| | | Initial HI and CF tests performed in Maracay with nb mouse brain antigen (sucrose-acetone) and several grouping immune ascitic fluids indicated that Aroa is a group B virus. Further CF testing at YARU indicated that Aroa immune serum (2 injections) homologous titer was 64 [1] . Reactions with dilutions 1:4 and 1:16 of antigens for all the group B viruses were either negative or 8, with the exception of Alfuy , Bussuquara , and Rocio , with which the titer was 32. | | Additional CF results, obtained also in YARU , were as follows: | | | | Serum | | | Serum |
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| Antigen | Aroa | Bussuquara | Alfuy | Rocio | | Antigen | Aroa | Bussuquara |
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| | a Antibody titer/antigen titer | | Aroa | 128/>256a | 8/8 | 8/8 | 8/8 | | Aroa | 128/1024 | 32/512 | | Bussuquara | 32/64 | 128/128 | 8/8 | | | Bussuquara | 64/128 | 256/256 | | Alfuy | 8/64 | 8/8 | 256/>256 | | | Control | 0 | 0 | | Rocio | 16/16 | | | 512/64 | | | |
| | It is concluded that, by CF, Aroa is a new virus of group B and that its closest relative is Bussuquara [1] . | | In addition, Aroa antigen and antibody were tested by CF against reagents for the following 21 vector-unassociated flaviviruses: Apoi (homologous antibody titer=1024), Saboya (4096), Sokoluk (2048), Israel turkey meningoencephalitis (2048), Batu Cave (1024), Phnom Penh bat (1024), Carey Island (512), Cowbone Ridge (64), Jutiapa (256), Modoc (2048), San Perlita (2048), Sal Vieja (2048), MA-387-72 (1024), Dakar bat (32), BP-111(45), Entebbe bat (1024), Koutango (128), MML (64), Negishi (128), Rio Bravo (256), Tamana bat (128). A close relationship was not detected with any of the vector-unassociated flaviviruses [2] . | | Serum dilution plaque-reduction neutralization tests (SDPRNT) indicated that Aroa and Bussuquara viruses were distinguishable both ways as shown below [3] . | | | | Antibody to: |
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| Virus | BSQ | AROA |
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| | b Reciprocal of antibody dilution giving 90% plaque reduction. | | BSQ | 640 b | <40 | | AROA | 80 | > 10240 |
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