God’spower R. Okoh(1,*), Haruna M. Kazeem(2) , Grace S.N. Kia(3,4) and Zhakum N. Ponfa(5)
1 Department of Veterinary Microbiology, Faculty of Veterinary Medicine, University of Abuja, P.M.B. 117, Nigeria
2 Department of Veterinary Microbiology, Faculty of Veterinary Medicine, Ahmadu Bello University, Zaria, P.M.B. 1045, Nigeria
3 Department of Veterinary Public Health and Preventive Medicine, Faculty of Veterinary Medicine, Ahmadu Bello University, Zaria, P.M.B. 1045, Nigeria
4 Center of Excellence in Neglected Tropical Diseases
and Forensic Biotechnology, Ahmadu Bello University Zaria, Nigeria
5 Central Diagnostic Laboratory, National Veterinary Research Institute, Vom, P.M.B. 01, Nigeria
There is a great need for a chemical method of tissue preservation that would allow sample storage for extended periods at room temperature. This study aimed at retrieving and detecting rabies virus antigen by direct fluorescent antibody test (DFAT) in formalin-fixed dog brain tissues. Forty fresh dog brain specimens were collected as paired samples from rabies suspected cases that were received for postmortem detection of rabies in the Central Diagnostic Laboratory, National Veterinary Research Institute, Vom. One portion of each paired sample was prepared for fresh ﬂuorescent antibody testing and the other portion was prepared for epitope retrieval and florescent antibody testing following fixation in 10% neutral buffered formalin. DFAT on formalin-ﬁxed tissue exhibited a sensitivity of 100% in comparison to DFAT on fresh-tissue. No false positive result was obtained in formalin-ﬁxed DFAT procedure, demonstrating 100% speciﬁcity. There was no apparent difference in the intensity of fluorescence in DFAT on fresh sample and formalin-fixed DFAT following heat induced epitope retrieval (concordance = 98%; 95% C.I. 0.9660 to 0.9903). The strength of agreement between DFAT on formalin-fixed and DFAT on fresh tissue was very good (Cohen’s kappa coefficient value= 1.000; 95% C.I. 1.000-1.000). This study provides new information on the retrieval of rabies antigen by heat induced epitope retrieval for DFAT on formalinized tissues. Formalin could therefore, be used henceforth to fix tissues of rabies suspected cases for routine diagnosis, transportation or archival purposes. The heat induced epitope retrieval can be routinely used to retrieve rabies virus antigen for DFAT in cases where only formalin-fixed tissues are available or when preservation by freezing is difficult.Keywords: Direct Fluorescent Test, Formalin-fixed brain tissues, Heat induced epitope retrieval, Rabies virus.