9- Diagnosis of Viral Infections (electron microscopy) Flashcards
Q: why isn’t it always possible to diagnose a disease clinically, requiring a labatory diagnostic test?
clinically many infections present with similar symptoms - hard to identify the causative agent without lab tests
requires diagnostic tests beyond clinical evaluation - e.g. labatory diagnostic tests, medical history, examination and special investigations
Q: rapid diagnosis of viral infections can reduce the need for unnecessary tests - how does this aid the treatment of unrelated infections?
allows healthcare providers to focus on the appropriate treatment - if it’s a viral infection, there’s no need to prescribe antibiotics as they’re ineffective against viral agents
can focus treatment plans on thing that’ll be effective = reduces the risk of antibiotic resistance and unnecessary side effects
Q: what are the implications on public health and infection control in diagnosing a disease?
may require isolating infected patients, alerting those more vulnerable to the infection
Q: why must consent be obtained for certain infections?
some infections may have serious future implications - e.g. HIV
allows patients to make informed decisions about their own healthcare
Q: differentiate between diagnostic, screening and monitoring tests with examples
diagnostic = identify the cause of a current health condition - e.g. PCR
screening = detect a disease or condition in asymptomatic individuals - e.g. mammography for breast cancer screening
monitoring = tracking disease progression and/or its response to treatment overtime - e.g. blood glucose monitoring in diabetic patients
list the 6 possible test types
electron microscopy
virus isolation (cell culture)
antigen detection
antibody detection by serology
nucleic acid amplification tests – NAATs (e.g. PCR)
sequencing for genotype and detection of antiviral resistance
why is electron microscopy used to visualize viruses?
viruses are too small to be visualised by light microscopy
offers higher resolution, up to x20,000 magnification
how has electron microscopy been replaced in diagnostic techniques? how are they still being used?
molecular techniques are replacing EMs diagnostically - nucleic acid amplification techniques like PCR as they have high sensitivity and specificity
EMs are still useful in research, for examining specimens, characterizing emerging pathogens, and providing quick identification of viruses from patients’ specimens for rapid diagnosis
describe the method for visualizing viruses using electron microscopy
collecting patient specimens from suspected infection sites and drying them on a grid
stain specimen with heavy metal dyes like uranyl acetate
concentrate the specimen through various methods - e.g. ultracentrifugation, antibody application, antibody binding through immuno-electron microscopy
electron microscopy uses beams of electrons to produce images - have a shorter wavelength than light, produce more high resolution images to visualise and identify the virus
what are the advantages of electron microscopy?
it’s rapid
some viruses can’t be detected any other way; allows us to detect viruses that can’t be grown in cell culture
can visualise a broad range of different viruses
what are the disadvantages of electron microscopy?
has low sensitivity = need millions of a virus to visualise it, and sometimes there isn’t enough virus to visualise despite concentrating it
requires maintenance, it’s expensive and requires highly skilled and trained people
harder to differentiate between viruses of the same family as they look structurally similar, but may cause different diseases
list which viral infections may be diagnosed by electron microscopy
norovirus
herpes virus - e.g. HSV, VZV, CMV
adenovirus
rotavirus
poxvirus - e.g. smallpox, monkeypox
why is it challenging to differentiate between herpes viruses based solely on electron microscopy visuals?
herpes virus family has many different types within it - they have a similar structural appearance but cause different diseases, makes them hard to differentiate
clinical context such as vesicle location and symptoms need to be considered for diagnosis
how does electron microscopy assist in distinguishing between herpes and pox viruses?
VZV which causes chickenpox and smallpox look similar - can obtain vesicular fluid from the pox blisters and examine them under EM
EM can differentiate between herpes and pox viruses
what is virus isolation in cell culture? what are its limitations? why has it become less common in diagnostic practice?
virus isolation in culture = growing viruses in cultured cells which are incubated in cell layers, sometimes used to demonstrate the cytopathic effects of a virus in patient samples
limitations:
- slow method
- not all viruses grow in all cell types = need to select the appropriate cell line
- ethical concerns when cells need to be obtained from animals
less common now as it’s been replaced with advanced molecular techniques like PCR = less ethical, faster, greater sensitivity and accuracy
