmonella choleraesuis, Streptococcus suis, or Haemophilus parasuis typically occur concurrently with PRRSV infections. Understanding why some herds undergo devastating episodes of clinical disease and others show no apparent effects is central to solving the problem of clinical PRRS for swine producers. Understanding the ecology and epidemiology of PRRSV is the key to preventing and controlling PRRSV in the future. The objective of this article is to review recent developments in these areas.

Actinobacillus pleuropneumoniae infections in pigs: the role of virulence factors in pathogenesis and protection

Abstract: This paper discusses the possible role of virulence factors of Actinobacillus pleuropneumoniae in pathogenesis and protection. Special attention is paid to the Apx-exotoxins and to adhesins.

Mycoplasma hyopneumoniae infection in pigs; duration of the disease and evaluation of four diagnostic assays

Abstract: 200 SPF pigs were infected by aerosol with Mycoplasma hyopneumoniae and the development of clinical signs, serological and pathological reactions were studied. Mean time to onset of coughing was 13 days. A mean delay of 9 days was observed from onset of coughing until seroconversion against M. hyopneumoniae as measured by ELISA. At an individual level, the sensitivity for this ELISA was estimated to 98-100% and the specificity to 93-100%. Pasteurella multocida was isolated from the majority of the lungs 4 weeks post inoculation with M. hyopneumoniae and the lung lesions in pigs were significantly larger when P. multocida was present as compared to pigs with M. hyopneumoniae alone. An evaluation of cultivation, immunofluorescence, ELISA and polymerase chain reaction for demonstration of M. hyopneumoniae in lungs showed that all four methods have a high sensitivity in the acute stages of pneumonia. In the later stages the sensitivity of cultivation was superior to the other methods. No differences in specificity were observed between the methods. The antigen-ELISA OD values and the immunofluorescence scores revealed a strong positive correlation. Nasal swabs were additionally used for demonstration of M. hyopneumoniae and the polymerase chain reaction was found superior to the other methods.

The characterisation of Brucella strains isolated from marine mammals

Abstract: Small Gram negative coccobacilli isolated from seals, porpoises, dolphins and from an otter road casualty were identified as Brucellae by their colonial and cell morphology, staining characteristics, biochemical activity, agglutination by monospecific antisera and susceptibility to lysis by Brucella specific bacteriophage. Their characterisation, including metabolic profiles, is described. These strains could not be assigned to recognised nomen species of the genus Brucella and it is suggested that they comprise a new nomen species to be called B. maris (sp. nov., type strain 294). It is further suggested the nomen species be subdivided into three biovars corresponding to their CO2 requirement, metabolic activity on galactose, dominant antigen and animal host.

Distribution and characterization of faecal verotoxin-producing Escherichia coli (VTEC) isolated from healthy cattle

Abstract: Faecal swabs obtained from a random sample of 268 cows and 90 calves on 19 Lugo farms were examined for verotoxin-producing Escherichia coli (VTEC). We found VTEC on 95% of the farms. The prevalence rates of VTEC infection in asymptomatic cows and calves were estimated to be 35 and 37%, respectively. The proportion of animals infected on each farm ranged from 0 to 100%. VTEC strains isolated from healthy cattle belonged to 27 O serogroups; however, 57% (85 of 149) were of one of 8 serogroups (O2, O8, O22, O77, O82, O105, O113 and O171). Nearly 60% of the bovine VTEC strains belonged to serogroups that cause haemorrhagic colitis and haemolytic uraemic syndrome in humans. The VTEC were all non-O157:H7; 91% were eae-negative and 86% produced VT2 or VT1 and VT2. These characteristics are different from those of VTEC isolated from calves with diarrhoea.

Porcine reproductive and respiratory syndrome virus: routes of excretion.

Abstract: This study was conducted to delineate potential sites of exit and duration of shedding of porcine reproductive and respiratory syndrome virus (PRRSV). Two experiments of 6 pigs each were conducted. Pigs were farrowed in isolation, weaned at 7 days of age, and housed in individual HEPA filtered isolation chambers. In each experiment, 3 pigs served as controls and 3 were inoculated intranasally with PRRSV (ATCC VR-2402) at 3 weeks of age. In a first experiment, on days 7, 14, 21, 28, 35, and 42 post-inoculation (p.i.), pigs were anesthetized and intubated. The following samples were collected: serum, saliva, conjunctival swabs, urine by cystocentesis, and feces. Upon recovery from anesthesia, the endotracheal tube was removed, rinsed, and the rinse retained. In the second experiment, the sampling schedule was expanded and serum, saliva, and oropharyngeal samples were collected from day 55 to day 124 p.i. at 14 day intervals. Virus was isolated in porcine alveolar macrophages up to day 14 from urine, day 21 from serum, day 35 from endotracheal tube rinse, day 42 from saliva, and day 84 from oropharyngeal samples. No virus was recovered from conjunctival swabs, fecal samples, or negative control samples. This is the first report of isolation of PRRSV from saliva. Virus-contaminated saliva, especially when considered in the context of social dominance behavior among pigs, may plan an important role in PRRSV transmission. These results support previous reports of persistent infection with PRRSV with prolonged recovery of virus from tonsils of swine.

In-vitro antimicrobial susceptibility of Clostridium perfringens from commercial turkey and broiler chicken origin

Abstract: The minimum inhibitory concentrations (MIC) of eight antibiotics and two anticoccidial agents were determined for Clostridium perfringens strains isolated from 26 commercial broiler farms and 22 commercial turkey farms. Isolates were obtained from the intestines of birds on the farm or as the processing plant using standard culture and identification techniques. The microbroth dilution test was used to determine the MIC for each compound. Most isolates from chickens had MICs in the range of 2-16 mg/L for tilmicosin, tylosin and virginiamycin, whereas the MICs for avilamycin, avoparcin, monensin, narasin and penicillin were or = 64 mg/L) and appeared to be resistant to bacitracin and lincomycin. Most turkey isolates had MICs in the range of 2-16 mg/L for bacitracin, tilmicosin, tylosin and virginiamycin, with strains exhibiting MICs or = 64 mg/L to lincomycin. No attempt was made to associate farm usage of a particular antibiotic to the antibiograms.

Clinical signs and economic losses caused by porcine reproductive and respiratory syndrome virus in a large breeding farm

Abstract: In July of 1994 an acute onset of maternal reproductive failure occurred in a 2,330 sow farrow-to-finish farm. Clinical signs observed in the affected sows were typical for porcine reproductive and respiratory syndrome (PRRS). During the first 6 weeks of the epizootic 1,117 sows farrowed; 216 (19.33%) farrowed before the 110th day of gestation. The majority of piglets born before term died within a few days of birth and the mortality rate for term piglets increased to a maximum of 75.56% during the 5th week of the epizootic when 1,562 out of 2,067 piglets were either born dead or died prior to weaning. Preweaning mortality rates gradually returned to normal values within 16 weeks. The incidence of respiratory disease in the weaned and fattening pigs increased during this time. Although specific prophylactics against respiratory diseases were administered, the death rate doubled for the weaned and fattening pigs.

Distribution of Salmonella contamination in ten animal feedmills.

Abstract: Detailed sampling of spillage and dust from milling equipment was carried out in nine animal feedmills, three of which were sampled twice. The salmonella isolation rate ranged from 1.1% to 41.7% of the samples and the most contaminated mills were those where the inside of the cooling systems for pellet or mash had been colonised by salmonella. A wide range of salmonella serotypes were isolated which included Salmonella typhimurium and S. enteritidis. Limited sampling every two weeks for an 18-month period in another animal feedmill showed marked variation in the contamination rate of samples and range of salmonella serotypes found. Contamination of ingredient intake pits and outloading gantries for finished products by wild bird droppings containing salmonella was also found in four mills.

Pathogenesis of Salmonella enteritidis phage type four after experimental infection of young chickens.

Abstract: White leghorn specific-pathogen-free chickens were inoculated orally with Salmonella enteritidis phage type 4 at the age of one day (group 1) and four weeks (group 2). From 3 h until 4 weeks post inoculation (pi), birds were sacrificed. Gross lesions were recorded and different sites of the intestine and visceral organs were collected for bacteriological and histopathological examination. Clinical disease and mortality were only observed in group 1. Mortality was 8%. The birds were depressed, had diarrhoea and an indurated yolk sac. Infection of the liver and the heart was present within 12 h pi in both groups. The percentage of infected organs was very high and similar in both groups during the first week pi. Thereafter the isolation rate of Salmonella was declining faster in group 2. The crop, the proventriculus, the lower intestinal tract and the bursa of Fabricius were the predilective sites of isolation in both groups. Most prevalent lesions were serous typhlitis, omphalitis and polyserositis. Histopathology revealed inflammation in the intestines and visceral organs. In some birds granulomatous nodules were present in the caeca. Antibodies were detected from 18 and 5 days pi in group 1 and 2, respectively. Granulomatous nodules were typical of infection with this strain of S. enteritidis phage type 4. These granulomatous nodules together with the retained yolk sac possibly are a source of Salmonella organisms that may account for intermittent faecal shedding by carrier birds.

Identification of mycobacteria infecting fish to the species level using polymerase chain reaction and restriction enzyme analysis

Abstract: An assay is described utilizing PCR technology for a rapid diagnostic test to identify fish infection with Mycobacterium marinum, M. fortuitum and M. chelonae. A 924 bp DNA fragment from a highly conserved area of the mycobacterial 16S rRNA gene was amplified using mycobacteria genus-specific primers and digested with restriction enzymes (BanI and ApaI). This examination yielded unique restriction patterns for each mycobacterial specie enabling identification of mycobacteria infecting fish to the species level. The protocol can be applied to purified DNA, a simple colony preparation or infected fish tissue. This protocol can be completed in 1-2 days.

Immunity to PRRSV: Double-edged sword

Abstract: The immune system is a double-edged sword for porcine reproductive and respiratory syndrome virus (PRRSV) infection. On one edge PRRSV has a predilection for immune cells and the disease manifestations can be linked directly to changes in the immune system. PRRSV appears to replicate extensively, if not exclusively, in cells of the immune lineage, notably macrophages; the direct replication of which may lead to immunosuppression, precipitate secondary infection and/or mediate disease. On the other edge, the virus stimulates immunity post-infection that protects an animal from re-infection. A vast array of structural and functionally distinct antibody specific to PRRSV are generated following infection or vaccination. Discrete populations of functional antibodies appear at different times and possibly reflect reactivity to different PRRSV polypeptides. Cell-mediated immune responses specific to PRRSV can be detected in various exposed pigs as well. Thus, the immune system appears to be intimately involved in both the disease process and protection from disease. It is unclear at this state of understanding what immune compartment provides protective immunity. It is humoral (i.e. antibodies), selective functionally distinct populations of antibodies specific for selected PRRSV polypeptides or is cellular immunity essential for protection, or both. This review will attempt to summarize the current state of knowledge of the complex interaction of the immune system and PRRSV.

Molecular characterization of Lelystad virus

Abstract: Lelystad virus (LV), the prototype of porcine reproductive respiratory syndrome virus, is a small enveloped virus, containing a positive strand RNA genome of 15 kb. LV is tentatively classified in the family Arteriviridae, which consists of lactate dehydrogenase-elevating virus (LDV), equine arteritis virus (EAV) and simian hemorrhagic fever virus (SHFV). These viruses have a similar genome organization and replication strategy as coronaviruses, but the size of the genome is much smaller (12-15 kb) and they have different morphological and physicochemical properties. The genome of LV contains eight open reading frames (ORFs) that encode the replicase genes (ORFs 1a and 1b), envelope proteins (ORFs 2 to 6) and the nucleocapsid protein (ORF7). Genomic comparison of European and North American isolates has shown that the structural proteins encoded by ORFs 2 to 7 vary widely. The amino acid sequences of ORFs 2 to 7 of North American strains share only 55 to 79% identical amino acids with those of European strains. Using polyvalent porcine anti-LV serum, gene-specific anti-peptide sera and monoclonal antibodies, we have identified six structural proteins of LV and their corresponding genes. These are: the 15 kDa unglycosylated nucleocapsid protein (N) encoded by ORF7, an 18 kDa unglycosylated integral membrane protein M encoded by ORF6, a 25 kDa N-glycosylated protein encoded by ORF5, a 31-35 kDa N-glycosylated protein encoded by ORF4, a 45-50 kDa N-glycosylated protein encoded by ORF3 and a 29-30 kDa N-glycosylated protein encoded by ORF2. A nomenclature for these structural proteins is proposed.

Pathogenesis and virulence of Rhodococcus equi

Abstract: Inhalation of the soil-borne organism, Rhodococcus equi, can lead to a chronic and severe pyogranulomatous pneumonia in young horses and immunocompromised people. In addition, ulcerative colitis is a common sequela to infection in foals, and dissemination from the lung to other body sites is not uncommon in either the horse or man. Although the facultative intracellular bacterium is susceptible to neutrophil-mediated killing, it is able to resist innate macrophage defenses and establish residence within the intracellular environment of that phagocyte. Definitive virulence factors of R. equi have not yet been determined, but potential candidates include capsular polysaccharide, the exoenzyme cholesterol oxidase, cell wall mycolic acids, and the products encoded by a virulence-associated plasmid. The ability to replicate within the macrophage is associated with virulence, and correlates in animals with the possession of a large plasmid and expression of the plasmid-encoded, surface-expressed lipoprotein, VapA. All strains of R. equi isolated from horses with clinical disease possess a large plasmid and express VapA antigens. In addition, bacterial clearance and granuloma development in mice is linked to plasmid possession and VapA expression. Plasmid containing strains replicate within the tissues of the mouse. whereas plasmid-cured strains are rapidly cleared. At present, the function of the VapA protein is unknown. In contrast to what is observed in the foal, only a small percentage of R. equi strains isolated from humans with rhodococcal disease express VapA antigens, although a high proportion of others express a related protein which is associated with reduced virulence and is also plasmid-encoded. In a limited number of plasmid-negative human isolates, virulence has been linked to beta-lactam resistance, and preliminary evidence suggests that the phenotype may be phage encoded. It is likely that the immune status of the patient can influence whether a particular strain of R. equi is able to produce clinical disease, and certainly experimental infection in mice has confirmed that an intact cellular immune response is necessary for clearance of the organism.

Diagnosis of proliferative enteritis in frozen and formalin-fixed, paraffin-embedded tissues from a hamster, horse, deer and ostrich using a Lawsonia intracellularis-specific multiplex PCR assay.

Abstract: Proliferative enteritis (PE) is an enteric disease that has been reported in a variety of animals. It is caused by an obligate intracellular bacterium identified in swine as Lawsonia intracellularis. The organism can be detected ante-mortem in swine with PE using molecular diagnostic methods. The disease can be diagnosed post-mortem in all species by gross examination of tissues and special histologic staining procedures. In this study we extracted total DNA from frozen or formalin-fixed, paraffin-embedded tissues from cases of pig, hamster, horse, deer and ostrich PE. The samples were subjected to a multiplex PCR reaction using primers specific for a swine isolate of L. intracellularis. Identical sized PCR products were detected in samples from all animals with PE and the specificity of the PCR reaction for L. intracellularis was demonstrated by Southern-blotting and hybridization using specific probes. These results suggest that the intracellular organism of PE in these species are all very closely related to the causative agent of PE in swine, L. intracellularis. In addition, this multiplex PCR assay can be used to detect the organism in frozen or archival tissues, facilitating retrospective diagnosis of PE.

Detection of Mycoplasma agalactiae in sheep milk samples by polymerase chain reaction

Abstract: We developed a simple and rapid method for DNA extraction from sheep milk to use for polymerase chain reaction (PCR) diagnosis of Mycoplasma agalactiae. We tested 357 samples from 21 newly infected flocks (group 1) and 87 samples from 8 flocks infected in the past (group 2). PCR results were compared with those of conventional culture. By PCR we detected 175 positives in group 1, while by culture we detected only 153. Milk samples from group 2 were negative, both by PCR assay and by culture. Our PCR is much faster than culture and reduces the time required for diagnosis from several days to 5 h. The method could be used for the routine diagnosis of contagious agalactia caused by Mycoplasma agalactiae.

Examination of virus shedding in semen from vaccinated and from previously infected boars after experimental challenge with porcine reproductive and respiratory syndrome virus.

Abstract: Danish artificial insemination (AI) centres house several boars antibody positive to porcine reproductive and respiratory syndrome virus as well as PRRSV-naive boars which may become acutely infected. The risk of transmission of PRRSV by semen may therefore constitute a serious problem to the Danish pig industry. The use of a vaccination-program may be a way to avoid or reduce the problem. This study evaluates the use of two vaccines: One live, attenuated vaccine and one inactivated vaccine. A pronounced reduction in viremia and shedding of virus in semen was demonstrated by use of the live vaccine compared to the non-vaccinated control animals. In contrast, no changes in onset, level and duration of viremia and shedding of virus in semen were observed using the inactivated vaccine. Neither viremia nor seminal shedding of virus was detected in previously PRRSV-infected, PRRSV-antibody positive boars after challenge with a Danish field strain of PRRSV.

Distribution of K88 Escherichia coli-adhesive and nonadhesive phenotypes among pigs of four breeds

Abstract: Enterotoxigenic Escherichia coli expressing K88 fimbrial adhesins often cause diarrhea in young pigs. However, some pigs are inherently resistant to colibacillosis, because they lack receptors on their epithelial cell brush borders to which the fimbriae bind. Phenotypic diversity with respect to the binding of E. coli expressing K88 of the three variant types (K88ab, K88ac, and K88ad) was reported by Bijlsma et al. (1982), and binding specificities for each phenotype were described: A (adhesive to all three variants), B (adhesive to K88ab and K88ac), C (adhesive to K88ab and K88ad), D (adhesive to K88ad) and E (nonadhesive). Because brush border adhesiveness has been correlated with disease susceptibility, swine K88 adhesive phenotypes are of significance in the control of enteric disease. To determine the prevalence of the various K88 adhesive phenotypes in the swine population in the Midwestern United States, we tested epithelial cell brush borders of 24 purebred pigs from each of four breeds (Chester White, Duroc, Hampshire and Yorkshire) for adhesiveness to each of the K88 variants. Four, 4-week-old pigs (the largest and smallest healthy female littermates from two litters) were collected from each of 24 farms. Brush border vesicles from the pigs were tested for ability to bind E. coli expressing each K88 variant. The five brush border adherence patterns described for phenotypes A-E were observed. In addition, brush borders from some pigs only bound K88ab + bacteria. Nearly three quarters of the pigs whose brush borders tested, were found to be phenotype A (43%) or phenotype E (28%). These were the most common phenotypes in each breed, except Hampshire, in which case phenotypes C (17%) and D (25%) were more common than E (8%). There appeared to be no relationship between the phenotype of a pig and its weight relative to its littermate.

Bacteriological and serological investigation of persistent Salmonella enteritidis infection in an integrated poultry organisation

Abstract: Bacteriological monitoring of broiler breeder farms, the hatchery, rendering plant and animal feed mill during 1991 identified a number of potential cross-contamination hazards, such as the use of processed poultry proteins in the company feed mill and contamination of egg trolleys and trays, which may have led to widespread dissemination of Salmonella enteritidis within an integrated poultry organisation. Serological monitoring of the flocks suggested that, in most cases, substantial exposure to S. enteritidis infection occurred during the mid-rearing stage whereas routine bacteriological monitoring of poultry house litter and dust samples, and meconium samples taken in the hatchery identified infection only after the onset of the laying period. At least 10 phage types and six plasmid profile types of S. enteritidis were identified in historic submissions from the organisation including one apparently specific plasmid profile type that was distributed throughout the various parts of the company. During sampling for this investigation, most of these strains were not identified, and the number of plasmid profile types was reduced to a single common UK type.

Porcine reproductive and respiratory syndrome virus (PRRSv) interaction with Haemophilus parasuis

Abstract: The interaction of bacteria and virus has been well demonstrated in the pathogenesis of respiratory disease in swine. The interaction between porcine respiratory and reproductive syndrome virus (PRRSv) and Haemophilus parasuis has not been studied. We initiated studies to evaluate a possible effect of the PRRSv on the pathogenesis of polyserositis caused by H. parasuis. A group of 30 three week old piglets were distributed in 4 groups. Group I (10 pigs) was inoculated with PRRSv and H. parasuis. Group II (10 pigs) was inoculated with H. parasuis alone. Group III (5 pigs) was inoculated with virus alone and group IV (5 pigs) was inoculated with culture media. Lesions consisted of a severe fibrinous polyserositis affecting 7 of 10 animals in group II and a mild fibrinous pleuritis in 1 of 10 animals of group I. Three of ten animals dually infected with the two agents died during the course of the study. These animals had pulmonary congestion and focal lung hemorrhages. No other animals died from other groups. Group III and IV had no macroscopic lesions. Microscopically group III had interstitial pneumonia. Immunomodulating virus effect may explain the differences in terms of lesions severity between groups I and II. Septic shock was suspected as cause of sudden death.

Passive protection of neonatal calves against bovine coronavirus-induced diarrhea by administration of egg yolk or colostrum antibody powder.

Abstract: The protective effect of egg yolk and colostrum powders prepared from hens and cows vaccinated with inactivated bovine coronavirus (BCV) antigen was evaluated in a challenge model with a virulent BCV strain. Twenty three calves from BCV-free herds were randomly divided into control and several treatment groups. All calves were orally challenged with 1 × 109 TCID50 of the virulent Kakegawa strain of BCV at 24 to 36 h after birth. Calves in treatment groups received either egg yolk powder or cow colostrum containing BCV specific antibodies. Daily treatment with these antibody preparations started 6 h until 7 days post-challenge. Control calves which received no antibody had severe diarrhea and all died within 6 days after infection. In contrast, calves fed milk containing egg yolk or colostrum with neutralization titers of 1:2560 or 1:10 240 respectively all survived and had positive weight gain unlike the other treatment groups. These results indicate that the orally administered egg yolk and colostrum powders protected against BCV-induced diarrhea in neonatal calves and that the egg yolk used provided a higher degree of protection compared to colostrum powder on a titer basis. Treatment with whole egg yolk from immunized hens therefore provides a more efficacious alternative to the existing methods of specific passive protection against BCV.

Duration of homologous porcine reproductive and respiratory syndrome virus immunity in pregnant swine.

Abstract: The duration of porcine reproductive and respiratory syndrome virus (PRRSV) homologous immunity was tested in this study and found to last for at least 604 days post experimental exposure to field PRRSV. Eleven gilts (group A) received a primary exposure to field PRRSV by either an oronasal (n = 6) or an intrauterine (n = 5) route. The gilts were naturally bred at selected times (143 to 514 days) after primary virus exposure. They were oronasally exposed a second time to the same strain of virus on or about gestation day 90. Ten age-matched control sows free of PRRSV-specific antibody from the same source farm (group B) were naturally bred and were oronasally exposed to aliquots of the homologous challenge virus on or about gestation day 90. Nine of the 11 gilts in group A and all animals in group B became pregnant following one breeding cycle. The two nonpregnant gilts in group A were each naturally bred during four additional estrus cycles and neither became pregnant. They were exposed to homologous challenge virus 562 and 604 days post primary exposure, respectively. All animals were necropsied 21 days post homologous challenge. Sera and alveolar macrophages from each dam, and sera from each fetus were tested for virus. Transplacental infection was detected in 0/9 and 8/10 litters in groups A and B, respectively. Virus was detected in 0/11 and 10/10 of the alveolar macrophage samples collected in groups A and B, respectively. Serum was harvested at selected times throughout the experiment and tested for PRRSV-specific antibody by indirect immunofluorescence microscopy. All gilts in group A were seropositive for the duration of the experiment, and all animals in group B seroconverted following exposure to field PRRSV. This study shows that adult swine can produce a homologous protective immunity after PRRSV exposure that may persist for the production life of the animal.

Phenotypic characterisation of Pasteurella multocida isolates from Australian poultry

Abstract: A phenotypic characterisation of 110 isolates of bacteria previously identified as Pasteurella multocida was performed. Reference strains of many of the currently recognised species within the genus Pasteurella were included in the study. All the isolates had been obtained from Australian poultry - 67 from chickens, 42 from turkeys and one from a duck. Ten different biochemical biovars were recognised amongst the isolates. Four of these biovars, representing 91 isolates, were identified as P. multocida subsp. multocida. One biovar, consisting of one isolate, was identified as P. multocida subsp. septica and another biovar, consisting of five isolates, as P. multocida subsp. gallicida. Two further biovars were tentatively identified as ornithine decarboxylase negative P. multocida subsp. multocida (five isolates) and maltose positive P. multocida subsp. septica (one isolate). The final two biovars, consisting of five and two isolates each, could not be assigned to any of the currently recognised subspecies of P. multocida.

Studies of porcine reproductive and respiratory syndrome (PRRS) virus infection in avian species

Abstract: Porcine reproductive and respiratory syndrome virus (PRRSV) is a recently recognized virus of swine. As a newly emerging virus, much of the basic information regarding PRRSV is in the process of discovery. We report three experiments with PRRSV in birds, and a fourth experiment to evaluate the infectivity and transmissibility of avian-derived PRRSV in swine. Experiment 1 compared the susceptibility of Muscovy ducks, Mallard ducks, guinea fowl, and chickens to PRRSV. Birds were exposed to PRRSV (ATCC VR-2402) in drinking water and virus isolation was attempted from feces collected from cages. Based on the duration of fecal shedding of the virus, this experiment showed that Mallard ducks were particularly susceptible to PRRSV. Experiment 2 was done in mallards to corroborate and augment the observations of experiment 1. Virus was isolated from pooled mallard feces up to 25 days post exposure (PE) and from the intestinal contents of 8 of 20 birds euthanized on day 38 PE. No gross or microscopic lesions were observed in ducks collected between 0 and 15 days PE. Experiment 3 evaluated the infectivity and transmissibility of mallard-derived PRRSV in mallards. A cage of mallards orally exposed to PRRSV shed the virus in feces. Exposure of a second cage of mallards to feces from the first cage resulted in fecal shedding of PRRSV by birds in cage two. In turn, exposure to feces from the second cage led to fecal shedding by mallards in a third cage. Experiment 4 assessed the infectivity and transmissibility of mallard-derived virus in swine. Pigs intranasally exposed to PRRSV isolated from mallard feces in experiment 2 became viremic, seroconverted by ELISA, and transmitted the virus to sentinel swine. Collectively, these studies show that the possibility exists for avian species to be involved in the epidemiology of PRRSV. This is the first report of PRRSV infection in a species other than swine.

Virulence mechanisms of avian fimbriated Escherichia coli in experimentally inoculated chickens

Abstract: Virulence mechanisms of avian pathogenic Escherichia coli were investigated by inoculating commercial broiler chickens via the left caudal thoracic air sac with three highly pathogenic and three less pathogenic E. coli isolates. At 6 h postinoculation, all isolates had colonized the respiratory tract (trachea, lungs, and air sacs) and internal organs (liver, spleen, and kidney) of inoculated birds, but bacteria were recovered from pericardial fluid and blood only of birds inoculated with the more pathogenic isolates. F1 fimbriae were expressed on a high proportion of bacteria colonizing the trachea and to a lesser extent on bacteria in the lungs of birds inoculated with each of the isolates. F1 fimbriae were also expressed on bacteria in air sacs only for the less pathogenic isolates. P(F11) fimbriae were expressed on bacteria present in air sacs, lungs, kidney, blood, and pericardial fluid of birds inoculated with one of the more virulent isolates. On electron microscopy, bacteria of the more pathogenic isolates but not of the less pathogenic isolates were observed often associated with or within macrophages, which appeared to be viable, in the air sacs and lungs. In in vitro assays, the more pathogenic but not the less pathogenic isolates, were resistant to opsonization and phagocytosis in the absence of F1 fimbriae, whereas bacteria of all isolates were rapidly killed by avian macrophages when they expressed F1 fimbriae. These results suggest that resistance to phagocytosis may be an important mechanism in avian colisepticemia. They also suggest that F1 fimbrial phase variation to the nonfimbriated phase is favored in the avian lower respiratory tract, is more marked for the more pathogenic isolates, and may be a virulence mechanism.