A 62-year-old renal transplant recipient presents with abdominal pain and bloody diarrhoea. Cytomegalovirus (CMV) serology is positive, but plasma viral load is negative.
a) Explain this result in this context. (10% marks)
b) How is the diagnosis of CMV colitis confirmed? (10% marks)
a) This immunocompromised patient has presented with positive serology (i.e. CMV antibodies in the blood), but no viral load per se. The abdominal pain and bloody diarrhoea are therefore probably not due to CMV colitis, as a positive CMV serology simply indicates that the patient had been exposed to CMV at some stage. Positive CMV serology is itself not enough to make the diagnosis of a current active infection.
b) CMV colitis requires a viral load to be detected, and for colonic biopsies to demonstrate characteristic cellular features ("owl's eye" inclusions, for example)
Gandhi, Maher K., and Rajiv Khanna. "Human cytomegalovirus: clinical aspects, immune regulation, and emerging treatments." The Lancet infectious diseases 4.12 (2004): 725-738.
Vancikova, Z., and P. Dvorak. "Cytomegalovirus infection in immunocompetent and immunocompromised individuals--a review." Current drug targets. Immune, endocrine and metabolic disorders 1.2 (2001): 179-187.