Detection of Foot-and-Mouth Disease Virus in the Absence of Clinical Disease in Cattle and Buffalo in South East Asia.

Ashish Sutar,Jonathan Arzt,Sengxay Phonthasy,Rudolfo Bueno,Mary Van Andel,Viliddeth Souriya,Carolyn Hamill,Émilie Vallée ,Blesilda Verin,Khin Ohnmar Lwin ,Myo Thiha,Chattouphone Keokhamphet,Andrew Mcfadden ,Wendi D Roe ,Richard P Spence ,Kelly Buckle,Fernanda Castillo-Alcala ,Htun Htun Win ,Anna B Ludi ,Valérie Mioulet ,Ronello Abila ,Bolortuya Purevsuren,Syseng Khounsy

doi:10.3389/fvets.2021.691308

Abstract

Foot-and-mouth disease virus (FMDV) is widespread throughout much of the world, including parts of South East Asia. Surveillance is often limited in endemic areas, relying predominantly on passive outbreak reporting. As part of the World Organisation for Animal Health (OIE)'s South East Asia and China Foot-and-Mouth Disease Project (SEACFMD), field sampling was performed to help understand evidence of widespread virus exposure observed in previous studies. Serum and dry mucosal swabs were collected to evaluate the presence of FMDV RNA on the nasal, oral, and dorsal nasopharyngeal mucosal surfaces of 262 healthy cattle (n = 84 in Laos; n = 125 in Myanmar) and buffalo (n = 48 in Laos; n = 5 in Myanmar) immediately following slaughter in three slaughterhouses. Swabs and serum were tested by the OIE/FAO World Reference Laboratory for foot-and-mouth disease (WRLFMD) using pan-serotypic real-time reverse transcription-PCR (rRT-PCR) and serum was evaluated using the FMD PrioCHECK non-structural protein (NSP) ELISA. In total, 7.3% of animals had detectable FMDV RNA in one or more of the three sites including 5.3% of nasopharyngeal swabs, 2.3% of oral swabs, and 1.5% of nasal swabs. No FMDV RNA was detected in serum. Overall, 37.8% of animals were positive for NSP antibodies, indicating likely past natural exposure to FMDV. Results were comparable for Laos and Myanmar, and for both cattle and buffalo, and were not significantly different between age groups. Detectable FMDV RNA present on the oral and nasal mucosa of clinically-healthy large ruminants in Laos and Myanmar demonstrates the importance of sampling asymptomatic animals as part of surveillance, and may indicate that subclinical infection plays a role in the epidemiology of FMD in these countries.

Highlights

Foot-and-mouth disease virus (FMDV) is a contagious Picornavirus of cloven-hoofed ungulates (Artiodactyla), present in approximately two-thirds of the world’s countries
As part of addressing this research need, the present study evaluated whether FMDV is detectable on the mucosal surfaces of healthy cattle and buffalo in Laos and Myanmar, with samples taken at slaughter
When pharyngeal swabs were added to the oral and nasal swabs, 7.3% (19/262, 95% CI 4.42–11.09%) of all animals in both countries had detectable FMDV RNA on at least one swab (Table 1), including 10.4% (5/48, 95% CI 3.47–22.66%) buffalo and 6.0% (5/84, 95% CI 1.96–13.34%) cattle in Laos, and 0% (0/5, 95% CI 0.00– 52.18%) buffalo and 7.2% (9/125, 95% CI 3.34–13.23%) cattle in Myanmar

Summary

Introduction

Foot-and-mouth disease virus (FMDV) is a contagious Picornavirus of cloven-hoofed ungulates (Artiodactyla), present in approximately two-thirds of the world’s countries. In these countries, it acts as a significant barrier to trade [1, 2]. The subclinical cycles of FMD in the approximately 128 countries where the virus circulates are less-well documented, and the characteristic, “fulminant” herd-wide disease may be observed or reported inconsistently in endemic regions compared to what is documented in epidemic contexts [5, 6]. Almost 50 years ago, Anderson et al [7] wrote that “the occurrence of clinical outbreaks does not necessarily give a true assessment of the amount of virus in the environment as subclinical or in apparent infection could occur, in partially immune cattle.”. Almost 50 years ago, Anderson et al [7] wrote that “the occurrence of clinical outbreaks does not necessarily give a true assessment of the amount of virus in the environment as subclinical or in apparent infection could occur, in partially immune cattle.” Much uncertainty remains about how FMD manifests in endemically-infected herds, and the various states by which subclinical infection exists [8]

Methods

Results

Conclusion