Bloodborne pathogens

Question 1

Transmission of BB pathogens

Answer 1

Direct contact with infected blood fluids
Infection via contaminated needles, syringes or other unsterilised instruments
Direct infection into bloodstream by arthropod vectors e.g. mosquitoes

Question 2

HIV transmission

Answer 2

Three routes:

• 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

HIV family and types

Answer 3

Family - retroviridae
genus - lentivirus

HIV1 and HIV2 pathogenic for humans
HIV1 most common
HIV2 less virulent

Question 4

HIV viral features

Answer 4

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

Question 5

Reverse transcriptase inhibitors

Answer 5

Zidovudine (nucleoside)

Nevirapine (non-nucleoside)

Question 6

Protease inhibitors

Answer 6

Ritonavir

Saquinavir

Question 7

HIV progression to AIDS

Answer 7

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

Question 8

Name some AIDS-defining features

Answer 8

Candidiasis of bronchi, trachea, lungs
Cervical carcinoma
CMV retinitis (with loss of vision)
Recurrent penumonia
Salmonella
Wasting syndrome

Question 9

Anti-retroviral therapy (ART)

Answer 9

Many possible regimes and combinations
Initial tx:
- 1 NRTI and 1 PI
- 2 NRTIs and 1 NNRTI

Question 10

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

Prevention of HIV infection

Answer 11

No vaccine available yet
Screening of blood products
Needle exchange programmes
Anti-retroviral prophylaxis for needle stick injuries - avoiding high-risk sexual partners, uses of barrier contraception, effective C-section

Question 12

HBV viral features

Answer 12

Hepadnavirus
Double-stranded DNA genome
Enveloped

Question 13

HBV antigens

Answer 13

HBsAg - surface antigen

• Indicates infectivity
• Anti-HBsAg provided immunity and appears late

HBcAg - core antigen - appears early in infection

HBeAg - pre-core antigen - indicates high transmissibility

Question 14

HBV stages of infection

Answer 14

Long incubation period - up to 6 months
Development of acute hepatitis
Fulminant disease carries 1-2% mortality rate
50% patients develop chronic active hepatitis - cirrhosis, hepatocellular carcinoma

Question 15

HBV clinical features

Answer 15

Pre-icteric (jaundice) stage - malaise, anorexia, nausea, pain in RUQ (tender liver)
Icteric stage - jaundice and dark urine (bilirubin)

Question 16

HBV treatment

Answer 16

Pegylated interferon (peginterferon) is superior compared to alpha-interferon in sustaining suppression of viral replication
Anti-viral activity of nucleoside analogues e.g. oral lamivudine may be successful even in chronic HBV patients

Question 17

HBV prevention

Answer 17

HBsAg vaccine - good protection following 3 injections over 6 month period
HBV immunoglobulin
Blood screening
Needle exchange programmes
Sexual health education

Question 18

HCV viral features

Answer 18

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

Question 19

HCV transmission

Answer 19

Blood and blood proeducts
Body piercing
Haemodialysis
Sexual and vertical transmission uncommon

Question 20

HCV clinical features

Answer 20

usually asymptomatic

Fatigue, nausea, weight loss, may rarely progress to cirrhosis, small proportion may develop hepatocellular carcinoma

Question 21

HCV treatment

Answer 21

Interferon reduces liver transaminases in 80% patients
Ribavirun works well in combination with pegylated a-interferon
Combination therapy - sofosbuvir (nucleotide analogue) with PI and another nucleotide analogue

Monitor viral load by NAAT, no vaccine yet

Question 22

HCV screening

Answer 22

NAAT performed on blood samples

Therefore current incidence of transfusion associated HCV is low

Question 23

Malaria causes

Answer 23

caused by 5 species of genus plasmodium

P.falciparum, p.vivax, p.ovale, p.malariae, p.knowlesi

Question 24

Malaria clinical features

Answer 24

fever, flu-like symptoms, p.falciparum infection can regularly progress to death, p.falciparum affects every organ - wide range of complications e.g. cerebral malaria, circulatory shock, hepatitis

Question 25

malaria diagnosis

Answer 25

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

Question 26

malaria treatment and prevention

Answer 26

Chemotherapy kills blood stages of parasite
Resistance means tx advice should be changed regularly
Comb therapy is norm - quinine, chloroquine, doxy, proguanil, malarone

Bed nets, cover skin, repellants, prophylaxis tx for prevention