Hepatitis C virus — Questions

The per-percutaneous-exposure transmission risk is about 1.8% (range 0 to 7%), highest with hollow-bore needles.

a. Immediate wound care. Wash with soap and running water, allow to bleed, do not scrub or squeeze, and report to occupational health at once.

b. Workup of the source. Anti-HCV alone cannot separate active from resolved infection, so HCV RNA PCR is the determining test for transmission risk. Repeat HIV and HBV serology to exclude window-period infection, and document any prior HCV treatment, with consent and privacy safeguards.

c. Workup of the worker. Baseline within 48 hours: anti-HCV, HCV RNA, ALT, HIV, and HBV serology. The RNA is the earliest marker of acquisition. Check HBV immunity; because the source is HBsAg negative, HBIG is not needed, though a non-immune worker should complete the vaccine series.

d. Prophylaxis. There is no effective HCV post-exposure prophylaxis: immunoglobulin does not work and DAAs are not validated for this use. The pathway is surveillance with treatment if seroconversion occurs.

e. Surveillance. HCV RNA at week 4 for early detection, with anti-HCV, RNA and ALT repeated at weeks 12 and 24 (and HIV serology repeated). A positive RNA means acute HCV: refer for DAA therapy, which cures over 95% even in acute infection.

f. Reporting. Document on the occupational injury register and notify the Compensation Fund if seroconversion occurs.

a. Interpretation. A positive HCV total antibody at 2 days does not indicate infant infection. It almost always reflects passive transfer of maternal IgG anti-HCV across the placenta, which persists in the infant for up to 18 months. Vertical transmission is around 2 to 4% in HIV-negative mothers, rising to 10 to 25% with HIV co-infection, so most such infants ultimately test negative once maternal antibody clears.

b. Follow-up testing. The aim is to separate true infection from passive antibody:

• HCV RNA PCR at 2 to 6 months, the earliest diagnostic; a positive result at or after 2 months confirms transmission. Repeat a single negative, as early viraemia can be intermittent.
• Anti-HCV antibody at 18 months: persistence confirms the infant has made its own antibody, indicating true infection.
• ALT at each visit as a marker of liver inflammation.

c. Maternal and supportive care. Test the mother for HCV RNA (active viraemia defines the infant’s risk) and for HIV (co-infection raises transmission and follow-up intensity). Breastfeeding is not contraindicated unless the nipples are cracked and bleeding. Reassure the parents, and refer a confirmed case to paediatric hepatology, where pan-genotypic DAAs are licensed from age 3.

An indeterminate result means the serum reacts with fewer than the full panel of HCV antigens the immunoblot needs to call a definite positive. The historical recombinant immunoblot assay required at least two of four bands (core, NS3, NS4, NS5); a single band was reported as indeterminate.

Three explanations exist:

• Resolved past infection with waned antibody breadth. HCV RNA is negative.
• Early or acute infection with a maturing response. HCV RNA may be positive.
• False-positive cross-reactivity to one antigen. HCV RNA is negative and the screen should be repeated on another platform.

HCV RNA polymerase chain reaction (PCR) is the decisive test: a positive result confirms active infection whatever the immunoblot shows, and a negative result excludes it. Modern algorithms have largely dropped the immunoblot in favour of direct RNA confirmation of any reactive screen.

A complete answer places HCV in Baltimore class IV, then walks the fully cytoplasmic cycle from receptor entry through the negative-strand intermediate to lipoprotein-coated progeny release.

Group

HCV is a class IV, positive-sense single-stranded RNA virus: the genome acts directly as a messenger RNA, sharing this property with the picornaviruses, togaviruses, and other flaviviruses.

Entry

The virion tethers to heparan sulfate proteoglycans, then binds CD81, the scavenger receptor B1, and the tight-junction proteins claudin-1 and occludin; the low-density lipoprotein receptor takes up the characteristic lipo-viro-particles via their host apoE and apoB coats. Clathrin-mediated endocytosis internalises the particle, and pH-dependent fusion in the endosome releases the genome.

Translation

An internal ribosome entry site (IRES) in the 5’ untranslated region recruits the 40S subunit without a cap, and the ~9.6 kb open reading frame is translated as one polyprotein of about 3,000 amino acids. Host signal peptidase cuts the structural junctions, the NS2/3 autoprotease cuts NS2/NS3, and NS3/4A cuts the downstream non-structural junctions, releasing 10 mature proteins.

Negative-strand intermediate

NS5B RNA-dependent RNA polymerase copies the genome into a short-lived, low-copy negative-strand intermediate within a membranous web induced by NS4B. NS5B lacks proofreading, so a quasispecies swarm arises that drives HVR1 immune escape and drug resistance.

Positive-strand progeny and exit

The negative strand templates many new positive-strand genomes, which are both translated and packaged by core protein at lipid droplets. Envelopment at the endoplasmic reticulum adds the E1/E2 spikes, and virions egress through the very-low-density lipoprotein (VLDL) pathway, emerging as lipo-viro-particles. The cycle is entirely cytoplasmic, with no DNA intermediate and no integration.

A complete answer states the current absence of a vaccine, the biological reasons it is uniquely hard, the strategies tried, and why a vaccine still matters despite curative therapy.

Current status

There is no licensed HCV vaccine after three decades of work. Curative direct-acting antivirals (DAAs) treat but do not prevent, and the World Health Organization 2030 elimination targets cannot be met in high-incidence groups, above all people who inject drugs (PWID), where reinfection after cure runs at 3 to 15% per year.

Why it is uniquely difficult

• Extreme diversity: eight genotypes at ~30 to 35% divergence, and a within-host quasispecies swarm from the proofreading-deficient NS5B polymerase.
• Hypervariable envelope: the immunodominant E2 HVR1 mutates under antibody pressure, so neutralising responses are routinely escaped.
• No sterilising immunity: reinfection after spontaneous clearance is well documented, undermining the classical correlate-of-protection model.
• Adaptive failure: CD4 help failure and CD8 T-cell exhaustion (PD-1, TIM-3, LAG-3) mark progression to chronicity.
• Tools: loss of the chimpanzee model leaves no tractable small-animal model, and correlates of protection remain ill-defined.

Strategies attempted

A T-cell vaccine (ChAd3-NSmut prime, MVA-NSmut boost) reached phase 2 in active PWID: safe and immunogenic, it reduced peak viraemia but did not prevent chronic infection. Recombinant E1/E2 subunit vaccines target neutralising antibody and are in early trials, and combination platforms aim to pair both arms. Controlled human infection models, now safer because DAAs can rescue any infected volunteer, could accelerate screening.

Why a vaccine is still needed

DAA cure gives no protective immunity, DAA and diagnostic access are uneven, and modelling argues elimination in PWID-driven epidemics is not feasible without one. The next generation will likely combine broadly neutralising antibody induction against the conserved CD81-binding site with polyfunctional T-cell responses, with mRNA multi-antigen platforms a promising delivery route. The strategic case has shifted from individual cure to interrupting transmission at the population level.

A complete answer covers what genotyping and RAS testing once decided, how the pan-genotypic era narrowed both, and how South Africa organises them.

Genotyping

Eight major genotypes (1 to 8) differ by ~30 to 35% at the nucleotide level. Historically genotype drove regimen choice and duration in the interferon and early direct-acting antiviral (DAA) era, and genotype 3 carries prognostic weight through steatosis and faster fibrosis. In the pan-genotypic era (sofosbuvir/velpatasvir, glecaprevir/pibrentasvir) routine pre-treatment genotyping is often unnecessary, retained mainly for treatment-failure work-up, surveillance, and distinguishing reinfection from relapse.

South African genotype distribution

South Africa is pan-genotypic with a distinctive signature: genotype 5a was first identified here and stays largely confined to southern Africa. In the general population genotypes 1 and 5 co-dominate, with genotype 4 rising; in people who inject drugs, genotype 1a (~73%) and 3a (~15%) dominate and genotype 5 has not been detected.

Resistance-associated substitutions

RAS are amino acid changes that reduce DAA binding or efficacy, present at baseline or selected during therapy.

Class	Target	Key RAS
Protease inhibitors (-previrs)	NS3/4A	Q80K (genotype 1a)
NS5A inhibitors (-asvirs)	NS5A	Y93H, L31M
Polymerase inhibitors (-buvirs)	NS5B	S282T

NS5A RAS matter most because they persist for years off therapy, whereas sofosbuvir’s high genetic barrier makes NS5B resistance rare. RAS testing is mainly indicated after DAA failure, to guide retreatment; it is not needed before first-line pan-genotypic therapy.

South African operational context

Genotyping runs on the NHLS network and RAS testing is centralised at a single national reference centre using polymerase-gene sequencing, reserved for treatment failure and selected complex cases. Pre-treatment RAS testing is not routine, since pan-genotypic regimens hold high cure rates across baseline RAS profiles.

A complete answer traces the agent from non-A non-B hepatitis (NANBH) defined by exclusion, through the chimpanzee studies, to the 1989 molecular cloning and the 2020 Nobel Prize.

The pre-discovery era

Once assays for hepatitis A and hepatitis B existed, a chronic transfusion-associated hepatitis remained that neither could explain, and it was labelled non-A non-B hepatitis. Post-transfusion rates reached up to one in three in open-heart surgery, and many recipients progressed to cirrhosis and hepatocellular carcinoma. Harvey Alter led prospective transfusion-recipient cohorts showing an infectious bloodborne agent distinct from HAV and HBV, with a long incubation and a high rate of chronicity.

Chimpanzee transmission and physical characterisation

Chimpanzees were the only permissive model. Serial inoculation showed the agent was filterable at 30 to 60 nanometres, inactivated by chloroform (an envelope), and inactivated by solvent-detergent treatment of blood products. These properties pointed to a small enveloped RNA virus, though it could not be cultured.

Molecular cloning, 1989

Michael Houghton’s team at Chiron built a complementary DNA library from high-titre chimpanzee plasma and screened it with serum from a chronic NANBH patient. After roughly a million clones, clone 5-1-1 bound patient antibody but not control serum. Two 1989 Science papers reported the agent, now named hepatitis C virus, and the clone became the first anti-HCV ELISA, deployed for blood-donor screening from 1990.

Rice and the Nobel Prize

Charles Rice proved the cloned genome was infectious and built the replicon and JFH-1 cell-culture systems that underwrote direct-acting antiviral discovery. In October 2020 the Nobel Prize in Physiology or Medicine went jointly to Alter, Houghton, and Rice.

The discordance is unidirectional (new positive, old negative), so the answer weighs the competing explanations and then sets out a staged resolution.

Possible causes

True positives the old assay missed. The new platform may be more sensitive (a third-generation design detecting core, NS3, NS4 and NS5), or the samples were taken in the window period with antibody below the old cut-off. This is the most clinically important possibility, because the new assay is right.

False positives from the new assay. Lower specificity at the current cut-off, non-specific binding in autoimmune disease, rheumatoid factor or heterophile antibody cross-reactivity, or miscalibration.

Sample-related. Storage degradation at minus 20 (rather than minus 70), freeze-thaw effects, contamination or plate carry-over from high-positive wells, or mislabelling.

Reagent and operational. Lot variability, calibrator drift, plate-edge effects, operator error. Rarely, an original false-negative on the day.

Investigation

• Repeat the 10 samples in duplicate on the new platform with known controls, and inspect QC charts for run excursions.
• Cross-platform comparison on at least one alternative anti-HCV assay to triangulate the true status.
• HCV RNA nucleic acid testing as the decisive marker: a positive resolves the discrepancy in favour of the new assay, while a negative does not exclude resolved past infection. HCV core antigen is a secondary virological marker.
• Clinical and risk-factor review of the 10 patients, and a fresh sample where possible to exclude storage artefact.
• Recompute sensitivity and specificity against a corrected reference (RNA plus cross-platform agreement).

Conclusion

If most discordants are RNA-confirmed, the new assay has improved sensitivity and should be adopted with reflex RNA confirmation. If most are RNA-negative and negative elsewhere, it has a specificity problem needing recalibration or rejection. The 100% concordance on the 50 known positives confirms acceptable sensitivity, so the decision rests on specificity.

Active HBV co-infection (HBsAg positive) demands a nucleos(t)ide analogue started before or with the DAA and continued for at least 12 months after DAA completion. Hepatitis C normally suppresses HBV replication; rapid DAA-driven HCV clearance lifts that suppression, and HBsAg-positive patients reactivate almost universally without cover, sometimes with severe flares. Tenofovir disoproxil fumarate, tenofovir alafenamide, or entecavir are the high-genetic- barrier agents of choice.

A baseline HBV DNA below 2,000 IU/mL (A) does not remove reactivation risk in an HBsAg-positive patient. Deferral (B) is wrong: the infections are safely co-treated. Lamivudine monotherapy (C) has an unacceptable HBV resistance rate. Vaccination (D) is futile in someone already HBsAg positive.

Direct-acting antiviral cure lowers but does not remove hepatocellular carcinoma (HCC) risk in established cirrhosis, so cirrhotic patients continue six-monthly abdominal ultrasound, with or without alpha-fetoprotein, for life. Established cirrhosis, pre-existing dysplastic foci, and durable epigenetic changes all persist after the virus is gone. Non-cirrhotic patients at SVR generally need no HCC surveillance unless specific risk factors apply.

Stopping surveillance (A) misses curable early HCC, because cure does not reverse established cirrhosis. Triphasic computed tomography (B) is for characterising a lesion found on ultrasound, not primary surveillance. Risk does not normalise within a year (D) or at any fixed 10-year point (E); it persists and is highest in the early years after cure.

SVR12 is undetectable HCV RNA 12 weeks after the last dose of direct-acting antiviral therapy, and is equivalent to virological cure with a lifetime late-relapse rate well below 1%. The defining feature is persistence of suppression off therapy, not on it. SVR4 predicts SVR12 with about 99% positive predictive value. Cure does not confer sterilising immunity, so reinfection remains possible in ongoing-risk groups, and HCC surveillance continues in cirrhotic patients.

A single on-treatment undetectable result (A) is not SVR12. Anti-HCV antibody persists for life and does not serorevert (B). A ten-fold fall at week 12 (C) was the interferon-era early virological response, now irrelevant. Core antigen (E) is an RNA surrogate, not the defining cure endpoint.

Harvey Alter, Michael Houghton, and Charles Rice shared the 2020 prize. Alter identified non-A non-B hepatitis as a distinct bloodborne agent in transfusion recipients; Houghton’s team cloned the virus in 1989 by immunoscreening a chimpanzee-plasma complementary DNA library, identifying clone 5-1-1; Rice proved the cloned genome was infectious and built the cell-culture systems that enabled direct-acting antiviral development.

The other trios won for different agents: Montagnier and Barré-Sinoussi for HIV (2008); Blumberg for HBV and Temin for reverse transcriptase; Watson, Crick and Wilkins for the DNA double helix (1962); Karikó and Weissman for modified-mRNA technology (2023). HCV has no licensed vaccine, and Susan Solomon is not a laureate.

The same enzyme both matures the virus and disarms innate immunity: NS3/4A cleaves the four downstream non-structural polyprotein junctions, and it also cleaves the adaptors MAVS and TRIF, abolishing RIG-I and TLR3-driven type I interferon induction in the infected hepatocyte. The -previr protease inhibitors (glecaprevir, voxilaprevir, grazoprevir, and the obsolete telaprevir and boceprevir) block the active site and, as a bonus, spare MAVS and TRIF.

The structural junctions are cut by host signal peptidase, not NS3/4A, so D is wrong, and lamivudine has no HCV activity. NS3 does carry a separate helicase domain (B), but that is not the immune-evasion function, and sofosbuvir targets NS5B. NS3/4A disables rather than activates innate immunity, so C is wrong, and the -asvirs target NS5A. miR-122 is bound by the HCV RNA itself (E), the target of miravirsen, not by NS3/4A.

Vertical transmission from a viraemic mother runs at ~2 to 4% when the mother is HIV-negative, rising to ~10 to 25% with HIV co-infection. Transmission is mainly intrapartum, through micro-transfusion of maternal blood, with a smaller in-utero component; maternal antibody is not protective. Caesarean section does not reduce the risk, and breastfeeding is not contraindicated unless the nipples are cracked and bleeding.

The ~30% figure (A) fits HBeAg-positive HBV, not HCV, and HIV does modify the risk. Transmission is not zero without HIV (B), and there is no protective transplacental immunity. It is not 50%, and caesarean section does not lower it (C). It is well above 1% and not purely postnatal (D).

Anti-HCV antibody screening identifies exposure but cannot separate current infection from cleared infection, so a reactive screen is confirmed with HCV RNA by polymerase chain reaction (PCR), or HCV core antigen where nucleic acid testing is unavailable. Many laboratories now reflex the RNA test automatically onto every antibody-positive sample, and point-of-care RNA supports same-day test and treat.

Antibody alone (A) misses the key question of active viraemia. Genotyping (C) is not a screening test; it follows confirmation and only where the regimen depends on it. The recombinant immunoblot (D) is obsolete, superseded by direct RNA. Core antigen (E) is a useful RNA surrogate but is less sensitive than antibody in early infection, so it does not replace the screen.

Genotype 5 (subtype 5a) was first identified in South Africa and stays mostly confined to southern Africa, where genotypes 1 and 5 co-dominate in the general population while genotype 4 is rising with migration. In people who inject drugs the picture shifts to genotype 1a (~73%) and 3a (~15%), with genotype 5 not yet detected in that group. Pan-genotypic regimens (sofosbuvir/velpatasvir, glecaprevir/pibrentasvir) cover genotype 5 with sustained virological response above 95%.

Genotype 1a (A) is globally dominant but was not first identified in South Africa. Genotype 3a (B) drives steatosis and faster fibrosis but is global. Genotype 4 (C) is increasing locally yet originates in Egypt and central Africa. Genotype 8 (E) is the most recently described genotype, first found in a Punjabi Indian cohort.

Sofosbuvir/velpatasvir for 12 weeks is a pan-genotypic first-line regimen, with sustained virological response (SVR12) above 95% across all eight genotypes, and is the standard in the South African NDoH 2019 guideline. Glecaprevir/pibrentasvir (8 weeks in treatment-naive non-cirrhotic patients) is the other first-line option, and sofosbuvir plus daclatasvir is the low-cost generic alternative.

Pegylated interferon plus ribavirin (A) is the obsolete pre-DAA standard. Telaprevir and boceprevir (C) are withdrawn first-generation protease inhibitors. The drugs in D are antiretrovirals with no HCV activity. Ribavirin monotherapy (E) is not curative and is only ever an adjunct to DAAs.

Sofosbuvir is a uridine nucleotide analogue prodrug that the HCV NS5B RNA-dependent RNA polymerase incorporates into the growing RNA chain, where its modified 2’-fluoro-2’-methyl sugar terminates chain extension. Its high genetic barrier makes clinical resistance rare, and it is the backbone of most pan-genotypic regimens.

The other options misassign the target. Ganciclovir inhibits the cytomegalovirus DNA polymerase (after UL97 phosphorylation), not HIV integrase. Simeprevir is an HCV NS3/4A protease inhibitor, not a neuraminidase inhibitor. Cabotegravir is an HIV-1 integrase strand-transfer inhibitor, not an HBV reverse transcriptase inhibitor. Lenacapavir is an HIV-1 capsid inhibitor, not a SARS-CoV-2 protease inhibitor.

Drug	Virus	Target
Sofosbuvir	Hepatitis C virus	NS5B RNA-dependent RNA polymerase
Simeprevir	Hepatitis C virus	NS3/4A serine protease
Ganciclovir	Cytomegalovirus	DNA polymerase
Cabotegravir	HIV-1	Integrase
Lenacapavir	HIV-1	Capsid