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Rna Viruses

RNA VIRUSES

ORTHOMYXOVIRUS
(influenza viruses)
- 3 antigenic types (A, B, C)
- A: has great antigenic variability
- B: has lower antigenic variability
- C is relatively stable
- the antigenic variability results from the combination of the segmented RNA ( 8 segments)
Laboratory diagnosis
I. Direct diagnosis
1. Samples: pharyngeal and nasal exudates, nasal and pharyngeal washing, necroptic fragments
2. Influenza antigens may be demonstrated within the epithelial cells using fluorescent antibodies.
3. Isolation: on embrionated egg (in amniotic or alantoidian liquid) or cell culture
4. Identification is made mainly by hemagglutinoinhibation with specific serum
using cock (rooster) erythrocytes.
Other techniques for identification: complement fixation
II. Serologic tests
Are based on the at least four-fold rising of antibodies titer in the serum collected in convalescence.
Hemagglutinoinhibation (HIA)
-place diluted serum in a plate with wells
-place standard antigens (A or B from one of the circulating variants N1H1, N1H2, N1H3, N2H1, N2H2, N2H3)
-incubate for 60 minutes
-place a suspension of cock erythrocytes
-incubate for 1 hour and read
The principle of the reaction:
Influenza viruses have hemagglutinin antigens (H) so that if a suspension of viral antigen is placed in contact with erythrocytes the erythrocytes will be agglutinated.
If anti-hemagglutinin antibodies are present in the serum they will form complexes with the Ag (H) and hemagglutination will be inhibited.
(+) reaction: erythrocytes remain in suspension ( HIA +)
(-) reaction: erythrocytes are agglutinated (HIA – because there were no Ab to neutralize the Ag (hemagglutinin).
The titer of Ab is the highest dilution which still inhibit the agglutination.
Other techniques for identification:
-complement fixation
-radial hemolysis (agar+virus+complement, wells with serum, if serum contains Ab => hemolysis because complement is activated by the Ag-Ab complex)
The diameter...