Evaluation of a rapid immunochromatographic assay for the diagnosis of rabies in regional laboratories of Costa Rica

Rabies is a viral, lethal, and zoonotic disease with worldwide distribution, primarily transmitted through bites from infected dogs and bats. The Biosafety Laboratory (LSE-LANASEVE) of the Animal Health Service of Costa Rica (SENASA) serves as the national reference laboratory for diagnosing rabies in humans and animals. Since regional laboratories lack the equipment for the direct fluorescent antibody test (FAT), we evaluated the rapid immunochromatographic diagnostic test (RIDT) from BioNote, employing FAT as a reference, to improve rabies diagnosis. We analyzed 193 brain tissue samples between 2014 and 2019. Out of these, 174 came from species that RIDT has been validated for: bovines (162), dogs (10), and raccoons (2). The rest were from unvalidated species, including horses (7), humans (1), and others. Among the 174 validated samples, 26 bovine samples were positive for both RIDT and FAT. Reviewing all 193 samples, 28 were positive and 165 negative using both methods. Two horse samples presented inconsistencies, being positive on FAT but negative on RIDT; these were subsequently verified as false negatives by RT-PCR. RIDT exhibited a sensitivity of 94 % (CI95, 83.9-102.3), specificity of 100 %, positive predictive value (PPV) of 100 %, and negative predictive value (NPV) of 99 % (CI95, 97.1-100.5). RIDT has demonstrated reliability in quickly diagnosing rabies for validated species. We advise its application in SENASA's regional laboratories for those particular species. If there's uncertainty, samples should be sent to LSE-LANASEVE for FAT or RT-PCR confirmation.