Part 2: Laboratory Diagnosis of Viral Infections

When symptoms are nonspecific, what are the three measures of diagnosis?

• direct detection

• viral isolation

• serology

Why is rapid diagnosis important with viral infections?

• could result in delayed/improper treatment

• waiting too long could mean treatment is not necessary/ effective

When is viral shedding highest?

• during early infection 

What swab types are acceptable in taking a viral swab?

• dacron

• rayon

• nylon 

What are the different mediums used for viral transport?

• protein 

• buffered solutions, salts, pH indicator

How should viral specimen be transported? 

• on ice, wet ice/refrigerate until it reaches laboratory 

• if greater than 4 days, freeze sample and ship on dry ice 

How should viral specimen be stored

• refrigerated at 4 degrees

  • up to 3 days fresh, up to 4 days in VTM/UTM

• if greater than 4 days, freeze at -70 degrees

Samples should never be freezed at what temperature?

• -20 degrees

  • facilitates formation of ice crystals and disrupts host cell

What are different specimen types?

• blood and bone marrow specimens

• respiratory specimen 

• genital 

• ocular 

• skin

• urine 

• gastrointestinal 

• CNS 

Blood and bone marrow specimen

• cytomegalovirus

• enterovirus

• HIV 

Respiratory Specimen

• influenza

• parainfluenza

• RSA
  adenovirus

• coronavirus 

genital specimen

• HSV

• HPV

• CMV 

what is the purpose of the VTM/UTM swab

• collection method

• it inhibits normal bacterial/fungal microbiota 

Ocular Specimen 

• Conjunctivitis, keratitis

• HSV, adenovirus, CMV 

Skin Specimen

• isolated vesicular/lesions or viral exanthems 

• HSV, VSV 

Urine Specimen

• CMV

• first morning specimen is best because it is most concentrated 

gasatrointestinal specimen

• rotavirus, adenovirus, norovirus 

CNS specimen 

• HSV, CMV, enterovirus 

what are direct detection methods of viruses in clinical specimen? 

• microscopy 

• pathology/cytology

• immunofluorescence

What is an advantage of using a microscope to identify viruses

• can determine isolation/admission decisions

What is an disadvantage of using a microscope to identify viruses

• only electron microscopy is acceptable

• sensitivity is very low/expensive

What does a pathology/cytology detection method look for when identifying a virus? 

• looks for CPE 

  • used in pap and tzanck smears 

What method is used to detect viral antigens?

• lateral flow tests

• quick and good sensitivity 

how are viral nucleic acids detected? 

• probes, PCR, and multiplex PCR assays 

• qualitative or quantitative 

What is the advantage of PCR assays?

• highly sensitive

• can detect 20 or more viruses and bacteria 

what are disadvantages of PCR assays to detect viral nucleic acids?

• cost 

• detection of latent viruses 

what is the “gold standard” for laboratory diagnosis of viral infections? 

• viral isolation 

Shell vial cultures

• cells grown on round coverslip in a shell vial 

• apart of viral isolation 

What does a detection of a high titer of IgM antibody indicate? 

• acute/very recent infection 

What does a four-fold rise in titer (IgG) mean? 

• establishes a previous/recent infection 

  • acute 1:2

  • convalescent 1:8 

what are limitations of viral serology

• measures hosts response rather than detecting virus 

• serologic studies are often retrospective 

what are reasons for conducting viral serology? 

• diagnosis of infections

• diagnosis of past (IgG) or acute (IgM) viral infections 

• determination of patients immune status

• monitoring patients following transplantation