Lesions In Pigs Research Articles

Intestinal lesions in pigs affected with postweaning multisystemic wasting syndrome

Samples of mesenteric lymph nodes and intestines from 79 unthrifty 3- to 5-month-old postweaning pigs, confirmed as naturally affected with postweaning multisystemic wasting syndrome (PMWS), were studied. Pigs originated from 12 farms in southern Brazil and were selected on the basis of clinical signs and/or gross lesions suggestive of enteric disorder. Lymphohistiocytic infiltrates of varying intensity were associated with anti-porcine circovirus type 2 (anti-PCV2) immunostaining (IS) in samples of intestines and mesenteric lymph nodes from all pigs. Although most findings were similar to those described in PCV2-associated enteritis, anti-PCV2 IS in association with depletion of the goblet cell mucin stores (24 pigs), diffuse ileal villous atrophy and fusion (18 pigs), and dilatation of the lymphatic vessels (11 pigs) combined or not with lymphangitis were also observed. PCV2 antigen was immunohistochemically demonstrated in the cytoplasm and nuclei from intralesional epithelial cells, histiocytes, and endothelial-like cells in intestinal tissues. Together these findings imply an association with PCV2. The presence of co-infections by Lawsonia intracellularis, Brachyspira spp., Mycobacterium spp., Salmonella spp., rotavirus, parvovirus, coronavirus and enteric calicivirus with PCV2 in the intestinal lesions was investigated.

Proliferative and necrotising pneumonia and severe vascular lesions in pigs naturally infected with porcine circovirus type 2

Severe disease induced by porcine circovirus type 2 (PCV2) was observed in three pigs originating from a large herd affected by respiratory and digestive signs as well as wasting. Proliferative and necrotising pneumonia (PNP) was diagnosed in two animals, while severe acute interstitial pneumonia characterised by the presence of abundant hyaline membrane in the alveoli and fibrin in the bronchioles was found in one pig. In all cases, large amounts of PCV2 antigen were found in each tissue sample collected from the lungs and mediastinal lymph nodes. Neither porcine reproductive and respiratory syndrome virus (PRRSV) nor swine influenza virus (SIV) was detected, and no bacteria could be cultured in any of the cases. Vascular lesions, e.g. degeneration of endothelial cells, perivascular and intramural oedema, fibrinoid necrosis, vasculitis, perivasculitis, and vascular thrombi were observed in all cases, associated with the presence of PCV2 antigen. The viral antigen was present in the intravascular mononuclear cells, endothelial cells, myocytes and infiltrating inflammatory cells in lymph and blood vessels. In one case, obliterating thrombi in the lymph and blood vessels were directly connected to areas of tissue necrosis and were associated with abundant PCV2 antigen. The results further suggest the causative role of PCV2 infection in PNP, and the importance of the vascular system in the pathogenesis of PCV2-associated diseases of swine.

Tail and ear biting lesions in pigs: an epidemiological study

AbstractTail and ear biting lesions have a negative effect both on the animal welfare status of pigs (Sus scrofus) and the economical revenue of the pig farm. Tail biting behaviour is an unpredictable, abnormal behaviour that is thought to have a multifactorial origin. On-farm factors influencing tail biting have been described, but the real triggers are poorly understood. Much of the research into tail biting has been done on a small scale within a well-controlled environment and small sample sizes. This well-controlled environment is not always representative of the contemporary commercial conditions. Therefore, an observational epidemiological approach at farm level was adopted to gain a better insight into the factors influencing the occurrence of tail and ear biting lesions. Tail and ear biting lesions were observed at pen level three times a year on sixty farms across Belgium. A questionnaire was conducted to build a multifactorial model indicating different risk factors concerning the lesions scored. The temperature and the number of feeding places per animal in the nursery, the percentage of floor space covered with slats in the farrowing unit, the feed type in the growing unit and the overall hygiene policy were the most important indicators for the appearance of tail and ear biting lesions during fattening. The leave-one-out cross validation of the model demonstrated an intraclass correlation coefficient of 0.55 between the predicted model outcomes and the observed data. This epidemiological study provides important potential risk factors in relation to the incidence of tail and ear biting lesions. However, experimental and/or longitudinal studies have to confirm that the correlations found in this work are causal factors.

The involvement of Fas/FasL interaction in porcine circovirus type 2 and porcine reproductive and respiratory syndrome virus co-inoculation-associated lymphocyte apoptosis in vitro

Lymphoid depletion of various lymphoid organs is one of the major lesions in pigs suffering from postweaning multisystemic wasting syndrome (PMWS). The co-existence of porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) in PMWS-affected pigs along with the more severe and wider range of lymphocyte depletion of lymphoid organs in PCV2 and PRRSV dually-inoculated pigs imply that PCV2 and PRRSV may interact in the pathogenesis of PMWS. The mechanism for the development of lymphoid depletion in PMWS-affected pigs remains controversial. The objective of the present study was to evaluate and compare the effects of inoculation of both viruses, singularly or in combination, on swine splenic macrophages (SMs) and co-cultured splenic (SLs) and peripheral blood (PBLs) lymphocytes in vitro. A significant reduction in the survival rate and increase in the apoptotic rate of the co-cultured SLs and PBLs and concurrent increase in the expression levels of Fas ligand (FasL) in SMs and Fas in co-cultured SLs and PBLs were demonstrated in PRRSV alone- and PCV2 and PRRSV dually-inoculated groups with the latter more prominent. The increased FasL was proven capable of inducing Fas/FasL-mediated apoptosis in co-cultured FasL-sensitive Jurkat T cells. The de novo expression and production of FasL in PCV2 and PRRSV dually-inoculated SMs and concurrently increased surface expression of Fas in co-cultured lymphocytes may contribute, at least partially, to lymphoid depletion in PMWS-affected pigs with PCV2 and PRRSV dual infection.

Brain Lesions in Pigs Affected with Postweaning Multisystemic Wasting Syndrome

Anti-porcine circovirus type 2 (anti-PCV2) immunostaining was associated with cerebellar lymphohistiocytic vasculitis combined with hemorrhages (50 pigs) or with lymphohistiocytic meningitis (23 pigs) in pigs naturally affected with postweaning multisystemic wasting syndrome (PMWS). The animals originated from 12 farms in Rio Grande do Sul, Brazil. In total, 456 unthrifty 3- to 5-month-old postweaning pigs confirmed as PMWS cases were necropsied. Although most findings mimicked those extensively reported in PMWS-affected pigs, there were distinctive brain lesions that included multiple hemorrhages in the cerebellar leptomeninges associated with lymphohistiocytic vasculitis and fibrinoid degeneration in vessels of the cerebellum and periventricular areas (69 pigs). These vascular lesions were also seen in conjunction with lymphohistiocytic meningitis (38 additional pigs). PCV2 antigen was immunohistochemically demonstrated in the cytoplasm and nuclei from intralesional perivascular macrophages and endothelial-like cells in brain tissues. Together these findings suggest that these lesions were caused by PCV2.

Cannulation and Cardiopulmonary Bypass Produce Selective Brain Lesions in Pigs

Whether cardiopulmonary bypass alone or together with manipulation of the aorta produces neurologic complications remains controversial. Using a pig model, the immediate effects of aortic cannulation and cardiopulmonary bypass on neural injury in different brain regions were investigated in 3 experimental groups: non-operated controls; operated controls with aortic cannulation without cardiopulmonary bypass; and operated animals undergoing cardiopulmonary bypass. Immunohistochemistry using a monoclonal antibody against calretinin was used to show possible ischemic damage in the hippocampal formation which is one of the most vulnerable regions to ischemia. Both cannulation of the aorta alone and cardiopulmonary bypass resulted in numerous argyrophilic neurons in discrete regions of the prefrontal and cerebellar cortex. Decreased calretinin immunoreaction and a reduced number of calretinin-positive neurons were observed following aortic cannulation or cardiopulmonary bypass compared to the non-operated controls. This suggests that both cannulation of the aorta alone and cardiopulmonary bypass affect a selected population of neurons. Therefore, off-pump, aorta no-touch technique may prevent neurologic complications.

Prevalence of Noroviruses and Sapoviruses in Swine of Various Ages Determined by Reverse Transcription-PCR and Microwell Hybridization Assays

Noroviruses (NoVs) and sapoviruses (SaVs) are emerging enteric pathogens that cause diarrhea in humans and animals. Porcine genogroup II (GII) NoVs replicate in pigs, but their pathogenesis is undefined. The porcine SaV/GIII/Cowden/80/US strain causes diarrhea and intestinal lesions in pigs. Recently, genetically diverse porcine NoVs (genotypes 11, 18, and 19 within GII) and SaVs comprising at least two genogroups (GIII and GVI?/JJ681-like) and two unclassified strains (G?/QW19 and G?/LL26) were identified; however, their prevalence has not been reported. To investigate the prevalence of porcine NoVs and SaVs, 621 fecal samples were collected from swine of various ages from seven swine farms and one slaughterhouse in three states in the United States. Fecal samples were tested by reverse transcription-PCR and microwell hybridization assays with porcine NoV- and SaV-specific primers and probes, respectively. Porcine GII NoVs were detected exclusively from finisher pigs with an overall prevalence of 20%. Porcine GIII SaVs were detected in 62% of pigs, with the highest prevalence in postweaning pigs and lowest in nursing pigs. Porcine GVI?/JJ681-like SaVs and the G?/QW19-like SaVs were detected infrequently in pigs. The G?/LL26-like SaVs were detected mainly in younger pigs. Because some porcine NoVs and SaVs are genetically or antigenically related to human strains and recombinants within NoVs or SaVs occur for human and pig strains, the high prevalence and subclinical infection rate of these viruses in pigs raise questions of whether pigs may be reservoirs for human strains or for the emergence of new human and porcine recombinants.

Brain Lesions in Pigs Dually Infected with Porcine Reproductive and Respiratory Syndrome Virus and Pseudorabies Virus

Four pigs were inoculated with an aerosol containing porcine reproductive and respiratory syndrome virus (PRRSV) followed 14 days later by inoculation with pseudorabies virus (PRV). The four dually infected pigs showed severe clinical signs, and one died on day 6 after infection with PRV. As demonstrated previously, the clinical disease was much more severe than that produced by either virus alone. All four dually infected pigs developed severe non-suppurative encephalitis, two had tonsillitis, two had necrotizing bronchiolitis, and one had lymphadenitis. The distribution of lesions corresponded closely with the detection of intranuclear inclusion bodies and PRV antigen. High numbers of TUNEL-positive cells detected in the thymus were associated with thymic atrophy.

Cardiovascular Lesions in Pigs Naturally or Experimentally Infected with Porcine Circovirus Type 2

Abundant intracytoplasmic porcine circovirus type 2 (PCV2) was associated with myocardiocyte swelling or necrosis, or myocardial fibrosis (or both) in three naturally infected pigs aged 4-7 weeks from three different farms. One 6 week old pig from a fourth farm had severe diffuse segmental to circumferential lymphohistiocytic and plasmacytic periarteritis and endarteritis in several organs, PCV2 antigen was demonstrated in endothelial cells, and inflammatory cells in the arterial walls. In three pigs experimentally infected with PCV2, viral antigen was also associated with obliterated blood vessels in areas of granulomatous and necrotizing lymphadenitis. Together these findings suggest that the cardiovascular system in general and endothelial cells in particular play an important role in the pathogenesis of PCV2-associated diseases.

Evidence of a Major Gene From Bayesian Segregation Analyses of Liability to Osteochondral Diseases in Pigs

Bayesian segregation analyses were used to investigate the mode of inheritance of osteochondral lesions (osteochondrosis, OC) in pigs. Data consisted of 1163 animals with OC and their pedigrees included 2891 animals. Mixed-inheritance threshold models (MITM) and several variants of MITM, in conjunction with Markov chain Monte Carlo methods, were developed for the analysis of these (categorical) data. Results showed major genes with significant and substantially higher variances (range 1.384-37.81), compared to the polygenic variance (sigmau2). Consequently, heritabilities for a mixed inheritance (range 0.65-0.90) were much higher than the heritabilities from the polygenes. Disease allele frequencies range was 0.38-0.88. Additional analyses estimating the transmission probabilities of the major gene showed clear evidence for Mendelian segregation of a major gene affecting osteochondrosis. The variants, MITM with informative prior on sigmau2, showed significant improvement in marginal distributions and accuracy of parameters. MITM with a "reduced polygenic model" for parameterization of polygenic effects avoided convergence problems and poor mixing encountered in an "individual polygenic model." In all cases, "shrinkage estimators" for fixed effects avoided unidentifiability for these parameters. The mixed-inheritance linear model (MILM) was also applied to all OC lesions and compared with the MITM. This is the first study to report evidence of major genes for osteochondral lesions in pigs; these results may also form a basis for underpinning the genetic inheritance of this disease in other animals as well as in humans.

Juvenile kyphosis in pigs

The development of kyphotic lesions in pigs with different weights from herds with a high frequency of the lesion was analysed pathologically, radiologically, and for alkaline phosphatase, calcium, magnesium, and phosphate in blood samples. The development of kyphosis was caused by the formation of ventral hemivertebrae due to the absence of ventral vertebral epiphyseal centres of ossification. Within the ventral parts of affected vertebral epiphyses, the retained chondroid tissue was dysplastic and the contents of cartilage canals with vessels often clotted with fibrin were reduced. As lesions such as fractures and inflammation that may be a secondary cause of kyphosis in pigs were absent and all blood parameters were within normal range, secondary causes of the condition, including metabolic disturbances, were excluded. It can be seen that the present type of porcine kyphosis does not develop until later in life as the ossification centres within the epiphyses of vertebrae have a retarded appearance. As the present porcine type of kyphosis pathomorphologically is comparable with Scheuermann's kyphosis in man, it constitutes a spontaneous model for this common cause of structural kyphosis of the thoracic or thoracolumbar spine.

Mycobacterial infections in cattle and pigs caused by Mycobacterium aviumcomplex members and atypical mycobacteria in theCzech Republicduring 2000-2004

Bovine tuberculosis was last detected in cattle and pigs in the CzechRepublicin 1995. Since March, 31, 2004(Commission Decision No. 2004/320/EC) the Czech Republichas been included amongst states free from bovine tuberculosis within the European Union. The purpose of the present study was to evaluate results of intravital and post-mortem diagnosis of mycobacterial infections in slaughtered cattle and pigs from 2000 to 2004. When bovine tuberculosis in cattle was investigated, a tuberculin skin test with bovine tuberculin was performed every year and a skin test with avian tuberculin was simultaneously conducted in the animals with a positive response. A total of 2 419 889 animals were examined with a positive response being found in 123 (0.005%) of them. After slaughter, bovine tuberculosis was not detected in any of these animals by gross and/or laboratory examinations. With avian tuberculin, 40 349 animals were tested and positive responses were detected in 43 (0.1%) of them; the incidence was similar in all the years monitored. Tuberculous lesions were detected in 209 (0.01%) of 1 967 211 slaughtered cattle. Mycobacteria were present in 40 (21.3%) of 188 animals examined by laboratory methods: 26 isolates of Mycobacterium avium subsp. avium (18 isolates of serotype 2 and 8 isolates not typeable), 11 isolates  of M. a. hominissuis (1 isolate of serotype 8 and 10 isolates not typeable), and 3 isolates of atypical mycobacteria. Tuberculous lesions were detected in 49 312 (0.22%) of 22 312 580 slaughtered pigs by veterinary-meat inspection. During the 5-year-period monitored, the incidence of tuberculous lesions decreased from 0.37% in 2000 to 0.10% in 2004. The following mycobacteria were isolated from 757 (33.5%) of 2 261 animals whose organs were examined by culture: 203 isolates of M. a. avium (180 isolates of serotype 2, 3 isolates of serotype 2/8, and 20 isolates not typeable), 442 isolates of M. a. hominissuis (1 isolate of serotype 1, 262 isolates of serotype 8, 35 isolates of serotype 9, 1 isolates of mixed serotypes 8/9, and 143 isolates not typeable), and atypical mycobacteria (n = 112). In both animal species, M. avium complex members prevailed: M. a. avium was the most prevalent subspecies in cattle, M. a. hominissuis in pigs. The main sources of M. a. avium and M. a. hominissuis are free living birds and contaminated external and stable environments (i.e. drinking water, feeds, and feed supplements), respectively. During the entire period monitored, miliary or generalized tuberculosis was not detected in any of the animals. The decreased incidence of tuberculous lesions in pigs was particularly a result of preventive measures adopted to control the occurrence of atypical mycobacteria.

Two Amino Acid Mutations in the Capsid Protein of Type 2 Porcine Circovirus (PCV2) Enhanced PCV2 Replication In Vitro and Attenuated the Virus In Vivo

Porcine circovirus type 2 (PCV2) is the primary causative agent of postweaning multisystemic wasting syndrome (PMWS) in pigs. To identify potential genetic determinants for virulence and replication, we serially passaged a PCV2 isolate 120 times in PK-15 cells. The viruses harvested at virus passages 1 (VP1) and 120 (VP120) were biologically, genetically, and experimentally characterized. The PCV2 VP120 virus replicated in PK-15 cells to a titer similar to that of the PK-15 cell line-derived nonpathogenic PCV1 but replicated more efficiently than PCV2 VP1 with a difference of about 1 log unit in the titers. The complete genomic sequences of viruses at passages 0, 30, 60, 90, and 120 were determined. After 120 passages, only two nucleotide mutations were identified in the entire genome, and both were located in the capsid gene: the mutations were located at nucleotide positions 328 (C328G) and 573 (A573C). The C328G mutation, in which a proline at position 110 of the capsid protein changed to an alanine (P110A), occurred at passage 30 and remained in the subsequent passages. The second mutation, A573C, resulting in a change from an arginine to a serine at position 191 (R191S), appeared at passage 120. To experimentally characterize the VP120 virus, 31 specific-pathogen-free pigs were randomly divided into three groups. Ten pigs in group 1 received phosphate-buffered saline as negative controls. Each pig in group 2 (11 pigs) was inoculated intramuscularly and intranasally with 10(4.9) 50% tissue culture infective doses (TCID(50)) of PCV2 VP120. Each pig in group 3 (10 pigs) was similarly inoculated with 10(4.9) TCID(50) of PCV2 VP1. Viremia was detected in 9 of 10 pigs in the PCV2 VP1 group with a mean duration of 3 weeks, but in only 4 of 11 pigs in the PCV2 VP120 group with a mean duration of 1.6 weeks. The PCV2 genomic copy numbers in serum in the PCV2 VP1 group were significantly higher than those in the PCV2 VP120 group (P < 0.0001). Gross and histopathologic lesions in pigs inoculated with PCV2 VP1 were more severe than those inoculated with PCV2 VP120 at both day 21 and 42 necropsies (P = 0.0032 and P = 0.0274, respectively). Taken together, the results from this study indicated that the P110A and R191S mutations in the capsid of PCV2 enhanced the growth ability of PCV2 in vitro and attenuated the virus in vivo. This finding has important implications for PCV2 vaccine development.

Encephalomalacic Lesions in Pigs Dually Infected with Porcine Reproductive and Respiratory Syndrome Virus and Pseudorabies Virus

Four pigs (group 1) were infected with an aerosol containing porcine reproductive and respiratory syndrome virus (PRRSV) followed 7 days later by pseudorabies virus (PRV). Three further pigs (group 2) received PRRSV alone, two (group 3) received PRV alone, and two (group 4) remained as uninfected controls. Despite the admittedly small numbers of animals, the experiment appeared to throw light on aspects of synergy. Thus, the group 1 pigs showed severe neurological signs characterized by ataxia and muscular tremors. Total cell numbers in the bronchoalveolar lavage fluid were increased in all PRRSV-infected pigs, and PRRSV antigen was detected in the alveolar macrophages. Total cell numbers in the cerebrospinal fluid of group 1 pigs were considerably greater than those demonstrated in group 3, but no PRV antigen was found. Pigs of groups 1 and 2 showed pulmonary lesions, characterized by interstitial pneumonia and PRRSV antigen immunolabelling. Non-suppurative encephalitis was found in five of the six pigs of groups 1 and 3. In particular, one group 1 animal had severe necrotizing encephalitis with intranuclear inclusion bodies and associated immunolabelling of PRV antigen. The other three group 1 pigs had prominent malacic lesions, with macrophages. These neuropathological findings strongly suggested that PRRSV infection in pigs enhances the severity of brain lesions caused PRV.

Tuberculous lesions in pigs in the Czech Republic in the years 1990-1999: occurrence, causal factors and economic losses

In the decade monitored a total of 45 873&amp;nbsp;318 pigs were slaughtered and examined according to veterinary hygiene standards. Apart from 1991, when results of tuberculous findings were not obtained, tuberculous lesions were found in 134 088 (0.32%) of the 41&amp;nbsp;458&amp;nbsp;565 pigs examined in the remaining nine years. During a detailed analysis of the pathological anatomical examination of 190&amp;nbsp;940 pigs slaughtered in one district, tuberculous lesions in lymph nodes were found in 4&amp;nbsp;107 (2.2%) pigs: mesenteric (65.3% pigs), submandibular (18.6% pigs), inguinal (0.1% pigs) and simultaneously intestinal and head lymph nodes (15.9% pigs). Miliary tuberculosis was found only in the parenchymatous organs of four (0.1%) pigs. The following financial losses resulted: 6% for confiscating the head, intestines and stomach, and from 22 to 24% for assessing meat as conditionally edible after processing, i.e. intended only for heat-processed products. Mycobacteria were isolated from 7 246 (41.8%) pigs through the cultivation of tissue samples from 17&amp;nbsp;326 pigs. Mycobacterium bovis was detected in only five (0.07%) animals which originated from the last outbreak of bovine tuberculosis in cattle in the Czech Republic in 1995. M.&amp;nbsp;avium complex (MAC) isolates came from 6&amp;nbsp;870 (94.8%) animals: 55.7% M.&amp;nbsp;a.&amp;nbsp;avium isolates were mainly of serotypes 2 and 3 and genotype IS901+ and IS1245+ and 39.2% M.&amp;nbsp;a.&amp;nbsp;hominissuis isolates were mainly of serotypes 4, 8 and 9 and genotype IS901&amp;ndash; and IS1245+. Conditionally pathogenic mycobacteria (M.&amp;nbsp;chelonae, M.&amp;nbsp;terrae, M.&amp;nbsp;phlei and M.&amp;nbsp;fortuitum) were isolated from 371 (5.1%) pigs. In the whole period monitored, two marked increases in the findings of tuberculous lesions were recorded: In the mid-1990s as a result of using deep bedding with wood shavings and at the end of the 1990s as a result of supplementing the pigs&amp;rsquo; feed with peat. The predominant occurrence of M.&amp;nbsp;a.&amp;nbsp;avium isolates of genotype IS901+ and IS1245+ in the first half of the 1990s was replaced above all by M.&amp;nbsp;a.&amp;nbsp;hominissuis isolates of genotype IS901- and IS1245+. The reason for this was probably a change in the sources of infection for pigs. While at the beginning of the 1990s the most frequent source of infection were wild and domestic birds, various parts of the external environment became the source of the infection for pigs from the mid-1990s. In the years 1996 to 1999, Rhodococcus equi was isolated from 203 (11.6%) of the 1&amp;nbsp;745 animals examined. It was solely isolated from 154 (8.8%) animals and from 49 (2.8%) animals together with mycobacteria.

Comparison of intestinal mucosa homogenate and pure culture of the homologous Lawsonia intracellularis isolate in reproducing proliferative enteropathy in swine

Little information is available on reproduction of proliferative enteropathy (PE) using a virulent pure culture of Lawsonia intracellularis. Reproduction of the disease using PE-diseased mucosa homogenates, however, is well-characterized. The aims of this study were to evaluate and compare clinical signs, growth performance and the severity of lesions in pigs inoculated with intestinal mucosa homogenate or pure culture of the homologous L. intracellularis isolate. Five-week-old pigs were inoculated with pure culture of L. intracellularis (isolate PHE/MN1-00; n=10), PE-diseased mucosa ( n=10), or control media ( n=4). The L. intracellularis isolate PHE/MN1-00 used in the pure culture inoculum was extracted from a fragment of the same intestine used to prepare the mucosa homogenate. Clinical signs and growth performance were evaluated throughout the study. Fecal shedding was evaluated in all animals weekly during the experiment. All animals were euthanized 22 days post-inoculation, the intestines were examined grossly and histologically. Results showed that both the infection procedures reproduced clinical disease, macroscopic and histologic lesions typical of PE. Fecal shedding was detected in animals in both challenge groups. In conclusion, the L. intracellularis isolate PHE/MN1-00 reproduces typical clinical signs and lesions of PE similar to the homologous infection with an intestinal mucosa homogenate.

Experimental dual infection of specific pathogen-free pigs with porcine reproductive and respiratory syndrome virus and pseudorabies virus.

SummaryTwenty 6‐week‐old specific pathogen‐free pigs were divided into four groups. On day 0 of the experiment, PRRSV–PRV (n = 6) and PRRSV (n = 4) groups were intranasally inoculated with porcine reproductive and respiratory syndrome virus (PRRSV) (105.6 TCID50). On day 7, the PRRSV–PRV and PRV (n = 6) groups were intranasally inoculated with pseudorabies virus (PRV) (103.6 TCID50). Control pigs (n = 4) were kept as uninoculated negative controls. Half of the pigs in each group were euthanized and necropsied on day 14 or 21. Clinical signs such as depression and anorexia were observed in the PRRSV–PRV and PRV groups after inoculation with PRV. Although febrile response was observed after virus inoculations, the duration of that response was prolonged in the PRRSV–PRV group compared with the other groups. The lungs in the PRRSV–PRV group failed to collapse and were mottled or diffusely tan and red, whereas the lungs of the pigs in the other groups were grossly normal. Histopathologically, interstitial pneumonia was present in all PRRSV‐inoculated pigs, but the pneumonic lesions were more severe in the PRRSV–PRV group. Mean PRRSV titres of tonsil and lung in the PRRSV–PRV group were significantly (P < 0.05) higher than that in the PRRSV group on day 21. These results indicate that dual infection with PRRSV and PRV increased clinical signs and pneumonic lesions in pigs infected with both viruses, as compared to pigs infected with PRRSV or PRV only, at least in the present experimental conditions.

Differences in metabolic parameters and gene expression related to osteochondrosis/osteoarthrosis in pigs fed 25-hydroxyvitamin D3.

Osteochondrosis/osteoarthrosis (OC/OA) are common terms for various joint pathologies that occur in pigs. Pathologies that may contribute to these disorders have been described, but the primary cause(s) remain unknown. We hypothesised that as OC has some similarities to dyschondroplasia, which involves a failure of growth plate chondrocytes to fully differentiate and hypertrophy, treatment with 25-hydroxyvitamin D3 (25-D) might reduce the incidence and/or severity of lesions in pigs, as it does in chickens with dyschondroplasia. Control pigs were fed a commercial diet ad libitum. In the treated group this diet was supplemented with 25-D at 0.1 mg/kg. Ten pigs from each of the control and treated groups were sampled at 7, 12, 16 and 21 weeks. Treatment with 25-D had no effect on the incidence or severity of OC/OA lesions. Cartilage dry weight, total collagen content and proteoglycan content, and plasma levels oftotal calcium, inorganic phosphorous, vitamin C, insuline-like growth factor-I, parathyroid hormone and tumour necrosis factor alpha were unaffected by treatment. In addition, none of these parameters were correlated with the incidence or severity of OC/OA lesions. The mRNA expression levels of 21 out of 23 genes assayed by RT-PCR were unaltered in articular cartilage from OA lesion samples as compared to normal articular cartilage. However, collagen type II was reduced and collagen type X increased in OA lesion and near lesion samples. These results suggest that OA in pigs may share some features of osteoarthritis in other mammalian species.

Cloned genomic DNA of type 2 porcine circovirus is infectious when injected directly into the liver and lymph nodes of pigs: characterization of clinical disease, virus distribution, and pathologic lesions.

Infection of animals with a molecular viral clone is critical to study the genetic determinants of viral replication and virulence in the host. Type 2 porcine circovirus (PCV2) has been incriminated as the cause of postweaning multisystemic wasting syndrome (PMWS), an emerging disease in pigs. We report here for the first time the construction and use of an infectious molecular DNA clone of PCV2 to characterize the disease and pathologic lesions associated with PCV2 infection by direct in vivo transfection of pigs with the molecular clone. The PCV2 molecular clone was generated by ligating two copies of the complete PCV2 genome in tandem into the pBluescript SK (pSK) vector and was shown to be infectious in vitro when transfected into PK-15 cells. Forty specific-pathogen-free pigs at 4 weeks of age were randomly assigned to four groups of 10 each. Group 1 pigs served as uninoculated controls. Pigs in group 2 were each inoculated intranasally with about 1.9 x 10(5) 50% tissue culture infective doses of a homogeneous PCV2 live virus stock derived from the molecular clone. Pigs in group 3 were each injected intrahepatically with 200 microg of the cloned PCV2 plasmid DNA, and pigs in group 4 were each injected into the superficial iliac lymph nodes with 200 microg of the cloned PCV2 plasmid DNA. Animals injected with the cloned PCV2 plasmid DNA developed infection resembling that induced by intranasal inoculation with PCV2 live virus stock. Seroconversion to PCV2-specific antibody was detected in the majority of pigs from the three inoculated groups at 35 days postinoculation (DPI). Viremia, beginning at 14 DPI and lasting 2 to 4 weeks, was detected in the majority of the pigs from all three inoculated groups. There were no remarkable clinical signs of PMWS in control or any of the inoculated pigs. Gross lesions in pigs of the three inoculated groups were similar and were characterized by systemically enlarged, tan lymph nodes and lungs that failed to collapse. Histopathological lesions and PCV2-specific antigen were detected in numerous tissues and organs, including brain, lung, heart, kidney, tonsil, lymph nodes, spleen, ileum, and liver of infected pigs. This study more definitively characterizes the clinical course and pathologic lesions exclusively attributable to PCV2 infection. The data from this study indicate that the cloned PCV2 genomic DNA may replace infectious virus for future PCV2 pathogenesis and immunization studies. The data also suggest that PCV2, although essential for development of PMWS, may require other factors or agents to induce the full spectrum of clinical signs and lesions associated with advanced cases of PMWS.

Effect of Vessel Size on Creation of Hepatic Radiofrequency Lesions in Pigs

The effect of vessels and their size on radiofrequency lesion creation in the liver was evaluated with respect to potential for vascular injury and perfusion-mediated "heat sink" effect. Radiofrequency lesions targeted to tissue adjacent to a variety of vessels were created in vivo in the liver of 10 Yorkshire pigs. Postablation contrast-enhanced CT and then histopathologic analysis of the vessels and lesions were performed after sacrifice of the pigs. Degree of vascular injury and viability of perivascular hepatocytes were recorded and tabulated according to vessel size for both CT and histologic data sets. At CT, 42 (95%) of 44 veins greater than 3 mm remained patent, and four (20%) of 20 veins less than 3 mm were occluded. Heat sink effect, indicated by invagination of enhancing tissue between vessel and radiofrequency lesion, was observed in 32 (73%) of 44 veins greater than 3 mm and in zero of 20 veins less than 3 mm. On histopathology, 111 (100%) of 111 vessels less than 3 mm showed at least partial vessel wall injury, characterized by endothelial cell necrosis and luminal thrombus. In 24 vessels greater than 3 mm, the extent of vessel wall injury decreased with increasing vessel diameter. Viable perivascular tissue indicative of heat sink effect was identified in 12 of 24 veins greater than 3 mm, increasing to seven of seven veins greater than 5 mm. None of 96 vessels less than 2 mm and three of 111 vessels less than 3 mm showed any heat sink effect. There appears to be a narrow transition zone for hepatic vessels at 2-4 mm, beyond which the heat sink effect was seen consistently and substantial vascular injury was rare.