Storage stability of dengue IgM and IgG antibodies in whole blood and serum dried on filter paper strips detected by ELISA.

Blood specimens from 133 patients clinically diagnosed as dengue virus infection by physicians in Nakhon Phanom Hospital, Thailand, were examined to detect anti-dengue IgM and IgG antibodies by antibody capture ELISA. The blood specimens were divided into 3 types of storage; (1) frozen serum aliquots, (2) whole blood dried on filter paper strips, and (3) sera dried on filter paper strips. These specimens were stored for the periods of 1, 3, 4, and 5 months, at -20 degrees C in the case of frozen serum aliquots, or at room temperature in the case of specimens dried on filter paper strips, before examined in paralleled by the ELISA. Anti-dengue IgG antibodies were stable for at least 5 months of storage as dried whole blood or serum on filter paper strips. So were the anti-dengue IgM antibodies in the dried whole blood from secondary dengue cases. Anti-dengue IgM antibodies from primary dengue cases declined slowly in whole blood and more rapidly in serum, both dried on filter paper strips. In the serum dried on filter paper strips, even anti-dengue IgM antibodies from secondary cases decreased significantly on storage. We suggest that diagnosis on dengue infections by IgM-capture ELISA should be performed within 1 month after the test specimens are collected as whole blood, not as serum, when the filter paper method is used for sample collection.

Comparative nucleotide and deduced amino acid sequence of the envelope glycoprotein gene among three dengue virus type 2 strains isolated from patients with different disease severities in Maha Sarakham, northeast Thailand.

The nucleotide (nt) sequence of the envelope glycoprotein (E) gene of dengue virus type 2 was determined by the primer-extension dideoxy chain-termination method for 3 dengue virus type 2 (D2) strains which had been isolated from patients with dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS), in Maha Sarakham, Northeast Thailand, in 1986-1987. Their nt sequences were essentially the same except for a single silent nt replacement in each DHF and DSS strain compared with DF strain. Therefore, these 3 strains possessed identical deduced amino acid (AA) sequences in their E protein. The result indicated that the primary structure of the E protein of D2 virus is not related to the clinical severity of the infected patients. Eleven nt replacements which resulted in 4 amino acid replacements were found to be unique to these 3 Northeast Thai strains. Sequence similarity showed that the 3 Northeast Thai strains were closest to the DSS isolate (H) followed by the DHF isolate (D) identified in Bangkok in 1980.