lab diagnosis of dengue

1. Laboratory diagnosis of Dengue
(Based on WHO guidelines)
Dr.M.Malathi
Postgraduate
Department of Microbiology
Chengalpattu Medical College

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. Clinical diagnosis
• Early recognition of symptoms
• Three phases – febrile, critical and recovery
• Rational approach to case management

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. Methods
• Detection of virus
• Detection of viral nucleic acid
• Antigen detection
• Antibody detection

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. 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. 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. • 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. 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. • 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. 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. ELISA Antibody detection
• IgM/ IgG ratio
• Primary infection – greater than 1.2 / 1.4
• Secondary infection – lesser than 1.2 / 1.4

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. • Haemoconcentration
• Increase in haemotocrit of 20% or more
compared with convalescent values is
suggestive of hypovolaemia

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. THANK YOU