Bloodborne Viruses (HIV, Hepatitis B and C)

HIV taxonomy

-Genus: Lentivirus (means slow)

-Family: Retroviridae (retrovirus)

2 species of HIV

HIV1: Most common globally

HIV2: Confined mainly to regions in West Africa

HIV virus genome

Positive RNA with a reverse transcriptase enzyme

Which cells does HIV infect

- CD4+ cells

- Macrophages

- Dendritic cells

HIV Viral structure

- GP-120 used to bind to CD4+ cells

- RNA genome with reverse transcriptase

- Integrase to put DNA into host genome

Life cycle of HIV

1. Adheres to CD4+ by GP120 and fuses with host cell

2. Enters host cell and uncoats

3. Viral DNA formed by reverse transcriptase

4. Integrase allows it to go into host genome

5. Transcription, translation, virus assembly

7. Viral maturation by protease and release

Natural reservoir of HIV

Humans only in CD4+ cells

Mode of transmission from HIV

Sexual, blood borne, horizontal transmission

HIV virus is fragile and cannot exist on surfaces for long

3 stages of HIV infection

- Acute retroviral syndrome

- Chronic HIV infection

- AIDS

Acute retroviral syndrome

After initial exposure there is a rapid rise in virus and destruction of CD4+ cells

Lasts 1-2 weeks and presents as mononucleosis syndrome

Chronic HIV infection

Clinical latency, slow replication of virus and destruction of CD4+ cells

Lasts 10 years if patient is not being treated

AIDS

Acquired immunodeficiency syndrome, where CD4+ declines to less than 200 cells/uL or the person acquires a certain opportunistic infection

HIV diagnosis

Done by "HIV serology" which is a combined antibody and antigen test

If that is positive, a HIV-1 viral load (RNA NAAT) is ordered to quantify how much viral RNA is in the body

4th generation HIV tests

Tests for:

- HIV antibodies (IgG and IgM)

- HIV p24 antigen

HIV p24 antigen

Tested for in "HIV serology", advantage is that this is detected before antibodies so the test can be done quicker (within 2-3 weeks)

How HIV serology is done

Using human plasma, put in well with antibodies for p24 antigen, as well as antigens for HIV1 and HIV 2

Results of HIV serology

If HIV serology is positive, need to do a differentiation assay to determine if it is HIV1 or HIV2. If this is negative then it was likely a false positive or too early to detect. To confirm, must do test again in 4 weeks or do viral load test for HIV (RNA NAAT)

HIV susceptibility testing

Done on the first viral load, genotypic testing that sequences reverse transcriptase, integrase, and protease to determine if there is any mutations that will lead to drug resistance

Hepatitis C taxonomy

Part of Flaviviridae family

Genome of hepatitis C

Positive sense RNA genome, enveloped virus

Genotypes of hepatitis C

7 genotypes

1, 2, and 3 are the most responsible for infections in North America

Natural reservoir of hepatitis C

Humans only, 25% will clear the infection spontaneously, others develop chronic hepatitis C infection

Mode of transmission of hepatitis C

Blood, sexual, horizontal transmission

Blood borne is most common especially with injection drug use

Hepatitis C life cycle and drug targets

Targets hepatocytes

- NS5B allows for RNA replication

- NS3/4 protease is involved in protein processing

- NS5A involved in assembly of the virus

Pathogenesis of Hepatitis C

Replicates in the cytoplasm of hepatocytes with RNA dependent RNA polymerase which is prone to error and leads to many quasispecies which helps virus escape immune detection

Liver is damaged by T cell mediated attack on infected hepatocytes leading to inflammation, necrosis, apoptosis, and regeneration leading to fibrosis and cirrhosis

Additionally more systemic effects involving things like diabetes, vasculitis, atherosclerosis, etc.

Diagnosis of HCV

- Serology (ordered first)

- Hepatitis C viral load (RNA NAAT)

Serology for HCV

If someone has ever had HCV they will be positive for life

Viral load for HCV

Only positive in active infection

Genotyping for HCV

Used to be done a lot when treatment was genotype specific, less important with current treatments

Interpretation of test: Anti-HCV positive, HCV RNA positive

Active infection

Interpretation of test: Anti-HCV positive, HCV RNA negative

Previous infection

Hepatitis B taxonomy

Hepadnaviridae family

Hepatitis B genome

Mostly double stranded circular DNA that is enveloped

Infectiousness of HBV

50-100x more infectious than HIV, can survive outside of the body for 7 days

Natural reservoir of HBV

Humans

Chronic infection develops mostly in neonates, but lesser in children and adults

Transmission of HBV

Horizontal, blood borne, sexual

Life cycle of HBV

1. Virus attaches to hepatocytes by the NTCP receptor(bile acid receptor)

2. Virus DNA goes into the nucleus and forms covalently closed DNA (cccDNA)

3. DNA > RNA > Protein

4. RNA can also go back to DNA by reverse transcriptase

HBV pathogenesis

Liver injury by the host immune response, polyclonal T cell response especially by CD8+ T cells which targets infected hepatocytes leading to hepatocellular injury

Chronic infection of HBV

There is an inadequate or exhausted adaptive immune response which allows ongoing viral replication

Inflammation, fibrosis, cirrhosis, hepatocellular carcinoma all possible

Diagnosis of HBV

- Hep B antibody

- Hep B surface antigen

- Hep B core antigen

- NAAT for viral load (HBV DNA)

- HBeAg (hepatitis B e antigen, sign of active viral replication)

Chronic infection of HBV based on labs

Hepatitis B surface antigen for longer than 6 months

What does hepatitis B surface antigen tell you

You are infectious

What does hepatitis b core antigen tell you

You have been exposed to hepatitis B

What does hepatitis b surface antibody mean

You have antigen against surface antibody and are most likely immune

Interpretation of the lab test:

HBsAg: Positive

Anti-HBc: Positive

Anti-HB: Negative

HBsAg: Surface antigen

Anti-HBc: Core antibody for core antigen

Anti-HB: Protective surface antibody

Chronic hepatitis B infection, virus is present but there is no protective antibodies for it

Interpretation of the lab test:

HBsAg: Negative

Anti-HBc: Positive

Anti-HB: Positive

HBsAg: Surface antigen

Anti-HBc: Core antibody for core antigen

Anti-HB: Protective surface antibody

Previous exposure to Hepatitis B but no active infection, has immunity

Interpretation of the lab test:

HBsAg: Negative

Anti-HBc: Positive

Anti-HB: Negative

HBsAg: Surface antigen

Anti-HBc: Core antibody for core antigen

Anti-HB: Protective surface antibody

Previous exposure to Hepatitis B (past infection) but no active infection, does not have immunity

Interpretation of the lab test:

HBsAg: Negative

Anti-HBc: Negative

Anti-HB: Positive

HBsAg: Surface antigen

Anti-HBc: Core antibody for core antigen

Anti-HB: Protective surface antibody

No active or previous exposure but has been vaccinated

Interpretation of the lab test:

HBsAg: Negative

Anti-HBc: Negative

Anti-HB: Negative

HBsAg: Surface antigen

Anti-HBc: Core antibody for core antigen

Anti-HB: Protective surface antibody

No active or previous infection, no immunity (should vaccinate)