Vaccine-induced Rabies in a Red Fox in Poland

Rabies as a zoonosis threatens public health worldwide. Several thousand people die each year of infections by the rabies virus (RABV). Oral rabies vaccination (ORV) of wildlife was successfully implemented in many European countries and led to rabies being brought under control there. In Poland, ORV was introduced in 1993 using vaccines containing an attenuated strain of the rabies virus. However, attenuated rabies viruses may have residual pathogenicity and cause the disease in target and non-target animals.

A red fox carcass was tested as part of national rabies surveillance, and its brain was screened for RABV infection using two conjugates and a fluorescent antibody test (FAT). The rabies virus was isolated in mouse neuroblastoma cells by rabies tissue culture infection test (RTCIT), and viral RNA was detected by heminested reverse transcriptase PCR (hnRT-PCR) as well as by quantitative real-time RT-PCR (rtRT-qPCR). An amplicon of 600 bp was subjected to Sanger sequencing. To differentiate between vaccine and field RABV strains, PCR-restriction fragment length polymorphism (PCR-RFLP) using the Dra I, Msp I, Nla IV and Mbo II restriction endonucleases was performed.

The rabies virus was detected in the fox's brain using FAT, RTCIT and molecular tests. The PCR-RFLP revealed of vaccine-induced rabies, and full-length genome analysis showed 100% nucleotide sequence identity of the isolate with the reference sequences of Street Alabama Dufferin Bern (SAD Bern) vaccine strains and other vaccine-induced rabies virus isolates detected in animals and deposited in GenBank.

We detected vaccine-induced rabies for the first time in Poland in a fox during routine rabies surveillance.