Effective detection and elimination strategies for porcine viruses
Joachim Denner1, Hina Jhelum 1, Sabrina Hansen1, Konrad Fischer2, Martin Bender3, Barbara Kessler4, Sabrina Halecker1, Elisabeth Neumann5, Julia Radan5, Matthias Längin3, Jan-Michael Abicht3, Ludwig Krabben1, Angelika Schnieke2, Eckhard Wolf4, Bruno Reichart5, Benedikt Kaufer1.
1Institute of Virology, Free University Berlin, Berlin, Germany; 2 Chair of Animal Biotechnology, TUM School of Life Sciences Weihenstephan, Technical University Munich, Munich, Germany; 3Department of Anaesthesiology, University Hospital, LMU Munich, Munich, Germany; 4Gene Center, Institute of Molecular Animal Breeding and Biotechnology, LMU Munich,, Munich, Germany; 5Transregional Collaborative Research Center 127, Walter Brendel Centre of Experimental Medicine, , LMU Munich, Munich, Germany
Introduction: The transmission of the porcine cytomegalovirus (PCMV) during the first transplantation of a pig heart into a human patient calls for better strategies to screen donor pigs for viruses. PCMV is actually a porcine roseolovirus (PCMV/PRV) closely related to human herpesviruses 6 and 7, but not human CMV. PCMV/PRV infection has been shown to significantly reduce the survival time of pig kidneys and hearts in different non-human primates [1]. Hepatitis E virus (HEV) is a second well-known example of a zoonotic pig virus [2]. The zoonotic properties of many other pig viruses are not well studied.
Method: Highly sensitive PCR-based methods to detect numerous porcine viruses including PCMV/PRV, HEV, porcine endogenous retroviruses (PERVs), porcine lymphotropic herpes viruses (PLHV) and porcine circoviruses (PCV) were developed and used for screening pigs of different age and origin [3-5]. The same methods were also used in the screening of non-human primate transplant recipients. In parallel, recombinant viral proteins were produced and used in Western blot (WB) analyses of pig sera [5, 6].
Results: Using real-time PCR, PCMV/PRV was detected in young piglets in blood, bronchoalveolar lavage fluid, tonsils and heart, as well as in nasal and anal swabs. In adult animals, the virus was not detected by PCR in most cases as it established latency. Using WB analyses, virus-specific antibodies were detected in nearly all infected adults. In young piglets born from virus-positive mothers, PCMV/PRV-specific maternal antibodies derived from the colostrum were detected early in life that decreased over time and disappeared unless the animals were infected [5]. In cases PCMV/PRV was detected in adult animals by PCR, this was likely due to reactivation. Similarly, the detection of HEV was also difficult. HEVs detection in sows soon after delivery and their subsequent offspring, suggested vertical transmission of HEV. The presence of PCMV/PRV genome copies in pig oocyte samples, indicated that there may be a risk of virus infection during somatic cell nuclear transfer and cloning [7]. A high virus load of PCMV/PRV was found in baboons after transplantation of hearts from PCMV/PRV-positive pigs [8]. PLHV and PCV were found in pigs using PCR-based and immunological methods, PCV3 was transmitted to transplanted baboons. However, by early weaning PCMV/PRV and HEV could be successfully eliminated from a pig herd [9].
Conclusion: Using a combination of PCR-based and immunological methods, detection of PCMV/PRV and other viruses in donor pigs for xenotransplantation is feasible. A controlled elimination of all viruses with exception of PERVs by early weaning, colostrum deprivation, Caesarean delivery and other methods is possible.
Supported by the German Research Foundation.
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