Characterization of naturally occurring, new and persistent subclinical foot-and-mouth disease virus infection in vaccinated Asian buffalo in Islamabad Capital Territory, Pakistan

Authors: FAROOQ, UMER - National Agricultural Research Center - Pakistan; AHMED, ZAHEER - Animal And Plant Health Inspection Service (APHIS); NAEEM, KHALID - National Agricultural Research Center - Pakistan; BERTRAM, MIRANDA - Oak Ridge Institute For Science And Education (ORISE); BRITO, BARBARA - Oak Ridge Institute For Science And Education (ORISE); STENFELDT, CAROLINA - University Of Minnesota; Pauszek, Steven; Larocco, Michael; Arzt, Jonathan; Rodriguez, Luis

Submitted to: Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2018
Publication Date: 7/23/2018
Citation: Farooq, U., Ahmed, Z., Naeem, K., Bertram, M., Brito, B., Stenfeldt, C., Pauszek, S.J., Larocco, M.A., Arzt, J., Rodriguez, L.L. 2018. Characterization of naturally occurring, new and persistent subclinical foot-and-mouth disease virus infection in vaccinated Asian buffalo in Islamabad Capital Territory, Pakistan. Veterinary Research. https://doi.org/10.1111/tbed.12963.
DOI: https://doi.org/10.1111/tbed.12963

Interpretive Summary: Foot-and-mouth disease (FMD), caused by FMD virus (FMDV), is an important livestock disease that causes substantial animal health problems and economic losses in Africa, Asia, and the Middle East. In these regions many livestock are infected asymptomatically (without any signs). Nations that are free of FMD, like the USA, are at constant risk of outbreaks. The purpose of this study was to describe asymptomatic FMDV infection in Asian buffalo under natural conditions in Pakistan. Three different types of FMDV were detected (O, A, Asia-1), and multiple strains were detected within each type. A small number of buffalo were determined to be long-term carriers and several other buffalo were infected with two different strains or types of FMDV during the study. This study indicates a high prevalence of subclinical FMDV infection of Asian buffalo and suggests this host species plays a role in the dynamics of FMD in Pakistan. Additionally, this information is highly relevant to improve preparedness for FMD outbreaks in the USA.

Technical Abstract: A prospective, 12 month longitudinal study was conducted to assess subclinical foot-and-mouth disease virus (FMDV) infection in Asian buffalo (Bubalus bubalis) under natural conditions in Pakistan. To achieve this goal, oropharyngeal fluid (OPF) samples were obtained quarterly from 300 buffalo over the one-year study period. None of the 30 farms included in the study reported clinical foot-and-mouth disease (FMD) during the study period; however, antibodies against FMDV non-structural proteins (NSP) were detected at the beginning of the study in 77.7% of the 300 sampled buffalo, and seropositive animals were found on all farms. FMDV RNA was detected by rRT-PCR in OPF from at least one sample in 180 (60%) of the 300 buffalo. In 93 of the 180 FMDV-positive buffalo, FMDV was detected in a single OPF sample over the one-year study period, whereas in an additional 67 animals FMDV was detected in more than one serial OPF samples, but it was not possible to confirm if this detection represented the same or different viral strains. Over the course of the study, FMDV RNA or infectious virus were newly identified in OPF of 76 buffalo which were previously FMDV-free, indicating occurrence of acute subclinical infections. Eight buffalo were confirmed to be persistently infected based upon VP1-sequence confirmation of detection of the same virus in two or more OPF samples, and serial infection with different FMDVs was confirmed in 13 animals. The most prevalent serotype detected was Asia-1, followed by A, and O. Phylogenetic analysis of isolated FMDVs indicated multiple distinct clades of serotypes Asia-1 and A. Viruses recovered from the same persistently infected animals yielded identical or very closely related VP1 sequences despite these viruses being isolated up to six months apart. This study indicates a high prevalence of subclinical FMDV infection of Asian buffalo in Pakistan, and emphasizes the importance of clinically undetected infection in FMD dynamics in endemic regions.