Isolation of porcine circovirus-like viruses from pigs with a wasting disease in the USA and Europe

Samples of lung, liver, kidney, pancreas, spleen, and lymph node from pigs with postweaning multisystemic wasting syndrome from California (USA) and samples of mesenteric lymph nodes from similarly diseased pigs from Brittany (France) were examined by light microscopy, in situ hybridization (ISH), and/or virus isolation. Whole genomic probes for porcine circovirus (PCV) and chicken anemia virus (CAV) were used for ISH. Tissue homogenate supernatants were inoculated onto PK/15 cells for virus isolation, and the presence of viral antigen and viral particles was verified by indirect immunofluorescence, ISH, and electron microscopy. Histologic examination of lung from pigs from California revealed interstitial pneumonia, alveolar epithelial hyperplasia, and basophilic nuclear and cytoplasmic inclusions in mononuclear cell infiltrates and various pulmonary epithelial cells. Granulomatous lymphadenitis with syncytial cells typified the lesions seen in the pigs from France. PCV-like nucleic acid was detected by ISH in lung, pancreas, lymph node, kidney, and liver in pigs from California. Positive signal was also obtained in lymph node sections from pigs from France. Probes for CAV were consistently negative. PK/15 cell cultures inoculated with lung preparations from diseased California pigs and mesenteric lymph node preparations from pigs from France had positive fluorescence by indirect staining for PCV using pooled polyclonal pig sera and hyperimmune rabbit serum and had variable staining with a panel of 7 monoclonal antibodies specific for cell culture contaminant PCV. PCV-like nucleic acid was also detected by ISH in cell cultures. Cytopathic effect was not observed. Electron microscopic examination of inoculated cell cultures revealed 17-nm viral particles morphologically consistent with PCV. No other virus particles were observed. Although genomic analysis for the definitive identification of these viral isolates remains to be done, the evidence provided strongly suggests that these tissue isolates are closely related to, although antigenically distinct from, the original PCV cell culture contaminant.

Streptococcus suis: past and present

Steptococcus suis is a Gram-positive, facultatively anaerobic coccus that has been implicated as the cause of a wide range of clinical disease syndromes in swine and other domestic animals. In swine, the disease has spread worldwide but is more prevalent in countries with intensive swine management practices. The disease syndromes caused by S. suis in swine include arthritis, meningitis, pneumonia, septicaemia, endocarditis, polyserositis, abortions and abscesses. S. suis has also been implicated in disease in humans, especially among abattoir workers and swine and pork handlers. In humans, S. suis type 2 can cause meningitis, which may result in permanent hearing loss, septicaemia, endocarditis and death. The pathogenic mechanism of S. suis is not well defined. Several virulence factors have been identified, but their roles in pathogenesis and disease have not been well elucidated. Much work is in progress on characterization of virulence factors and mechanisms, with emphasis on the control of the disease. Because of the non-availability of suitable immunoprophylaxis, control of S. suis infection has depended mainly on the use of antimicrobials.

Potential for transmission of avian influenza viruses to pigs

Pandemic strains of influenza A virus arise by genetic reassortment between avian and human viruses. Pigs have been suggested to generate such reassortants as intermediate hosts. In order for pigs to serve as 'mixing vessels' in genetic reassortment events, they must be susceptible to both human and avian influenza viruses. The ability of avian influenza viruses to replicate in pigs, however, has not been examined comprehensively. In this study, we assessed the growth potential of 42 strains of influenza virus in pigs. Of these, 38 were avian strains, including 27 with non-human-type haemagglutinins (HA; H4 to H13). At least one strain of each HA subtype replicated in the respiratory tract of pigs for 5 to 7 days to a level equivalent to that of swine and human viruses. These results indicate that avian influenza viruses with or without non-human-type HAs can be transmitted to pigs, thus raising the possibility of introduction of their genes into humans. Sera from pigs infected with avian viruses showed high titres of antibodies in ELISA and neutralization tests, but did not inhibit haemagglutination of homologous viruses, cautioning against the use of haemagglutination-inhibition tests to identify pigs infected with avian influenza viruses. Co-infection of pigs with a swine virus and with an avian virus unable to replicate in this animal generated reassortant viruses, whose polymerase and HA genes were entirely of avian origin, that could be passaged in pigs. This finding indicates that even avian viruses that do not replicate in pigs can contribute genes in the generation of reassortants.

Pseudorabies virus variant in Bartha-K61-vaccinated pigs, China, 2012

The widely used pseudorabies virus (PRV) Bartha-K61 vaccine has played a key role in the eradication of PRV. Since late 2011, however, a disease characterized by neurologic symptoms and a high number of deaths among newborn piglets has occurred among Bartha-K61–vaccinated pigs on many farms in China. Clinical samples from pigs on 15 farms in 6 provinces were examined. The PRV gE gene was detectable by PCR in all samples, and sequence analysis of the gE gene showed that all isolates belonged to a relatively independent cluster and contained 2 amino acid insertions. A PRV (named HeN1) was isolated and caused transitional fever in pigs. In protection assays, Bartha-K61 vaccine provided 100% protection against lethal challenge with SC (a classical PRV) but only 50% protection against 4 challenges with strain HeN1. The findings suggest that Bartha-K61 vaccine does not provide effective protection against PRV HeN1 infection.

Giardia and Cryptosporidium in Canadian farm animals

Giardia intestinalis and Cryptosporidium spp. are commonly identified intestinal pathogens in humans and animals. In light of the clinical disease, production losses and zoonotic potential of both Giardia and Cryptosporidium infections, a study was undertaken to investigate the prevalence of these parasites in cattle, sheep, pigs and horses in Canadian farms at different geographical locations. A total of 104 cattle, 89 sheep, 236 pigs and 35 horses were sampled from 15 different Canadian geographical locations. Fecal samples were examined after concentration and immunofluorescent staining. Giardia and Cryptosporidium were present in cattle and sheep in six out of six sites sampled. In cattle the overall prevalence was 29% for Giardia and 20% for Cryptosporidium. Giardia was identified in 38% of sheep while 23% of sheep were positive for Cryptosporidium. Giardia and Cryptosporidium were identified in four out of six hog operations with an overall prevalence of 9% for Giardia and 11% for Cryptosporidium. All horse sampling locations (4/4) were positive for Giardia with 20% of animals infected. Cryptosporidium was identified in three out of four sampling sites with a prevalence of 17%. The prevalence of Giardia and Cryptosporidium was greater in calves and lambs compared to adults. This study demonstrates that both Giardia and Cryptosporidium appear to be prevalent in farm livestock.

Comparative pathogenicity of nine US porcine reproductive and respiratory syndrome virus (PRRSV) isolates in a five-week-old cesarean-derived, colostrum-deprived pig model

One hundred forty-six 5-week- old cesarean-derived, colostrum-deprived (CDCD) pigs were inoculated intranasally with 1 of 9 US porcine reproductive and respiratory syndrome virus (PRRSV) isolates. Differences were found in severity of clinical respiratory disease, rectal temperatures (P < or = 0.001), gross lung lesions (P < or = 0.001), and microscopic lung lesions (P < or = 0.05). Gross lung lesions were generally most severe 10 days postinoculation and were distributed primarily in the cranial, middle, and accessory lobes and ventromedial portion of the caudal lung lobes. Mean gross lung lesion scores estimating the percentage of lung affected by pneumonia at 10 days postinoculation ranged from 16.7% +/- 2.8% (mean +/- SEM, n = 10) for isolate ISU-51 to 62.4% +/- 5.7% (n = 10) for isolate ISU-28. Microscopic lung lesions were characterized by hyperplastic and hypertrophied type 2 pneumocytes, septal infiltration by mononuclear cells, and accumulation of necrotic alveolar exudate. Lymph node follicular hyperplasia and focal necrosis was seen with all 9 isolates. This CDCD pig model was useful for demonstration of significant differences in pathogenicity among US PRRSV isolates. This difference in pathogenicity may help explain the variation of severity of clinical disease observed in field outbreaks of porcine reproductive and respiratory syndrome and should provide for meaningful comparison of PRRSV genotypes.

Genetic variation in porcine reproductive and respiratory syndrome virus isolates in the midwestern United States

The nucleotide sequence of a 3266 bp region encompassing open reading frames (ORFs) 2 through 7 of the porcine reproductive and respiratory syndrome virus (PRRSV) was determined for 10 isolates recovered from the midwestern United States. Pairwise comparisons showed that genetic distances between isolates ranged from 2.5% to 7.9% (mean 5.8% +/- 0.2%) whereas the Lelystad strain from Europe was, on average, 34.8% divergent from US clones. Thus, US and European PRRSV isolates represent genetically distinct clusters of the same virus. ORF 5, which encodes the envelope glycoprotein, was the most polymorphic [total nucleotide diversity (pi) = 0.097 +/- 0.007] and ORF 6, encoding the viral M protein, was the most conserved (pi = 0.038 +/- 0.003). The substantial differences in nucleotide diversity among ORFs suggests that the virus is evolving by processes other than simple accumulation of random neutral mutations. In support of this hypothesis, statistical analyses of the nucleotide sequence provided strong evidence for intragenic recombination or gene conversion in ORFs 2, 3, 4, 5 and 7, but not in ORF 6. An excess of synonymous (silent) substitutions was observed in all six ORFs, indicating an evolutionary pressure to conserve amino acid sequences. Taken together, the data indicate that despite intragenic recombination among extant PRRSV isolates, purifying selection has acted to maintain the primary structure of individual ORFs.

Experimental porcine reproductive and respiratory syndrome virus infection in one-, four-, and 10-week-old pigs

One-, 4-, and 10-week-old pigs were exposed to porcine reproductive and respiratory syndrome virus (PRRSV) to determine the effect of age on clinical signs, hematologic alterations, the onset and duration of viremia, routes of virus shedding, antibody production, and microscopic lesions produced by PRRSV isolate ATCC VR-2332. The response to PRRSV infection was similar among age groups. Fever, usually prolonged, and a marked dyspnea with cutaneous erythema when restrained for sample collection were the most consistent clinical signs. Prolonged periocular edema was unique to the 1-week-old pigs. The white blood cell count was decreased on day 4 postexposure (PE) due to decreases in neutrophils and lymphocytes. The virus was isolated from buffy coats at day 1 PE and was isolated from serum, buffy coat, or plasma at each sample collection period through the end of the trial (day 28 PE). Virus was most consistently isolated from lung, lymph node, spleen, and tonsil on day 7 PE and exclusively from lymph node, spleen, and tonsil on day 28 PE. Virus was infrequently isolated from urine and fecal and nasal swabs. Consistent microscopic changes in all age groups included interstitial pneumonia and lymph node hypertrophy and hyperplasia on days 7 and 28 PE, lymph node necrosis on day 7 PE, and subacute mononuclear myocarditis on day 28 PE. Findings presented here indicate that interstitial pneumonia, lymphoid necrosis, and mononuclear myocarditis are characteristic lesions of PRRSV isolate ATCC VR-2332 infection in 1-, 4-, and 10-week-old pigs.

Characterization of the humoral immune response to porcine reproductive and respiratory syndrome (PRRS) virus infection

The development of the humoral immune response against porcine reproductive and respiratory syndrome (PRRS) virus was monitored by an indirect fluorescent antibody (IFA) test, immunoperoxidase monolayer assay (IPMA), enzyme-linked immunosorbent assay (ELISA), and serum virus neutralization (SVN) test over a 105-day period in 8 pigs experimentally infected with ATCC strain VR-2402. Specific antibodies against PRRS virus were first detected by the IFA test, IPMA, ELISA, and the SVN test 9-11, 5-9, 9-13, and 9-28 days postinoculation (PI), respectively, and reached their maximum values by 4-5, 5-6, 4-6, and 10-11 weeks PI, respectively, thereafter. After reaching maximum value, all assays showed a decline in antibody levels. Assuming a constant rate of antibody decay, it was estimated by regression analysis that the ELISA, IFA, IPMA, and SVN antibody titers would approach the lower limits of detection by approximately days 137, 158, 324, and 356 PI, respectively. In this study, the immunoperoxidase monolayer assay appeared to offer slightly better performance relative to the IFA test, ELISA, and SVN test in terms of earlier detection and slower rate of decline in antibody titers. Western immunoblot analysis revealed that antibody specific for the 15-kD viral protein was present in all pigs by 7 days PI and persisted throughout the 105-day observation period. Initial detection of antibodies to the 19-, 23-, and 26-kD proteins varied among pigs, ranging from 9 to 35 days PI. Thereafter, the antibody responses to these 3 viral proteins of PRRS virus continued to be detected throughout the 105-day study period.(ABSTRACT TRUNCATED AT 250 WORDS)

Nutritional regulation of porcine bacterial-induced colitis by conjugated linoleic acid

Excessive intake of saturated fatty acids and/or linoleic acid favors the induction of an array of lipid mediators and cytokines enhancing inflammatory responses. Conversely, dietary supplementation with (n-3) fatty acids or vitamin D ameliorates inflammation and autoimmune diseases. Although it was well accepted that conjugated linoleic acid (CLA) prevented diseases with a common inflammatory pathogenesis (i.e., cancer and atherosclerosis), no studies were available on the roles of CLA in mucosal inflammation. The present study was designed to investigate the anti-inflammatory actions and molecular mechanisms underlying the regulation of colonic health by CLA. We hypothesized that colonic inflammation can be ameliorated by dietary CLA supplementation. To test this hypothesis, inflammation of the colonic mucosa was triggered by challenging pigs fed either soybean oil-supplemented or CLA-supplemented diets with an enteric bacterial pathogen (i.e., Brachyspira hyodysenteriae). Immunoregulatory cytokines and peroxisome proliferator-activated receptor-gamma (PPAR-gamma) mRNA expression were assayed in colonic lymph nodes and colon of pigs. Colonic mucosal lesions and lymphocyte subset distribution were evaluated by histology and immunohistochemistry. Supplementation of CLA in the diet before the induction of colitis decreased mucosal damage; maintained cytokine profiles (i.e., interferon-gamma and interleukin-10) and lymphocyte subset distributions (i.e., CD4+ and CD8+), resembling those of noninfected pigs; enhanced colonic expression of PPAR-gamma; and attenuated growth failure. Therefore, CLA fed preventively before the onset of enteric disease attenuated inflammatory lesion development and growth failure.

Dual infections of feeder pigs with porcine reproductive and respiratory syndrome virus followed by porcine respiratory coronavirus or swine influenza virus: a clinical and virological study

Dual infections of pigs with porcine reproductive and respiratory syndrome virus (PRRSV) followed by a second common respiratory virus, either porcine respiratory coronavirus (PRCV) or swine influenza virus (SIV), were studied. The aim was to determine if dual infections, as compared to single virus infections, result in enhanced clinical manifestations. It was also examined if PRRSV replication affects replication of PRCV or SIV in the respiratory tract. Groups of conventional 10 week old pigs were inoculated with PRRSV-only (3 pigs), PRCV-only (4 pigs) or SIV-only (4 pigs). Dual inoculations with PRRSV-PRCV (4 pigs) and PRRSV-SIV (3 groups of 4, 4 and 5 pigs) were performed at a 3 day interval. A group of uninoculated control pigs (8 pigs) was included. The infection with PRRSV-only induced a transient fever (40.2 degrees C) at 2 DPI, but no respiratory signs. The PRCV-only infection remained subclinical. The SIV-only infection resulted in a one day fever (40.1 degrees C) with moderate tachypnoea and dyspnoea. Mean weight gain in the virus-inoculated groups was retarded compared with the control group. The PRRSV-PRCV infection induced a 9 day lasting fever (peak 40.9 degrees C) with tachypnoea, dyspnoea and productive coughing. The PRRSV-SIV infection resulted in fever and respiratory signs in all 3 groups. Clinical signs, however, were more pronounced in group 1 than in groups 2 and 3. Pigs of group 1 showed fever during 10 days (peak 41.4 degrees C), tachypnoea, marked dyspnoea with abdominal breathing, and a productive cough. Pigs of groups 2 and 3 had fever for 5 and 3 days (peaks 40.6 and 40.3 degrees C) respectively and mild respiratory disorders. Mean weight gain during 14 DPI of the 2nd virus was 5.9 kg in the PRRSV-PRCV group and 4.0, 6.8 and 6.7 kg in PRRSV-SIV groups 1, 2 and 3 respectively. Mean weight gain during the corresponding period in the PRRSV-only group was 8.6 kg. It was concluded that dual infections with viruses causes more severe disease and growth retardation than single PRRSV infection. PRCV excretion curves were similar in single and dual virus inoculated groups. Excretion of SIV was delayed by 2 days in the dual inoculated pigs. Thus, replication of the second virus is not (PRCV) or only slightly (SIV) affected by a prior infection with PRRSV.

Villus height and crypt depth in weaned and unweaned pigs, reared under various circumstances in The Netherlands

The height of the villi and depth of the crypts in the small intestine were studied after weaning in pigs reared under various circumstances in the Netherlands. Pigs taken from herds with a long history of postweaning diarrhoea had in general significantly shorter villi and deeper crypts than their counterparts from a specific pathogen-free herd. Weaning was associated with villus shortening, crypt deepening and subsequent villus lengthening in pigs from the specific pathogen-free herd. Giving supplementary feed during the sucking period was beneficial in preventing shortening of the villi and this villus shortening was less severe when the crypts were deep at weaning, a condition that perhaps lessens the severity of postweaning diarrhoea.

Persistence of porcine reproductive and respiratory syndrome virus in serum and semen of adult boars

Four seronegative adult boars were intranasally inoculated with porcine reproductive and respiratory syndrome virus (PRRSV) isolate VR-2332. Serum and semen were collected 2-3 times weekly for over 100 days postinoculation (DPI). Serum samples were assayed for PRRSV by virus isolation (VI) and a polymerase chain reaction (PCR) and screened for antibodies to PRRSV using the indirect fluorescent antibody (IFA) and virus neutralization (VN) tests. Semen was assayed for PRRSV RNA by PCR. Virus and viral RNA was detected in the serum of all boars within 1 DPI by Vi and/or PCR. However, VI results indicated that viremia was transient and occurred from 1 to 9 DPI. Viral RNA was detected in serum from 1 to 31 DPI. In the acute stage of the infection, PRRSV RNA was detected in serum by PCR prior to the presence of viral RNA in semen. The PRRSV RNA was detected in semen as early as 3 DPI and persisted for 25 DPI in 2 of the boars and 56 and 92 DPI in the remaining 2 boars. Detection of PRRSV RNA in semen occurred 2-8 and 28-35 days prior to the detection of antibodies by IFA and VN, respectively. PRRSV was isolated from the bulbourethral gland of the boar that shed viral RNA in semen for 92 DPI. These results suggest that PRRSV RNA can be detected by PCR in boar serum and semen, and may persist for variable periods of time. Viremia and the serologic status of the boar are not adequate indicators of when PRRSV or PRRSV RNA is being shed in the semen. Preliminary findings also indicated that neither shipping stress nor reinoculation with homologous PRRSV resulted in viremia or viral RNA shedding in semen.

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

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.

Strategies to reduce transmission of Toxoplasma gondii to animals and humans

Toxoplasma gondii is found in the tissues of food animals and is an important cause of abortion and mortality in sheep and goats throughout the world. It causes mental retardation and loss of vision in congenitally infected children and death in immunosuppressed patients. A live vaccine, using a nonpersistent strain of T. gondii, is available in New Zealand, the UK and Europe which prevents T. gondii abortion in sheep. A live vaccine using a mutant strain of T. gondii (T-263) is being developed in the USA to reduce oocyst shedding by cats. As yet, there are no drugs to kill T. gondii tissue cysts in human or animal tissues. Freezing to -12 degrees C, cooking to an internal temperature of 67 degrees C, or gamma irradiation (0.5 kGy) can kill tissue cysts in meat.

General overview of PRRSV: a perspective from the United States

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.

Pathogenesis of ruminant herpesvirus infections

Ruminants are hosts for members of both Alpha- and Gamma-herpesvirinae. A wide range of disease syndromes is associated with infections by these agents. The associated diseases reflect the biological nature of the causative viruses. Clinically, the symptoms may be mild and localized or include severe generalized disease, leading eventually to death. Much knowledge has been gained concerning the pathogenesis of some alpha-herpesviruses. Initially, these viruses replicate in epithelial cells at the portal of entry. The symptoms of the acute diseases are often associated with the destruction of those epithelial cells. However, as in the case of bovine herpesvirus 1 (BHV-1), the virus may spread in the infected host by viremia, gaining access to a broader range of tissues and organs, and causing a broader variety of diseases. Furthermore, many herpesviruses are capable of entering neuronal cells. There, they may replicate, which may lead to neuronal diseases, for example, encephalitis. In addition, the herpesviruses may establish latency in neuronal or lymphoid cells. During latency, apparently no viral antigens are synthesized but the genomes of the latent viruses are present in the nuclei of long living cells, such as, e.g., neurones of the ganglia corresponding to the sites of peripheral replication. Upon reactivation, the viruses re-establish the lytic cycle of replication. Shielded from the effectors of the immune system, they migrate back to the peripheral tissues where they are excreted and may be transmitted. Although a strong immune response is provoked during primary viral replication, these mechanisms help the herpesviruses to escape from immune surveillance during latency and to a lesser degree during reactivation. It has been observed that certain herpesviruses may behave differently upon infection of different hosts. Relatively little progress has been made concerning the understanding of the pathogenesis of ruminant herpesviruses but much has been learned about viral molecular biology. Many viral proteins have been identified and characterized and the technology to create recombinant viruses has been established. With these tools in our hands, it is now possible to address the really interesting questions concerning pathogenesis. We postulate that herpesviruses contain at least two sets of genes, a first set involved in gene expression and viral replication, and a second set responsible for functions, which may affect pathogenesis, latency, and virus/host interactions. Using recombinant virus technology, it will be possible in the future to design targeted deletions and gene transfers in ruminant herpesviruses in order to study the viral and host factors involved in pathogenesis on the molecular level.

PORCINE CONTAGIOUS PLEUROPNEUMONIA. I. EXPERIMENTAL TRANSMISSION, ETIOLOGY, AND PATHOLOGY

An acute frequently rapidly fatal respiratory illness occurring as an epidemic disease in Argentine swine has been shown to have a bacterium of the genus Hemophilus as its causative agent. This organism, for which the name Hemophilus pleuropneumoniae is suggested, causes a singular, fulminating pleuropneumonia in experimental swine. The very marked effectiveness of H. pleuropneumoniae as a respiratory pathogen contrasts strikingly with the relatively mild pathogenicity of the well known swine Hemophilus, H. influenzae suis, which, in concert with a virus, causes a less highly fatal respiratory ailment, swine influenza. Porcine contagious pleuropneumonia (PCP) is contagious under experimental conditions. In the pathogenesis of the disease, histopathological studies of early cases suggest that the lymphatics of the lung and pleura may be primarily involved and that the pneumonia and pleuritis then proceed from these initial sites of reaction.

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

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.

Genes coding for enterotoxins and verotoxins in porcine Escherichia coli strains belonging to different O:K:H serotypes: relationship with toxic phenotypes

Seventy-four E. coli strains isolated from piglets with diarrhea or edema disease in Spain were serotyped and examined for production of heat-labile (LT) and heat-stable (ST) enterotoxins (LT-I, LT-II, STaH, STaP, and STb) and verotoxins (VT1, VT2, and VT2v = VTe) by phenotypic (Vero cell assay and infant mouse test) and genotypic (colony hybridization and PCR) methods. In general, an excellent correlation was found between the results obtained with a PCR approach and those determined with biological assays. DNA probes used in the hybridization also showed a very good agreement with phenotypic results, with the exception of a VT1 probe that initially produced 10 false-positive reactions. The gene coding for STb (58 strains) was the most prevalent gene detected by PCR, followed by those coding for STa (46 strains), LT (19 strains), VT2v (11 strains), and VT1 (1 strain). Apparently, in Spain three seropathotypes are predominant: (i) O149:K91:H10 K88+ LT-I+ STb+, (ii) O141:K85ab:H- P987+ STaP+, and (iii) O138:K81:H14 or H- STaP+ VT2v+. We conclude that PCR is a fast, specific, and practical method for the identification of enterotoxin and VT genes in clinical and epidemiological studies.