Laboratory Investigation Dr Salmah Idris Microbiologist Hospital Sungai Buloh Objective • Diagnostic Test for diagnosis of Dengue • Option and indication of the test • Post mortem investigation • Collection of samples Diagnostic Test • Antibody detection- Serology • Viral Isolation • Detection of virus genetic material • Dengue Virus Antigen or protein Immune response Dengue IgM test • IgM capture enzyme-linked immunosorbent assay • • • (ELISA) Widely used IgM titre is higher in primary compared to secondary infection Peak at about 2 weeks and undetectable level by 60 – 90 days. Dengue IgM captured ELISA • Primary Dengue – 55% detectable between 4-7 days – 100% after day 7 • Secondary Level 7 – 78% after day 7 • 28% of secondary dengue infections were undiagnosed when IgM was the only test performed Level Level 9 9 Level 8 Level 8 Indirect IgG ELISA • Primary and secondary dengue – IgG was detected in 100% after day 7 of illness – Recommended if dengue IgM is still negative after day 7 in secondary dengue Level 7 Level 8 Level 8 Haemagglutination Inhibition Test (HI) • Gold standard • Labour intensive and gold standard • Paired samples for interpretation (Acute and • • convelescant samples – 2 weeks apart) Research purposes Differentiate between primary and secondary dengue infection Dengue rapid test • Immunochromatography • Qualitative detection of IgM and IgG • Yield is higher when samples were collected • later in the convalescent phase of infection Good specificity and could be used when ELISA facilities were not available Dengue Rapid test • Recommended - Dengue IgM Capture ELISA after a rapid test • Result had to interpreted in the clinical context because of false positive or negative Dengue Rapid test • False positive – Cross react with • Flavivirus- JE@ • Non-flavivirus – malaria, leptospirosis, toxoplasmosis, syphilis* • Connective Tissue Disorder – RA# @ # * Virus Isolation • Definitive test for dengue infection • Lab equipped with tissue culture facilities • Useful only at early phase of illness , blood • collected before day 5 of illness ( before the formation of Neutralizing antibodies) During febrile illness – Virus can be isolated from serum, plasma and leucocytes – Post mortem specimens • Expensive and time consuming (2 weeks to complete Virus Isolation • Virus isolation has a poor yield if compared with molecular test. IT most probably due to the viability of the virus and the quality of samples. Polymerase Chain Reaction (PCR) • Eg. RT-PCR • Diagnosis of dengue infection in the early phase (< 5 • days of illness) Sensitivity 100% in the first 5 days of illness, reduced to 70% by day 6 • Determine dengue serotype Overview of 3 Steps Used in Molecular Amplification Assays for Flaviviruses RNA extraction from : 1. RNA extraction Serum, csf, tissue & mosquito pools 2. Amplification 3. Detection Standard PCR Agarose gel Nucleic acid sequencing: Southern Blot TaqMan RT-PCR TaqMan probe ABI iCycler Smart Cycler OPTICAN etc. SYBR Green RT-PCR Melting curve analysis NASBA Lamp Micro RT-PCR Chip NucliSensTM Readerr/ECL Molecular beacons Gel Turbidometer Real Time Adapted from Lanciotti, 2003; Adv Virus Res 61:67-99 Polymerase Chain Reaction (PCR) • Limitation – Available in certain facilities and trained personal – Test is expensive – Specimens requires special storage temperatures and short transportation , time between collection and extraction • Use only be considered for in-patients who present with diagnostic challenges in the early phase of illness Non-structural protein -1 (NS1 Ag) • Highly conserved glycoprotein that seems to be • essential for virus viability Secretion of the NS1 protein is a hallmark of flavivirus infecting mammalian cells – Dengue infection, yellow fever and West Nile • High concentration in the sera of dengue infected patients during the early phase of the disease • Detection rate is much better in acute sera of primary infection (75% - 97.3%) when compared to acute sera of secondary infection (60%-70%) NS1 Antigen • The sensitivity drops from day 4-5 of illness and usually becomes undetectable in the convalescence phase Investigation of Post Mortem Case Caution: Massive blood transfusion may affect the test result mentioned above Collection of sample