**2.1 Recurrence of HCV post transplantation**

The viral infection recurs in almost all cases and occurs immediately after the graft reperfusion phase. The diagnosis of viral recurrence is purely virological and is established by detection in serum of HCV RNA using polymerase chain reaction (PCR) techniques. The levels of viraemia are generally far higher than those existing before the transplant (García-Retortillo et al, 2002). The diagnosis of relapse of the hepatitis or disease in the graft, however,is based on histological findings.

Pathophysiologically, two patterns of recurrence can be distinguished: (1) a pattern of chronic HCV hepatitis similar to that seen in non-transplanted patients but with a faster course, reaching states of advanced fibrosis or cirrhosis in a shorter time (9-12 years versus 20-50 years); (2) a second pattern, called fibrosing cholestatic hepatitis, which is less common (3-5%) but very severe, and generally appears in the context of intense immunosuppression. It can present as an initial manifestation of disease relapse or, less commonly, in the context of recurrent chronic hepatitis, and is characterised by marked jaundice with cholestasis and high titres of viraemia. This form usually progresses rapidly to acute liver failure, with graft loss soon after.

Histological confirmation is necessary to establish the diagnosis of HCV recurrence, as well as to assess the degree of activity and perform a periodic follow-up of histological disease progression. This not only provides information about the prognosis, it can also establish the differential diagnosis with other complications such as rejection, biliary disease, or vascular problems (Berenguer et al., 2001a, Berenguer et al., 2003, Roche & Samuel, 2010, Samuel et al., 2006).

A new non-invasive technique, transient elastography, has recently become available that appears to correlate well with the stage of fibrosis. This technique can detect an important degree of fibrosis (F≥2) with effect from the sixth month after transplantation, and has an excellent diagnostic capacity at 12 months post-transplantation (Carrión et al, 2010a).
