Pathogenesis of porcine reproductive and respiratory syndrome in growing pigs

A new reproductive and respiratory syndrome was recognized in the United States swine population in 1986. Tissue filtrates from affected pigs submitted to the Iowa State University Veterinary Diagnostic Laboratory were used to experimentally inoculate gnotobiotic pigs and reproduce respiratory disease and lesions similar to what was observed on the farms of origin. Cytopathic effects and virus particles consistent with porcine reproductive and respiratory syndrome virus (PRRSV) were observed in cell culture. Virus isolation and serology techniques were standardized. Sixteen U.S. PRRSV isolates from herds with varying disease severity and the European Lelystad virus were plaque-purified. A cesarean-derived-colostrum-deprived pig model was developed to study and compare the pathogenicity of a selected subset of these isolates. Significant differences were detected in severity of clinical disease and gross and microscopic lung lesions. Isolates were grouped into low and high virulence categories. An immunohistochemistry technique for detection of PRRSV antigen in formalin-fixed tissues was developed and standardized for diagnostic and research purposes. PRRSV antigen was detected in alveolar macrophages, macrophages throughout the lymphoid system, dendritic-like cells in tonsil, thymus, spleen and lymph nodes, endothelial cells in the heart, and Kupffer cells in the liver. Temporal analysis of the distribution of virus by isolation, and antigen by immunohistochemistry, suggests that oronasal inoculation results in infection of the tonsil and viremia in 12 to 24 hours with subsequent widespread distribution throughout the respiratory and lymphoid systems. PRRSV was found to persist in tonsils and lung for more than 28 days. Pneumonia likely results from the lysis of alveolar macrophages, altered alveolar macrophage function, and the inflammatory response to the enzymes and cytokines released by PRRSV-induced damage to alveolar macrophages. The prolonged viremia, the persistent infections, and the ineffective immune response may be the result of widespread damage to antigen presenting cells within which PRRSV antigen was consistently demonstrated by immunohistochemistry

Application of Immunohistochemistry and ELISA for the Diagnosis of Neospora-Infected Cattle

Studies were undertaken to adapt diagnostic methods for use in our laboratory for detection of Neospora sp. infection in cattle. An immunohistochemical (IHC) test was used for detection of Neospora sp. antigen in tissues of aborted bovine fetuses. Neospora sp. antigen was detected most frequently in fetal brain tissue. Polyclonal antibodies were tested for specificity and sensitivity of the IHC. Sera were obtained from Neospora sp. infected dairy herds for use as positive and negative controls in the continuing development of an enzyme-linked immunosorbent assay (ELISA)

Postweaning Multisystemic Wasting Syndrome (PMWS) Surveillance Study

PMWS is characterized by a clinical history of wasting or poor performance in weaned pigs and by severe lymphoid depletion and histiocytic replacement of follicles in lymphoid tissues. The detection of porcine circovirus type 2 (PCV2) antigen or nucleic acids within characteristic microscopic lesions is required for the diagnosis of PMWS. Swine veterinarians submitted a specified set of samples from one hundred field cases that they felt fit the clinical definition of PMWS. All these cases were further analyzed for the presence or absence and scored for severity of the hallmark microscopic lesions (lymphoid depletion) of PMWS, the amount of PCV2 antigen associated with the lesions, and identification of concurrent bacterial and viral infections. Fifty-four of the 100 field cases were confirmed to be PMWS, whereas, no association with PCV2 was found in 46 of the cases. This highlights the need for further diagnostic testing, specifically histopathology and antigen detection, for confirmation of cases clinically suspected to be PMWS. This will become particularly important as vaccines for PCV2-associated diseases become approved for use

Lack of reproduction of the hallmark porcine circovirus type 2-associated lesions in a mouse model

BALB/c, C57BL6, and C3H/HeN mice were experimentally-infected with porcine circovirus type 2 (PCV2). The mice were tested for their ability to become infected with porcine circovirus type 2 (PCV2) and to develop the hallmark PCV2-associated lymphoid depletion and histiocytic replacement of lymphoid follicles characteristic of postweaning multisystemic wasting syndrome. Since immunostimulation has been shown to increase PCV2-replication in the pig, half of the mice were immunostimulated with keyhole limpet hemocyanin in incomplete Freund’s adjuvant (KLH/ICFA) at the time of PCV2-inoculation. PCV2 inoculation was done twice at 4 and 5 weeks of age by using intramuscular and intranasal routes. Necropsies were performed in 5-day-intervals at 12, 17, 22, 27, 32, and 37 days post PCV2 inoculation. None of the mice developed clinical disease and none of the mice developed PCV2-associated lymphoid lesions. Immunohistochemistry (IHC) and in-situ-hybridization (ISH) for PCV2-antigen/nucleic acids was performed on all tissues of all mice and was negative. PCR was done on pooled tissues and serum samples obtained at necropsy. The majority of the mice (101/111 PCV2 infected mice) were positive for PCV2-nucleic acids in tissue samples. Forty-one percent of the mice (46/111 PCV2 infected mice) were positive for PCV2-nucleic acids in serum samples. There was no difference between treatment groups or lines. This study confirms that mice can be infected with PCV2 and could be important in the epidemiology of PCV2; however, the mouse model may not be useful to understand the pathogenesis of PCV2- associated lesions

Effect of different adjuvants on PCV2-associated lesions

Ninety, 12-14 day old pigs were randomly assigned to five groups. Group 1 (n=19) pigs were vaccinated with a Mycoplasma hyopneumoniae (M. hyopneumoniae) vaccine with an oil-in-water adjuvant (RespiSure®; Pfizer Animal Health, Inc.). Group 2 (n=17) pigs were vaccinated with a commercial M. hyopneumoniae vaccine with an aqueous adjuvant (Carbopol) (Suvaxyn® Respifend® MH; Fort Dodge Animal Health, Inc.). Group 3 (n=18) pigs were vaccinated using an oil-in-water adjuvanted vaccine containing the same amount and type of M. hyopneumoniae antigen as in group 2. Group 4 (n=18) pigs were vaccinated using an aluminum hydroxide adjuvanted vaccine containing the same amount and type of M. hyopneumoniae antigen as in group 2. Group 5 (n=18) pigs served as the controls and were sham-vaccinated with saline. Pigs were injected with 2 mL of one of the four M. hyopneumoniae vaccines at four and again at six weeks of age. PCV2 was inoculated intranasally on the day of the second vaccination at 6 weeks of age. Half of the pigs were necropsied at 21 days post inoculation (DPI). The remaining pigs were necropsied at 35 DPI. There were no differences among groups in clinical disease scores. At 21 DPI all vaccinated groups had significantly (p\u3c0.05) more severe lymphoid depletion than the saline injected group. At 35 DPI group 1 pigs had significantly (p\u3c0.05) higher amounts of PCV2 DNA in serum than pigs in groups 2, 4, and 5 as determined by quantitative real-time PCR. There was a significant (p\u3c0.05) increase in the severity of lymphoid depletion in the lymph nodes, tonsil, and spleen in groups 1 and 3 compared to groups 2, 4, and 5. Group 3 had significantly (p\u3c0.05) higher amounts of PCV2 antigen within lymph nodes, tonsil, and spleen compared to groups 2, 4 and 5. The results confirm that all adjuvants tested enhanced PCV2-induced lesions and oil-in-water products used in this study had a more severe effect

Effect of PRRSV Infection on MHC Expression by Macrophages and Monocytes

Porcine reproductive and respiratory syndrome virus (PRRSV) is a recent and widespread pathogen in the U.S. swine population. PRRSV infects cells of the macrophage/ monocyte/dendritic lineages which are important antigen presenting cells (APCs) of the immune system. Using flow cytometric (FACs) analysis, we demonstrated that PRRSV infection decreases the expression of the major histocompatibility complex (MHC) glycoproteins on the cell surface of infected macrophages. This decrease in MHC protein expression may reduce the ability of the macrophages to present viral antigens to the appropriate lymphocytes. The potential lack of viral antigen presentation may play a crucial role in the persistent viremia observed in PRRSV-infected pigs

Artificial Insemination and Its Role in Transmission of Swine Viruses

1. Introduction Artificial insemination (AI) in swine is not a new technique and reports as early as the 1930s (Lush, 1925) describe collecting semen for AI. However, because of farm structure changes, increasing farm sizes and separation of production stages, interest in intensive pig production is growing and AI has become a critical component in modern pig production. In 2001, nearly 60% of North American swine herds utilized AI (Singleton, 2001), a drastic increase from the estimated 5% in the 1990’s (Flowers & Esbenshade, 1993). This is still relatively low compared to the 90% or greater use of AI in Western Europe (Madsen, 2005; Maes et al., 2008). The extensive use of AI in pig reproduction in the last decade has facilitated the exchange of desirable genetic characteristics at an international level, allowing producers to make greater use of superior genetics at a lower cost than some natural-service systems (Gerrits et al., 2005). However, the growth in use of AI has increased the risk of quick and widespread transmission of venereally transmissible pathogens (Thacker et al., 1984). It has been reported that the porcine male reproductive tract is highly susceptible to viral infections (Phillips et al., 1972; Spradbrow, 1968). This, coupled with the ability of boars to produce tens to thousands of insemination doses per week and the widespread distribution of the processed semen (both nationally and internationally), further increases the risk of wide transmission of viral pathogens by semen.This book chapter is published as Opriessnig T, Giménez-Lirola LG, Halbur PG. (2012). Artificial insemination and its role in transmission of swine viruses. In: Carlos C Perez-Marin (Ed), A Bird’s-Eye View of Veterinary Medicine, pp. 255-280. InTech, Croatia. ISBN 978-953-51-0031-7. DOI: 10.5772/17961. Copyright 2012 InTech. Attribution 3.0 International (CC BY 3.0). Posted with permission

Evaluation of Vaccination and Antimicrobial Protocols in Nursery Pigs Coinfected with Porcine Reproductive and Respiratory Syndrome Virus and Streptococcus suis

We tested the efficacy of nine different intervention strategies to minimize losses associated with experimental coinfection of nursery age pigs with porcine reproductive and respiratory syndrome virus (PRRSV) and Streptococcus suis. The antibimicrobials tested included penicillin, ampicillin, tiamulin, and ceftiofur hydrochloride. Vaccines tested included two commercial modified live PRRSV vaccines, an autogenous killed S. suis vaccine, and an experimental live autogenous S. suis vaccine. We found that the most effective treatment was intramuscular injection of 5 mg/kg ceftiofur hydrochloride on three consecutive days following S. suis inoculation. The live autogenous S. suis vaccine and treatment with ceftiofur hydrochloride every third day for three treatments also significantly reduced mortality

Dairy Production Immersive Knowledge Experience (D-PIKE) and Swine Production Immersive Knowledge Experience (SPIKE)

D-PIKE and SPIKE are programs designed to develop an intense experience for veterinary students that have an interest in either dairy or swine production medicine. Students are housed in a learning community environment to facilitate discussion pertaining to their daily experiences. The program is a ten week effort to bring the respective industry to the students from a ground up approac

An Experimental Model for Porcine Circovirus Type 2 and Mycoplasma hyopneumoniae Co-infection

Sixty-seven pigs were randomly assigned to four groups. Group 1 served as negative control pigs, group 2 pigs were inoculated with Mycoplasma hyopneumoniae (M. hyopneumoniae), group 3 pigs were dually-inoculated with M. hyopneumoniae and porcine circovirus type 2 (PCV2) and group 4 pigs were inoculated with PCV2. Dual-infected pigs had moderate dyspnea, lethargy, and reduced weight gain. The overall severity of PCV2- associated microscopic lesions in lung and lymphoid tissues were significantly (p\u3c0.05) higher in the dualinfected pigs compared to all other pigs. Four of 17 dual infected pigs had lesions consistent with postweaning multisystemic wasting syndrome (PMWS) whereas none of the singular PCV2-infected pigs developed PMWS. This study indicates that M. hyopneumoniae potentiates the severity of PCV2-associated lesions and increases the incidence of PMWS. This co-infection model closely mimics the field situation were co-infections with PCV2 are commonly observed. In the future this model will be very useful for testing intervention strategies for the control of PCV2-associated disease in growing pigs