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PATH3308 > 17. Allograft-Transmissible Infections > Flashcards

17. Allograft-Transmissible Infections Flashcards

1
Q

Where do allografts rank in the most often transplanted tissue?

A

Musculoskeletal grafts are second behind blood

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2
Q

What are the three main characteristics of allograft infectious agents?

A

1) Asymptomatic infection in donor
2) Present in allograft
3) Can survive during subsequent storage/processing of the allograft

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3
Q

What microbes are transmitted via allograft?

A

Bacteria
Viruses
Protozoa
Prions

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4
Q

What factors increase risk to infection?

A

Increasing travel

Climate change - vectorborne diseases have widened distribution

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5
Q

What viruses can be transmitted via allografts?

A 
HIV 1 and 2
HTLV (Human T-lymphotropic Viurs)
Hep, B C and D
Human cytomegalovirus CMV
Herpes 6, 7 and 8 karposis sarcoma
Human erythrovirus
Herpes simplex virus - HSV1 and 2
Varicella Zoster Virus
EBV - Epstein Barr virus
Human Papilloma Virus
West Nile Virus
Rabies Virus
Lymphocytic choriomeningitis virus
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6
Q

What are some examples of bacteria transmitted via allografts?

A

Primarily Gram negative or enterococcus

  • Treponema Pallidum (Syphilis)
  • Clostridium sordelli (Sepsis)
  • Mycobacterium Sp (Tuberculosis)
  • Balamuthia mandrillaris (Balamuthia - severe encephalitis)
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7
Q

What are some protozoa transmitted by allografts?

A 
Plasmodium sp. malaria
Toxoplasma gondi (toxoplasmosis)
Trypanasoma cruzi (Chagas disease)
Babesia microti (Babesiosis)
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8
Q

What are some prions transmitted via allografts?

A

Spongiform Encephalopathies - TSE (Creutzfeldt Jacob Disease - CJD and variant

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9
Q

What are the two main modes of transmission for allograft infection?

A

1) Donor was infected - acute or latent
2) Allograft is contaminated
- Cadaveric, gut organisms etc
- Exogenous - during allograft processing

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10
Q

What is an example of an acute donor infection?

A

Acute Hep C infection

Infected donor with no anti-HCV infected 8/40 individuals

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11
Q

What is an example of a latent or chronic donor infection?

A

Latent Creutfeltz jakob disease
- Fuarrrrk can lay dormant for up to 40 years
Has occured in corneal dura and pericardium transplants

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12
Q

What is an example of in situ allograft contamination?

A

1) Clostridium sordelli sepsis from cadaveric allograft
- Microorganisms pass through wall and populate
- Low oxygen selects anaerobes
- Nutrients low, clostridia sporulates
- Spores can evade detection/sterilisation
2) Exogenous contamination
- Staphlococcus sp most frequently encountered in post op infections

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13
Q

How can transmission be prevented?

A

1) Effective donor screening
2) Optimize microbial inactivation/reduction during retrieval and processing
3) Undertake comprehensive surveillance for known and emerging agents

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14
Q

How can donor screening be optimized?

A 
Comprehensive screening
   - Infectious diseases
    - Minimum deferral period after cessation of symptoms
    - Deferrals for high risk behaviour
Physical examination
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15
Q

What are donors tested for?

A 
Syphilis
Hep B (DNA cadaveric only)
Hep C (RNA cadaveric donors only)
HIV (HIV RNA cadaveric only)
HTLV

Repeat testing performed on donors 6 months post operatively

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16
Q

How can contamination be reduced?

A

1) Aseptic technique at recovery
2) Bacteriological culture of tissue swabs and samples
3) Cadaveric donation time constraints
4) Allograft ‘bioburden’ reduction - gamma irradiation
- Soft tissue = 15kGy
- Bone = 25KG

17
Q

How can one practice Aseptic technique at recovery?

A

Retrieval
- Operating theatres

Processing
- clean room

Equipment and surfaces cleaned

Compliance audited by the Therapeutic Goods Administration (TGA)

18
Q

How can one effectively culture tissue swabs and samples?

A

Living Donors
- Milled bone - post saline wash sent for culture
Cadaveric Donors
- Single cadaveric donor material processed per sesh
- Allograft washed in sterile water, filtered
- Water sent for culture

19
Q

How can cadaveric donation time constraints be followed?

A

Body refrigerated within 12 hours of death

Tissue retrieval must occur within 24 hours from time of death

20
Q

How are novel/emerging agents surveyed?

A

Monitoring of post op infections (critical)

Rule out other sources of infection

Emerging infections - assess transmissibility of agent

  • Research (animal models)
  • Prevalence assessment in donors
  • Surveillance for infection in recipients
21
Q

How good are current serological tests for HIV, HCV etc?

A

Capable of detecting >99.9% of infectious donations

Not 100% due to “window period” time taken between point of infection to detection of pathogenic agent in blood

22
Q

What is the window period?

A

Time taken between point of infection to detection of pathogenic agent in bloodstream

23
Q

Is virus prevalence higher in musculoskeletal or blood donors?

A

Muskuloskeletal

Only bacterial reported in australia, 113/2321 (4.9%)

Skin infection rate = 15.7
Heart valve infection rate = 15.1

Staphylococcus sp most common

24
Q

What are the proposed infection rates of viruses?

A 
HIV = 1 / 161 000
HBV = 1 / 172 000
HCV = 1 / 55,000
HTLV = 1 / 118 000
25
Q

What is the Calman scale?

A

Easily understood risk continuum or scale so patient can provide informed consent

Negligible (1 in 1 million)
Minimal 100 000
Very low 10 000
Low 1000
Moderate 100 - 1000
High (1 in 100)
26
Q

What are allograft risk estimates as defined by Calman scale?

A

1 in 55 000 (very low) to

1 in 172 000 (minimal)

27
Q

What is Nucleic Acid Testing (NAT) and how does it reduce allograft transmission risk?

A

Reduces length of the Window Period
More sensitive to infection

HIV 22 - 9 days
   - 400 000 chance now
HCV 66 - 7 days
  - 500 000
HBV 44 - 22 days
  345 000

Many countries have not implemented screening

28
Q

What are some drawbacks of NAT testing?

A

Can potentially compromise viability of the organ
Better in cadaveric donors
HIV/HCV NAT under consideration by TGA for corneal grafts

29
Q

How can transmission risk be further reduced?

A

2) More stringent donor selection criteria
- Specific Qs - emerging/novel agents
3) Improved post transplant surveillance/report
4) Universal allograft bioburden reduction
- Number of bacteria on sample

PATH3308 (21 decks)

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