Lecture 11 Flashcards
(17 cards)
Allograft
A tissue graft a donor genetically unrelated to recipient but of same species
common = tissue, muscoskeletal, organ, cell
What are the 3 main criteria that generally need to be met for an agent to be transmitted by an allograft?
- It gives rise to asymptomatic infection in the donor
- It is present in the allograft
- It is able to survive during subsequent storage/processing of allograft
What microbes are transmitted by allografts?
- Bacteria
- Viruses
- Prions
- Protozoa
Viruses
- 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)
Bacteria
Primarily = Gram -ve or enterococcus
- Treponema pallidum (Syphilis)
- Clostridium sordelli (Sepsis)
- Mycobacterium Sp. (Tuberculosis)
- Balamuthia mandrillaris (Balamuthia – severe encephalitis)
Protozoa
Plasmodium sp. (malaria)
Toxoplasma gondii (toxoplasmosis)
Trypanasoma cruzi (Chagas disease)
Babesia microti (Babesiosis)
Prions
- Transmissable Spongioform Encephalopathies
creutzfeldt Jakob Disease (CJD)
Example of acute donor infection
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
Example of chronic/latent donor infection
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
In situ allograft contamination
- 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
What are the 3 transmission prevention techniques
- Implement effective donor screening
- Optimise microbial inactivation/reduction during retrieval and processing
- undertake comprehensive surveillance for known and emerging agents
What are the 4 methods of reducing contamination?
- Aseptic technique at recovery
- Bacteriological culture of tissue swabs and samples
- Cadaveric donation time constraints
- Allograft ‘bioburden’ reduction - gamma irradiation
Zika virus
- 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)
Modes of transmission
- Infection in the donor - acute or latent
- Allograft contamination
In situ - e.g. Cadaveric - from gut organisms infiltrating allograft prior to harvesting
Exogenous - during allograft processing
Exogenous contamination Example
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
Donor selection criteria
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)
How do we calculate rest instead residual risk of viral infection?
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
