A preliminary evaluation of a locally produced biotinylated polyclonal anti-rabies antibody for direct rapid immunohistochemical test (DRIT) in the Philippines.

Rabies is a fatal zoonotic disease endemic in developing countries of Asia and Africa. Recently, the direct rapid immunohistochemical test (DRIT) was recommended by the World Health Organization (WHO) and the World Organization for Animal Health (OIE) as a diagnostic test for rabies. Therefore, a biotinylated polyclonal antibody (pAb) against the rabies lyssavirus (RABV) nucleoprotein was developed using a plasmid cDNA vaccine derived from a challenge virus standard 11 strain. A preliminary evaluation on the efficacy of this reagent in recognizing the Philippine RABV strain was tested using banked canine hippocampal tissue samples with DRIT and the results were compared to dFAT. The effects of acetone and formalin fixation on DRIT were also assessed through immunoreactivity scores of the specimens. Of the 142 samples examined, 104 tested positive and 38 negative using both dFAT and DRIT, showing 100% agreement between the two diagnostic procedures. Moreover, no false positive or false negative results were observed using acetone and formalin fixation. Thus, locally prepared biotinylated pAb from plasmid cDNA can be used for DRIT, especially in resource-limited laboratories in the Philippines. However, these results should be confirmed with a more thorough evaluation of this technique, and the range of detection needs to be further evaluated in a larger panel of animal samples and on other lyssaviruses.

Phylogeographic analysis of rabies viruses in the Philippines.

Rabies still remains a public health threat in the Philippines. A significant number of human rabies cases, about 200-300 cases annually, have been reported, and the country needs an effective strategy for rabies control. To develop an effective control strategy, it is important to understand the transmission patterns of the rabies viruses. We conducted phylogenetic analyses by considering the temporal and spatial evolution of rabies viruses to reveal the transmission dynamics in the Philippines. After evaluating the molecular clock and phylogeographic analysis, we estimated that the Philippine strains were introduced from China around the beginning of 20th century. Upon this introduction, the rabies viruses evolved within the Philippines to form three major clades, and there was no indication of introduction of other rabies viruses from any other country. However, within the Philippines, island-to-island migrations were observed. Since then, the rabies viruses have diffused and only evolved within each island group. The evolutionary pattern of these viruses was strongly shaped by geographical boundaries. The association index statistics demonstrated a strong spatial structure within the island group, indicating that the seas were a significant geographical barrier for viral dispersal. Strong spatial structure was also observed even at a regional level, and most of the viral migrations (79.7% of the total median number) in Luzon were observed between neighboring regions. Rabies viruses were genetically clustered at a regional level, and this strong spatial structure suggests a geographical clustering of transmission chains and the potential effectiveness of rabies control that targets geographical clustering. Dog vaccination campaigns have been conducted independently by local governments in the Philippines, but it could be more effective to implement a coordinated vaccination campaign among neighboring areas to eliminate geographically-clustered rabies transmission chains.