Hepatits B Flashcards
Occult Hep B & it’s complications
Occult hepatitis B infection (OBI) is defined as the existence of low-level HBV DNA in the serum (<200 IU/mL), cells of the lymphatic (immune) system, and/or hepatic tissue in patients with serological markers of previous infection (anti-HBc and/or anti-HBs positive) and the absence of serum HBsAg.
replication-competent viral DNA is present in the liver (with detectable or undetectable HBV DNA in the serum) of individuals testing negative for the HBV surface antigen (HBsAg). In this peculiar phase of HBV infection, the covalently closed circular DNA (cccDNA) is in a low state of replication.
a) it can be transmitted, causing a classic form of hepatitis B, through blood transfusion or liver transplantation; (b) it may reactivate in the case of immunosuppression, leading to the possible development of even fulminant hepatitis; (c) it may accelerate the progression of chronic liver disease due to different causes toward cirrhosis; (d) it maintains the pro-oncogenic properties of the “overt” infection, favoring the development of hepatocellular carcinoma.
HBV structure, virology, and classification
Enveloped circular partially ds DNA virus.
rcDNA- relaxed circular DNA
cccDNA - covalently closed circular DNA
SEE IMAGE IN ALBUM
spherical virion comprises an envelope that is outside a nucleocapsid that encloses a circular DNA genome.
The lipid bilayer of the virion envelope incorporates the large (42-kD) hepatitis B virus surface protein (LHBs), the medium (33-kD) surface protein (MHBs), and the small (26-kD) surface protein (SHBs).
LIFE CYCLE:
- Viral cell entry using receptor NTCP
- Partial dsDNA moves into cell nucleus
- Viral DdDP (aka reverse transcriptase) AND HUMAN POLYMERASES creates full dsDNA inside the nucleus - cccDNA
- From this dsDNA, DdRP creates pgRNA (pre-genomic) - this is done by human cellular machinery
- This pgRNA is the template for both capsid protein translation and nee partial dsDNA reverse transcription
- Some of the cccDNA also integrates into the host genome
10 genotypes (A to J) and 24 subtypes
Genotype C more severe disease
Baltimore class: VII
HBeAg in Hep B
HBeAg positive infection - usually in young adults. High VL > 10^7 log but normal ALTs.
HBeAg positive disease - VL between 10^5 to 10^7. High ALTs. Exacerbations leading to necroin-
flammation and hepatic fibrosis.
Spontaneous HBeAg seroconversion occurs in approximately 15% of cases per annum. Transition to HBeAg-negative, inactive infection reduces the risk of progression, but the
disease necessitates longitudinal monitoring.
Conversely, HBeAg seroconversion can augur a change to HBeAg-negative disease, with mutations in the precore or basal core promoter down-regulating HBeAg, despite continued HBV replication. PRE-CORE MUTANT. HBsAg levels can remain high(>1000 IU per milliliter), which reflects expression predominantly from integrated HBV genomes.
Spontaneous seroclearance of HBsAg
has been associated with improved clinical outcomes but is infrequent (accounting for an estimated 1 to 2% of cases per year)
Although there is a linear rela-
tionship between HBV DNA levels and the risks of cirrhosis and HCC among
HBeAg-negative patients, among HBeAg-positive patients, the immediate risk is lower for those
with HBV DNA levels exceeding 8 log10 IU per ML than for those with HBV DNA levels of 5 to 7 log10 IU per ML.
In HBeAg-positive patients with active disease, the infection is likely to be transitioning from a low inflamma-
tory–high replicative state to a different immunologic phenotype and phase. The transition is characterized by a decrease in HBV DNA levels and an increase in necroinflammatory damage,
which lead to an increase in hepatocyte turnover (and to the gradual selection of HBeAg-negative
variants).
HBeAg is a secreted HBV protein, derived from the HBcAg reading frame with the use of the first of the two start codons, but is not required
to maintain infection. HBeAg in serum
signals high levels of replication and infectivity, but since HBeAg expression is affected at the transcriptional, translational, and post-translational levels, it may not necessarily correlate with HBV DNA levels.
HBSAg marker in HBV
Serologic assays for HBsAg de-
tect virion and subviral particles in blood.
Non–DNA-containing subviral HBsAg particles greatly outnumber virions. SHBs antigen is the pre-dominant component of 22-nm spherical parti-
cles; virion particles are enriched in LHBs antigen. The isoforms cannot be identified by current immunoassays, which target the common antigenic epitope within the “a” determi-
nant of HBsAg protein.
Neither can current HBsAg assays distinguish between HBsAg origi-
nating from covalently closed circular DNA (cccDNA) and HBsAg derived from integrated viral genomes.
Diagnostics to quantify HBV cccDNA
- HBV RNA: During HBV replication, pgRNA is reversely transcribed to minus-strand DNA. However, a minority of pgRNA transcripts are not transcribed but are encapsidated, releasing HBV RNA–containing capsids into serum. Several methods are available for quantitating pgRNA; two higher-throughput assays have been developed
- HBV core-related antigen (HBcrAg): HBcrAg measures a composite of HBeAg, HBcAg, and p22cr protein (a 22-kD truncated core protein). The components of HBcrAg thus originate
exclusively from HBV cccDNA. Serum
HBcrAg is measured by means of a chemiluminescent enzyme immunoassay (Lumipulse G sys-
tem, Fujirebio).
Nucleoside analogues in HBV
Nucleoside analogues: Tenofovir, Tenofovir alafenamide, & entecavir.
Compete with endogenous nucleotide substrate to bind the active site of HBV polymerase and disrupts 5’ to 3’ phosphodiester linkage - terminates DNA chain elongation.
ADR: Renal impairment and bone mineral density lowering with Tenofovir.
High LDL and cholesterol with Tenofovir alafenamide.
NAs target late stage of life cycle - act on RT step with no effect on pgRNA transcription and do not directly affect HBsAg expression from integrated genomes. Thus HBeAg loss is uncommon (20-30% in 1-2 years) and HBsAg seroclearance is VERY LOW (0.22% per year).
NAs also do not reduce risk of HCC.
Resistance rates - for entecavir after 5 years, 1%.
Entecavir resistance
1% resistance in 5 years
rtL180M
T184L
M204V
Also confers resistance to Tenofovir when in combinations
Peg IF alpha in Hep B
IF alpha - pleotropic cytokine
Can be used in Mild-moderate eAg pos or neg disease.
Inhibits transcription of pgRNA from cccDNA.
Tenofovir + IF alpha trial showed HBsAg loss in 9% patients (higher than mono therapy)
TEST THESE 4 before starting:
1. Genotype
2. quantitative surface Ag testing before starting IF alpha. (>20,000 IU/mL in genotype B&C OR no decline of levels at 12 weeks in genotype A&D @12 weeks associated with treatment failure).
3. eAg
4. DNA VL
DURING THERAPY, monitor:
1. FBC
2. ALT
3. TSH
4. DNA
5. sAg levels
Newer agents in HBV
- Entry inhibitors - Buleviritide - inhibits entry of HBV & HDV
- Nucleic acid polymers - REP 2139 (Replicor)
- Capsid assembly modulators - disrupts encapsulation of pgRNA
- RNA interference
- siRNA: Binds to complementary target mRNA leading to cleavage.
- ASOs: synthetic single stranded oligonucleotodes that bind to complementary HBV RNA transcripts to form ASO-RNA complexes causing cleavage.
Natural history of chronic HBV
- Immune tolerance phase: HBeAg pos, high DNA, low ALT
- Immune clearance phase: HBeAg pos, low DNA, high ALT- High risk of CLD
- Immune control phase: HBeAg neg, DNA neg, ALT normal
- Immune escape phase: HBeAg neg, DNA high, ALT high - High risk of cirrhosis
Treatment in HBeAg pos + compensated liver disease
- Tenofovir
- Entecavir second line
- Peg IF alpha for 48 weeks. CI in pregnancy.
HBeAg neg + compensated liver disease treatment
- Tenofovir
- Entecavir second line
- Peg IF alpha for 48 weeks. CI in pregnancy.
HBV treatment in pregnancy
Tenofovir disoproxil if DNA > 200,000 IU/mL OR sAg > 10^4 IU/mL in 3rd trimester to reduce transmission
Repeat DNA after 2 months and ALT monthly after birth
Stop Tenofovir 4-12 weeks after birth UNLESS mum fits criteria for long term treatment
Chronic HBV prophylaxis in immunosuppression
- sAg pos + DNA > 2000: Tenofovir or entecavir - start before immunosuppression and continue for 6 months after seroconversion and DNA neg.
- sAg pos + DNA < 2000: Lamivudine if immunosuppression expected to be more than 6 months. Check VL in 3 months and switch to entecavir/Tenofovir if DNA detectable.
Duration- start before go 6 months after stopping immunosuppression
Fibroscanning indications and cut-offs in HBV
- New diagnosis
- Antivirals if elastography score > 11KPa
- Antivirals & Liver biopsy if score 6-10 KPa
- Antivirals & liver biopsy if score < 6 BUT age < 30 + DNA > 2000 + ALT >30/19 twice 3 months apart
- Offer scan annually if not on antivirals
Indications & antivirals in chronic HBV
- > 30 years + DNA > 2000 + ALT >30/19 TWICE
- <30 years + DNA >2000 + ALT >30/19 TWICE + biopsy/fibroscan s/o inflammation (>6 KPa)
- DNA > 20,000 + ALT >30/19 TWICE
- CLD + detectable DNA
- DNA > 2000 + biopsy showing inflammation
- Family H/O HCC
HBV treatment in DCLD
NO IF
1. Entecavir first line
2. Tenofovir if lamivudine resistance
Treatment in HBV + HCV
DAAs for HCV + NA prophylaxis until 12 weeks post DAA for HBV.
Monitor for sAg in core Ab positive patients on DAAs.
HBV + HDV treatment
48 weeks peg IF 2a if evidence of fibrosis
Stop if no decrease in HDV RNA after 6 months.
If responding as they should, Stop treatment when HBsAg seroconverts
50% relapse risk. If ongoing viral load - consider NAs.
Immunosuppression - HBV prophylaxis in cleared infection
In the high risk group (>10%), including anti-HBc positive subjects who need to be treated with rituximab in the onco-hematological setting or those undergoing stem cell transplanta-tion, antiviral prophylaxis is recommended. Prophylaxis should continue for at least 18 months after stopping immunosuppres-sion and monitoring should continue for at least 12 months after prophylaxis withdrawal. LAM may be used safely in this setting although few cases of HBV exacerbation due to LAM resistance have been reported.210-212 Prophylaxis with ETV or TDF or TAF can be also considered in HBsAg-negative, anti-HBc positive patients receiving highly immunosuppressive regimens of extended duration.213,214
In HBsAg-negative, anti-HBc positive subjects with moderate (<10%) or low (<1%) risk of HBV reactivation, pre-emptive ther-apy, not prophylaxis, is generally recommended. 205,206 The main virological event in these anti-HBc positive patients is HBsAg reappearance (seroreversion), constantly associated with hepatitis flare; by converse HBV DNA detection leads to seroreversion and hepatitis in only 50% of cases.212 Pre-emptive therapy is based upon monitoring HBsAg and/or HBV DNA every 1-3 months during and after immunosuppression, and starting ETV, TDF or TAF treatment in case of detectable HBV DNA or HBsAg seroreversion. As HBsAg seroreversion can lead to a sev-ere, even fatal, acute hepatitis, NA should be started as early as possible, independently of ALT levels. For selected clinical set-tings, characterised by long duration of immunosuppression, limited compliance to monitoring or unknown risk of viral reactivation for new biologicals, universal prophylaxis, rather than pre-emptive therapy, is recommended.
Surveillance for HCC in HBV
- 6 monthly USG & AFP in patients with fibrosis or CLD
- 6 monthly USG & AFP with no fibrosis if >40 years + family h/o HCC + DNA > 20,000
