Microbiology: Hepatitis viruses 2 Flashcards
What are the microbiological characteristics of HBV?
Hepadnavirus
partially ds-DNA virus
Why does HBV give rise to chronic infection?
Dane particles = virions
non-infectious but immuongenic filaments with HBsAg = stimulation of long term inflammation.
What are the 5 proteins that are key for HBV replication?
- DNA polymerase with R-T activity
- Surface attachment protein = HBsAg
- Core Ag = HBcAg
- Secreted form of core Ag = HBeAg
- X-Antigen = regulator of gene expression
What diseases are caused by HBV?
Parenterally transmitted chronic hepatitis (serum hepatitis)
Younger people have a higher risk of developing chronicity
Most common caused of HCC
What are the epidemiological characteristics of HBV?
Endemic to sub-saharan Africa and China where infections occur earlier
What populations are at an increased risk for HBV?
Hospital worker, Hemophiliacs
Dudes, drug users
What is the prognosis for HBV?
25% die of liver disease in 50’s and 60’s
What is the pathogenesis of HBV?
HBV enters parenterally (blood, semen, vagina) –> replicates in liver (45-160d) –> Immune mediated destruction of infected cells
How does HBV replicate?
HBV enters nucleus –> Completes ds-DNA with host machinery –> Pre-genomic RNA from host RNA pol –> Core protein encapsidates pre-genomic DNA –> DNA POL RT creates L-DNA genome –> Most of residual RNA destroyed except for SDNA strand –> new virion buds from cell.
What are the 3 stages of HBV infection?
- Immune tolerance phase: high HBV DNA, HBeAg+. No CTL immune response, kids>adults
- Immune clearance phase: Seroconversion (HBeAg–>HBeAbs), CTL response, increased ALT levels from liver injury
- Residual phase: Decreased HBV DNA, Normal ALT,
What is the clinical presentation of HBV infection?
Chronic cases are usually asymptomatic until cirrhosis or hepatocellular carcinoma appears
If chronic HBV suddenly worsens think HDV superinfection
Greater than 6 months = chronic
What is used as the screening test for HBV?
HBsAg
all infected persons have this.
What test is best for detecting past HBV infection?What about current infection?
Anti-HBs Anti-bodies indicates past infection
HBeAg indicates active infection, high risk of transmission, especially with high HB DNA levels.
How does one distinguish an acute infection from a low risk carrier diagnostically?
Anti-HBe = low risk carrier Anti-HBc = acute infection
How can one distinguish past infection from a vaccinated individual?
Anti-HBc = past infection (notice there is no core capsid marker)
