Lack of transmission of foot-and-mouth disease virus from persistently infected cattle to naïve cattle under field conditions in Vietnam

Authors: BERTRAM, MIRANDA - Oak Ridge Institute For Science And Education (ORISE); VU, LE - Ministry Of Agriculture And Rural Development (MARD); Pauszek, Steven; BRITO, BARBARA - Oak Ridge Institute For Science And Education (ORISE); Hartwig, Ethan; Smoliga, George; HOANG, BUI - Ministry Of Agriculture And Rural Development (MARD); PHUONG, NGUYEN - Ministry Of Agriculture And Rural Development (MARD); STENFELDT, CAROLINA - University Of Minnesota; FISH, IAN - Oak Ridge Institute For Science And Education (ORISE); HUNG, VO - Ministry Of Agriculture And Rural Development (MARD); DELGADO, AMY - Animal And Plant Health Inspection Service (APHIS); VANDERWAAL, KIMBERLEY - University Of Minnesota; Rodriguez, Luis; LONG, NGO - Ministry Of Agriculture And Rural Development (MARD); DUNG, DO - Ministry Of Agriculture And Rural Development (MARD); Arzt, Jonathan

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/4/2018
Publication Date: 7/22/2018
Citation: Bertram, M.R., Vu, L.T., Pauszek, S.J., Brito, B.P., Hartwig, E.J., Smoliga, G.R., Hoang, B.H., Phuong, N.T., Stenfeldt, C., Fish, I.H., Hung, V.V., Delgado, A., VanderWaal, K., Rodriguez, L.L., Long, N.T., Dung, D.H., Arzt, J. 2018. Lack of transmission of foot-and-mouth disease virus from persistently infected cattle to naïve cattle under field conditions in Vietnam. Frontiers in Veterinary Science. https://doi.org/10.3389/fvets.2018.00174.
DOI: https://doi.org/10.3389/fvets.2018.00174

Interpretive Summary: Foot-and-mouth disease (FMD), caused by FMD virus (FMDV), is an important livestock disease that causes substantial animal health problems in many countries in Africa and Asia. Over half of infected cattle become carriers, meaning the virus is maintained in their tissues for 28 days or more after infection. Carrier animals eventually clear the infection, however the length of time required to clear the infection varies greatly. Although a large proportion of infected cattle become carriers, it is unclear whether carrier cattle can spread the infection to naïve cattle. The primary purpose of this study was to investigate the potential for transmission of FMDV from persistently infected cattle to naive cattle under typical husbandry conditions in Vietnam. This report describes a study in Vietnam, in which naturally infected carrier cattle were housed with naïve cattle to assess the potential for transmission of FMDV from carrier cattle to naïve cattle. No transmission occurred during 6 months of contact between carrier and naïve cattle, and the average duration of the carrier state was 27.7 months for carriers in this study. Additionally, this study describes the evolution of FMDV over 12 months within one carrier animal. This study provides novel insights into the role of carrier cattle in FMDV epidemiology and evolution under natural conditions in an endemic setting.

Technical Abstract: Background: Foot-and-mouth disease (FMD), caused by FMD virus (FMDV; Aphthovirus, Picornaviridae), is a highly contagious and economically important disease of cloven-hoofed domestic livestock and wildlife species worldwide. A large proportion of FMDV-infected ruminants become persistently infected carriers, defined by detection of FMDV in oropharyngeal fluid (OPF) samples 28 days or more post-infection. The goal of this study was to characterize several aspects of the FMD carrier state in cattle subsequent to natural infection under typical husbandry practices in Vietnam. Ten persistently infected cattle on eight farms in the Long An province in southern Vietnam were monitored by monthly screening of serum and oropharyngeal fluid samples for 12 months. In order to assess transmission from FMDV carriers, sixteen naïve cattle were identified and intentionally brought into direct contact with the persistently infected animals for six months. Results: The average duration of the FMD carrier state was 27.7 months, and the rate of decrease of the proportion of carrier animals was 0.03 per month. There was no evidence of transmission to naïve animals. Additionally, there was no detection of FMDV infection or seroconversion in three calves born to carrier animals during the study. The force of infection for carrier-to-contact transmission was 0 per month, with upper 95% confidence limit of 0.064 per month. Phylogenetic analysis of viral protein 1 (VP1) coding sequences obtained from persistently infected carriers indicated that all viruses recovered in this study belonged to the O/ME-SEA/PanAsia lineage, and grouped phylogenetically with temporally and geographically related viruses. Analysis of within-host evolution of FMDV, based upon full-length open reading frame sequences recovered from consecutive samples from one animal, indicated that most of the non-synonymous changes had occurred in Lpro, VP2 and VP3 protein coding regions. Conclusions: This study suggests that the duration of persistent infection in cattle may be longer than previously recognized, but the risk of transmission is low. This study provides novel insights into the role of persistently infected carriers in FMDV epidemiology and evolution under natural conditions in an endemic setting.