Clinical Microbiology Fifth Year

1. Bloodborne pathogens
• Bloodborne pathogens are infectious
microorganisms present in blood that can
cause disease in humans.
• These pathogens include HBV, HCV, HIV, but
are not limited to these 3 only.
• Workers exposed to bloodborne pathogens
are at risk for serious or life-threatening
infections or illnesses.

2. Source of infection- Potentially
infectious body fluids.
• Any body fluid that is visibly contaminated with
blood.
• Saliva (in dental procedures).
• Semen
• Vaginal secretions
• Cerebrospinal fluid
• Synovial fluid
• Pleural fluid
• Peritoneal fluid
• Amniotic fluid

3. Transmission - HBV and HIV are most
commonly transmitted through:
•
•
•
•
Sexual Contact
Sharing of hypodermic needles
From mothers to their babies at/before birth
Accidental puncture from contaminated needles,
broken glass, or other sharps
• Contact between broken or damaged skin and
infected body fluids
• Contact between mucous membranes and infected
body fluids

4. Infected blood can enter HUMANS
through:
•
•
•
•
•
Open sores
Cuts
Abrasions
Acne
Any sort of damaged or
broken skin such as
sunburn or blisters
• Bloodborne pathogens
may also be transmitted
through the mucous
membranes of the
• Eyes
• Nose
• Mouth

5. HIV- Human Immunodeficiency
Virus
• Family Retroviridae, subgroup Lentivirus.
• Enveloped spherical virus 90-120nm
• Envelope – outer lipid membrane, inner
glycoprotein, projecting knob like spikes
• Nucleocapsid – outer icosahedral shell, inner
cone shaped core covering RNP’s
• Genome – diploid has 2 identical ss +ve sense
RNA copies, in association with enzyme RT.

6. Viral genes and Antigens
• Genome of HIV has 3 Structural genes(gag, pol
env) Non structural and Regulatory genes.
• The products of these act as antigens, sera of
infected patients contains antibodies to them.
• Envelope ags
gp-120 (principal ag),
gp41 (transmembrane pedicle protein)
• Core ags – p24 principal core ag.

8. Antigenic Variation and Diversity of HIV
•
•
•
•
•
HIV highly mutable virus.
Most common in envelope proteins.
Error prone nature of Reverse Transcription.
Based on this 2 types of HIV – type1, 2.
HIV -Type 1 has 10 subtypes(based on gag and pol
genes)
• Frequent variations in antigens, nucleiotide
sequences, cell tropism, growth characters and
cytopathology.

9. Major differences between HIV 1 & 2
HIV 1
HIV 2
Present worldwide
West Africa
More virulent
Less sever form of
disease
2 genetic groups, M ??? Infection
(Major) , O (Out-lier) prevent against
M include 8 clades infection with HIV1
A,H

10. Pathogenesis
• Primary pathogenic mechanism - CD4 cell damage
Receptor - CD4(ag)cell or any cell bearing CD4 receptor
• Specific binding through gp120 of HIV to CD4
• After fusion, uncoating, internalisation, RT mediates
transcription of RNA into dsDNA, integrated into host
cell genome, latent infection.
• Reversal of cell ratio (CD4 & CD8)
• Polyclonal B cell activation- Hypergammaglobulinaemia
• Monocyte-Macrophage function affected

11. Clinical features of HIV infecton
•
•
•
•
•
Acute HIV infection
Asymptomatic or latent infection
Persistent generalised lymphadenopathy
AIDS related complex
AIDS

12. Opportunistic infections
• Bacterial – Mtb, MAC, Salmonella, Legionella,
Actinomyes, Nocardia, Campylobacter
• Viral- CMV, HHV 1,2.
• Fungal – Candida, Cryptococcal, Aspergillosis
• Parasitic – PCP, Toxoplasmosis, Isospora,
Cryptospora,
• Malignancies – Kaposi’s sarcoma, Lymphomas.

13. Diagnosis
•
•
•
•
•
ELISA for detecting Abs and as a screening test
Antigen Detection – p24
Western blot test for confirmation
PCR
Supportive evidence… – CD4 cell count.

14. Hepatitis viruses
• HBV
• HCV

15. Table 24.12

16. HBV : Structure
Most abundant form
2nd most abundant
3rd most abundant

17. HBV
• Hepadnaviridae family- Circular partially dsDNA virus
• Enveloped virus, inner core covering genome and
polymerase.
• 3 antigens of HBV are
- HBs Ag surface Ag from envelope
- HBc Ag nucleocapsid Ags from core
- Hbe Ag
• Genome – DNA 2 linear strands, one is incomplete,
DNA polymerase, has both DNA dependent DNA
polymerase n RNA dependent Reverse Transcriptase.

18. • Virion is also referred to as Dane particle
• Exists in 3 different forms
22nm spherical and filamentous forms
- no DNA in these forms so they are not
infectious (composed of surface antigen only)
- these forms outnumber the actual virions
42nm enveloped virus – complete virus,
most infectious.

19. • Replicates within hepatocytes
• Replication involves a reverse transcriptase.
• Does not grow in any conventional culture
system.
• HBV proteins have been cloned in bacteria
and yeasts.

20. Epidemiology
• Endemic in the human population and hyper
endemic in many parts of the world.
• Natural infection seen only in humans.
• Rich and poor countries differ in the age and
modes of infection.
• Carriers –healthy, asymptomatic, subclinical.
- Play major role in transmission of HBV.
• Transmission - Parenteral, Perinatal, Sexual

21. Concentration of Hepatitis B
Virus in Various Body Fluids
High
Moderate
blood
semen
serum
vaginal fluid
wound exudates
saliva
Low/Not
Detectable
urine
feces
sweat
tears
breastmilk

22. Pathogenesis of HBV-
Immune mediated

23. Clinical features- Spectrum of
Chronic Hepatitis B Diseases
• Acute to chronic course
• I P = 1-6 months, insidious in onset.
• Acute stage Mild flu-like symptoms
- Fatigue ‰
‰
-Loss of appetite
-Nausea
-Jaundice ‰
-Darkened urine
‰

24. Clinical features- Spectrum of Chronic
Hepatitis B Diseases
• 90-95% of infected recover in 1-2 months of onset,
eliminate virus from body within 6 months
• Chronic Persistent Hepatitis – asymptomatic (80-90%)
• Chronic Active Hepatitis - symptomatic
exacerbations of hepatitis (10-20%)
• Cirrhosis of Liver (<10%)
• Hepatocellular Carcinoma (<1%)

25. Diagnosis
• Clinical – jaundice, fever, yellow urine.
• Lab – serological markers HBs Ag, HBe Ag,
anti-HBc( core ag never appears in serum)
• HBe ag – acute infection, highly infectious

26. Prevention
• Vaccination - highly effective recombinant vaccines are now
available. Vaccine can be given to those who are at increased
risk of HBV infection such as health care workers. It is also
given routinely to neonates as universal vaccination in many
countries.
• Hepatitis B Immunoglobulin - HBIG may be used to protect
persons who are exposed to hepatitis B. It is particular
efficacious within 48 hours of the incident. It may also be given
to neonates who are at increased risk of contracting hepatitis B
i.e. whose mothers are HBsAg and HBeAg positive.
• Other measures - screening of blood donors, blood and body
fluid precautions.

27. HCV
• Flaviridae family, Hepacivirus genus
• Enveloped RNA virus (50-60nm)
• Shows considerable genetic and antigenic diversity.
6 different genotypes and many subtypes.
• Transmission- blood transfusion, blood products
• C/F – 5-80% chronic hepatitis, some cirrhosis and
hepato-cellular carcinoma.
• Diagnosis –ELISA( standard method),
immunoblotting, PCR.
• Treatment- interferon alpha, Ribavirin.
• Prevention – No vaccine, standard precautions

28. Risk Factors Associated with
Transmission of HCV
 Transfusion or transplant from infected donor
 Injecting drug use
 Hemodialysis (yrs on treatment)
 Accidental injuries with needles/sharps
 Sexual/household exposure to anti-HCVpositive contact
 Multiple sex partners
 Birth to HCV-infected mother

29. Laboratory Diagnosis
• HCV antibody - generally used to diagnose hepatitis C
infection. Not useful in the acute phase as it takes at least 4
weeks after infection before antibody appears.
• HCV-RNA - various techniques are available e.g. PCR and
branched DNA. May be used to diagnose HCV infection in
the acute phase. However, its main use is in monitoring the
response to antiviral therapy.
• HCV-antigen - an EIA for HCV antigen is available. It is
used in the same capacity as HCV-RNA tests but is much
easier to carry out.

30. Prevention of blood borne
pathogens
 Practice Standard precautions
 Treat all fluids, specimens, tissues as potential
infectous
 Screening of blood, organ, tissue donors
 High-risk behavior modification
 Blood and body fluid precautions

31. To summarise…