Hepatitis C virus Dr. Amanj Saeed MB.CH.B MSc PhD Clinical virologist
55-65 nm Hepatitis C Virus (HCV) Envelope • HCV is small enveloped positive sense RNA virus • Belongs to Genus Hepacivirus of Flaviviridae family • Genome is 9.6 kb. • 6 major genotypes. Core Envelope Glycoproteins Viral RNA (9400 nucleotides)
HCV • Hepatitis C virus (HCV) is a small, enveloped positive strand RNA virus belong to a genus Hepacivirus of the Flaviviridae family • An estimated 200?? million people worldwide are infected with HCV . • 80% of infected individuals will develop chronic persistent infection, and of these 30% will develop progressive liver diseases including chronic hepatitis, cirrhosis and hepatocellular carcinoma (HCC).
HCV • HCV infection has a major impact on public health, yet no vaccine is available to prevent the infection and the antiviral therapies are characterised by: • limited efficacy • high cost • substantial side effects.
Core NS4A 5’UTR 3’UTR E2 NS5B E1 NS4B NS5A P7 NS3 NS2 schematic representation of HCV genome STRUCTURAL GENES NON-STRUCTURAL GENES + ve ss RNA } Genomic organisation } FLAVIVIRUS
HCV– receptor interaction • E1 and E2 are essential for host cell entry by binding to receptors and inducing fusion of the host cell membrane • Several cell surface molecules have been proposed to play a role in mediating HCV attachment and entry: • the tetraspanin CD81 • scavenger receptor class B type 1 (SRB1) • heparin sulphate (HS) • and the low density lipoprotein (LDL) receptor, claudin-1 and occludin. • Epidermal growth factor Receptor • Ephrin receotor
Translation of HCV genome • Translation of HCV genome yields a polyprotein precursor that is subsequently processed by cellular and viral proteases. • Structural proteins include (core, E1, E2, P7) • Nonstructural proteins include: NS2, NS3, NS4A, NS4B, NS5A, NS5B.
HCV replication • HCV Replication proceeds via formation of complementary minus strand RNA using a viral genome as a template and subsequent synthesis of plus strand • Both these steps are dependent on NS5B (viral RNA Dependent RNA polymerase).
HCV • HCV genome replication is associated with a high mutation rate and sequence diversity which eventually results in a circulating population of diverse but closely related HCV variants, known as a quasispecies whichunderlies the following : • capacity to escape against immune responses • presence of multiple variants which facilitate the selection of adaptive mutations.
HCV genetic diversity: consequences • Diagnosis • may result in false negativity • Pathogenicity • are all genotypes equally dangerous? • Treatment • do all genotypes respond equally to therapy? • Vaccine development • creates problems
Models for studying HCV pathogenesis • Analyzing the effect of HCV on transformed cell lines. • transgenic technology. • Infection with related viruses (like GBV-B) • The best model for HCV study is using chimpanzees (economic and moral reasons limit the use of chimpanzee in research).
Models for studying HCV pathogenesis • Sub-genomic replicon systems . • generation of an infectious clone of a genotype 2 isolate of HCV known as JFH-1 which has the capacity to go through a full viral life cycle and produce infectious virus in hepatocyte derived cell lines.
Models for studying HCV pathogenesis • HCV pseudoparticles (HCVpp). • Recent studies developed an experimental system to use primary human hepatocytes as a model for studying HCV pathogenesis
Anti-HCV POSITIVE • Evidence of infection at some time • Gives no indication as to when infection occurred • Gives no indication as to whether infection was cleared or is still present
Anti-HCV: Negative • No evidence of infection with HCV • BUT - be aware of possible false negatives • if infection very recent (window period) • if patient immunosuppressed at time of infection
Genome Detection • Requires amplification eg Reverse Transcriptase Polymerase Chain Reaction • Technically more exacting • Expensive
POSITIVE infectious at risk of chronic liver disease requires liver biopsy NEGATIVE not infectious not at risk of chonic liver disease may not require biopsy Interpretation RT/PCR results
Hepatitis C virus: routes of transmission • Parenteral • Injecting drug use • Blood/blood products • Other needles • Failure of infection control eg outbreaks (see refs) • Mother-to-baby (5%) • Sexual (?real)
CLINICAL OUTCOMES OF HCV INFECTION ACUTE INFECTION Usually asymptomatic Infection Resolved 15-25% CHRONIC INFECTION 75-85% ASYMPTOMATIC, mild liver disease 20 yrs CHRONIC INFLAMMATORY HEPATITUS CIRRHOSIS eg 20% 5 yrs HEPATOCELLULAR CARCINOMA
Mechanism of hepatic fibrogenesis in HCV infected patient Chronic inflammation and the wound healing response are likely to be the framework within which HCV induces hepatic fibrosis
Hepatitis C Natural history of Hepatitis C Infection Infection by Hepatitis C Virus Acute Hepatitis (>90 % Asymptomatic) 6 Months Chronic hepatitis (75-85%) Spontaneous recovery (15-25%) Chronic active (20%) Asymptomatic (80%) 10-30 Years Treatment Cirrhosis (20%) Transplantation HCC
Clearance – 20% Chronic infection – 80% HCV: Natural History Infection
Prevention of patient-to-patient HCV transmission - screening Blood donors – anti-HCV Organ and tissue donors – anti-HCV Renal units – regular anti-HCV testing Antenatal screening – NOT currently recommended
Infected patient healthcare worker Infected healthcare worker patient Needlestick transmission of blood-borne hepatitis viruses
HCW-to-patient transmission of HCV: UK data Known transmissions from 5 surgeons (1 cardiac, 2 general, 2 O&G) thus far
Protection of patients:Guidelines?? • Known HCV RNA +ve HCWs – OUT • Current HCWs doing EPPs encouraged to be tested if risk factors . • Needlestick injuries – early Rx benefit to HCW • For HCWs entering EPP-specialties – test for HCV infection
Diagnosis • Test for viral antigen and Antibody (ELISA) • Test for genome (Quantitative RNA PCR)
Treatment • Pegylated INF-α + Ribavirin