Patterns of Mycoplasma hyopneumoniae Infections in Belgian Farrow‐to‐Finish Pig Herds with Diverging Disease‐Course

Patterns of Mycoplasma hyopneumoniae (Mh) infections were investigated in five clinically infected herds and in five herds subclinically infected with Mh. In the clinically infected herds, housing and management conditions were good whereas these conditions were poor in the subclinically infected herds. In each herd, serum antibodies against Mh were detected in pigs of different ages and nasal swabs were taken for Mh detection using nested PCR (nPCR). The percentage of seropositive pigs in the clinically infected herds increased from 8% in pigs of 9 weeks to 52% in pigs of 18 weeks and seroconversion was most shown between 12 and 15 weeks. In the subclinically infected herds, the percentages increased from 2 to 24% and most of the pigs became seropositive between 15 and 18 weeks. The percentage of nPCR positive pigs at 6 weeks was 16 and 0% in the clinically and subclinically infected herds, respectively. The results demonstrate that the seroprevalences were higher in the clinically infected herds and that most of the pigs became infected with Mh at a younger age. It can be concluded that additional factors different from housing and management, like differences among Mh strains, may determine the infection pattern of Mh and the clinical course of the infection.     

Chronological study of Mycoplasma hyopneumoniae infection, seroconversion and associated lung lesions in vaccinated and non-vaccinated pigs

A field trial was conducted to study Mycoplasma hyopneumoniae (Mh) infection dynamics by nested polymerase chain reaction (nPCR) and serology in pigs of a farm affected by enzootic pneumonia (EP). Moreover, correlation of Mh detection at different respiratory tract sites with presence of EP gross and microscopic lung lesions was assessed. These parameters were studied and compared between vaccinated (two doses at 1 and 3 weeks of age versus one dose at 6 weeks of age) and non-vaccinated pigs. Animals were monitored from birth to slaughter by nPCR from nasal swabs and by serology. From 3 to 22 weeks of age, an average of three pigs per treatment and per batch were necropsied (n = 302). The remaining pigs were sent to the slaughter (n = 103). Nasal, bronchial and tonsillar swabs were taken from the necropsied/slaughtered pigs; gross and microscopic EP-suggestive lung lesions were also assessed. Single and double vaccination resulted in earlier seroconversion and higher percentage of Mh seropositive pigs compared to control group. At slaughter, double vaccinated pigs showed lower percentage of EP-compatible gross lung lesions and lower Mh prevalence at upper respiratory tract sites (nasal cavity and tonsil) than control pigs.     

Effect of sow vaccination against Mycoplasma hyopneumoniae on sow and piglet colonization and seroconversion, and pig lung lesions at slaughter

The objectives of the present study were to compare Mycoplasma hyopneumoniae (Mh) colonization and serologic status on Mh vaccinated and non-vaccinated sows and to assess the effect of sow vaccination on colonization and serologic status of their piglets at weaning as well as presence of enzootic pneumonia (EP) lung lesions at slaughter. Fifty sows (25 vaccinated and 25 unvaccinated) as well as five of their piglets were included in the study. Blood samples and nasal swabs from sows at 7 weeks pre-farrowing and 1 week post-farrowing and from piglets at 3-4 weeks of age were taken. Nasal swabs and sera were tested by a nested polymerase chain reaction (nPCR) to detect Mh DNA and by an enzyme-linked immunosorbent assay (ELISA) test to detect antibodies to the pathogen, respectively. Finally, at 23 weeks of age, pigs were sent to the slaughter where the extension of EP-compatible gross lesions was assessed. Vaccination with two doses of Mh vaccine resulted in a significantly higher (p<0.05) percentage of seropositive sows than in the non-vaccinated group at 1 week post-farrowing. On the contrary, no statistical significant differences were found in the number of nasal nPCR positive sows among different treatments (p>0.05). At 3-4 weeks of age, a significantly higher percentage (p<0.001) of seropositive piglets came from vaccinated than from non-vaccinated sows. Although the number of Mh infected piglets coming from non-vaccinated sows was higher than the one from vaccinated sows, the difference was not statistically significant (p>0.05). Overall, piglets from vaccinated sows had a significant lower (p<0.05) mean of EP-compatible lung lesions (1.83+/-2.8) than piglets from non-vaccinated sows (3.02+/-3.6). Under the conditions described in this study, sow vaccination did not affect sow or piglet colonization but increased the percentage of seropositive sows and piglets at weaning and reduced significantly the mean EP-compatible lung lesion scoring at slaughter.     

Risk indicators for the seroprevalence of Mycoplasma hyopneumoniae, porcine influenza viruses and Aujeszky's disease virus in slaughter pigs from fattening pig herds.

Epidemiological aspects of Mycoplasma hyopneumoniae (Mh), influenza H1N1 and H3N2 viruses, and Aujeszky's disease virus (ADV) were investigated in slaughter pigs from 50 fattening pig herds. Herd factors as potential risk indicators for respiratory disease were obtained by means of a questionnaire. At slaughter, blood samples were collected from each herd, and the proportion of seropositive pigs per herd was assessed for each of these pathogens. The median herd-level seroprevalence of the agents were: Mh 88%, H1N1 100%, H3N2 60% and ADV 90%. The percentage of herds in which all investigated fattening pigs were seronegative for these agents was: Mh 0%, H1N1 0%, H3N2 12% and ADV 18%. The percentage of herds in which all investigated fattening pigs were seropositive for these agents was: Mh 8%, H1N1 71%, H3N2 22% and ADV 40%. A positive association was found between influenza H1N1 and H3N2 viruses, and a negative association between influenza H3N2 virus and ADV. There were no risk indicators for the seroprevalence of Mh. Three risk indicators were associated with the seroprevalence of influenza H1N1 virus: a fully slatted floor, an increasing number of pigs in the municipality and dry feeding. Three risk indicators were found for the seroprevalence of influenza H3N2 virus: purchase of pigs from > or = two herds, an increasing number of pigs in the municipality and natural ventilation. The seroprevalence of ADV was influenced by two risk indicators: an increasing number of pig herds in the municipality and an increasing number of pigs per pen.     

Serologic status of pseudorabies virus in growing-finishing pigs in quarantined herds

It has been reported that pseudorabies virus (PRV) stops spreading within growing-finishing sections of a large percentage of infected farrow-to-finish herds. This study was designed to follow the PRV status of growing-finishing pigs in a sample of infected herds. Fifteen infected herds were selected, of which 11 had seropositive finishing pigs and 4 had seronegative finishing pigs. These herds were visited quarterly for one year, and a cross section of growing-finishing pigs was tested for the presence of anti-PRV antibodies. The 4 herds that initially were seronegative remained seronegative, whereas of the 11 herds initially seropositive, 4 remained seropositive, 4 became seronegative, and 3 became temporarily seronegative before becoming seropositive again. Three characteristics serologic profiles were observed: one indicating continued viral spread; one indicating no spread for at least the preceding 3 months; and one indicating that PRV spread had recently ceased in this section of the herd. Results of our study indicated that periodic monitoring of a cross section of the growing-finishing pigs for their PRV serologic status was valuable for determining whether PRV was actively spreading in this section of the herd.     

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

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

Incidence of coccidioides infection among dogs residing in a region in which the organism is endemic

OBJECTIVE: To determine the incidence of Coccidioides infection among dogs residing in a region in which the organism is endemic (Pima and Maricopa counties, Arizona) and estimate the rate of clinical illness. DESIGN: Community-based longitudinal and cross-sectional studies. ANIMALS: 124 healthy 4- to 6-month-old seronegative puppies (longitudinal study) and 381 4- to 18-month-old dogs with unknown serostatus (cross-sectional study). PROCEDURE: Dogs in the longitudinal study were tested at 6-month intervals for at least 1 year for anticoccidioidal antibodies. Dogs that became ill were evaluated for coccidioidomycosis. Dogs in the cross-sectional study were tested for anticoccidioidal antibodies once, and clinical abnormalities were recorded. RESULTS: 28 of the 104 (27%) dogs that completed the longitudinal study developed anticoccidioidal antibodies. Thirty-two of the 381 (8%) dogs in the cross-sectional study had anticoccidioidal antibodies. Five seropositive dogs in the longitudinal study and 13 seropositive dogs in the cross-sectional study had clinical signs of disease. The remaining seropositive dogs were otherwise healthy and were classified as subclinically infected. Survival analysis indicated that the cumulative probability of infection by 2 years of age was 28%, and the cumulative probability of clinical infection by 2 years of age was 6%. Titers for clinically and subclinically infected dogs overlapped. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that young dogs living in the study area had a high likelihood of becoming infected with Coccidioides spp, but few developed clinical illness. Serologic testing alone was insufficient for a diagnosis of clinical disease because of the overlap in titers between clinically and subclinically infected dogs.     

A field evaluation of Nobi-Vac atrophic rhinitis vaccine

A field trial was carried out with Nobi-Vac AR vaccine in 11 swine breeding herds. One herd suffered from severe B. bronchiseptica (BB+) rhinitis in piglets, while no clinical Atrophic Rhinitis (AR) was observed. Ten herds were described as AR problem herds, because clinical AR was observed for at least 1 year in spite of the fact that medication of sows and piglets was carried out and adequate housing and management systems were available in most herds. BB+ was isolated in 9 of these 10 farms and the AR pathogenic P. multocida (PM+) in all these farms. The trial started when piglets were born of sows which had been vaccinated 3 times. All piglets between 7 and 10 weeks old were examined clinically for AR. Nasal swabs from 20 pigs on each farm were screened bacteriologically for BB+ and PM+ every other month. A severe reoccurrence of AR was found in 2 of the 10 AR problem farms. In these 2 herds the 'all in-all out' system was not applied in farrowing and weaning houses. In the 8 other AR problem herds the percentage of pigs with AR decreased significantly below the average level of 1% per year. The percentage of pigs infected with BB+ and PM+ also decreased significantly. PM+ was significantly related to the percentage of clinical AR piglets. Seasonal effects contributed to a minor extent to the percentage of AR piglets. After 2.5 years of this trial PM+ could not be isolated during the last 12 months in six of the remaining AR problems herds. The conclusion is that Nobi-Vac AR vaccination of the sow gave protection against clinical AR in piglets on those farms (80%) which provided adequate housing and management systems.     

Risk Indicators for the Seroprevalence of Mycoplasma hyopneumoniae,Porcine Influenza Viruses and Aujeszky's Disease Virus in Slaughter Pigs from Fattening Pig Herds

Epidemiological aspects of Mycoplasma hyopneumoniae (Mh), influenza H_***2N₁ and H₃N₂ viruses, and Aujeszky's disease virus (ADV) were investigated in slaughter pigs from 50 fattening pig herds. Herd factors as potential risk indicators for respiratory disease were obtained by means of a questionnaire. At slaughter, blood samples were collected from each herd, and the proportion of seropositive pigs per herd was assessed for each of these pathogens. The median herd-level seroprevalence of the agents were: Mh 88%, H_***3N₁ 100%, H₃N₂ 60% and ADV 90%. The percentage of herds in which all investigated fattening pigs were seronegative for these agents was: Mh 0%, H_***N₁ 0%, H₃N₂ 12% and ADV 18%. The percentage of herds in which all investigated fattening pigs were seropositive for these agents was: Mh 8%, H₁N₁ 71%, H₃N₂ 22% and ADV 40%. A positive association was found between influenza H₁N₁ and H₃N₂ viruses, and a negative association between influenza H₃N₂ virus and ADV. There were no risk indicators for the seroprevalence of Mh. Three risk indicators were associated with the seroprevalence of influenza H₁N₁ virus: a fully slatted floor, an increasing number of pigs in the municipality and dry feeding. Three risk indicators were found for the seroprevalence of influenza H₃N₂ virus: purchase of pigs from ≥two herds, an increasing number of pigs in the municipality and natural ventilation. The seroprevalence of ADV was influenced by two risk indicators: an increasing number of pig herds in the municipality and an increasing number of pigs per pen.     

A field evaluation of Nobi®‐Vac Atrophic Rhinitis vaccine

Summary

A field trial was carried out with Nobi‐Vac AR vaccine in 11 swine breeding herds. One herd suffered from severe B. bronchiseptica (BB+) rhinitis in piglets, while no clinical Atrophic Rhinitis (AR) was observed. Ten herds were described as AR problem herds, because clinical AR was observed for at least 1 year in spite of the fact that medication of sows and piglets was carried out and adequate housing and management systems were available in most herds. BB+ was isolated in 9 of these 10 farms and the AR pathogenic P. multocida (PM+) in all these farms.

The trial started when piglets were born of sows which had been vaccinated 3 times. All piglets between 7 and 10 weeks old were examined clinically for AR. Nasal swabs from 20 pigs on each farm were screened bacteriologically for BB+ and PM+ every other month.

A severe reoccurrence of AR was found in 2 of the 10 AR problem farms. In these 2 herds the ‘all in‐all out’ system was not applied in farrowing and weaning houses. In the 8 other AR problem herds the percentage of pigs with AR decreased significantly below the average level of 1% per year. The percentage of pigs infected with BB+ and PM+ also decreased significantly. PM+ was significantly related to the percentage of clinical AR piglets. Seasonal effects contributed to a minor extent to the percentage of AR piglets.

After 2.5 years of this trial PM+ could not be isolated during the last 12 months in six of the remaining AR problems herds.

The conclusion is that Nobi‐Vac AR vaccination of the sow gave protection against clinical AR in piglets on those farms (80%) which provided adequate housing and management systems.     

Longitudinal study of hepatitis E virus infection in Spanish farrow-to-finish swine herds

Hepatitis E is a zoonotic disease and is highly prevalent in European swine livestock. There is a need to compare the infection dynamics of hepatitis E virus (HEV) between herds with the same production system and determine the percentage of animals that could arrive infected at slaughter age. Therefore, a longitudinal study was performed in six Spanish farrow-to-finish affected farms. Twenty piglets per farm were monitored from nursery to slaughter. RT-PCR and serology techniques were applied to analyze longitudinally collected sera and/or faecal samples. Liver and bile samples were also taken at the abattoir. Anti-HEV IgM were firstly detected at 7 weeks of age in 5 farms whereas at 13 weeks of age in 1 farm (farm 2). At slaughter age 50–100% of pigs had seroconverted to anti-HEV IgG in the former 5 farms whereas in the other herd only 5% of pigs were IgG seropositive (farm 2). Six out of 96 livers and 5 out of 80 biles analyzed were HEV positive at the abattoir (total percentage of infected animals: 11.5%). All these positive animals had already seroconverted except 2 pigs of farm 2. Hence, pigs can be seronegative at slaughter age being infected during the latest fattening period. Manipulation of HEV-infected livers or other organs from pigs could be considered a possible route of transmission in Spanish abattoirs. This study represents the first longitudinal survey on swine HEV infection dynamics conducted in different herds.     

Exploratory field study on Mycoplasma hyopneumoniae infection in suckling pigs

The present study focused on Mycoplasma hyopneumoniae (M. hyopneumoniae) detection by nPCR in nasal swabs of 507 suckling pigs. These animals came from 69 sows (from 1 to 8 parity number) of a farrow-to-finish herd with Enzootic Pneumonia (EP) problems at finishing stages. At 1 and 3 weeks of age (still in the farrowing units), nasal swabs and blood samples were taken from all piglets. Moreover, from these 507 animals, 37 randomly selected pigs were necropsied at 3 weeks of age. From those necropsied pigs, M. hyopneumoniae presence was tested in bronchial and tonsillar swabs. At 1 week post-farrowing, blood samples from sows were collected and used to detect M. hyopneumoniae antibodies. From the 69 analysed sows, 19 (27.5%) were seropositive. Global percentage of pigs with M. hyopneumoniae detection in nasal swabs at 1 and 3 weeks of age was 1.5% (8 out of 507) and 3.8% (19 out of 507), respectively. From these nPCR positive pigs, 89% (24 out of 27) were seronegative and 11% were seropositive. From necropsied animals, the pathogen DNA was detected in two pigs at bronchus level and in another pig at tonsil. In this study, sow parity was not statistically related with sow seropositivity and piglet colonization. These results confirm that M. hyopneumoniae infection may be detected not only in nasal cavities of naturally infected suckling piglets but also at their low respiratory tract airways. Our results suggest that M. hyopneumoniae detection in lower and upper respiratory tract could be an indicator that respiratory problems associated to EP may start relatively early in the production system. In consequence, sow-to-piglet and/or piglet-to piglet transmission in farrowing barns should not be underestimated.     

Factors associated with spread of pseudorabies virus among breeding swine in quarantined herds.

Knowledge of the factors that place susceptible gilts at highest risk of pseudorabies virus (PRV) infection in a quarantined herd is crucial to reduce spread of PRV within the herd. Cohorts of PRV seronegative gilts were monitored in 17 herds that were endemically infected with PRV to determine the location of breeding females at the time of infection with PRV and identify herd characteristics and management and housing factors that may influence spread of PRV in the breeding section of swine herds endemically infected with PRV. Blood samples were collected every 1 to 2 months for an average of 13.6 months. In addition, blood was collected from a representative sample of finishing pigs (greater than or equal to 20 weeks old) 3 times per year to determine their serologic PRV status. Incidence rates and relative risks of PRV infection were estimated for 4 areas of the breeding section: gestation barn, gilt pool, farrowing room, and breeding area. Overall, 28, 11, 8, and 2 females became infected with PRV in each of these areas, respectively. The greater number of females infected in the gestation barns, compared with the number of females infected in other locations, is probably a consequence of being at risk for a longer period rather than of a higher incidence rate. Herd size, common housing for gilts in the gilt pool and sows, and serologic pattern of PRV infection in finishing pigs were associated with the detection of spread of PRV in the breeding section of the 17 herds.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prevalence of exposure and infection of Lawsonia intracellularis among slaughter-age pigs

The extent of clinical or subclinical infection associated with Lawsonia intracellularis within Dutch pig herds was uncertain. A case-control study of slaughter age pigs was used to study natural infection within Dutch herds and to compare diagnostic methods. From six case herds where clinical disease had been identified recently, and six disease-free herds, 40 pigs of slaughter-age were examined postmortem. The diagnostic methods used were: serology, gross examination, Haematoxylin and Eosin stain (HE), Warthin-Starry silver stain, Lawsonia-specific indirect immunoperoxidase of the ileum, and PCR of ileum mucosa and colon contents. There were 59% seropositive pigs in case herds and 26% seropositive pigs in control herds. Using immunohistochemistry, 57% of case herds and 46% of control herds were bacteria positive in the ileum mucosa. It was concluded that a majority of Dutch herds contain L. intracellularis infected finisher pigs. In some herds this is associated with clinical outbreaks of acute haemorrhagic enteropathy but in other herds no clinical disease is apparent. Many seropositive pigs in herds without clinical disease had evidence of Lawsonia antigen in sites other than the apical cytoplasm of proliferating epithelial cells, particularly the supranuclear region. It was uncertain whether to classify these pigs as having "recovered" from an infection or whether they have a sub-clinical or chronic form of the disease. We concluded that PCR examination of faeces and serology probably provide more specific results than gross examinations at slaughter, and that a monoclonal antibody-based examination of ileum mucosa should be the accepted screening method for this infection.     

The minor role of pigs in outbreaks of foot-and-mouth disease of northern Thailand

SUMMARY: A study was undertaken in northern Thailand to examine the involvement of pigs in outbreaks of foot-and-mouth disease (FMD). Data were collected by surveying selected villages, by serological monitoring of pigs and by investigating outbreaks. Fifty-three of 58 villages (91%) surveyed reported that pigs did not develop FMD during the most recent outbreak. The source of 49/60 (82%) outbreaks was attributed to either recent purchases of infected cattle and buffalo or commingling of cattle and buffalo with stock from an infected neighbouring village. One of 60 villages (1.7%) reported that the source was introduced infected pigs. There was no association between the various hypothesised risk factors relating to the management of pigs and the frequency of FMD outbreaks in the survey. The percentage of seropositive pigs during 3 rounds of serological monitoring conducted at 6-monthly intervals in selected villages was 3.5%, 2.6% and 0%, respectively. No clinically affected pigs were observed in 11 outbreak investigations. It was concluded that pigs did not commonly become infected when there were outbreaks of FMD in village cattle and buffalo in northern Thailand. This was probably due to the pig feeding and housing practices employed by villagers that protected pigs from exposure to virus from infected cattle or buffalo, or their products.     

Validation of a bulk tank milk antibody ELISA to detect dairy herds likely infected with bovine viral diarrhoea virus in New Zealand

AIMS: To assess the sensitivity and specificity of a bulk tank milk (BTM) antibody enzyme-linked immunosorbent assay (ELISA) to detect likely infection of a dairy herd with bovine viral diarrhoea virus (BVDV). The ELISA was subsequently used to estimate the prevalence of likely infected herds in parts of the North Island of New Zealand. METHODS: BTM samples from 724 randomly selected dairy herds in the Waikato, Bay of Plenty and Northland regions of New Zealand were tested for BVDV antibodies. From this group, 20 herds were again randomly selected from each of the quartiles of the ELISA percentage inhibition (%INH) result. From each participant herd, serum from 15 randomly selected calves aged 6-18 months and 15 cows was collected and tested using an indirect blocking ELISA for BVDV antibodies. RESULTS: Among serum results from calves from 50 herds available for analysis, 34 (68%) herds were classified as likely non-infected (0-3 seropositive among 15 calves) and 16 (32%) as likely infected (5-15 seropositive among 15 calves). Receiver-operator characteristic (ROC) analysis identified an optimal cut-off for BTM of 80%INH associated with 81% sensitivity and 91% specificity for likely herd infection. The prevalence of BVDV antibodies in cows within herds and %INH for BVDV in bulk milk were positively correlated (p<0.01). The association between bulk milk %INH and the prevalence of BVDV antibodies in calves was stronger than the same association in cows. Based on the threshold of 80%INH, the 95% confidence interval (CI) for prevalence of likely infection in the 724 herds in the Waikato, Bay of Plenty and Northland regions of New Zealand was 12-17%. Vaccination against BVDV was not significantly associated with the likely infection status of the herd based on prevalence of BVDV antibodies among calves. CONCLUSION: An ELISA test result for BVDV antibodies in BTM >/=80%INH can be used as a threshold to indicate the presence of likely infection with BVDV in dairy herds in New Zealand, with 81% sensitivity and 91% specificity.     

Bordetella Agglutinating Antibody in Swine. A Herd Study

An agglutination test with killed Bordetella bronchiseptica, suspended in 0.85% saline, standardized photometrically to contain approximately 20 billion microorganisms per ml as antigen, was used to detect naturally-occurring antibody against this bacterium in the sera of 451 pigs ranging in age from one month to over 36 months. Agglutinating antibody was demonstrated in 32.8% of 201 sera of pigs one to six months old, 61.5% of 52 pigs six to 12 months old, 83.8% of 62 pigs 13 to 18 months old, 92.3% of 39 pigs 19 to 24 months old and 100% of 97 adults older than 24 months. Nasal swab cultures did not reliably detect the carrier state of subclinically infected pigs, however, detection of agglutinating antibody against B. bronchiseptica may be useful for diagnosing infection in swine herds.     

Factors associated with circulation of pseudorabies virus within swine herds

Data were collected from 104 Minnesota swine farms quarantined for pseudorabies virus (PRV) infection. Each herd was serologically evaluated for the presence of antibodies to PRV in finishing pigs. Herd management practices, swine housing design, and disease profiles were described for each farm. Multiple logistic regression analysis was used to determine which factors were associated with circulation of PRV in the finishing pigs of farrow-to-finish farms. Sixty-seven (64%) of the herds had no serologic evidence of PRV circulation in the finishing section, whereas 37 herds (36%) contained at least one PRV seropositive finishing pig. The odds of a given finishing herd being seropositive for PRV were 2.85 times higher if the finishing pigs were housed in confinement (P = 0.01), 2 times higher if Actinobacillus (Haemophilus) pleuropneumoniae was a clinical problem in the herd (P = 0.03), 1.36 times less for each year that passed since the herd quarantine was issued (P = 0.01), 1.74 times higher if clinical signs of PRV were reported (P = 0.04), and 1.52 times higher if animal protein was included in at least one of the rations (P = 0.08).     

Pig herds having a single reactor to serum antibody tests to Aujeszky's disease virus.

The introduction of Aujeszky's disease virus into a herd of pigs usually results in a rapid spread of the virus and a high percentage of pigs become seropositive. However, herd monitoring for the virus occasionally reveals a single seropositive breeding pig, referred to as a single reactor. The seropositive status of single reactors may be due to previous vaccination against Aujeszky's disease, or to exposure to a field strain of the virus, or to a false positive reaction in the serological assay. During a monitoring programme in Minnesota, 30 pig herds with single serological reactors were detected. Twenty-seven of these single reactors from 19 herds were segregated from their herds immunosuppressed with dexamethasone. Aujeszky's disease virus was isolated from four of the 27 pigs. Three of the four herds subsequently had outbreaks of Aujeszky's disease, suggesting that some single reactors were infected with Aujeszky's disease virus and had the potential to spread the virus within and between herds.