Bloodborne Pathogens Flashcards
How are bloodborne pathogens transmitted?
- Direct contact with infected blood fluids.
- Infection via contaminated needles, syringes, or other unsterilised instruments.
- Direct infection into the bloodstream by arthropod vectors (e.g. mosquitos).
How is HIV transmitted?
- Occurs by 3 routes:
- Via blood / blood products or contaminated needles.
- Sexually (virus is present in semen and vaginal secretions).
- Perinatally (transplacentally during delivery, ingestion of breast milk).
Describe the classification of HIV.
- Family - retroviridae
- Genus - lentivirus
- HIV-1 and HIV-2 pathogenic for humans
- HIV-1 is most common
- HIV-2 is less virulent
Describe the viral features of HIV.
- Spherical (80-100nm)
- Enveloped
- RNA genome
- Retrovirus - uses reverse transcriptase to make DNA copy from viral RNA.
Describe the time course of HIV infection.
Describe the progression of HIV to AIDS.
- Exposure to HIV
- Seroconversion
- Asymptomatic
- Persistent generalised lymphadenopathy
- AIDS-related clinical features
- AIDS
What are the defining conditions associated with AIDS?
How does the viral load of HIV affect the development of AIDS?
-
Viral RNA copy number (viral load) in blood:
- 13% of those with <1,500 copies/mL blood will develop AIDS within 9 years.
- 93% of those with >55,000 copies/mL blood will develop AIDS within 9 years.
What are the available drugs for the treatment of HIV?
-
Anti-retroviral therapy (ART):
- Nucleoside reverse transcriptase inhibitors (NRTIs).
- Non-nucleoside reverse transcriptase inhibitors (NNRITs).
- Protease inhibitors (PIs).
- There are many possible regimens and combinations.
- Initial treatment often contains:
- 1 NRTI + 1 PI
- OR
- 2 NRTIs + 1 NNRTI
Describe the diagnosis of HIV infection.
- Diagnosis of HIV specific antibodies.
- ELISA
- Western Blotting
- NAAT used to detect viral RNA in serum.
- Quantitative NAAT used to measure viral load.
- Individual testing must be preceded by counselling.
- An initial negative result should always be followed-up.
Describe the prevention of HIV infection.
- No vaccine yet available
- Screening of blood products
- Needle exchane programmes
- Anti-retroviral prophylaxis for needlestick injuries
- Avoiding high-risk sexual partners
- Use of barrier contraception
- Elective caesarian section
Describe the viral features of hepatitis B (HBV).
- Hepadnavirus
- Double-stranded DNA genoma
- Enveloped
What are the antigens associated with hepatitis B virus (HBV)?
- HBsAg - surface antigen
- Indicated infectivity
- Anti-HBsAg provides immunity and appears late
- HBcAg - core antigen
- Appears early in infection
- HBeAg - pre-core antigen
- Indicates high transmissibility
How is HBV transmitted?
- Via blood or blood products.
- Contaminated needles and equipment used by IV drug users.
- Association with tattooing, body piercing and acupuncture.
- Sexual intercourse
- Intra-uterine, peri- and post- natal infection.
- Contaminated haemodialysis equipment.
What are the stages of HBV infection?
- Long incubation period - up to 6 months.
- Development of acute hepatitis.
- Fulminant disease carries 1-2% mortality rate.
- 50% of patients develop chronic active hepatitis.
- Cirrhosis
- Hepatocellular carcinoma
Describe the development of an acute HBV infection which is self-limited.
Describe the development of a chronic HBV infection which is persistent.
What are the clinical features of HBV.
- Pre-icteric stage
- Malaise
- Anorexia
- Nausea
- Pain in RIQ (tender liver)
- Icteric stage
- Jaundice
- Dark urine (bilirubin)
Describe jaundice. What causes it?
- Yellowish pigmentation
- Skin
- Sclera
- Other mucous membranes
- Caused by hyperbilirubinaemia
What are the treatments for HBV?
- Pegylated interferon (peginterferon) is superior compared to α-interferon in sustaining suppression of viral replication.
- Antiviral activity of nucleoside analogues (e.g. oral lamivudine) may be successful even in chronic HBV patients.
What are the prevention strategies for HBV?
- HBsAg vaccine
- Good protection following 3 injections over a 6 month period.
- HBV immunoglobulin
- Blood screening
- Needle exchange programmes
- Sexual health education
What are the viral features of hepatitis C virus (HCV)?
- Flavivirus
- Single-stranded RNA genome
- Enveloped
- Replicated primarily in hepatocytes
- Destroys liver cells
- Virus cannot be cultured
How is HCV transmitted?
- Via blood and blood products.
- Tattooing, body piercing and acupuncture.
- Haemodialysis.
- Sexual transmission uncommon.
- Vertical transmission uncommon.
What are the clinical features of HCV?
- Usually asymptomatic
- Fatigue
- Nausea
- Weight loss
- May rarely progress to cirrhosis
- Small proportion may develop hepatocellular carcinoma
What are the treatments for HCV?
- Interferon reduces liver transaminases in 80% of patients.
- Ribavirin works well in combination with pegylated α-interferon.
- Combination therapy
- Sofosbuvir (nucleotide analogue)
- Boceprevir (protease inhibitor)
- Telaprivir (nucleotide analogue)
- Daclatasvir (inhibits NS5A)
- Monitor viral load by NAAT
- No vaccine available
How is HCV screened for?
- NAAT performedon blood samples.
- Therefore, current incidence of transfusion-associated HCV is low.
What is the cause of malaria?
- Caused by 5 species of the genus Plasmodium
- P. falciparum
- P. vivax
- P. ovale
- P. malariae
- P. knowlesi
- Female Anopheles mosquito injects sporozoa into the blood stream.
- Zoonotic disease.
What are the clinical features of malaria?
- Fever
- Flu-like symptoms
- P. falciparum infection can rapidly progress to death
-
P. falciparum affects every organ - wide range of complications. Examples:
- Cerebral malaria
- Circulatory shock
- Hepatitis
How is hepatitis diagnosed?
- At least 3 blood films (both thick and thin) obtained from different times for microscopy.
- NAAT - useful for detecting drug resistance.
What are the available treatments for malaria?
- Chemotherapy kills blood stages of parasite.
- Resistance means treatment advice should be changed regularly.
- Combination therapy is the norm:
- Quinine
- Chloroquining
- Doxycyclin
- Proguanil
- Malarone (= proguanil + atovaquone)
- Artemether
Describe the prevention strategies for malaria.
- Sleep under bed nets
- Cover exposed skin between dusk and dawn
- Use of mosquito repellants
- Prophylaxis
- Vaccines currently being developed
