Viral infections in transplant recipients

Viruses are major opportunistic pathogens that cause significant morbidity and mortality after transplantation. They do not only cause direct clinical illness, but have indirect effects that increase the risk of graft failure and mortality. The clinical presentation of viral infections is very nonspecific, and hence, the role of the clinical laboratory is essential in confirming diagnosis. There have been remarkable improvements in the laboratory diagnosis and monitoring of viral infections, with the evolution from conventional culture methods to more sensitive molecular assays. A number of nucleic acid-based detection assays are currently used in clinical practice for the diagnosis, surveillance, and monitoring of viral infections in transplant patients. Some have the ability to quantify viral load, which is useful for differentiating latent from active infection, for differentiating mild from potentially severe disease, and for monitoring therapeutic response.The majority of molecular tests for viral diagnosis in transplantation lack standardization, and their clinical uses across different testing sites have been difficult. Variability in specimen type, nucleic acid extraction methods, target sequence, limit of detection, and quantitative and calibration standard are some of the reasons for varying viral load reports from different assays. This lack of standardization not only complicates management of individual patients, but also hampers the development of consensus interpretive and treatment guidelines. This book chapter discusses the clinical application of molecular tests for the diagnosis of adenovirus, BK virus, parvovirus B19, cytomegalovirus, Epstein Barr virus, and the other members of the herpes virus family.