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Dengue

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lab diagnosis of dengue

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Dengue

  1. 1. Laboratory diagnosis of Dengue (Based on WHO guidelines) Dr.M.Malathi Postgraduate Department of Microbiology Chengalpattu Medical College
  2. 2. Introduction • Dengue is the most rapidly spreading mosquito borne viral disease in the world. • An estimated 50 million dengue infections occur annually. • Approximately 2.5 billion people live in dengue endemic countries.
  3. 3. Clinical diagnosis • Early recognition of symptoms • Three phases – febrile, critical and recovery • Rational approach to case management
  4. 4. Laboratory diagnosis • Efficient and accurate diagnosis is important 1. Early detection of cases 2. Case confirmation 3. To obtain the diagnosis in case of clinically differential diagnosis picture 4. Surveillance 5. Outbreak control 6. Clinical trials 7. Academic research
  5. 5. Methods • Detection of virus • Detection of viral nucleic acid • Antigen detection • Antibody detection
  6. 6. ONSET OF ILLNESS 4 to 5 days Virus detected in serum, plasma and Circulating blood cells and tissues Virus isolation Nucleic acid detection Antigen detection (NS1 Ag)
  7. 7. After the acute phase…..? • Antibody detection • Antibody response to infection differs according to the immune status of the host. • First antibody to appear – IgM • Secondary antibody – IgG
  8. 8. Dengue infection occurs in a person who have not previously been infected with flavivirus Patient develops primary antibody response (IgM – slow increase) Detectable in • 50% of patients – Day 3 to 5 • 80% of patients – Day 5 • 99% of patients – Day 10
  9. 9. • IgM peaks at 2 weeks after the onset of symptoms • Declines to undetectable levels over 2 to 3 months. • Anti dengue serum IgG detectable at low titres, increases slowly and detectable after several months and even for life
  10. 10. Secondary dengue infection • Previously been infection by a dengue virus • Antibody titres rise rapidly • IgG detectable at high levels even in acute phase and persists for periods lasting from 10 months to life
  11. 11. • Early convalescent stage IgM levels are significantly lower in secondary infections than in primary • To distinguish primary and secondary – IgM/IgG antibody ratios are commonly used
  12. 12. Antigen detection • Sample – Serum • NS1 antigen is produced by all flaviviruses and secreted from mammalian cells. • Commercial kits gives rapid results, easy to perform • Helpful in field settings • Do not differentiate between dengue serotypes • Rapid card test - Less sensitive (SENSITIVITY – 77 TO 80%) • NS1 antigen ELISA – sensitivity 86% and specificity 100%
  13. 13. ELISA Antibody detection • IgM/ IgG ratio • Primary infection – greater than 1.2 / 1.4 • Secondary infection – lesser than 1.2 / 1.4
  14. 14. Haemotological tests • Platelet count • Haematocrit value • Thrombocytopenia – below 1,00,000/ul is suggestive of DHF • Usually observed in day 3 to day 8
  15. 15. • Haemoconcentration • Increase in haemotocrit of 20% or more compared with convalescent values is suggestive of hypovolaemia
  16. 16. Summary • Upto five days of illness (acute stage) – NS1 antigen detection • From three days to 2 months (Depends upon the immunity) – IgM detection • After 3 weeks upto life sometimes – IgG detection • To differentiate primary and secondary infection – IgM/IgG ratio • Patient monitoring – Platelet count and haemotocrit values
  17. 17. THANK YOU

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