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Lecture 11 Flashcards

1
Q

Allograft

A

A tissue graft a donor genetically unrelated to recipient but of same species

common = tissue, muscoskeletal, organ, cell

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2
Q

What are the 3 main criteria that generally need to be met for an agent to be transmitted by an allograft?

A
  1. It gives rise to asymptomatic infection in the donor
  2. It is present in the allograft
  3. It is able to survive during subsequent storage/processing of allograft
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3
Q

What microbes are transmitted by allografts?

A
  • Bacteria
  • Viruses
  • Prions
  • Protozoa
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4
Q

Viruses

A
  • HIV-1 & HIV-2
  • Human T-Lymphotropic Virus
  • Hepatitis B, C and E
  • Human Herpes Virus
  • Herpes Simplex Virus
  • Human Cytomegalovirus - CMV
  • Human Erythrovirus
  • Zika
  • EBV
  • Rabies
  • VZV (Varicella Zoster)
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5
Q

Bacteria

A

Primarily = Gram -ve or enterococcus

  • Treponema pallidum (Syphilis)
  • Clostridium sordelli (Sepsis)
  • Mycobacterium Sp. (Tuberculosis)
  • Balamuthia mandrillaris (Balamuthia – severe encephalitis)
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6
Q

Protozoa

A

 Plasmodium sp. (malaria)
 Toxoplasma gondii (toxoplasmosis)
 Trypanasoma cruzi (Chagas disease)
 Babesia microti (Babesiosis)

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7
Q

Prions

A
  • Transmissable Spongioform Encephalopathies

creutzfeldt Jakob Disease (CJD)

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8
Q

Example of acute donor infection

A

Acute Hepatitis C infection

  • HCV infected donor without detectable anti-HCV but RNA positive donated organs & tissues

Allograft to recipient HCV transmission occurs in 8/40 recipients

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9
Q

Example of chronic/latent donor infection

A

Latent CJD infection

  • CJD transmission to allograft donor - e.g. familial by vertical transmission
  • Allograft to recepient CJD transmission can potentially occur –> asymptomatic up to 4yrs

Anything involving CNS is at risk

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10
Q

In situ allograft contamination

A
  • Clostridium sordelli sepsis from cadaveric allograft

–> during dying process microorganisms pass through intestinal wall and populate blood or tissue

–> Low oxygen conditions of cadaveric tissue ‘select’ for anaerobics like clostridium sp.

–> As nutrients become exhausted cl sp. sporulate

–> spores in allograft evade detection/sterilisation & infect recipient

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11
Q

What are the 3 transmission prevention techniques

A
  1. Implement effective donor screening
  2. Optimise microbial inactivation/reduction during retrieval and processing
  3. undertake comprehensive surveillance for known and emerging agents
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12
Q

What are the 4 methods of reducing contamination?

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
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13
Q

Zika virus

A
  • discovered rhesus monkey
  • Arbovirus - transmitted via mosquitoes
  • large outbreak on Yap island
  • sexual transmission/ transfusion
  • detected in urine (<3 months), blood (<2 months) and semen (<6 months)
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14
Q

Modes of transmission

A
  1. Infection in the donor - acute or latent
  2. Allograft contamination

 In situ - e.g. Cadaveric - from gut organisms infiltrating allograft prior to harvesting

 Exogenous - during allograft processing

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15
Q

Exogenous contamination Example

A

Exogenous micro-organisms can contaminate allograft retrieval and/or subsequent processing

Staphlococcus sp. are the most frequently encountered organism in post operative infections at the PBTB

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16
Q

Donor selection criteria

A

Comprehensive Medical/Social History (with next of kin for cadaveric donors)

 Infectious diseases- asymptomatic deferral (exclusion) period >incubation period

 Minimum deferral period after cessation of symptoms

 Additional deferrals for high risk behaviour, immunisations, medications, travel, transfusion, carcinoma etc.

 Physical examination (post mortem for cadaveric donors)

17
Q

How do we calculate rest instead residual risk of viral infection?

A

Estimates derived from prevalence ratio (tissue/first time donors) extrapolated to incidence rates in first time blood donors

Incidence = rate of newly acquired infection (expressed as ‘x’ per 100,000 person years of observation)

Residual Risk = Incidence rate x duration of the WP (Window period)

HIV – 1 in 161,000
HBV – 1 in 172,000
HCV – 1 in 55,000
HTLV – 1 in 118,000

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