In Vivo and In Vitro Cross Neutralization Studies of Local Rabies Virus Isolates with ERA Based Cell Culture Anti-Rabies Vaccine Produced In Ethiopia

Abstract

Rabies is a worldwide problem, and the case is most severe in developing countries where cell culture anti-rabies vaccines are unaffordable or the available nervous tissue-derived vaccines are of questionable immunogenicity and may cause neurological complications. The aim of this research was to study cross protection of local rabies virus isolates with Evenyl Roktincki Abelseth (ERA) based cell culture anti-rabies vaccine produced in Ethiopia and to develop challenge virus from local isolates. The viruses were isolated from rabid dogs’ brains and human saliva, and adapted on Swiss albino mice and cell lines. Cross protection with ERA based vaccine was studied by in vivo and in vitro methods. For in vivo method, a group of mice were immunized on day zero and seven with 0.5 ml (1:5 dilutions) of ERA based cell culture anti-rabies vaccine produced locally. On day fourteenth, mice were challenged with working dilution of each local isolates and one group with challenge virus standard (CVS-11), and observed for further 14 days. High protection was recorded in CVS-11 challenged mice and low protection in all local isolates (p=0.045); specifically protection to HOS challenged mice was very low. In vitro test was done by fluorescent antibody virus neutralization (FAVN) test on BHK-21 cell lines. Sera from dog immunized with locally produced vaccine and OIE serum were incubated with local virus isolates and CVS-11 for 48 hours in the presence of cell lines. Maximum antibody titer (2.74 IU/ml) was obtained with CVS-11 challenge virus and minimum antibody titer (1.55 IU/ml) was obtained with cow origin (CO) virus isolate. All locally isolated rabies virus show low antibody titer when compared to CVS-11 and PV-12 (p=0.000). From the results, it can be concluded that local isolates have some genetic variation from fixed virus strain which can affect efficacy of the candidate vaccine and potency value should be set in-terms of local isolate using as challenge virus. Generally, the exact genetic relationship should be studied by molecular techniques and locally isolated virus should be used as challenge virus for vaccine quality control.