Detection of porcine circovirus type 2 and viral replication by in situ hybridization in primary lymphoid organs from naturally and experimentally infected pigs.

Porcine circovirus type 2 (PCV2) infection is the cause of postweaning multisystemic wasting syndrome (PMWS). It has been speculated whether cell types permissive of replication are found in the primary lymphoid organs and whether infection of these tissues has an important role in the pathogenesis of PMWS. The aim of this study was to determine if primary lymphoid organ cells support viral replication during PCV2 infection. This was done by histopathological examination of thymus and bone marrow from pigs experimentally inoculated with PCV2 (n = 24), mock-infected pigs (n = 12), pigs naturally affected by PMWS (n = 33), and age-matched healthy control animals (n = 29). In situ hybridization (ISH) techniques were used to detect PCV2 nucleic acid irrespective of replicative status (complementary probe, CP) or to detect only the replicative form of the virus (replicative form probe, RFP). PCV2 was not detected in the experimentally PCV2-inoculated pigs or the control animals. Among the PMWS-affected pigs, 19 of 20 (95%) thymuses were positive for PCV2 by CP ISH, and 7 of 19 (37%) of these also supported viral replication. By CP ISH, PCV2 was detected in 16 of 33 (48%) bone marrow samples, and 5 of 16 (31%) of these also supported replication. The 2 ISH probes labeled the same cell types, which were histiocytes in both organs and lymphocytes in thymus. The RFP labeled fewer cells than the CP. Thus, PCV2 nucleic acids and replication were found in bone marrow and thymus of PMWS-affected pigs, but there was no evidence that primary lymphoid organ cells are major supporters of PCV2 replication.

Postweaning multisystemic wasting syndrome in Danish pig herds: productivity, clinical signs and pathology.

A case-control study of 74 herds with postweaning multisystemic wasting syndrome (pmws) and 74 matched control herds was carried out. In the case herds the mortality rates of weaner and finisher pigs were 11.2 and 5.2 per cent respectively, compared with 3.1 and 3.2 per cent in the control herds. In most case herds, pmws developed within the first four weeks after weaning. Wasting, diarrhoea and respiratory signs were observed in 10 per cent of the weaner pigs (7 to 30 kg) in the case herds compared with 7 per cent in the control herds. The average daily gains of the weaner pigs and finisher pigs were 36 g and 52 g less in the case herds than in the control herds. By examining three weaner pigs from each herd the pmws diagnosis was confirmed by histopathology and immunohistochemistry in 78 per cent of the case herds, but at least one pmws-positive weaner pig was found in 19 of the control herds. The prevalence of pmws-positive pigs among illthriven weaner pigs was 45 per cent (101/222) in the case herds, and 12 per cent (27/222) in the control herds. Specific gross pathological findings were associated with a positive pmws diagnosis; pigs with heavy, rubber-like lungs, atonic intestines, and enlarged bronchial and inguinal lymph nodes, had a 0.7 probability of a positive pmws diagnosis by laboratory examinations. However, for illthriven pigs, this probability of having pmws was equal in the case herds and the control herds.

Distinction between porcine circovirus type 2 enteritis and porcine proliferative enteropathy caused by Lawsonia intracellularis.

The presence of porcine circovirus type 2 (PCV2) was studied immunohistochemically in formalin-fixed, paraffin wax-embedded samples of intestinal tissue from 80 pigs with a clinical history suggestive of Lawsonia intracellularis-associated diarrhoea. Histopathologically, enteritis of varying intensity was diagnosed in 64 of the pigs. Of these 64 animals, 34 (18%) were infected with both PCV2 and L. intracellularis. Of the remaining 30 cases of enteritis, 23 (77%) were attributed to PCV2 infection alone. The PCV2-associated enteritis cases showed necrotizing ileitis and colitis, indistinguishable macroscopically from proliferative enteritis (PE) due to L. intracellularis. Histopathologically, L. intracellularis-positive intestines showed adenomatous proliferation of crypt enterocytes, whereas PCV2 enteritis was characterized by histiocytosis of varying intensity, with PCV2-positive cells in the submucosa, lamina propria and crypt epithelium, as well as in the lymphoid tissue of the ileum and colon. Multinucleated giant cells, however, were seen in both infections. PCV2 was about three times more likely to be detected in L. intracellularis-negative than in L. intracellularis-positive samples (P<0.001). There was no association between PCV2 and other intestinal bacterial pathogens. The study demonstrated that PCV2 enteritis should be borne in mind in the differential diagnosis of L. intracellularis infection in pigs aged 2-4 months with a clinical history of diarrhoea.

Pathogenicity of selected Toxoplasma gondii isolates in young pigs.

The pathogenicity in 7-week-old pigs to five different Toxoplasma gondii strains of various host species origin was compared after i.v. inoculation of 10(4) tachyzoites. Additionally, one group of pigs was inoculated i.v. with 10(6) tachyzoites of the reference strain, SSI 119. In response to the infection a significant effect of T. gondii tachyzoite inoculation dose as well as differences among strains could be observed in several parameters. The 10(6)-dose inoculated pigs showed variable degrees of clinical illness and recurrent episodes of fever 4-17 days p.i., while pigs of four of the 10(4) tachyzoite inoculated groups experienced a short-lived rise in body temperature from day 6-8 p.i. without any apparent illness or inappetence. Control pigs and pigs infected with the least pathogenic strain had normal body temperature throughout the experiment. In all inoculated pigs, T. gondii-specific IgM and IgG antibodies appeared from day 8-10 and 10-17 p.i., respectively. Serum levels of alkaline phosphatase and the acute phase protein haptoglobin were decreased or increased, respectively, in response to the infection. Differential leukocyte count on peripheral blood revealed a significant lymphocytopenia on day 6 p.i. equal to both CD4+ and CD8+ T-cells, but shifting towards a reduced ratio of CD4+/CD8+ T-cells from day 8-14 p.i. In the 10(6)-dose inoculated pigs a considerable increase in zymosan induced and spontaneous oxidative burst capacity of peripheral blood leukocytes was observed from 6 days p.i. compared with control pigs. Oxidative burst capacity was not examined for other pigs. In conclusion, several useful parameters to identify differences in T. gondii pathogenicity other than mortality were identified. Furthermore, even at low doses, significant differences between recently collected Danish T. gondii field isolates were demonstrated after i.v. inoculation in young pigs.

Experimental corticosteroid induction of Pneumocystis carinii pneumonia in piglets.

Animal models of Pneumocystis carinii (Pc) pneumonia (PCP) play a central role in research on the Pc microorganism itself and the disease, especially the pathogenesis and the host defence. The classic rat model with corticosteroid-induced reactivation of a latent infection has been most widely used. In our search for alternative non-rodent models, six 31/2-week-old piglets were injected intramuscularly with methylprednisolone acetate, at 18 mg/kg body weight, once a week for 6 weeks. Six littermate piglets constituted the control group. The principals showed a markedly lower growth rate than the controls. Furthermore, they developed "moon face" and "pot belly", snoring sounds while eating, and pronounced respiratory distress during handling. Significant changes in haematological parameters, including lymphopenia, were observed in the principal group. The Pc antibody titres of the controls increased to high levels, whereas the principals were all low-titred or seronegative for Pc at the last blood sampling. At necropsy, the mean body weight of the principals was about half that of the controls. In addition, they had an extreme reduction of the thymus together with dark red consolidations of the frontal lung lobes and/or atelectatic looking diaphragmatic lobes. Histopathologically, there was a focal interstitial pneumonia. Alveolar walls and interstitia had mononuclear cell infiltrations and the alveolar lumina were occluded by foamy acidophilic honeycomb material with a varying number of Pc cysts. The reduced body weight, the thymus involution, and the lymphopenia, together with the reduced levels of specific Pc antibodies and the histomorphology of the PCP, were consistent parameters of the principal group and comparable to the findings of the classic rat model. Thus, the present study is the first to describe that prolonged administration of high doses of methylprednisolone acetate can induce PCP in piglets.

Experimental porcine neosporosis.

Six gilts were inoculated intramuscularly with 2.5x10(6) tachyzoites of Neospora caninum on three different days of gestation to study the pathogenic effect of Neospora infection in pigs, including possible transplacental transmission. The gilts were euthanized 59, 30, and 9/10 days postinoculation (p.i.), corresponding to days 107, 102/106 and 110/111 of pregnancy. With the exception of one animal (euthanized day 9 p.i.) all gilts seroconverted as measured by the indirect, fluorescent antibody test (IFAT). Neosporosis with multifocal intralobular necrotizing hepatitis was seen in the two gilts inoculated 9/10 days before euthanasia. The uterus of one gilt inoculated 59 days before euthanasia revealed granulomatous and focal necrotizing endometritis with a corresponding multifocal necrosis of the trophoblasts of two fetuses. Transplacental neosporosis was indicated in the two fetuses by strongly elevated Neospora IFAT titres in pleural fluid and by the presence of multifocal necrotizing encephalitis and hepatitis together with non-suppurative myocarditis, pneumonitis, nephritis and hepatitis. Furthermore, N. caninum was re-isolated in cell culture from one of these fetuses. A third fetus from the same gilt revealed only disseminated, pinpoint necroses in the liver. Immunohistochemically, N. caninum tachyzoites were detected in association with histopathological changes in the liver and the endometrium of the gilts, and in the brain, liver, and allantochorion of the three fetuses.

Identification of porcine Pneumocystis carinii as a genetically distinct organism by DNA amplification.

DNA was amplified from lung samples from three piglets infected with Pneumocystis carinii, using oligonucleotide primers designed to the P. carinii mitochondrial large subunit ribosomal RNA gene. The nucleotide sequence of the amplification product was determined and indicated lack of sequence variation among these pig-derived P. carinii samples at this locus. The data showed that porcine P. carinii was genetically distinct from P. carinii isolated from other mammalian host species.

Animal models of pneumocystosis.

As in vitro culture systems allowing to isolate Pneumocystis samples from patients or other mammal hosts are still not available, animal models have critical importance in Pneumocystis research. The parasite was reported in numerous mammals but P. carinii pneumonia (PCP) experimental models were essentially developed by using rats, mice, rabbits and ferrets. The rat treated with corticosteroids for 9-12 weeks is a useful PCP model. Like laboratory rats, conventional mice develop PCP after prolonged corticosteroid administration. The ferret (Mustela putorius furo) also develop PCP under corticosteroid regime. Whilst bronchoalveolar lavage (BAL) is really difficult to perform on live laboratory rodents, serial BAL sampling can be performed on live ferrets. Rabbits currently develop spontaneous PCP at weaning without corticosteroid administration. For this reason this model has been used for studying the host immune response as well as Pneumocystis-surfactant interactions. Pigs and horses also develop spontaneous PCP. Treated with corticosteroids, piglets develop extensive PCP and could be used as a non-rodent model. Pneumocystis was detected in many non-human primates. Primates could represent a source of parasites taxonomically related to P. carinii sp. f. hominis. Moreover, primates might be used as experimental hosts to human Pneumocystis. A marked variability of parasite levels among corticosteroid-treated animals and the fact that the origin of the parasite strain remains unknown, are important drawbacks of the corticosteroid-treated models. For these reasons, inoculated animal models of PCP were developed. The intratracheal inoculation of lung homogenates containing viable parasites in corticosteroid-treated non-latently infected rats resulted in extensive, reproducible Pneumocystis infections. Extensive PCP can be obtained within 5-7 weeks, whilst 9-12 weeks are needed in the classical model. The severe combined immunodeficiency (SCID) mouse inoculated by nasal route and the athymic nude rats intratracheally inoculated were used to test the infectivity of Pneumocystis samples coming from cultures or from different hosts. They were also used to test the anti-Pneumocystis activity of antimicrobial molecules.

Isolation of porcine reproductive and respiratory syndrome (PRRS) virus in a Danish swine herd and experimental infection of pregnant gilts with the virus.

The first case of porcine reproductive and respiratory syndrome (PRRS) in Denmark was diagnosed in March 1992 by the detection of specific antibodies against PRRS virus in serum samples originating from sows in a herd located on the island of Als. Subsequently, PRRS virus was isolated from a 200-sow farrow-to-finish herd with clinical signs consistent with PRRS. The virus was isolated by inoculation of pleural fluid from a stillborn piglet onto porcine pulmonary alveolar macrophages. The isolate was identified as PRRS virus by staining with a specific antiserum. By electron microscopy, the virus particle was found to be spherical and enveloped, measuring 45-55 nm in diameter and containing a 30-35 nm nucleocapsid. Only minor antigenic differences were found between the Danish and a Dutch isolate. Following intranasal inoculation of 3 pregnant gilts with the Danish isolate transplacental infection was demonstrated by the re-isolation of PRRS virus from approximately 45% of the piglets from the experimentally infected gilts. However, the experimental infection produced no significant reproductive disorders or other clinical signs. At autopsy, histopathological examination revealed slight interstitial pneumonia in a few piglets.

Experimental inoculation of swine at various stages of gestation with a Danish isolate of porcine reproductive and respiratory syndrome virus (PRRSV).

Following intranasal inoculation of three groups of pregnant swine (in total 11 dams) with a Danish isolate of porcine reproductive and respiratory syndrome virus (PRRSV) on or about day 85, 70 and 45 of gestation, respectively, reproductive disturbances were observed in the first two groups. Transplacental transmission of PRRSV occurred in four out of five litters from dams inoculated around day 85 of gestation and in two out of three litters from dams inoculated on day 72 of gestation. In the third group, inoculated around day 45 of gestation, transplacental infection could not be demonstrated. Thirty-two (56%) piglets from dams inoculated on day 85 of gestation and 14 (33%) piglets from dams inoculated on day 72 of gestation, were transplacentally infected. Sixteen (28%) and six (14%) piglets, respectively, in these groups became infected in the perinatal period. Thirty-two (56%) piglets from dams inoculated on day 85 of gestation were stillborn or died within a 6-8 weeks observation period, 29 being stillborn or dying within the first two weeks of observation. Thirteen (30%) piglets from dams inoculated on day 72 of gestation died within the two weeks observation period. The duration of the viraemic phase varied considerably, from one day to four weeks, for both dams and their offspring. Most frequently, PRRSV was isolated from lung and/or tonsil tissues from dead and euthanized piglets younger than 14 days of age. Histopathological investigations of piglets typically revealed focal nonsuppurative inflammatory conditions, especially in the lung and heart. In conclusion, the present results support the hypothesis, that PRRSV infection of dams late in pregnancy has the greatest likelihood of transplacental infection of fetuses.

Experimental inoculation of late term pregnant sows with a field isolate of porcine reproductive and respiratory syndrome vaccine-derived virus.

The use of a live attenuated porcine reproductive and respiratory syndrome virus (PRRSV) vaccine in piglets has been associated with reproductive disorders in non-vaccinated sows. Vaccine-derived virus (VDV) has been isolated from foetuses, stillborn pigs, and dead piglets, indicating that the live vaccine spread from vaccinated piglets to non-vaccinated sows, and that the virus might be implicated in the severe reproductive problems observed. In the present study, one such VDV isolate was used to experimentally infect pregnant sows in the last trimester. The chosen isolate, which had more than 99.6% identity to the attenuated vaccine virus, originated from the lungs of a stillborn pig from a swine herd with a sudden high level of stillborn pigs and increased piglet mortality in the nursing period. Intranasal inoculation of sows with the virus isolate resulted in congenital infection, foetal death, and preweaning pig mortality. As such, the present study showed that vaccine-derived PRRSV can cause disease in swine consistent with PRRS.

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.

Detection of Streptococcus suis by in situ hybridization, indirect immunofluorescence, and peroxidase-antiperoxidase assays in formalin-fixed, paraffin-embedded tissue sections from pigs.

Streptococcus suis is an important pathogen in pigs and is considered a zoonotic agent. To aid diagnosis of infection caused by S. suis, a species-specific probe targeting 16S ribosomal RNA was designed and used for fluorescent in situ hybridization. Two additional immunohistochemical detection methods, an indirect immunofluorescence assay and a peroxidase-antiperoxidase method, using polyclonal antibodies also were developed. The specificity of the oligonucleotide probe was examined by whole-cell and dot-blot hybridization against reference strains of the 35 serotypes of S. suis and other closely related streptococci and other bacteria commonly isolated from pigs. The probe was specific for S. suis serotypes 1-31. The specificity of the polyclonal antibodies, which has previously been evaluated for use in diagnostic bacteriology for typing of serotype 2, was further evaluated in experimentally infected murine tissue with pure culture of different serotypes of S. suis, related streptococci, and other bacteria commonly found in pigs. The polyclonal antibodies against S. suis serotype 2 cross-reacted with serotypes 1 and 1/2 in these assays. The in situ hybridization and the immunohistochemical methods were used for detection of S. suis in formalin-fixed, paraffin-embedded tissue sections of brain, endocardium, and lung from pigs infected with S. suis. The methods developed were able to detect single cells of S. suis in situ in the respective samples, whereas no signal was observed from control tissue sections that contained organisms other than S. suis. These techniques are suitable for determining the in vivo localization of S. suis for research and diagnostic purposes.

Toxoplasmosis in a colony of New World monkeys.

In a colony of New World monkeys five tamarins (Saguinus oedipus, Saguinus labiatus and Leontopithecus rosal. rosal.), three marmosets (Callithrix jacchus and Callithrix pygmaea) and one saki (Pithecia pithecia) died suddenly. The colony comprised 16 marmosets, 10 tamarins and three sakis. The main pathological findings were necrotic lesions in the lung, the intestine, and the liver. Histopathologically T. gondii parasites were observed in organs from the tamarins and the marmosets but not in the saki. Some considerations on epidemiology are presented. Preventive measures were directed against the bottom layer of the cages, on cockroach extermination, and on freezing of raw meat.

Clinical observations, pathology, bioassay in mice and serological response at slaughter in pigs experimentally infected with Toxoplasma gondii.

Experimental infections of a total of 47 pigs with tachyzoites of the Toxoplasma gondii RH-strain, tissue cysts of the SSI-119 and R92 strains as well as oocysts of the SSI-119 strain were performed to determine the sensitivity of an indirect IgG-ELISA, using tachyzoite lysate of the RH-strain as antigen. The infections led to a dose dependent moderate clinical affection (inappetence, fever and poor general condition). Pigs infected with 10000 oocysts or with 1/2 mouse brain containing tissue cysts of the SSI-119 strain showed a significant decrease in weight gain compared to uninoculated pigs during the first 2 weeks p.i., followed, however, by compensatory growth during the next 6 weeks. At slaughter 3 to 4 months after inoculation 39/41 (95.1%) of pigs positive by bioassay in mice were seropositive in ELISA. Tissue cysts were not demonstrable by immunohistochemistry. ELISA OD-values obtained by analysis of meat juice from heart muscle and tongue (diluted 1:40) correlated strongly with OD-values by analysis of serum (diluted 1:400) (r heart juice = 0.942; r tongue juice = 0.915). Thus, meat juice samples were shown to provide a suitable alternative to serum for serological detection of Toxoplasma infection in pigs.

Pathogenicity of Cryptosporidium parvum--evaluation of an animal infection model.

With the intention of developing a standardised method for assessment of pathogenicity of Cryptosporidium parvum, the CPB-0 isolate was studied by propagation in 1-day-old calves followed by inoculation into specific pathogen free (SPF) piglets. The experiment was repeated. Diarrhoea and shedding of oocysts were seen in all animals infected with the CPB-0 isolate. Clinical signs included depression, inappetence, vomiting (exclusively in the piglets), and death. Histological examination at 17 and 19 days post-infection revealed parasitic stages and microscopic changes primarily restricted to colon and rectum. The unintended presence of rotavirus in some of the experimental animals revealed an additive or synergistic effect between rotavirus and C. parvum as indicated by prolonged diarrhoea, increased oocyst shedding, decreased weight gain and elevated levels of serum haptoglobin and serum amyloid A (SAA) in piglets infected simultaneously with both pathogens. The difference in daily weight gain between infected and control animals was significant only for piglets co-infected with rotavirus. The acute phase response of haptoglobin and SAA was characterised by a large individual variation. In piglets, co-infected with rotavirus, the levels of serum haptoglobin were 3.5 and 4.6 times higher in the infected versus the controls 6 and 9dpi, respectively (mean values: 2411microg/ml+/-S.D. 2023 and 1840 microg/ml+/-S.D. 1697). In the controls infected with rotavirus, peak haptoglobin concentration was seen 3dpi (mean: 1022 microg/ml+/-S.D. 425). Elevated levels of SAA were seen in 1 of 6 piglets infected with C. parvum, and in 5 of 6 piglets co-infected with rotavirus. Tumour necrosis factor alpha (TNFalpha) was undetectable in all serum samples from piglets. The obvious advantages of the SPF pig model are the naturally acquired intestinal microflora, the development of distinct clinical signs similar to cryptosporidiosis in humans and calves, the size of the animals, and the accessibility of individuals born within a short time span. This makes the model ideal for dose-response studies, evaluation of therapeutic agents as well as for assessment of differences in the clinical response to isolates of diverse genetic background. In conclusion, it was shown that the CPB-0 isolate was pathogenic to calves and piglets at a dose of 2.5 x 10(5) oocysts, and that the clinical signs could be replicated during separate experiments. Moreover, diarrhoea, oocyst shedding, body weight changes, histological alterations, and the acute phase response of haptoglobin and SAA were identified as useful parameters for discrimination of isolate-specific differences of pathogenicity.

Cryptosporidium andersoni from a Danish cattle herd: identification and preliminary characterisation.

In November 1997, Cryptosporidium andersoni, for the first time, was isolated from a Danish heifer. The isolate was characterised morphologically, molecularly, and furthermore inoculated into mice and one calf. Data on the distribution of cryptosporidia in the herd of origin were obtained at two separate visits in December 1997 and April 1998. C. andersoni was detected in 27 (19.0%) of 142 cattle examined at the first visit, whereas C. parvum was found in six (4.2%). At the following visit 42 (28.0%) of 150 cattle excreted C. andersoni, while 25 (16.7%) were positive for C. parvum. Oocysts of the Danish C. andersoni isolate were ovoid, 7.3(6.5-8.0) x 5.7(5.0-7.0) microm(2) (n=25), with smooth, colourless, single layer oocyst wall and distinct oocyst residuum. The length to width ratio was 1.27 (1.14-1.40, n=25). The identification was verified by sequencing of a 246bp fragment of the rDNA, which was identical to Cryptosporidium muris, the calf genotype (AF093496). The Danish C. andersoni isolate was not transmissible to mice, whereas oocysts were detected in the faeces of one experimentally infected calf from 25 days post-infection (DPI) and shed intermittently at low numbers until 165 DPI, the day of euthanasia. No macroscopic or microscopic changes that could be attributed to infection with C. andersoni were seen in the gastro-intestinal tract of the experimentally infected calf following necropsy and histological examination. This is to our knowledge the first report of C. andersoni in Scandinavia.

Transplacental transmission of Toxoplasma gondii in minipigs infected with strains of different virulence.

Infections with the zoonotic protozoan Toxoplasma gondii during pregnancy can result in severe fetal infections. To investigate the use of pigs as animal models for congenital toxoplasmosis, tachyzoites of 5 T. gondii strains, with low to intermediate virulence in mice, were intravenously inoculated into pregnant minipig gilts. Two strains caused abortions of uninfected fetuses following severe disease of the mothers. One strain caused no disease in the gilts but slightly elevated anti-T. gondii antibodies in 2 of 9 fetuses. One strain produced clinical disease with 4 mummified fetuses and 2 full-term, congenitally infected piglets in 1 gilt and no clinical disease but elevated specific fetal antibodies in both piglets of the other gilt. Infection with the fifth strain (SVS-O14), which was considered apathogenic to both pigs and mice based on the clinical course of this and previous experiments, resulted in significant numbers of congenitally infected piglets, as indicated by production of anti-T. gondii antibodies in all 12 fetuses; the parasite was identified in 3 of these fetuses. This pattern of infection indicates that pigs infected with SVS-O14 (or a similar strain) are relevant animal models for studies of transplacental transmission and pathogenesis of congenital toxoplasmosis.

Staphylococcus hyicus virulence in relation to exudative epidermitis in pigs.

Staphylococcus hyicus strains with different phage types, plasmid profiles, and antibiotic resistance patterns were isolated from piglets with exudative epidermitis. The strains could be divided into virulent strains, producing exudative epidermitis, and avirulent strains, producing no dermal changes when injected in experimental piglets. The results showed that both virulent and avirulent strains were present simultaneously on diseased piglets. This constitutes a diagnostic problem. Concentrated culture supernatants from nine virulent strains injected in the skin of healthy piglets produced a crusting reaction in all piglets. Acanthosis was observed in the histopathological examination of the crustaceous skin. Concentrated culture supernatants from nine avirulent strains produced no macroscopic or microscopic skin changes. Protein profiles from all virulent strains and seven out of nine avirulent strains showed a high degree of protein band homology. An approximately 30 kDa protein present in all concentrated culture supernatants capable of producing skin changes, could not be detected in samples that did not produce skin changes. No other protein showed a similar association. It is concluded that crusting reaction of piglet skin is a suitable indicator of virulence in S. hyicus in relation to exudative epidermitis, and that virulent strains produce a 30 kDa protein, absent in concentrated culture supernatants from avirulent strains. This 30 kDa protein might be an exfoliative toxin.

Experimental airborne transmission of porcine postweaning multisystemic wasting syndrome.

The objective of these studies was to investigate if porcine postweaning multisystemic wasting syndrome (PMWS) could be induced in healthy pigs following contact with air from pigs with clinical signs of PMWS. The pigs were housed in different units. Either 31 (study I) or 25 (study II) pigs with clinical symptoms of PMWS from a PMWS-affected herd and 25 healthy pigs from a PMWS-free, but PCV2-positive, herd were housed in unit A. Fifty pigs from a PMWS-free herd were housed in unit B, which were connected by pipes to unit A. In unit C, 30 pigs from a PMWS-free herd were housed as controls. In study II, the pigs in units A and B from the PMWS-free herd developed clinical signs of PMWS 2-3 weeks after arrival. PMWS was confirmed at necropsy and the diseased pigs had increased PCV2 load and increased antibody titers against PCV2 in serum that coincided with the development of clinical signs typical of PMWS. Sequence analysis revealed that the PCV2 isolate belonged to genotype 2b. In conclusion, the present study showed that PMWS can be induced in pigs from a PMWS-free herd by airborne contact with pigs from a PMWS-affected herd.