Detection and molecular characterization of foot and mouth disease virus from persistently infected bovine
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Date
2023-07
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Abstract
Foot-and-mouth disease (FMD) is an OIE-listed highly contagious and economically devastating disease of cloven-hoofed animals. Routinely, FMD virus (FMDV) 3AB3 non-structural protein (NSP) based indirect ELISA test is used for population serosurveys as an indicator of exposure to virus to differentiate between infected and vaccinated animals (DIVA) in India. For this, serum samples (n=377) collected from 6-18 month old cattle and buffaloes from nine villages of district Hisar, Haryana during 2022 as per the sample plan developed by ICAR-NIVEDI were subjected to DIVA ELISA. NSP reactivity was found to be 5.3% (20/377) in both, cattle (11.3%; 12/106) and buffaloes (3.0%; 8/271). Two buffaloes from 20 NSP reactors when sampled at a gap of nine months were found to be negative for FMDV 3AB3 NSP Abs as well as for FMDV by real time RT-PCR and RT- Multiplex PCR (RT-mPCR). No FMD outbreak was reported from Haryana during 2022. Further sampling was carried out from an organized cattle farm in which bi-annual FMD+HS combined vaccination has been carried out regularly. There was no history of FMD outbreak on this farm for more than a decade. DIVA reactivity of 43.75% (7/16) was observed in cattle (6-18 months age) of this farm which could be linked to either false positive reactions or scars of past exposure and virus elimination at the time of OPF sampling. The blood parameters between NSP positive and NSP negative animals were statistically insignificant. The only animal exhibiting antibody titres <log10 1.5 i.e., unprotected for the structural proteins of FMDV serotype O, A and Asia-1 by SPC ELISA, was found to be NSP negative by DIVA ELISA both at the time of first sampling as well as re-sampling after a gap of 28 days because a carrier is an animal from which live-virus or viral genome can be detected for more than 28 days after first exposure. Since, no clinical FMD was observed in any of the animal, therefore, to detect persistent infection amongst cattle, OPF (n=16) was collected and subjected to real time RT-PCR and RT-mPCR but none of the sample was found positive for FMDV. Similarly, none of the apparently healthy cattle (n=9) from a Gaushala of district Hisar could be identified as carrier or neoteric for FMDV. However, the number of samples tested is limited to draw any comprehensive conclusion regarding circulation of FMDV in the population. For molecular characterization, full length VP1 gene of FMDV serotype O detected by RT-mPCR from OPF of cattle collected during 2021 from Gaushala of district Hisar, was processed amplified and sequenced commercially. The sequence RRC_Hisar_FMDV O exhibited 91-99% identity with FMDV serotype O isolates from different parts of the world and it was placed in a separate group along with other FMDV serotypes of India rather than the isolates from other parts of the world. Active surveillance of animals without apparent clinical signs of FMD along with molecular epidemiological studies may help in identifying geographic regions for creating ‘FMD controlled zones’ with zoo sanitary measures and vaccination.