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United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Foreign Animal Disease Research

2012 Annual Report

1a. Objectives (from AD-416):
1. Determine the molecular epidemiology of FMDV in local livestock in Vietnam including cattle, buffaloes and pigs. 2. Better understand the transmission mechanism of FMDV from persistently infected to susceptible local livestock in natural setting. 3. Enhance strategies for identification of persistently infected animals using new technology. Amendment 1: 4. Vaccine matching between field strains and current vaccine viruses will be carried out to assess efficacy against currently circulating strains.

1b. Approach (from AD-416):
1. Acute samples: A systematic FMD monitoring program to determine the molecular epidemiology of FMDV in local livestock in Vietnam will be initiated. All FMD cases from all species reported to the Department of Animal Health (DAH) and FMD-suspected animals at infected area quarantine stations will be included in the program. Epithelial or vesicular fluid, lesions swabs, sera, oral swab, and oropharyngeal fluid (probing sample) will be collected from clinically infected or suspected animals on the premises. All samples will be sent to the laboratory within 24 hours. Sera will be kept at -20oC until tested using various detection methods including liquid phase blocking ELISA (LP ELISA) and non structural protein ELISA (NSP ELISA), realtime RT-PCR and virus isolation. All samples will be sent to the Plum Island Animal Disease Center (PIADC) for collaborative studies. Information including animal species, location of infected premise (GPS coordinates), address of the premise, number of affected animals, number of susceptible animals, movement history, vaccination history, purchase history, husbandry management, etc will be collected at the time of sample collection and stored in predesigned computer database. 2. A longitudinal field study will be conducted to determine viral and host genomic factors influencing viral persistence in local livestock in Vietnam including cattle, buffaloes, goats, and pig, and to better understand persistence mechanism in these species. Individual animals with well documented persistent infections will be purchased and slaughtered to collect relevant tissues for virological and pathological investigations. A longitudinal collection of samples (sera, oral swabs, and oropharyngeal samples) will be done from all carrier and susceptible animals at the beginning of the study, and then followed up first 30 days and then 3-6 months interval for a period of two years. All samples will be sent to the DAH within 24 hours. Sera will be kept at -20oC until tested using ELISA. Oral swabs will be kept at -80oC until tested using realtime RT-PCR and virus isolation. Oropharyngeal fluids will be kept at -80oC until tested using realtime RT-PCR and virus isolation. Oropharyngeal fluids will be kept at -80oC and used for sequencing of whole FMD genome. Apart from testing, all samples will be stored at an appropriate condition for later reference. 3. Various pen-side and laboratory based diagnostic tests will be evaluated during field studies. Analyses will be performed to evaluate and compare the performance of the different diagnostic methods for detection of FMDV in clinically and non-clinically infected animals, in various stages of carriers, and during the early state of infection in susceptible animals. Amendment 1: 4. Sera from cattle vaccinated with different strains of serotype O will be sent to ARS, PIADC for vaccine matching. These Vietnamese field strains will be used for this objective. In accorance to the OIE Terrestrial Manual, a relationship coefficient will be determined between the vaccine viruses and field viruses and the resulting value will be assessed as to whether there is a vaccine match.

3. Progress Report:
Vietnam is a country where Foot-and-Mouth Disease virus (FMDV) is endemic in the livestock population; inclusive of cattle, buffalo, pigs and goats and targeted vaccination of susceptible animals is practiced. Recent outbreaks in livestock have occurred in 2011 and 2012. It is known that animals that recover from FMD infection can develop a prolonged, persistent infection with the FMDV, potentially serving as a continued source of new infections in susceptible populations. Previous studies have shown that persistent infection, defined as virus being isolated over 28 days post-infection, could be induced in cattle, with live virus isolated from various tissues. However, little is known about the role of persistently infected animals, especially the role of buffalo, in maintenance and transmission of the FMDV virus within susceptible populations. During FY 2012 sixty-nine selected viruses and specimens have been sent to ARS, PIADC for sequencing and further characterization in an effort to determine the molecular epidemiology (phylogenetics) of circulating FMDV strains in Vietnam. In addition, a sero-survey was conducted to screen for sero-positive cattle and buffaloes. Upon the outcomes of the survey, persistently infected cattle and buffaloes were identified by probang testing of convalescent animals identified through FMDV-Non-structural protein (NSP) sero-surveillance. Probang samples were screened by rRT-PCR at Department of Animal Health (DAH) laboratories. Test transmission cells are being established. Information derived from these studies will aid in the understanding of the role of persistent carriers in disease transmission in the natural environment, in interspecies transmission between infected Asian buffalo and naïve cattle and be used to develop standardized protocols for the detection of carrier animals, particularly in cattle and buffalo and develop sampling strategies for freedom from disease for quarantine/export certification. Another major area of progress has been the strengthening of the collaborative relationship of the USDA ARS with the central government of Vietnam, including the national, provincial and local animal health officials. The testing of animals enrolled in the test transmission cells will be continued by collaborators at the DAH, National Center Veterinary Diagnostics and Regional Animal Health Office 6 in Vietnam in FY 2013. The maintenance of data pertaining to the longitudinal monitoring of transmission test cells will be continued. Information from updated farm surveys will also be analyzed for potentially significant risk factors affecting disease transmission. It is also anticipated that the continued sharing of information and educational materials relevant to the study will be continued. Apart from monitoring the TTC, five buffalo with FMDV-positive probangs will be purchased and transferred to appropriate location for euthanasia, necropsy, and sample collection. An additional activity has led to the proposal of having the Agreement amended, so as a new activity be added "Vaccine matching between field strains and current vaccine viruses will be carried out to assess efficacy against currently circulating strains". No new technologies have been produced or transferred to date from this ongoing work. No peer-reviewed publications have been produced to date from this ongoing work.

4. Accomplishments

Last Modified: 10/17/2017
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