A Revisit of Porcine Teschovirus Pathogenesis in Pigs
Date Issued
2014
Date
2014
Author(s)
Chiu, Shu-Chun
Abstract
Porcine teschoviruses (PTV) induce, in virgin epidemic, a variety of clinical symptoms and lesions including encephalomyelitis, diarrhea, pneumonia, and reproductive disorders. In the recent past, Taiwan has had two waves of virgin epidemic, the first one in year 2000 and the second in year 2004. The PTV infection in swine herds of Taiwan had since increased and peaked at year 2008 (endemic), judged by the isolation rates of PTV from submitted specimens to Animal Health Research Institute. One feature of the last two waves of epidemics was the multiple infection status. That meant other common swine pathogens such as classical swine fever virus (CSFV), porcine reproductive and respiratory virus (PRRSV), porcine circovirus type 2 (PCV2), and pseudorabies virus (PrV) were frequently co-isolated. When pigs have no anti-PTV antibody, the main route of infection and pathogenesis is believed to be fecal-oral-viremia. However in endemic situation when most pigs have antibody, the models of pathogenesis can be multiple. The earlier studies of PTV pathogenesis were largely published in 1960s. Through these years, virus has evolved and new laboratory techniques have been developed, so that it warranted a revisit of PTV pathogenesis. In this study, three groups of animals were experimentally infected via intranasal route. Group I animals were 12-week-old specific-pathogen-free (SPF) pigs infected with PTV-1 Taiwan isolate. Virus could be isolated from various organs at day postinfection (DPI) 2 and pigs succumbed to clinical signs of fever, diarrhea, and neurological symptoms. Because the frequency of neurological symptoms and severity of polioencephalomyelitis were not high, the virulence of PTV-1 Taiwan isolate was consistent that of moderate virulent Talfan strain. It was interesting to note that all infected animals (14/14) has interstitial pneumonia and the neutralizing antibody rose quickly to 1:256-512 at days postinfection (DPI) 4 suggestive of low level of PTV and PRRSV contamination in SPF pigs. This also showed that, in addition to fecal-oral, intranasal route could establish infection in pigs. Group II were 12-week-old pigs that were PTV-seropositive (neutralization antibody) infected with PTV-1 Taiwan isolate. These infected animals were also vaccinated with CSFV LPC vaccine at DPI 21. It showed that PTV superinfection could occur in the presence of high serum neutralizing antibody titers and the vaccination with LPC seemed to induce a higher rate of PTV shedding via feces. Group III were 12-week-old PTV-seronegative SPF pigs infected with PTV-1 Taiwan isolate. It showed that fecal shedding continued, in infected animals, until DPI 33, while the nasal shedding occurred until DPI 17. Notably PTV could be isolated intermittently from the control pig, which also developed hindlimb paralysis. This indicated that, although the control pig was housed separately from the infected pigs, the control pig could be infected if its housing, sewage or airflow, were located in the downstream of those of the infected pigs. In addition the control pig could be infected by the workers for frequent handling during the study period. This may be particularly important in long-term study and this also implicated the similar situation in the field. This study furthers our understanding on the pathogenesis of PTV. PTV is a widespread and seems unavoidable contaminant in nowadays swine industry. When co-exist with the other common swine pathogens such as PRRSV, PCV2 and CSFV, as very typical in nowadays swine production, PTV’s role in causing disease is not negligible.
Subjects
鐵士古病毒
致病機轉
鼻口接種
糞-口-病毒血症
SDGs
Type
thesis
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