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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology


Porcine reproductive and respiratory syndrome (PRRS) is the most economically devastating disease syndrome of swine in the world. PRRS affects pigs of all ages causing respiratory disease with mortality in suckling and weaned pigs, as well as late term abortions or pre-mature farrowing with stillborn or weak born piglets in breeding herds. In 1991, the causative agent was identified as a single-stranded RNA virus. Transmission of porcine reproductive and respiratory syndrome virus (PRRSV) through insemination with infected semen, pig-to-pig contact, and aerosols has been described. With the increasing use of artificial insemination of swine in the United States and Europe, transmission of PRRSV through semen has become a major problem. RespPRRS® is a commercial modified-live virus vaccine licensed for use in piglets and in sows and gilts prior to breeding. Currently, no vaccine is licensed for use in boars. However, extra-label vaccination of boars with RespPRRS® has been practiced in the field, and boars vaccinated with RespPRRS® may still shed infectious virus in semen. Since PRRSV is transmitted through mucosal surfaces, mucosa} immunity may represent the first line of defense against the virus. We previously demonstrated a reduction or elimination of PRRSV shedding in semen following intramuscular vaccination with RespPRRS®; therefore, we hypothesized that giving the vaccine through the intranasal route would stimulate mucosal immunity and further reduce or eliminate viral shedding after wild-type PRRSV challenge. Intranasal (IN) vaccination for other viruses has been reported to induce mucosa immunity, but experiments to test this hypothesis using the RespPRRS® vaccine had not yet been performed. To address our hypothesis, sixteen PRRSV-seronegative boars were intranasally vaccinated with either 1/10th of the current label dosage or the full current label dosage of RespPPRS®. Each group consisted of two non-vaccinated controls and six vaccinates. Twenty-eight days after intranasal vaccination, all boars were challenged with a virulent, heterologous PRRSV isolate. Pre-vaccination, post vaccination and post challenge samples of semen, serum, whole blood, nasal swabs and saliva swabs were collected. Semen samples were collected three times weekly and evaluated for the presence of PRRSV RNA using a RT-nPCR procedure. PCR results on semen indicated 4 of 11 vaccinated boars shed vaccine virus after vaccination. Only one boar in each vaccination group showed a viremia from vaccination However, following challenge all boars of the 1/10th dose group and 1 of 6 vaccinates of the full dose group became viremic. Ten of the eleven vaccinated boars that were collected still shed wild-type virus in semen after subsequent challenge, intermittently or continually for 2 days (6 boars), 3 days (2 boars), 5 days (1 boar) or 7 days (l boar) during the 21 day post challenge period. One boar given a 1/10th dose of vaccine did not shed wild-type virus in semen after challenge, suggesting that vaccination induced protection from shedding in this case. In comparison, non-vaccinated boars shed PRRSV in semen for 7 days (3 boars) or 6 days (1 boar) post challenge. Nasal swabs and saliva swabs were virus isolation negative throughout the experiment. Complete blood counts and semen quality parameters remained normal after intranasal vaccination and challenge. Pre-vaccination samples from vaccinated boars and pre-challenge samples from control boars were used to determine normal levels of lgA, IgG and IgM in boar semen. The most prominent antibody in swine seminal plasma is IgG at 22.4 μg/ml ± 11.0 μg/ml. [gA and IgM concentrations are 5.3 μg/ml ± 2.5 μg/ml and 4.3 μg/ml ± 1.2 μg/ml, respectively. Although we were unable to detect PRRSV-specific antibodies in semen, we were able to develop a better understanding of immunology in the boar reproductive tract. We attempted a number of modifications to a variety of immunoassays, yet no PRRSV specific antibodies were detectable in seminal plasma by any method attempted herein. Extra-label use of the modified-live vaccine in boars is still controversial since vaccinated boars may shed wild-type virus after subsequent challenge. IN vaccination with RespPRRS® did reduce the number and duration of days PRRSV was shed in semen compared to non-vaccinated boars challenged with PRRSV. Furthermore, sperm quality was not adversely affected by IN vaccination. This study also proved that wild-type virus rather than vaccine virus is shed in semen following challenge of IN vaccinated boars. However, IN vaccination with RespPRRS® was not fully effective in preventing infection and subsequent shedding of wild-type PRRSV in semen.

Library of Congress Subject Headings

Swine -- Virus diseases
Swine -- Vaccination



Number of Pages



South Dakota State University