Detection of Persistence of Foot and Mouth Disease Virus in Local and Crossbred Cattle of Assam

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Background: This study aimed to investigate the persistence of Foot-and-Mouth Disease Virus (FMDV) in clinically recovered cattle following an outbreak, focusing on both local indigenous breeds (Lakhimi) and crossbred cattle (Holstein Friesian-cross) in Assam. Methods: A total of 129 cattle (36 local and 93 crossbred), clinically recovered from FMD, were included in the study. Oropharyngeal fluid (OPF) samples (n=178) were collected at various intervals post-recovery. FMDV detection was carried out using three molecular diagnostic techniques: Multiplex PCR, reverse transcription loop-mediated isothermal amplification (RT-LAMP) and SYBR Green real-time PCR, all targeting the FMDV 3D gene. Result: FMDV was detected in 38 samples (21.35%) by multiplex PCR, 47 samples (26.40%) by RT-LAMP and 49 samples (27.53%) by SYBR Green real-time PCR. While all three methods showed comparable diagnostic accuracy, real-time PCR proved to be the most sensitive, rapid, reliable and cost-effective technique. FMDV persistence was observed in 24.81% (32/129) of cattle up to the 1st month post-recovery, 11.63% (15/129) up to the 3rd month and 1.55% (2/129) up to the 6th month. Local non-vaccinated Lakhimi cattle exhibited higher rates of viral persistence for serotype O, with 33.33% (12/36), 22.22% (8/36) and 5.55% (2/36) showing persistence at the 1st, 3rd and 6th months post-recovery, respectively. In contrast, vaccinated Holstein Friesian-cross cattle, demonstrated lower persistence rates, with 19.23% for Serotype A and 22.39% for Serotype O at the 1st month and 10.45% for Serotype O at the 3rd month post-recovery. Importantly, no transmission of the virus to healthy in-contact animals was detected during the study period. Statistical analysis (P=0.23, Chi-square=5.57) revealed no significant difference in viral persistence between local and crossbred cattle, suggesting that factors beyond vaccination status might influence FMDV persistence. However, the findings underscore the critical role of vaccination in reducing viral persistence in recovered cattle.

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