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Flashcards in Blood borne viruses Deck (27)

What are blood borne viruses?

Viruses with a viraemic phase that may be self-limited (acute with recovery) or persistent (chronic)


What's the virology of Hep B?

 Hepadnaviridae
 Enveloped virus
 Double stranded DNA genome


What are the clinical features of Hep.B?

 Incubation period average 60-90 days (45-180)
 Virtually all infants and children asymptomatic, up to 50% adults asymptomatic, especially likely if HIV infected
 Acute case-fatality rate: 0.5%-1%  If symptomatic, prodrome, icteric phase
 May see signs of chronic liver disease
 Chronic infection: 5 yrs, 2%-10%


What's the burden of chronic Hep B infection?

 Premature mortality from cirrhosis and HCC  15%-25%
 Worldwide HBV infection accounts for 30% of all cases of cirrhosis and 53% of all HCC cases (lower for UK)


What's the management of acute hepB?

 Supportive, antivirals not given
 Counsel regarding transmission
 Screen for other bloodborne viruses, STDs
 Notifiable disease  Trace, test, and immunise relevant contacts


What's the management of chronic Hep B?

 Defined as on-going infection for >6 months
 If ALT/ HBV viral load/ liver biopsy suggest risk of progression- antiviral therapy


What's Hep B antiviral therapy?

 Nucleoside analogues  Lamivudine, adefovir, entecavir,
tenofovir  Effective rapid reduction in HBV DNA  Antiviral resistance may develop  Prolonged or life long therapy
 Immunomodulators  Interferon alpha (pegylated)  Response rate 60% at best  Side effects


How can you prevent Hep B infection?

 Avoid or reduce risk • Safe sex, needle exchange, infection control
 Screening • Blood products, risk groups, pregnancy
 Vaccine  Safe, recombinant sAg  Primary prevention, post exposure  Active or passive (HBIG)  Know your status


What's the virology of Hep C?

 Flavivirus, Hepacivirus, 1989
 Positive single stranded RNA
 Enveloped
 Many different genotypes distributed geographically


What's the natural history of Hep C?

1. Incubation period 6-8 weeks
2. Acute Hep C
3. Develops to chronic Hep C (85%)
4. Cirrhosis (20%)
5. Liver cancer, liver failure (25%)


What's the burden of Hep C?

Worldwide HCV infection accounts for 27% of all cases of cirrhosis and 25% HCC
HCV infection is now the major indication for liver transplant in USA and Europe


How can you diagnose Hep C?

 Usually picked up by screening risk groups or contacts or as part of liver disease work up
 Antibody or nucleic acid (RNA)
 Seroconversion window period
 Some patients never make detectable antibody, esp. immunosuppressed


How can you manage acute Hep C?

 Difficult to spot-usually asymptomatic
 High dose interferon alpha clears infection in most people
 Notifiable to public helath


How can you manage chronic Hep C?

 Assessment  LFT, symptoms, liver biopsy or
fibroscan to measure severity
 Immunise against HAV, HBV
 Antiviral therapy to clear virus and prevent progression
 Combination antiviral therapy
 Pegylated interferon and ribavirin can clear virus in up to 80% non-genotype 1, and 50% genotype 1
 Side effects and adherence
 Promising new agents-protease, polymerase inhibitors


How can you prevent Hep C?

 No vaccine
 Risk reduction and counselling  E.g. needle exchanges
 Screen and test donors  Virus inactivation of plasma-derived
 Safe injection and infection control practices


What is the virology of Human Immunodeficiency Virus (HIV)?

•Diploid RNA genome


What's the origin of HIV?

• HIV (or similar) antibody found in sera from Zaire 1959
• HIV1 related to chimpanzee virus
• Evidence of spread among gay American males from 1977
• HIV2 related to virus found in Sooty Mangabey
• Human epidemic probably result of exposure to blood during animal butchering, spread occurring via urbanisation in 1950’s and international travel from 1970’s


What's the risk of HIV transmission?

 From known HIV infected individual:
 Blood transfusion (one unit)  Receptive anal intercourse  Receptive vaginal intercourse  Insertive vaginal intercourse  Insertive anal intercourse
 Receptive oral sex (fellatio)  Needle–stick injury  Sharing injecting equipment  Mucous membrane exposure
90-100% 0.1-3.0% 0.1-0.2% 0.03-0.09% 0.06% 0-0.04% 0.3% (95% CI 0.2%-0.5%) 0.67%
0.09% (95% CI 0.006%-0.5%)
 >>Variable according to viral load in genital tract, breeches in mucosal barrier, other STI (HSV)


How can you diagnose HIV?

 First antibody tests developed 1985 (blood screening)
 Screen/ test • Risk groups, in pregnancy, contacts, or investigation
of illness
 Sensitivity increased by use of ‘dual’ assays
• Detect virus antigen and antibody- 4th generation tests
• Reducesseroconversionwindowperiod-timefrom infection to being antibody positive
 Detection of virus genome (viral load) may reduce window further


What's the pathogenesis of HIV?

 HIV infects CD4 positive cells
 T cells, macrophages, dendritic cells, microglia
 CD4 cell turnover 108-9 cells/day  Virus production up to 1010/day  Immune cell production cannot ‘keep up’  Immunodeficiency results
 Virus escapes full immune control • High turnover and mutation rate of envelope antigen target • Integrated into dormant cell genome
• Interference with immune function signalling


What's the clinical progression of HIV?

1. Acute retroviral syndrome, oral or oesophageal candidiasis.
2. Herpes zoster (shingles), vaginal candidiasis
3. Oral oesophageal candidasis, Kaposi's sarcoma, TB
4. Pneumocystosis, cryptococcosis, histoplasmosis
5. Resistant candidiasis, CMV disease, MAC disease.


What is Kaposi's sarcoma?

An opportunistic infection.
Characteristic raised purple lesions occur anywhere throughout body
Associated with HHV8 infection Rare now in the era of HIV therapy


What's oral hairy leukoplakia?

An opportunistic infection.
Non-painful white plaques along lateral tongue borders
Associated with EBV infection
Correlates with smoking
AIDS defining
Treatment is by improving CD4 count


What's the management of HIV?

 Investigate for other infections, assess general health, counsel regarding transmission
 Assess need for antiretroviral therapy based on symptoms, CD4 count, and viral load
 Not everyone needs ART (antiretroviral therapy) at the time of diagnosis
 Balance side effects and drug resistance with protection against immune deficiency


What's combination therapy?

Standard of care is currently to use HAART (highly active antiretroviral therapy)
Multiclass combination therapy
o More potent
o Less risk drug resistance
o (more side effects)


What's the practice for needlestick injuries?

 Avoid- safe practice  First aid  Report  Risk assess
 May not be appropriate for recipient of injury to do
Risk of transmission depends on amount of virus exposed to and pre- existing immunity
 Hollow bore/ solid needle; venepuncture/ injection; scratch/deep wound/ mucosal exposure; viral load of source
 HBV 30-3%; HCV 1-3%; HIV 0.3%


How should you manage a significant needlestick injury?

 If significant event
 Prophylaxis- HBV vaccine/ HBIG
 Follow up and early treatment for HCV
 Storage sample (prove not already infected)
 Managed by occupational health