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Virology basics: do’s and don’ts
David Muir Consultant Virologist
Department of Infection & Immunity Imperial College Healthcare NHS Trust
Charing Cross Hospital, London
April 2015
Summary
• Sample types (blood tubes, virology swabs)
• Audits: VZV IgM, HSV IgM, CFTs
• Serology markers
• Hepatitis serology
• Exotic virus investigations
• Lymphocytic choriomeningitis virus
• Useful Virology contact numbers
http://pathology.imperial.nhs.uk/
Virology Specimen types
• Blood samples
– Serology: 5ml gel SSTTM II tubes (rust top)
Virology Specimen types
• Blood samples
– Serology: 5ml gel SSTTM II tubes (rust top)
Virology Specimen types
• Blood samples
– Serology: 5ml gel SSTTM tubes (rust top)
– PCR: 6ml EDTA (pink top)
• Virology swabs:
– Flocked swab
– Viral transport medium (VTM)
Virology Specimen types
VZV IgM audit
• Audit findings over a 4-month period:
– 34 VZV IgM tests performed:
• 3 positive samples: • Zoster X 2
• Hirsutism X 1 (?)
– VZV IgM did not identify a single case of chickenpox, despite the fact that some of the patients had a diagnosis of chickenpox confirmed by PCR
• Conclusion: VZV PCR on swab is the recommended sample type
VZV IgM audit
HSV IgM audit
• Audit findings over a 6 month period:
– Main indication for requests was “TORCH” screen
– Out of 140 HSV IgM tests performed:
• 88% were negative
• 11% were equivocal
– The single positive HSV IgM result was from a child presenting with infectious mononucleosis
• Recommendation: HSV PCR on swab preferred
Atypical pneumonia serology (CFTs) audit mycoplasma, chlamydia & coxiella burnetii
• Low specificity: – Glycolipid antigen mixture found on other microorganisms
and some human tissues
– Also cross reactivity with other mycoplasma species (eg M. genitalium)
• Sensitivity limited by the following: – Period of 10-14 days required for significant titres to
develop
– Antibiotic administration gives rise to false negative results
• Recommendation: – Process only samples that have been collected 10 days or
more post-onset of illness
IgM vs IgG
IgM IgG
Acute phase of disease :
Duration : ~3 months Lifelong
Example:
IgM vs IgG
• Acute/recent infection
– Measles IgM
– Rubella IgM
– Parvovirus IgM
– VZV PCR (swab)
• Contact, ?past infection, ?vaccinated
– Measles IgG
– Rubella IgG
– Parvovirus IgG
– VZV IgG
Epstein Barr virus (EBV)
Epstein Barr virus (EBV) serology
Infectious mononucleosis
• EBV IgM +
• EBV VCA IgG +/-
• EBNA Ab -
Past EBV infection
• EBV IgM -
• EBV VCA IgG +
• EBNA Ab +
Reactivation or false +ve IgM
• EBV IgM +
• EBV VCA IgG +
• EBNA Ab +
• Acute infection : Surface Ag + Core IgM + “e” Ag & HBV DNA +
• Chronic infection / carrier status : Surface Ag + Core Ab + (IgM -) “e” Ag/Ab +/-
& HBV DNA +
• Past infection (naturally immune) : Core Ab + Surface Ab +/- “e” Ab +/- (surface Ag, “e” Ag
& HBV DNA: -ve)
Surface antigen
Core antibody
Hepatitis B markers
Test request:
• Immunised :
Surface Ab+
Core Ab–ve
• Surface antibody titres :
< 10mIU/ml : Non-responder - ? cAb+
10–100mIU/ml : Weak response (single booster!)
> 100mIU/ml : Strong response
Hepatitis B markers
Hepatitis screens
Hepatitis (transaminitis)
• HAV IgM
• HBV surface antigen
• HCV Ab
Past hepatitis
• HAV IgG
• HBV core antibody
• HCV Ab
…also consider • CMV & EBV (tonsillitis,
lymphadenopathy, rash)
• HEV IgM Response to vaccine
• HAV IgG
• HBV surface antibody
Exotic virus investigations dengue, chikungunya…
Please always provide a full travel history with dates of travel & return from travel, and of onset of illness
Lymphocytic choriomeningitis virus LCMV
• Source: Rodents
• Long term shedding from urine & faeces
• Transmission: Inhalation of contaminated dust or droplets (eg while sweeping up)
• Presentation: Asymptomatic, biphasic febrile illness, myalgia headache, meningitis, encephalitis
• Complications: Myelitis, Guillain Barre-type syndrome, orchitis, arthritis, parotitis, pancreatitis, myopericarditis
• Prognosis: Majority self limiting. Rarely permanent neurological sequelae
• Treatment: Supportive. In theory ribavirin may have some activity
• LCMV in pregnancy:
– Transplacental transmission congenital infection
– If 1st trimester infection, risk of miscarriage
– Post-1st trimester: Fetal intracranial calcification, microcephaly, hydrocephalus, mental retardation, seizures, chorioretinitis, optic atrophy.
– Prognosis: 30% infant mortality. 2/3 survivors have long term neurological sequelae including epilepsy and blindness
– Prevention: Avoid exposure to rodents as a precaution
Lymphocytic choriomeningitis virus LCMV
• Epidemiology: Very rare (“n=0 in UK!”)
• Current Testing: Very limited
Only research PCR available (PHE)
No serology!
Lymphocytic choriomeningitis virus LCMV
Virology contact numbers
For Virology test results:
• Pathology Call Centre:
020 331 35353
For Virology clinical queries:
• Infection & Immunity Service:
020 331 10130
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