opportunistic infections Flashcards
how are viruses classified
Baltimore classification
(by their replicative life cycle)
all produce positive sense mRNA -> generate proteins for their replication
nature of genomes mean different classes achieve this through different mechanisms -> implications of life cycle, dx and rx
definition of opportunistic infection
An infection caused by an organism that does not normally cause disease
…Or symptomatology may be altered in the immunocompromised compared to immunocompetent
what are endogenous opportunistic infections
Latent viruses that reactivate in the absence of a normal immune system
Acquired in the past prior to immune suppression – eg Varicella Zoster (VZV) and can get disemminated herpes zoster
what are exogenous opportunistic infections
acquired from the environment
Increased severity in the immunocompromised – eg influenza, SARS-CoV-2.. Or even primary acquisition of VZV
AIDs defining illness
How do we diagnose viruses
indirect detection
* see if ever had infection
* response of immune system to virus
direct detection
* currentlt have infection
* viral proteins - lateral flow/ag test
* viral genetic material
* PCR
summarise indirect detection of virus using serology
measure levels of Ab in serum
IgM - active or resolving infection
IgG - indicates past infection >6wks ago
Ab levels are reduced in immunocomp
serological course may differ wih different virus eg hepatitis
hepatitis A serology
hepatitis B serology
PCR to detect virus
detect viral genome via amplification
sensitive and specific
viral load can be used to monitor infection
can remain +ve after infection has resolved.
how are viruses diagnosed in the immunocompromised
cant use serology - no immune system
screen for viral infections before give immunosuppression - identify infections that might reactivate, guide antiviral prophylaxis
**monitor with PCR **- means can see viral reactivation promptly -> Rx, detect infection
A 51-year-old with a recent HSCT is unwell. Which is the most appropriate test?
ALT = 800 IU/mL
EBV IgG/IgM
HBV sAb
Parvovirus PCR
HEV PCR
CMV IgG/IgM
HEV PCR
scale of immunosuppression and how it relates to risk of getting opportunistic viral infections
As go up list – immunosuppression increases – allogenic gives highest risk of opportunistic viral infections
summarise immunosuppression for transplant
In Hematopoietic stem-cell transplantation: conditioning regimen, eradicating pre-exisiting disease. Then ongoing immunosuppression to prevent graft versus host.
Solid organ: induction to prevent T cell activation and maintenance therapy to prevent rejection
haematopoietic: Conditioning – wipe out the disease – when conditioned – do the transplant – then wait while ait for transplant to take - neutrophils start to go up – need immunosuppression to prevent graft vs host disease.Can stop immunosuppression
In solid organ – not completely irradiating body but will be on lifelong immunosuppression. Trying to prevent T cell activation
sources of viral infection in transplant recipients
virus from graft - eg HBV (serostatus, risk assessment)
virus from host - eg HSV (serostatus, monitoring PCR, prophylaxis, pre-emptive therapy)
novel infection from infected individual eg VZV (isolation-barrier nursing, post exposure prophylaxsis, vaccinating contacts, control of diet)
chronology of HSCT infections
day 0 is day of transplant - wait 30 days for neutrophils to start recoving
so in 1st 30 days - most worried about bacterial/fungal
then more concerned of viruses
chronology of solid organ transplant infections
things screen for when immunosuppressed become unwell
Screen and molecular test according to symptoms
Screen for specific infections knowing that they are immunocompromised
Blood – PCR
Biopsy of gut/PCR
difference between HSV in immunocompetent and immunocompromised
increased frequency
increased severity/risk of dissemination
more organs involved - pneumonitis, eosophagitis, hepatitis
increased risk of acyclovir resistance
varicella in immunosuppressed
chicken pox:
* pneumonitis
* encephalitis
* hepatitis
* purpura fulminans in neonate
shingles:
* multi-dermatomal/disseminated
* often late - presenting immunosuppresion
issues with CMV in immunosuppressed
HIV/AIDS: CD4 less than 50
* Ocular (retinitis)
* Polyradiculopathy
* Pneumonitis
* GI tract
SOT (solid organ transplant)
* Allograft disease
* GI tract (i.e. renal)
difference between CMV in transplant between SOT and BMT
SOT: CMV remains latent in dendritic cells so if some of these are transplanted with organ -> very sick because dont have immune system to fight it
Likewise if a bmt is received from a donor who has never seen CMV before and the reciepent reactivates the latent CMV -> greater morbidity and mortality – donor immune system is naive to CMV and finds it hard to clear
how do we prevent CMV in transplant patients
BMT patients we monitor and if the virus goes above a certain level we treat
Solid organ prophylaxis
serology of hep B
The hepatitis B envelope antigen(HBeAg) is found between the core and lipid envelope within HBV and is present inbothacuteandchronic infection.
* indicatesactive viral replication-> higher risk oftransmissibility.
* used to distinguish activeandinactive chronic infection.
HBeAg seroconversionis the development ofantibodies against HBeAg(anti-HBe);
it marks a transitionfromactive diseaseto aninactive ‘carrier’ state.
Anti-HBe remains in serum for life and indicates acquired, natural immunity (i.e. immunity from a previous infection only)
what is a possible case of monkeypox
