Bloodborne Pathogens

Question 1

How are bloodborne pathogens transmitted?

Answer 1

• 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).

Question 2

How is HIV transmitted?

Answer 2

• 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).

Question 3

Describe the classification of HIV.

Answer 3

• Family - retroviridae
• Genus - lentivirus
• HIV-1 and HIV-2 pathogenic for humans
• HIV-1 is most common
• HIV-2 is less virulent

Question 4

Describe the viral features of HIV.

Answer 4

• Spherical (80-100nm)
• Enveloped
• RNA genome
• Retrovirus - uses reverse transcriptase to make DNA copy from viral RNA.

Question 5

Describe the time course of HIV infection.

Answer 5

Question 6

Describe the progression of HIV to AIDS.

Answer 6

• Exposure to HIV
• Seroconversion
• Asymptomatic
• Persistent generalised lymphadenopathy
• AIDS-related clinical features
• AIDS

Question 7

What are the defining conditions associated with AIDS?

Answer 7

Question 8

How does the viral load of HIV affect the development of AIDS?

Answer 8

• 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.

Question 9

What are the available drugs for the treatment of HIV?

Answer 9

• 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

Question 10

Describe the diagnosis of HIV infection.

Answer 10

• 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.

Question 11

Describe the prevention of HIV infection.

Answer 11

• 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

Question 12

Describe the viral features of hepatitis B (HBV).

Answer 12

• Hepadnavirus
• Double-stranded DNA genoma
• Enveloped

Question 13

What are the antigens associated with hepatitis B virus (HBV)?

Answer 13

• 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

Question 14

How is HBV transmitted?

Answer 14

• 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.

Question 15

What are the stages of HBV infection?

Answer 15

• 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

Question 16

Describe the development of an acute HBV infection which is self-limited.

Answer 16

Question 17

Describe the development of a chronic HBV infection which is persistent.

Answer 17

Question 18

What are the clinical features of HBV.

Answer 18

• Pre-icteric stage
  
  • Malaise
  • Anorexia
  • Nausea
  • Pain in RIQ (tender liver)
• Icteric stage
  
  • Jaundice
  • Dark urine (bilirubin)

Question 19

Describe jaundice. What causes it?

Answer 19

• Yellowish pigmentation
  
  • Skin
  • Sclera
  • Other mucous membranes
• Caused by hyperbilirubinaemia

Question 20

What are the treatments for HBV?

Answer 20

• 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.

Question 21

What are the prevention strategies for HBV?

Answer 21

• HBsAg vaccine
  
  • Good protection following 3 injections over a 6 month period.
• HBV immunoglobulin
• Blood screening
• Needle exchange programmes
• Sexual health education

Question 22

What are the viral features of hepatitis C virus (HCV)?

Answer 22

• Flavivirus
• Single-stranded RNA genome
• Enveloped
• Replicated primarily in hepatocytes
• Destroys liver cells
• Virus cannot be cultured

Question 23

How is HCV transmitted?

Answer 23

• Via blood and blood products.
• Tattooing, body piercing and acupuncture.
• Haemodialysis.
• Sexual transmission uncommon.
• Vertical transmission uncommon.

Question 24

What are the clinical features of HCV?

Answer 24

• Usually asymptomatic
• Fatigue
• Nausea
• Weight loss
• May rarely progress to cirrhosis
• Small proportion may develop hepatocellular carcinoma

Question 25

What are the treatments for HCV?

Answer 25

* 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

Question 26

How is HCV screened for?

Answer 26

* NAAT performedon blood samples. * Therefore, current incidence of transfusion-associated HCV is low.

Question 27

What is the cause of malaria?

Answer 27

* 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.

Question 28

What are the clinical features of malaria?

Answer 28

* 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

Question 29

How is hepatitis diagnosed?

Answer 29

* At least 3 blood films (both thick and thin) obtained from different times for microscopy. * NAAT - useful for detecting drug resistance.

Question 30

What are the available treatments for malaria?

Answer 30

* 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

Question 31

Describe the prevention strategies for malaria.

Answer 31

* Sleep under bed nets * Cover exposed skin between dusk and dawn * Use of mosquito repellants * Prophylaxis * Vaccines currently being developed