Quantification and evaluation of rabies virusneutralizing antibody titers by modified rapid fluorescent focus inhibition test Mohd G.1, Upmanyu V.1,*, Rather M.M.1, Pande T.1, Rai V.1, Singh S.1, Koherwal N.2, Pandey A.B.1, Dhar P.1, Tiwari A.K.3 1Division of Biological Standardization, ICAR-Indian Veterinary Research Institute, Izatnagar, Uttar Pradesh, India 2Human Hospital, ICAR-Indian Veterinary Research Institute, Izatnagar, Uttar Pradesh, India 3ICAR-Central Avian Research Institute, Izatnagar, Uttar Pradesh, India *Corresponding author E-mail id: vupmanyu17@rediffmail.com
Online published on 29 August, 2023. Abstract Rabies is a fatal, vaccine-preventable viral zoonotic infection. The rabies virus belongs to the genus Lyssavirus of the family Rhabdoviridae and is maintained in various natural reservoirs such as bats, mongoose, foxes, etc. Human infections are primarily associated with dog bites and occasionally with bat or other wild animal exposure. Prophylactic vaccination is recommended for high-risk groups, including veterinarians and personnel working in rabies laboratories. Determination of the titer of rabies virus neutralizing antibodies (RVNA) in different vaccinated species is generally conducted by the rapid fluorescent focus inhibition test (RFFIT) in an eight-well Lab-Tek chamber. In the present study, a modified 96-well plate RFFIT protocol was optimized for the detection of RVNA titers in the serum of vaccinated and unvaccinated individuals. RFFIT conditions, such as cell seeding concentration per well (4X104 cells/well), the amount of virus (300 FFID50), and the dilution of FITC conjugate (1:80), were optimized for the 96-well format. A total of 50 serum samples were tested with the modified RFFIT. Rabies vaccination history was documented for 45 individuals. Among the vaccinated individuals, less than 0.5 IU RVNA titer was observed in three persons, and a marginal protective titer (0.5 to 0.6 IU) was observed in three cases. Adequate protective titer (0.5 IU/mL) was observed in the remaining thirty-nine individuals. The individuals with a history of multiple booster doses showed >30 IU/mL neutralizing antibody titer. Rabies vaccination invariably develops protective neutralizing antibody titers. However, in a small fraction of vaccinated individuals, the titer falls below protective limits by 6-12 months after the first vaccination. Based on the RFFIT results of 50 samples and their correlation with vaccination history, it can be stated that the current protocol can be used for periodic monitoring of rabies antibody titers in high-risk group individuals, including veterinarians and rabies laboratory workers. Top Keywords Rabies, RFFIT, Antibody titer, Human, Booster dose. Top |