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