Longitudinal assessment of two Mycoplasma hyopneumoniae enzyme-linked immunosorbent assays in challenged and contact-exposed pigs

The objective of the current study was to compare the sensitivity of 2 Mycoplasma hyopneumoniae enzyme-linked immunosorbent assays (ELISAs) in experimentally challenged and contact-exposed pigs in a long-term longitudinal assessment. On day 0 of the assessment, twelve 2-month-old M. hyopneumoniae-negative pigs were inoculated with M. hyopneumoniae strain 232 (group A). Twelve negative pigs were placed alongside the inoculated pigs, allowing direct contact exposure (group B). A third group of 12 pigs was allocated into 2 independent pens; no direct contact was allowed (group C). A longitudinal serologic profile was performed; samples were collected on days 0, 28, 35, 42, 49, 63, 91, 119, 154, and 170 of the study. Serum samples were tested using a blocking ELISA and an indirect ELISA. Results of the study demonstrated higher sensitivity of the blocking ELISA during early infection (clinical signs). Both ELISAs were 100% sensitive in challenged and naturally infected groups at several testing points during late infection (63, 91, 119, 154, and 170 days of the study) and showed a long antibody detection period. Both tests worked equally well during the chronic phase of infection but the blocking ELISA was more sensitive during acute stages of infection.

Effect of cross-fostering on transfer of maternal immunity to Mycoplasma hyopneumoniae to piglets

The aim of this study was to assess the effect of cross-fostering on transfer of maternal Mycoplasma hyopneumoniae-specific humoral and cell-mediated immunity (CMI) from gilts to piglets. Cross-fostering, carried out within gilt pairs, was based on the gilts' M hyopneumoniae vaccination status in accordance with the following scheme: six pairs of vaccinated gilt × non-vaccinated gilt (V × N); five pairs of non-vaccinated gilt × vaccinated gilt (N × V); and five pairs of vaccinated gilt × vaccinated gilt (V × V). The piglets were cross-fostered at 0, six, 12 or 20 hours after birth. Two piglets per gilt per time point were cross-fostered (that is, eight piglets per gilt were moved) and the remaining piglets served as non-cross-fostered controls. In addition, four litters served as non-cross-fostered controls. A maximum of 10 piglets per gilt were sampled. The piglets' M hyopneumoniae-specific humoral immunity was assessed by ELISA and their CMI was assessed by delayed-type hypersensitivity testing. M hyopneumoniae-specific antibodies were detected in non-cross-fostered piglets from vaccinated dams and from piglets cross-fostered within the V × N gilt pair at six hours or more, and within the V × V gilt pair at all time points. Piglets cross-fostered within the N × V gilt pair had detectable M hyopneumoniae-specific antibodies only if they had been moved within six hours of birth. The transfer of M hyopneumoniae-specific CMI to piglets appeared to be source-dependent, and was detected only in piglets maintained on their vaccinated dams for at least 12 hours after birth.

An experimental model to evaluate Mycoplasma hyopneumoniae transmission from asymptomatic carriers to unvaccinated and vaccinated sentinel pigs

The objective of this study was to determine the effect of vaccinating susceptible animals on the transmission of Mycoplasma hyopneumoniae from experimentally infected pigs during the chronic phase of infection. Thirty-six seeder pigs were experimentally infected with M. hyopneumoniae. Eighty and 200 d post-infection (dpi) 18 seeder pigs were placed in direct contact with 15 vaccinated and 15 unvaccinated age-matched naïve animals. Direct animal contact occurred over 14 d. Pigs were euthanized at the end of the contact period and bronchial swabs were collected and lung tissue examined. At 94 dpi, 15 out of 15 unvaccinated sentinels and 14 out of 15 vaccinated sentinels tested positive for M. hyopneumoniae by nested polymerase chain reaction (N-PCR). At 214 dpi, M. hyopneumoniae DNA was detected by PCR in 8 out of 15 unvaccinated and 6 out of 15 vaccinated sentinels. Vaccination against M. hyopneumoniae did not prevent colonization of sentinels in contact with infected animals. Transmission of M. hyopneumoniae from asymptomatic carriers to unvaccinated and vaccinated sentinels was not different.

Effect of Mycoplasma hyopneumoniae colonization at weaning on disease severity in growing pigs

To determine whether Mycoplasma hyopneumoniae colonization at weaning in off-site weaning systems is associated with the severity of respiratory disease due to this agent in growing pigs, we studied 20 groups, each group representing a different week in production, in sow herds at 3 farms of 3000 sows each that had a prevalence of M. hyopneumoniae colonization at weaning higher than 5%. The calculated sample size for assessment at weaning was 39 piglets for each group under study; 39 litters were randomly selected, and 1 piglet was randomly selected from each litter for testing and ear-tagged. In total, 780 piglets were tested. The presence of M. hyopneumoniae in nasal swabs at weaning was established by nested polymerase chain reaction (PCR). All groups were followed until slaughter, at which time blood samples were collected from each ear-tagged pig to test for M. hyopneumoniae antibodies, bronchial swabs were collected for detection of M. hyopneumoniae DNA by nested PCR, and the lung lesion score and percentage of affected lungs in the same animals were calculated. Correlation analyses showed a positive correlation between colonization at weaning and all 4 dependent variables indicating infection at slaughter: average lung lesion score, percentage of affected lungs, presence of M. hyopneumoniae on the bronchial epithelium, and seroconversion. This study provides evidence that severity of the disease can be predicted by the prevalence at weaning in segregated systems. Therefore, strategies focused on reducing colonization at weaning seem to be important elements in the global control of M. hyopneumoniae in segregated production systems.

Impact of a modified-live porcine reproductive and respiratory syndrome virus vaccine intervention on a population of pigs infected with a heterologous isolate

The objectives of this study were to evaluate the effects of a therapeutic vaccine intervention with a modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine on the dynamics of a heterologous viral infection in a population of pigs, and to determine the clinical and virological response of previously exposed and vaccinated pigs against a second virulent heterologous challenge. A population of 320 pigs were infected with a field isolate, PRRSV MN-30100, alone or followed by Ingelvac PRRS MLV vaccine administered one to three times at 30 days intervals beginning 1 week after infection. Vaccine intervention reduced the duration of viral shedding, but did not reduce the viral load in tissues or the proportion of persistently infected pigs. A different and highly virulent field isolate, MN-184, was then given as a heterologous viral challenge at 97 days after first exposure. Previously infected and vaccinated pigs showed a significant reduction in clinical signs and enhanced weight gain after the highly virulent challenge with PRRSV MN-184, but infection with and shedding of the challenge isolate were not prevented.

Characterization of dental fillings found in skulls from individuals buried in San Jeronimos Church, New Spain: historical and archaeological evidences

Repair of teeth during the XIX century was often a very costly and painful procedure. During this period, restoration of teeth was a procedure limited only to those who could afford such care. In this study we analyzed teeth from a skull sample found in San Jeronimo's Church. The characterization of molar fillings was made with techniques such as X-ray fluorescence, X-ray diffraction and electron microscopy. The purpose of this investigation was to establish technical procedures for analysis, and to discuss the results within the context of the socioeconomic status of these individuals and the written descriptions of the dental practice during the XIX century.

Further evaluation of alternative air-filtration systems for reducing the transmission of Porcine reproductive and respiratory syndrome virus by aerosol

The purpose of this study was to compare 4 methods for the reduction of aerosol transmission of Porcine reproductive and respiratory syndrome virus (PRRSV): high-efficiency particulate air (HEPA) filtration, 2x-low-cost filtration, bag filtration, and use of a filter tested against particles derived from dioctylphthalate (DOP). The HEPA-filtration system used a prefilter screen, a bag filter (Eurovent [EU] 8 rating), and a HEPA filter (EU13 rating). The low-cost-filtration system contained mosquito netting (prefilter), 2 fiberglass furnace filters, and 2 electrostatic furnace filters. Bag filtration involved the use of a filter rated EU8 and a minimum efficiency reporting value (MERV) of 14. The 95%-DOP, 0.3-microm-filtration system involved a pleat-in-pleat V-bank disposable filter with a 95% efficiency rating for particles 0.3 microm or greater in diameter and ratings of EU9 and MERV 15. No form of intervention was used in the control group. The experimental facilities consisted of 2 chambers connected by a 1.3-m-long duct containing the treatments. Recipient pigs, housed in chamber 2, were exposed to artificial aerosols created by a mechanically operated mister containing modified live PRRSV vaccine located in chamber 1. Aerosol transmission of PRRSV occurred in 0 of the 10 HEPA-filtration replicates, 2 of the 10 bag-filtration replicates, 4 of the 10 low-cost-filtration replicates, 0 of the 10 95%-DOP, 0.3-microm-filtration replicates, and all 10 of the control replicates. Using a similar approach, we further evaluated the HEPA- and 95%-DOP, 0.3-microm-filtration systems. Infection was not observed in any of the 76 HEPA-filtration replicates but was observed in 2 of the 76 95%-DOP, 0.3-microm replicates and 42 of the 50 control replicates. Although the difference between the 95%-DOP, 0.3-microm and control replicates was significant (P < 0.0005), so was the level of failure of the 95%-DOP, 0.3-microm system (P = 0.02). In conclusion, under the conditions of this study, some methods of air filtration were significantly better than others in reducing aerosol transmission of PRRSV, and HEPA filtration was the only system that completely prevented transmission.

Evaluation of systems for reducing the transmission of porcine reproductive and respiratory syndrome virus by aerosol

The purpose of this study was to compare 3 methods for the reduction of aerosol transmission of Porcine reproductive and respiratory syndrome virus (PRRSV): high-efficiency particulate air (HEPA) filtration, low-cost filtration, and ultraviolet light (UV) irradiation. The HEPA-filtration system involved a pre-filter screen, a bag filter (EU8 rating), and a HEPA filter (EU13 rating). The low-cost-filtration system contained mosquito netting (pre-filter), a fiberglass furnace filter, and an electrostatic furnace filter. For UV irradiation, a lamp emitted UVC radiation at 253.7 nm. No form of intervention was used in the control group. The experimental facilities consisted of 2 chambers connected by a 1.3-m-long duct. Recipient pigs, housed in chamber 2, were exposed to artificial aerosols created by a mechanically operated mister containing modified live PRRSV vaccine located in chamber 1. Aerosol transmission of PRRSV occurred in 9 of the 10 control replicates, 8 of the 10 UVC-irradiation replicates, 4 of the 10 low-cost-filtration replicates, and 0 of the 10 HEPA-filtration replicates. When compared with no intervention, HEPA filtration and low-cost filtration significantly reduced PRRSV transmission (P < 0.0005 and = 0.0286, respectively), whereas UV irradiation had no effect (P = 0.5). However, low-cost filtration and UV irradiation were significantly less effective (P = 0.043 and P < 0.0005, respectively) than HEPA filtration. In conclusion, under the conditions of this study, HEPA filtration was significantly more effective at reducing aerosol transmission of PRRSV than the other methods evaluated.

Evaluation of an air-filtration system for preventing aerosol transmission of Porcine reproductive and respiratory syndrome virus

The purpose of this study was to evaluate the ability of a commercial air-filtration system to reduce aerosol transmission of Porcine reproductive and respiratory syndrome virus (PRRSV). The system consisted of a pre-filter and 2 filters with EU8 and EU13 ratings. In each of 4 trials, 5 PRRSV-infected donor pigs and 1 naive recipient pig (each 25 kg) were housed in opposing chambers connected by a 1.3-m-long duct. The system filtered air entering 1 recipient-pig chamber (filtered facility) from the donor-pig chamber but not a 2nd recipient-pig chamber (nonfiltered facility). The donor pigs had been experimentally infected with PRRSV MN-184, an isolate previously documented to be shed at a high frequency in contagious aerosols. On days 3 to 7 after infection of the donors, the 2 groups were housed in their respective chambers for 6 h and then in separate facilities, where samples were collected for testing by polymerase chain reaction and enzyme-linked immunosorbent assay over 14 d. Aerosol transmission was observed in 6 of the 20 replicates in the nonfiltered facility, whereas all pigs remained PRRSV-negative in the filtered facility; the difference was significant at P < 0.01. Thus, under the conditions of this study, the air-filtration system evaluated appeared to be highly effective at reducing aerosol transmission of PRRSV.

Evaluation of the aerosol transmission of a mixed infection of Mycoplasma hyopneumoniae and porcine reproductive and respiratory syndrome virus

To evaluate the transmission of Mycoplasma hyopneumoniae and porcine reproductive and respiratory syndrome virus (PRRSV) by aerosol as either a single or mixed infection, 28 pigs were inoculated intratracheally with M hyopneumoniae on day 0 and infected intranasally with PRRSV on day 35; they were housed together in a barn. To assess the aerosol transmission of M hyopneumoniae as a single infection, one trailer (A) containing 10 five-week-old sentinel pigs was placed along the south side of the infected barn (1 m from the fans) on day 28. To assess the mixed infection, two trailers (B and C), each containing 10 five-week-old sentinel pigs, were placed along each side of the barn on day 42. The sentinel pigs in the three trailers were exposed to the exhaust from the fans for seven days. No M hyopneumoniae infection was detected in the sentinel pigs in trailer A, but it was detected in the sentinel pigs in trailers B and C. No PRRSV was detected in any of the sentinel pigs.

Dynamics and persistence of Mycoplasma hyopneumoniae infection in pigs

The purpose of this study was to describe the dynamics (shedding and transmission) of Mycoplasma hyopneumoniae infection within a population of swine and to determine the duration of the infection (persistence) through the identification of the agent in bronchial samples. Sixty-three 2-month-old pigs were used in this study. The pigs (n = 28) were experimentally infected by the intratracheal route with M. hyopneumoniae and considered as seeder pigs. The remaining pigs (n = 32) were not inoculated and randomly allocated to 2 different groups: direct contact exposure pigs (n = 12) and indirect contact exposure pigs (n = 20). Blood samples and nasal swabs were collected throughout the study on days 0, 28, 35, 42, 49, 63, 91, and 119 postinfection. To assess the duration of M. hyopneumoniae infection, 9 seeder and 6 contact exposure pigs were slaughtered at days 155 (group 1), 170 (group 2), and 185 (group 3) postinfection. Direct contact pigs showed evidence of infection on day 28 by polymerase chain reaction (PCR) and on day 35 by serology. The indirect contact exposure pigs presented a very delayed and slow seroconversion pattern; they did not present evidence of transmission until 42 d after the infection of seeder pigs. Identification of M. hyopneumoniae in bronchial swabs was confirmed by nested-PCR from days 155 to 185 postinfection. At the last slaughter date, 77.7% and 100% of the seeders and contact exposure pigs, respectively, tested positive. The results of this study reconfirmed direct infection of M. hyopneumoniae and suggest that indirect transmission can occur in a population. Finally, duration of the infection in this study was longer than previously described.

Laboratory model to evaluate the role of aerosols in the transport of porcine reproductive and respiratory syndrome virus

The aim of this study was to develop a model to evaluate the aerosol transmission of porcine reproductive and respiratory disease virus (PRRSV). PRRSV (MN 30-100 strain, total dose 3 x 10(6) virus particles) was aerosolised and transported up to 150 m and a portable air sampler was used to collect air samples at 1, 30, 60, 90, 120 and 150 m (five replicates at each distance) and the air samples were tested by TaqMan PCR and virus isolation. The infectivity of the aerosolised PRRSV was tested by exposing six PRRSV-naive pigs for three hours to aerosolised virus that had been transported 150 m. PRRSV RNA was detected in all five replicate air samples collected at 1, 30, 60 and 90 m, in four of the five collected at 120 m, and in three of the five collected at 150 m. Infectious PRRSV was detected by virus isolation at 1 and 30 m (all five replicates), 60, 90 and 120 m (three of the five) and 150 m (two of the five). There was a 50 per cent reduction in the log concentration of PRRSV RNA every 33 m. Three of the six pigs exposed to PRRSV-positive aerosols became infected, and PRRSV RNA was detected in air samples and on swab samples collected from the interior of the chambers that housed the infected pigs while they were being exposed.

Osteopoikilosis in an ancient skeleton: more than a medical curiosity

We describe the palaeopathologic and radiographic findings of the human skeletal remains that belonged to a female who lived in Mexico's viceroyship period (seventeenth and eighteenth centuries A.D.). Radiographic studies showed numerous, radiodense, ovoid, small and well-defined foci in the long tubular bones, sacrum, scapulae and iliac bones. Computed tomography (CT) examination revealed multiple hyperdense foci located in the central marrow portion of the bones. Measurements of attenuation coefficient revealed +1548 HU. The findings are consistent with osteopoikilosis, an uncommon, benign sclerosing bone dysplasia transmitted in an autosomal dominant fashion, which in the clinical setting is important to set apart from different bone pathologies to avoid unnecessary interventions and treatments. To the best of our knowledge, this is the first report of osteopoikilosis in ancient human remains.

Spatial dispersal of porcine reproductive and respiratory syndrome virus-contaminated flies after contact with experimentally infected pigs

OBJECTIVE

To determine whether flies can acquire porcine reproductive and respiratory syndrome virus (PRRSV) and disperse the virus throughout a designated area.

ANIMALS

60 four-month-old pigs.

PROCEDURE

On day 0, 28 of 60 pigs were inoculated with PRRSV MN 30-100 (index variant). On the same day, 100,000 pupae of ochre-eyed houseflies and 100,000 pupae of red-eyed (wild-type) houseflies were placed in the swine facility for a release-recapture study. Flies were recaptured at 2 locations within the swine facility, 6 locations immediately outside the facility, and 30 locations 0.4, 0.8, 1.3, 1.7, 1.9, and 2.3 km from the facility. Traps were emptied on days 2, 7, 8, 10, and 14. Samples derived from flies were tested by use of a polymerase chain reaction assay, virus DNA was sequenced, and viruses were tested for infectivity by means of a swine bioassay.

RESULTS

PRRSV RNA homologous to the index PRRSV was detected in trapped flies collected inside and immediately outside the facility and from 9 of 48 samples collected at 0.4 km, 8 of 24 samples collected at 0.8 km, 5 of 24 samples collected at 1.3 km, and 3 of 84 samples collected at > 1.7 km from the facility. Two samples collected at 0.8 km contained genetically diverse variants of PRRSV. Swine bioassays revealed the virus in flies was infectious.

CONCLUSIONS AND CLINICAL RELEVANCE

Flies appeared to become contaminated with PRRSV from infected pigs and transported the virus > or = 1.7 km. Fly-born transmission may explain how PRRSV is seasonally transported between farms.

An evaluation of disinfectants for the sanitation of porcine reproductive and respiratory syndrome virus-contaminated transport vehicles at cold temperatures

The objective of this study was to evaluate the efficacy of commercially available disinfectants to sanitize porcine reproductive and respiratory syndrome virus (PRRSV) contaminated trailer models in cold climates (-20 degrees C and 4 degrees C). Disinfectants evaluated included Synergize, Aseptol 2000, Biophene, Sentramax, Virkon, Tek Trol, and DC&R. All products were applied to trailers via fumigation at 4 degrees C. Following experimental contamination of model trailers with PRRSV MN 30-100 (5 x 10(5) TCID50), models were tested for the presence or absence of PRRSV-RNA by polymerase chain reaction (PCR) on swabs collected 0, 30, and 60 min after treatment. Treatments included washing only, washing plus disinfectant fumigation, washing plus fumigation, and washing plus overnight drying. The PRRSV-RNA detected across trailers ranged from 0/12 replicates in trailers treated with Synergize or allowed to dry for 8 h. These trailers were also negative for the presence of infectious PRRSV, based on the lack of sentinel pig infection (0/4 replicates). In contrast, the detection of PRRSV-positive swabs by PCR ranged from 3/12 (Aseptol) to 10/12 (Biophene). Based on these results, the efficacy of Synergize was evaluated at -20 degrees C. In an attempt to reduce the impact of freezing on disinfectant activity, 30 mL of disinfectant was added to a 3840 mL of a 40% methanol solution, a 10% propylene glycol (PG) solution, or water alone. The PRRSV-contaminated trailers were treated with 1 of 3 disinfectant mixtures via fumigation, stored for 8 h at -20 degrees C, allowed to thaw, and sampled as described. Trailers treated with 40% methanol or 10% PG did not freeze and were negative for PRRSV-RNA and infectious virus following thawing. In contrast, trailers treated with disinfectant and water were frozen within 60 min at -20 degrees C, and decontamination was not successful.

An evaluation of thermo-assisted drying and decontamination for the elimination of porcine reproductive and respiratory syndrome virus from contaminated livestock transport vehicles

The purpose of this report is to validate a new protocol, the thermo-assisted drying and decontamination (TADD) system, for eliminating porcine reproductive and respiratory syndrome virus (PRRSV) from contaminated transport vehicles. Scale models of weaned pig trailers were used. The principle of TADD is to raise the interior temperature of trailers to 71 degrees C for 30 min to promote drying and degradation of PRRSV. Trailer interiors were artificially contaminated with 5 x 10(5) TCID50 of PRRSV strain MN 30-100, then treated with 1 of 4 treatments: 1) TADD; 2) air only (no supplemental heat); 3) overnight (8 h) drying; and 4) washing only. Following treatment, swabs were collected from the trailer interiors at 0, 10, 20, and 30 min post-treatment and from the overnight group after 8 h. Swabs were tested for PRRSV-RNA by polymerase chain reaction (PCR). As a measure of the presence of infectious PRRSV, sentinel pigs were housed in treated trailers for 2 h post-treatment and supernatants from swabs were injected IM into naive pigs (bioassay), the recipient pigs were then tested for PRRSV infection. All trailers were PRRSV positive by PCR immediately after washing, prior to treatment (pt). At 10 min pt, 7/10 swabs were positive from the TADD trailers; however, all swabs collected at 20 and 30 min pt were PRRSV negative by PCR, and trailer interiors were visibly dry. In contrast, 9/19, 6/10, and 6/10 swabs collected at 10, 20, and 30 min, respectively, from trailers treated with air only were positive and visibly wet. All swabs (10/10) collected from trailers treated with washing only were PRRSV positive by PCR and all swabs collected at 8 h of drying were PRRSV negative by PCR. All tests for the presence of infectious PRRSV were negative for trailers treated with TADD and overnight drying, while infectious PRRSV was detected in sentinel pigs and bioassay pigs in the other groups. Under the conditions of this study, the efficacy of the TADD system was equal to that of the overnight drying treatment, and it required a shorter period of time to complete its objective.

Eradication of porcine reproductive and respiratory syndrome virus by serum inoculation of naïve gilts

The acclimatization program included exposure to serum and recovery. A continuous flow unit (nursery to finishing) from the same farm was selected as a potential source of porcine reproductive and respiratory syndrome virus (PRRSV). Negative gilts were inoculated 5 d after arrival by intramuscular injection of serum from selected animals. There was a significant reduction in seroprevalence in the sow herd 1 y after implementation of the gilt inoculation program (P < 0.05). At that time, all of the tested nursery pigs were negative for PRRSV. The fully segregated finisher population had a significant reduction in the frequency of PRRSV positive animals (P < 0.05) by enzyme-linked immunosorbent assay (ELISA), with all animals testing negative by the end of the study. However a persistent seroconversion was observed in the partially segregated finisher pigs (P > 0.05). In conclusion, the gilt serum inoculation program achieved sow herd stabilization, as defined by the production of negative weaned pigs and this resulted in the eradication of PRRSV in the fully segregated flow.

Comparison between Haemophilus parasuis infection in colostrums-deprived and sow-reared piglets

The aim of this study was to compare the development of Glasser's disease in sow-reared and colostrum-deprived piglets. Ninety piglets from a commercial pig farm in Spain were used. The farm was positive for Haemophilus parasuis. Fifty-two pigs were sow-reared (SR) and 38 were colostrum-deprived (CD) piglets. The animals were intratracheally inoculated with H. parasuis serovar 5 and sacrificed at 1, 2 and 3 days post-infection. To assess the development of disease, antibody titers, clinical signs, pathological lesions, microbiological isolation and PCR amplification were compared between the groups. Inoculation of SR pigs did not cause clinical signs or lesions of Glasser's disease. In SR pigs, H. parasuis isolation and specific PCR amplification from tissues showed a very low number of positive samples. In contrast, in CD pigs, inoculation resulted in the typical signs and lesions of Glasser's disease. Positive microbiological isolation and specific PCR products were obtained from the majority of the tissues tested, and no antibodies against H. parasuis were detected. The experimental infection using CD pigs describes a successful method to study this microorganism and confirms the important role that maternal antibodies play in protection against clinical signs and disease.

Virological and immunological responses to porcine reproductive and respiratory syndrome virus in a large population of gilts

Porcine reproductive and respiratory syndrome virus (PRRSV) causes a prolonged active infection followed by a persistent infection in lymphoid tissues lasting for several months. Pigs develop both an antibody and cell-mediated immune response following PRRSV infection, but the specific role of each type in the development of protective immunity and clearance of the virus is not yet known. The aims of this study were to characterize the dynamics of PRRSV persistence from 0 to 135 d post infection (pi), characterize the kinetics of the antibody mediated immune response following PRRSV infection, and characterize the cell mediated immune responses to PRRSV infection. Eighty, 4-month-old PRRSV-free gilts were obtained from a source known to be negative for PRRSV. On day 0, gilts were infected intranasally with 10(2.4) TCID/50 MN 30-100 PRRSV. Following infection, animals were bled between days 0 to 135 pi. Viremia was detected up to day 30. Serum antibody response (by enzyme-linked immunosorbent assay [ELISA] and virus neutralization antibody) was detected from day 14 to 120 pi. Cell-mediated immune response represented by interferon gamma (IFN-gamma) was detected from day 14 to 120 pi. Persistence of PRRSV in tissues was confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) between days 30 to 135. These results indicate that serum neutralizing antibodies and IFN-gamma play an important role in the clearance of PRRSV. Nevertheless none of the parameters measured (virus neutralizing antibodies), either alone or in combination, are solely responsible for the clearance of the virus from the host and the development of sterilizing immunity.

An assessment of sanitation protocols for commercial transport vehicles contaminated with porcine reproductive and respiratory syndrome virus

The objective of this study was to develop and test a rapid (< 2 h) sanitation protocol designed for porcine reproductive and respiratory syndrome virus (PRRSV) positive commercial transport vehicles involving cold water washing and disinfection via fumigation using scale models of weaned pig trailers. The study consisted of 2 phases. Following experimental contamination of model trailers with PRRSV MN 30-100 (5 x 10(5)TCID50), phase 1 evaluated the presence or absence of PRRSV RNA by polymerase chain reaction (PCR) on swabs collected from the trailer interiors 0, 60, and 90 min after treatment. Phase 2 consisted of evaluating the infectivity of trailers 90 min posttreatment by monitoring changes in the PRRSV-status of naive sentinel pigs housed for 2 h. Treatments included washing only (treatment 1), washing plus formaldehyde fumigation (treatment 2), washing plus fumigation with glutaraldehyde-quaternary ammonium chloride (treatment 3), and washing plus overnight drying (treatment 4). Porcine reproductive and respiratory syndrome virus RNA was detected in all trailers (20 out of 20 replicates) at 60 and 90 min following the application of treatments 1 and 2. These trailers also contained infectious PRRSV, as determined by the infection of naive pigs housed in treated trailers and the testing of organic debris collected from the interior of trailers by swine bioassay. At 90 min posttreatment, all trailers treated with glutaraldehyde-quaternary ammonium chloride were PCR-negative, non-infectious to sentinel pigs, and swine bioassay negative. Similar results were observed in trailers allowed to dry for 8 h. Under the conditions of this study, it appears certain disinfectants may possess different levels of efficacy against PRRSV and PRRSV-positive models may be effectively sanitized in the absence of overnight drying.

Attempts to transmit porcine reproductive and respiratory syndrome virus by aerosols under controlled field conditions

An experimental infection with porcine reproductive and respiratory syndrome virus (PRRSV) was established in 150 five-month-old pigs housed in a fan-ventilated finishing facility, the infected barn. To determine whether air exhausted from the wall fans contained infectious PRRSV, a trailer containing 10 four-week-old PRRSV-naive sentinel pigs was placed 10 m from the building from day 3 after the 150 pigs were infected until day 10. To connect the two airspaces, one end of an opaque plastic tube, 15 m in length and 5 cm in diameter, was fastened to the wall fan of the infected barn, and the other end was placed inside the trailer. Air from the building was exhausted into the trailer 24 hours a day for seven consecutive days and PRRSV infection was monitored in the infected pigs and the sentinel pigs. Air samples were collected from the infected barn and the trailer. PRRSV infection was detected in the infected pigs three and seven days after they were infected, but not in the sentinel pigs. All the air samples were negative for PRRSV by PCR, virus isolation and a pig bioassay.

An experimental model to evaluate the role of transport vehicles as a source of transmission of porcine reproductive and respiratory syndrome virus to susceptible pigs

The objectives of this study were to determine the concentration of porcine reproductive and respiratory syndrome virus (PRRSV) in a scale-model trailer that was required to infect susceptible pigs, evaluate the potential of PRRSV-contaminated transport vehicles to infect naïve pigs and assess 4 sanitation programs for the prevention of virus spread. To maximize study power, scale models (1:150) of weaned-pig trailers were constructed that provided an animal density equal to that of an actual weaned-pig trailer capable of transporting 300 pigs. The 1st aim involved contaminating the interior of the model trailers with various concentrations (10(1) to 10(4) TCID50/mL) of PRRSV MN 30-100, then housing sentinel pigs in the trailers for 2 h. Pigs exposed to trailers contaminated with > or = 10(3) TCID50/mL became infected. The 2nd aim involved housing experimentally infected seeder pigs in trailers for 2 h, then directly introducing sentinel pigs for 2 h. Infection of sentinels was demonstrated in 3 of 4 replicates. The 3rd aim involved applying 1 of 4 sanitation procedures (treatments) to contaminated trailers. Treatment 1 consisted of manual scraping of the interior to remove soiled bedding (wood chips). Treatment 2 consisted of bedding removal, washing (80 degrees C, 20,500 kPa), and disinfecting (with 1:256 phenol; 10-min contact time). Treatment 3 consisted of treatment 2, followed by freezing and thawing. Treatment 4 consisted of bedding removal, washing, disinfecting, and drying. Ten replicates were conducted per treatment. Pretreatment swabs from all trailers tested positive by polymerase chain reaction (PCR). Post-treatment swabs were PCR-positive for all trailers except those that were washed, disinfected, and dried. Infection of sentinel pigs by PRRSV was also detected by PCR after all treatments except washing, disinfecting, and drying. Under the conditions of this study, drying appeared to be an important component of a sanitation program for ensuring PRRSV biosecurity of transport vehicles.

Evaluation of the role of mallard ducks as vectors of porcine reproductive and respiratory syndrome virus

To assess the transmission of porcine reproductive and respiratory syndrome virus (PRRSV) from pigs to mallard ducks, 10 adult (one-year-old) female mallard ducks were housed with pigs infected experimentally with PRRSV, and allowed to be in close contact with them for 21 days. To evaluate the transmission of PRRSV from mallard ducks to pigs, two adult ducks were inoculated orally with PRRSV (total dose 10(6.0) TCID50) and allowed to drink PRRsv-infected water; 24 hours later, two four-week-old PRRsv-naive sentinel pigs were housed in pens below the cages housing the ducks for 14 days. In both experiments, cloacal and faecal samples were collected three times a week from the ducks and tested by PCR, virus isolation and a pig bioassay. Blood samples from the pigs were tested by ELISA, PCR and virus isolation. Sera from the ducks were tested by serum neutralisation. The ducks were examined postmortem and selected tissues were tested by PCR, virus isolation, histopathology and pig bioassay. In both experiments all the cloacal swabs, faecal samples, tissues and sera from the ducks were negative by all the tests. The sera from the pigs in the first experiment were PCR positive at three, seven, 14 and 21 days after infection and ELISA positive at 14 and 21 days. Sera from the pigs in the second experiment were negative by all the tests. The virus was isolated from the oral inoculum and the drinking water provided for the ducks in the second experiment. Under the conditions of this study, it was not possible to demonstrate the transmission of PRRSV either from the pigs to the ducks or from the ducks to the pigs.

Haemophilus parasuis: new trends on diagnosis, epidemiology and control

Haemophilus parasuis is a commensal organism of the upper respiratory tract of conventional pigs, but under appropriate conditions can invade and cause severe systemic disease, characterized by fibrinous polyserositis, arthritis and meningitis. Factors involved in systemic invasion by H. parasuis remain largely unknown. However, major advances in our knowledge of H. parasuis include (1) development of a species-specific PCR test to detect H. parasuis in clinical samples, (2) study of molecular epidemiology within and between herds, by use of a repetitive element-based PCR, (3) the proposal of an alternative serotyping technique, (4) development and testing of a new in vivo model for pathogenesis and virulence studies, and (5) use of controlled exposure of young pigs to low doses of live, virulent H. parasuis strains to reduce nursery mortality in affected swine herds.

Studies on the carriage and transmission of porcine reproductive and respiratory syndrome virus by individual houseflies (Musca domestica )

The objectives of the study were to determine the site of porcine reproductive and respiratory syndrome virus (PRRSV) in individual houseflies, to assess whether an individual housefly could transmit PRRSV to a susceptible pig, and to compare the ability of PCR, virus isolation and a pig bioassay to detect PRRSV in houseflies. In the first experiment 26 houseflies were fed on a pig infected experimentally with PRRSV; 13 were processed as a whole fly homogenate, while an exterior surface wash and a gut homogenate were collected from the other 13. Infectious PRRSV was recovered from nine of the whole fly homogenates, 12 of the gut homogenates and one of the exterior surface washes. In the second experiment, two of 10 individual houseflies, which had fed on an infected pig, transmitted PRRSV to a susceptible pig in a controlled manual transmission protocol. In the third experiment, single flies or pools of 30 flies were immersed in different concentrations of a PRRSV inoculum, then tested by PCR, virus isolation and bioassay. The virus was detected at a concentration of 10(1) TCID50/ml by PCR, 10(2) TCID50/ml by the bioassay and 10(3) TCID50/ml by virus isolation.

Computer-based analysis of Haemophilus parasuis protein fingerprints

The present study aimed to compare the whole-cell protein profiles of Haemophilus parasuis field isolates by using a computer-based analysis, and evaluate the relationship between polyacrylamide gel electrophoresis (PAGE) type and virulence potential based on isolation site. A dendrogram clustering isolates with similar protein profiles was generated. Haemophilus parasuis isolates were grouped into 2 major PAGE type groups. The PAGE type II isolates were characterized by the presence of major proteins with molecular weights varying from between 36 and 38 kDa and included 90.7% of the isolates recovered from systemic sites, such as pleura, pericardium, peritoneum, lymph nodes, joints, and brain. Isolates classified as PAGE type I were characterized by the absence of this group of proteins and included 83.4% of the isolates recovered from the upper respiratory tract of healthy animals. The present study further corroborates the existence of a unique group of major proteins in potentially virulent H. parasuis isolates.

Evaluation of 4 intervention strategies to prevent the mechanical transmission of porcine reproductive and respiratory syndrome virus

Four intervention strategies were tested for their ability to prevent the mechanical transmission of porcine reproductive and respiratory syndrome virus (PRRSV): the use of disposable plastic boots to prevent contamination of personal footwear, the use of boot baths to disinfect PRRSV-contaminated plastic boots, the use of plastic slatted (Polygrate) flooring in the anteroom to prevent PRRSV contamination of incoming personal footwear, and the use of bag-in-a-box shipping methods to prevent PRRSV contamination of the contents of a container destined for a swine farm. Ten PRRSV-positive replicates and 10 PRRSV-negative (sham-inoculated) replicates were used for each strategy. Swabs were collected from selected sites and tested by TaqMan polymerase chain reaction for PRRSV RNA and by swine bioassay to confirm the presence of infectious PRRSV. Results indicated that the use of disposable boots, bleach boot baths or bag-in-a-box shipping methods was highly efficacious in preventing mechanical transmission of PRRSV. In contrast, the use of Polygrate flooring in the anteroom did not prevent contamination of personal footwear. The numbers of PRRSV-positive samples from the Polygrate surface and the soles of incoming footwear placed directly on the Polygrate surface were not significantly different (P = 0.24) from those of footwear that directly contacted the floor of the contaminated anteroom. Although these results are promising, this study should be considered a pilot project and the intervention strategies not considered biosecurity protocols. The model used may or may not represent field conditions. Therefore, the information should be used to develop larger experimental studies, with sufficient statistical power, in combination with field-based epidemiologic studies to better assess the role of mechanical transmission of PRRSV under field conditions.

Evaluation of mosquitoes, Aedes vexans, as biological vectors of porcine reproductive and respiratory syndrome virus

The objective of this study was to determine whether mosquitoes, Aedes vexans (Meigen), could serve as biological vectors of porcine reproductive and respiratory syndrome virus (PRRSV). Specifically, the study assessed the duration of viability and the site of PRRSV within mosquitoes, and evaluated whether PRRSV could be transmitted to a susceptible pig by mosquitoes following a 7- to 14-day incubation period after feeding on an infected pig. For the first experiment, a total of 100 mosquitoes were allowed to feed on a pig, experimentally infected with PRRSV (day 7 post-inoculation) and were then maintained alive under laboratory conditions. A set of 10 mosquitoes were collected at 0 hour (h), 6 h, 12 h, 24 h, 48 h, 72 h, 5 days (d), 7 d, 10 d, and 14 d post-feeding (pf). Samples of exterior surface washes, salivary glands, thorax carcasses, and gut homogenates were collected from each set of mosquitoes, and tested for PRRSV. Infectious PRRSV was detected by polymerase chain reaction and swine bioassay only from the gut homogenates of mosquitoes collected at 0 h and 6 h pf. For the second experiment, a total of 30 mosquitoes were allowed to feed on a pig, experimentally infected with PRRSV and the mosquitoes were then maintained under laboratory conditions. On each of day 7, 10, and 14 pf, a set of 10 mosquitoes were allowed to feed on a susceptible pig. Transmission of PRRSV to susceptible pigs did not occur, and PRRSV was not detected from the mosquitoes. These findings indicate that mosquitoes are not likely to serve as biological vectors of PRRSV.

Survival of porcine reproductive and respiratory syndrome virus in houseflies

The objectives of the study were to determine the duration of porcine reproductive and respiratory syndrome virus (PRRSV) survival in houseflies (Musca domestica Linnaeus) following feeding on an infected pig, and to determine whether the virus was present on the exterior surface or within the internal viscera of the fly. A total of 210 laboratory-colonized houseflies were allowed to feed to repletion on a pig, experimentally infected with PRRSV on day 7 postinoculation, and then maintained alive under laboratory conditions (27 degrees C). Two subsets (A and B) of 30 flies were collected at each of the following sampling points; 0, 6, and 12 hours post feeding (pf). Subset A contained an extra group of 30 flies collected at 24 hours pf due to the availability of extra flies. Flies in subset A were processed as whole fly homogenates, while the exterior surface washes and digestive organs were collected from flies in subset B. Whole fly homogenates, collected at 0, 6, and 12 hours pf, were positive by both polymerase chain reaction (PCR) and swine bioassay. Digestive organs, collected at 0 and 12 hours pf, were positive by PCR and swine bioassay. The PRRSV RNA was detected by PCR from the exterior surface wash of subset B flies collected at 0, 6, and 12 hours pf; however, only the subset collected at 0 hour pf was swine bioassay-positive. This study indicates that infectious PRRSV can survive within the intestinal tract of houseflies for up to 12 hours following feeding on an infected pig, but only for a short period on the exterior surface of the flies.

Naturally-farrowed, artificially-reared pigs as an alternative model for experimental infection by Haemophilus parasuis

The use of naturally-farrowed, artificially-reared piglets as an alternative model to study Haemophilus parasuis infections was evaluated. Two trials were performed in order to evaluate the proposed model. In trial 1, animals were vaccinated and challenged with H. parasuis. Results showed that the proposed model was effectively used to evaluate protective immunity against this organism. In trial 2, animals were challenged with different doses of H. parasuis. Results showed that the severity of clinical signs and lesions tended to increase with higher doses. The reproduction of clinical signs and lesions characteristic of H. parasuis systemic infection was successful in both trials, proving that this model is a viable alternative to specific-pathogen free and cesarean-derived, colostrum-deprived pigs.

Characterization of the diversity of Haemophilus parasuis field isolates by use of serotyping and genotyping

OBJECTIVE

To characterize the genetic diversity of Haemophilus parasuis field isolates with regard to serovar, herd of origin, and site of isolation.

SAMPLE POPULATION

Isolates of H parasuis obtained from pigs in 15 North American herds and multi-farm systems.

PROCEDURE

98 H parasuis isolates were genotyped with the enterobacterial repetitive intergeneic consensus based-polymerase chain reaction (ERIC-PCR) technique and serotyped via agar gel precipitation test. Genomic fingerprints were analyzed and dendrograms were constructed to identify strains from the same serovar group, herd of origin, or isolation site and to evaluate the genetic variability within these categories.

RESULTS

Serovar 4 (39%) and nontypeable (NT) isolates (27%) were most prevalent. Thirty-four distinct strains were identified among the 98 isolates, using a 90% similarity cutoff. Strains from serovar 4 and NT isolates had high genetic diversity (12 and 18 strains, respectively). One to 3 major clusters of prevalent strains could be identified in most of the evaluated herds. Haemophilus parasuis strains isolated from the upper respiratory tract were either serovar 3 or NT isolates. Potentially virulent strains (isolated from systemic sites) were either serovars 1, 2, 4, 5, 12, 13, or 14, or NT isolates.

CONCLUSIONS AND CLINICAL RELEVANCE

Although H parasuis had high genetic diversity overall, only a few strains caused disease in these herds. The ERIC-PCR technique was more discriminative than serotyping, and a broad genetic variety was observed within particular serovar groups.

Identification and characterization of cytopathogenic Mycoplasma hyorhinis from swine farms with a history of abortions

A virus-like cytopathic agent isolated from swine farms with a history of recurrent abortion episodes was investigated. We employed a differential display reverse transcription-polymerase chain reaction (ddRT-PCR) to obtain genetic information of the cytopathic agent. Partial nucleotide sequence (527 bp) obtained from differentially displayed PCR fragments showed 88.7% similarity with the 23S rRNA gene of Mycoplasma hyopneumoniae. Unexpectedly, the 5' portion (1-333 bp) of the sequence shared 96.1% similarity with 5' untranslated region (UTR) of human prostate tumor inducing gene 1 (PTI-1). Cytopathic effects and extranuclear DNA fluorescence were no longer observed when BM-cyclin was added in the culture medium, suggesting that BM-cyclin sensitive mycoplasma-like organisms caused the cell death. Further evidence supporting the cytopathic agent as a mycoplasma-like organism was obtained by the capability of (3)H-thymidine and (3)H-uridine incorporation, a single peak in buoyant density gradient profile (1.20-1.24 g/ml), and ultrastructural morphology. Unlike M. hyopneumoniae, the organism was not propagated in Friis medium. Nucleotide sequence of 16S rRNA obtained from the cytopathic agent showed 0.8-1.0% divergences with other M. hyorhinis strains, suggesting that the newly isolated cytopathogenic swine mycoplasma was a variant form of M. hyorhinis. Striking homology between a portion of the 23S rRNA gene of M. hyorhinis and 5' UTR of human PTI-1 implicated that M. hyorhinis might potentially be related to the evolution of human PTI-1.

Transmission of porcine reproductive and respiratory syndrome virus by houseflies (Musca domestica)

Three hundred houseflies were allowed to feed on donor pigs viraemic with porcine reproductive and respiratory syndrome virus (PRRSV) on the fifth, sixth and seventh days after the pigs had been inoculated with the virus. After 60 seconds, the flies' feeding was interrupted, and they were transferred manually to feed to repletion on a naive recipient pig housed in a separate room. To enhance the chance of the flies obtaining the pigs' blood, the back of each pig was scarified with sandpaper until a slight haemorrhage was visible. The PRRSV was transmitted from the donor to the recipient pigs, and PRRSV RNA was detected by reverse transcriptase-PCR from homogenates of the flies. In a second experiment, 210 houseflies were allowed to feed to repletion on a PRRSV-infected pig on the sixth day after it had been inoculated, and were then maintained under laboratory conditions. Groups of 30 flies were collected immediately after they had fed and six, 12, 24, 48, 72 and 96 hours later, and were tested for PRRSV. Homogenates of the flies collected up to six hours after feeding were PCR- and pig bioassay-positive, but the others were negative by both tests.

Mechanical transmission of porcine reproductive and respiratory syndrome virus throughout a coordinated sequence of events during warm weather

Mechanical transmission of porcine reproductive and respiratory syndrome virus (PRRSV) throughout a coordinated sequence of events that replicated common farm worker behavior during warm weather (10 degrees C to 16 degrees C) was assessed using a field-based model. The model involved fomites (boots and containers), vehicle sanitation, transport, and personnel movement. In a previous study, the model successfully demonstrated mechanical transmission of PRRSV in 8 out of 10 replicates during cold weather. A field strain of PRRSV was inoculated into carriers consisting of soil samples, which were adhered to the undercarriage of a vehicle. The vehicle was driven approximately 50 km to a commercial truck washing facility where the driver's boots contacted the carriers during washing, introducing the virus to the vehicle interior. The vehicle was then driven 50 km to a simulated farm site, and the driver's boots mechanically spread virus into the farm anteroom. Types of containers frequently employed in swine farms contacted drippings from the footwear on the anteroom floor. The truck wash floor, vehicle cab floor mats, boot soles, anteroom floor, and the ventral surface of containers were sampled to track the virus throughout the model. Ten replicates were conducted, along with sham-inoculated controls, and control replicates. In 2 replicates, infectious PRRSV was detected on the anteroom floor and in 1 replicate, infectious PRRSV was detected on the surface of the container by swine bioassay. All sham-inoculated controls and protocol controls were negative. These results indicate that mechanical transmission of PRRSV throughout a coordinated sequence of events in warm weather can occur, but in contrast to data from studies conducted during cold weather, it appears to be a relatively infrequent event.

Mechanical transmission of porcine reproductive and respiratory syndrome virus throughout a coordinated sequence of events during cold weather

Using a field-based model, mechanical transmission of porcine reproductive and respiratory syndrome virus (PRRSV) wa assessed throughout a coordinated sequence of events that replicated common farm worker behavior during cold weather (< 0 degrees C). The model involved fomites (boots and containers), vehicle sanitation, transport, and the movement of personnel. A field strain of PRRSV was inoculated into carriers consisting of snow and water, and carriers were adhered to the undercarriage of a vehicle. The vehicle was driven approximately 50 km to a commercial truck washing facility where the driver's boots contacted the carriers during washing, introducing the virus to the vehicle interior. The vehicle was then driven 50 km to a simulated farm site, and the driver's boots mechanically spread virus into the farm anteroom. Types of containers frequently employed in swine farms (styrofoam semen cooler, metal toolbox, plastic lunch pail, and cardboard animal health product shipping parcel) contacted drippings from footwear on the anteroom floor. The truck wash floor, vehicle cab floor mats, boot soles, anteroom floor, and the ventral surface of containers were sampled to track the virus throughout the model. Ten replicates were conducted, along with sham-inoculated controls. At multiple sampling points PRRSV nucleic acid was detected in 8 of 10 replicates. In each of the 8 PCR-positive replicates, infectious PRRSV was detected on the surfaces of containers by virus isolation or swine bioassay. All sham-inoculated controls were negative. These results indicate that mechanical transmission of PRRSV can occur during coordinated sequence of events in cold weather.

Mechanical transmission of porcine reproductive and respiratory syndrome virus by mosquitoes, Aedes vexans (Meigen)

The objective of this study was to determine whether porcine reproductive and respiratory syndrome virus (PRRSV) could be transmitted to naive pigs by mosquitoes following feeding on infected pigs. During each of 4 replicates, mosquito-to-pig contact took place on days 5, 6, and 7 after PRRSV infection of the donor pig. A total of 300 mosquitoes [Aedes vexans (Meigen)] were allowed to feed on each viremic donor pig, housed in an isolation room. After 30 to 60 s, feeding was interrupted, and the mosquitoes were manually transferred in small plastic vials and allowed to feed to repletion on a naïve recipient pig housed in another isolation room. Prior to contact with the recipient pig, the mosquitoes were transferred to clean vials. Swabs were collected from the exterior surface of all vials, pooled, and tested for PRRSV. Separate personnel handled the donor pig, the recipient pig, and the vial-transfer procedure. Transmission of PRRSV from the donor to the recipient pig occurred in 2 out of 4 replicates. The PRRSV isolated from the infected recipient pigs was nucleic-acid-sequenced and found to be 100% homologous with the virus used to infect the donor pigs. Homogenates of mosquito tissues collected in all replicates were positive by either polymerase chain reaction or swine bioassay. All control pigs remained PRRSV negative, and PRRSV was not detected on the surface of the vials. This study indicates that mosquitoes (A. vexans) can serve as mechanical vectors of PRRSV.

Assessing the duration of persistence and shedding of porcine reproductive and respiratory syndrome virus in a large population of breeding-age gilts

Porcine reproductive and respiratory syndrome virus (PRRSV) is an RNA virus in the order Nidovirales, family Arteriviridae, genus Arterivirus. The virus induces a prolonged viremia, replicates in macrophages, and produces persistent infection. The purpose of this study was to determine if PRRSV could persist for 90 d or more in a large population of breeding-age gilts housed under environmental conditions typical of commercial swine production and to determine if experimentally infected gilts could shed virus to naive sentinel gilts beyond 90 d postinfection. Using the intranasal route, we inoculated 120 PRRSV-naïve gilts, 4 mo of age, with 5 mL of cell culture fluid containing a total dose of 10(2.4) TCID50 of a field isolate (MN-30100) of PRRSV. The index gilts were organized into 3 groups (A, B, and C), 40 gilts per group. To assess the dynamics of the experimental infection, a monitor group of 30 index gilts was blood-tested on days 0, 3, 7, 14, 30, 60, 90, 120, 150, and 180 postinfection. PRRSV viremia was detected with the polymerase chain reaction (PCR) on days 3, 7, and 14 and by virus isolation (VI) on days 7 and 14. PRRSV antibodies were detected from day 14 by enzyme-linked immunosorbent assay (ELISA). To assess shedding, 30 PRRSV-naïve sentinel gilts were commingled with the index gilts on day 90 postinfection and tested by PCR, VI, and ELISA every 15 d until 180 d postinfection; all samples were negative. To assess persistence, 40 index and 10 sentinel gilts were slaughtered at 120 (group A), 150 (group B), or 180 (group C) d postinfection. Evidence of PRRSV was not detected by PCR or VI in any tissue samples from the 120 index gilts. These results indicate that persistence and shedding of PRRSV are of short duration in breeding-age gilts.

Evaluation of aerosol transmission of porcine reproductive and respiratory syndrome virus under controlled field conditions

The aim of this study was to determine whether porcine reproductive and respiratory syndrome virus (PRRSV) could be transmitted by aerosol under field conditions. A total of 210 five-month-old PRRSV-negative pigs were housed in a mechanically ventilated finishing facility containing 11 pens. Pen 1 contained 10 pigs (indirect contact controls) and pen 2 remained empty, providing a barrier of 2.5 m from the remaining pigs in pens 3 to 11. Fifteen or 16 of the pigs in each of pens 3 to 11 were infected experimentally with a field isolate of PRRSV and the other six or seven pigs served as direct contact controls. Five days after the pigs were infected, two trailers containing 10 five-week-old PRRSV-naive sentinel pigs were placed along each side of the building; one was placed 1 m from the exhaust fans on one side of the building, and the other was placed 30 m from the fans on the other side, and the sentinel pigs remained in the trailers for 72 hours. They were then moved to separate buildings on the same site, 30 and 80 m, respectively, from the infected barn, and their PRRSV status was monitored for 21 days. The direct and indirect contact control pigs became infected with PRRSV but the sentinel pigs did not.

Mycoplasma hyopneumoniae colonization of pigs sired by different boars

Differences in Mycoplasma hyopneumoniae colonization were evaluated in experimentally inoculated pigs sired by 3 different boars of the same genetic line. Forty-six pigs were used, including a treatment group and positive and negative control groups. The pigs were intratracheally inoculated with an M. hyopneumoniae suspension or with Friis media as a placebo. To evaluate differences in the magnitude of colonization during a 35-day period, nasal and tracheal swabs were collected weekly and tested by nested polymerase chain reaction (N-PCR). Temperature, weight and circulating antibodies were measured for 35 days. At 11 and 35 d postinoculation the pigs were necropsied and macroscopic and microscopic lesions were determined. A section of bronchus was tested by the indirect immunofluorescence test (IFAT), scanning electron microscopy (SEM) and N-PCR. The N-PCR results from the nasal and tracheal swabs showed that the pigs sired by one boar (B3) had a distinctive colonization pattern, different from that of the pigs from the other 2 boars and from the positive controls. SEM studies demonstrated that at 35 d postinoculation a higher proportion of B3 pigs had lower numbers of mycoplasmas attached to the cilia compared with B1 and B2 offspring. No significant differences were observed in temperature and weight gain among groups by ANOVA; however, with use of a 2 x 2 table, temperature differences were observed between pigs sired by boars B1 and B2 at 4 d postinoculation. No pigs seroconverted, showed gross or microscopic lesions, or had positive IFAT results. These results provide evidence of differences in patterns of colonization between pigs sired by different boars, suggesting a possible genetic effect.

Plasmid and restriction endonuclease patterns in Pasteurella multocida isolated from a swine pyramid

Restriction endonuclease analysis (REA) and plasmid profile were used to study the epidemiology of Pasteurella multocida in a swine pyramid structure. The studied pyramid was comprised of a group of 12 swine farrow-to-finish farms related by unidirectional animal movement. P. multocida isolates were obtained from the lungs of 275 slaughtered pigs. Serotyping was performed by hyaluronidase sensitivity test and toxicity was investigated by the ELISA test. HpaII was used to cleave the P. multocida extracted DNA. REA patterns relationships were studied using the Sokal-Michener coefficients, and the dendrogram was built using the UPGMA system. The 218 P. multocida isolates obtained were distributed in 17 REA patterns. In 9 of the 12 farms studied only 2-3 REA patterns were detected, with one clearly predominant pattern. The 81 strains with plasmids were assigned to six plasmid profiles. REA and plasmid profiles proved to be good epidemiological tools for identifying different strains of P. multocida with the same phenotype.

Development of a PCR test to diagnose Haemophilus parasuis infections

A polymerase chain reaction (PCR) test was developed in order to improve the accuracy and speed of diagnosis of Haemophilus parasuis, an economically important respiratory pathogen that affects swine. The gene sequence of the 16S small subunit ribosomal RNA of H. parasuis (GenBank M75065) was compared with 56 16S sequences of related bacteria, including those frequently isolated from pig tissues. Two species-specific primers were designed: HPS forward and HPS reverse. The predicted size of the amplified PCR product was 821 bp. The PCR test could detect a minimum of 102 bacteria and 0.69 pg of DNA. Thirty-one H. parasuis isolates, including 12 different serovars and 19 field isolates, were positive using the PCR test. No amplification was observed when the test was run using DNA from 15 other bacterial species commonly isolated from swine tissues. A weak band was observed when the PCR test was performed using Actinobacillus indolicus DNA as template. Clinical samples tested by PCR included tissues and swabs from 5 animals naturally infected with H. parasuis and 1 experimentally infected animal. The PCR was positive in 26 of 30 clinical samples. Four samples showed weak bands, and these results were not considered positive. Haemophilus parasuis was isolated from 18 of 30 of these samples. Tissues from specific pathogen-free (SPF) pigs and from unrelated species were negative for H. parasuis isolation and PCR. The developed PCR was successfully used in the diagnosis of H. parasuis infection, especially when compared with traditional microbiology techniques.

The effect of vaccination with the PAV-250 strain classical swine fever (CSF) virus on the airborne transmission of CSF virus

The airborne transmission of Classical Swine Fever (CSF) virus to susceptible pigs, as well as the effect of vaccination with the CSF virus PAV-250 strain was investigated on this mode of transmission. Experiment I: four pigs were inoculated with the ALD CSFV strain (10(4.3) 50% TCID) by the intramuscular route, and at the onset of fever, they were introduced into an enclosed chamber. At the end of the experiment surviving pigs were sedated, anesthetized and euthanatized. Experiment II: four pigs were previously vaccinated with the CSF virus PAV-250 strain, and at 14 days post-vaccination they were challenged with the CSF virus ALD strain. In both experiments, four susceptible pigs were exposed to infectious aerosols by placing them in a chamber connected by a duct to the adjacent pen containing the infected animals and were kept there for 86 hs. In Experiment I, pigs exposed to contaminated air died as a result of infection with CSF virus on days 14, 21 and 28 post-inhalation. These four pigs seroconverted from day 12 post-inhalation. CSF virus was isolated from these animals, and the fluorescent antibody test on tonsils was positive. In Experiment II, a vaccinated pig exposed to contaminated air did not seroconvert, nor was CSF virus isolated from lymphoid tissues. However, mild fluorescence in tonsil sections from these pigs was observed. In conclusion, CSF virus was shown to be transmitted by air at a distance of 1 m to susceptible pigs. Vaccination with the PAV-250 CSF virus strain protected the pigs from clinical disease under the same conditions.

Experimental colonization of piglets and gilts with systemic strains of Haemophilus parasuis and Streptococcus suis to prevent disease

Haemophilus parasuis and Streptococcus suis are both major causes of losses during the nursery period, especially in herds using the segregated early weaning system. In this system, only a few piglets may be colonized with the herd's prevalent systemic strain, which results in infection of naive penmates late in the nursery. In view of these factors, the objectives of this study were: (1) to evaluate the early colonization of piglets with the farm's prevalent systemic strain of H. parasuis and S. suis as an alternative method for disease prevention; and (2) to evaluate 2 different protocols for experimental colonization: direct colonization of piglets and colonization of piglets through nose-to-nose contact with inoculated sows. Haemophilus parasuis and S. suis isolates recovered from diseased nursery pigs were characterized by the rep-PCR technique and the herd's prevalent strains were used for colonization. Piglets in the experimentally colonized groups were inoculated at 5 days of age by the oral route using a spray pump. Sows were colonized at 2 weeks prior to farrowing using a similar protocol. Although both colonization protocols were successful in getting the piglets colonized, direct inoculation of 5-day-old piglets with the herd's systemic strains of H. parasuis and S. suis tended to be more effective in reducing the morbidity and the mortality than the colonization of piglets by nose-to-nose contact with inoculated sows.

Diagnostic investigation of chronic porcine reproductive and respiratory syndrome virus in a breeding herd of pigs

Forty-five sows and 15 boars were selected at random from a breeding herd known to be chronically infected with porcine reproductive and respiratory syndrome virus (PRRSV) and lymphoid, immune-privileged, and non-lymphoid/non-immune-privileged tissues were tested for the presence of the virus by PCR, virus isolation, and immunohistochemistry. The virus was isolated from the lateral retropharyngeal lymph node of one sow; the isolate was nucleic acid sequenced and determined to be of field origin, and it was inoculated into two PRRSV-naive pregnant sows (A and B) at 95 days of gestation. They were necropsied 14 days later and samples of maternal and fetal tissue and blood samples were collected. Sow A had 10 fresh, six partially autolysed, and two mummified fetuses, and sow B had six fresh and viable fetuses. Viral nucleic acid was detected by PCR in tissue pools from each sow and also from pooled fetal tissues, and the virus was isolated from fetal pools from sow A.