Foot and mouth disease (FMD) is a prominent transboundary disease among animals that can seriously impact livestock production and disrupt the trade in animals and animal products at both the regional and international levels [1
]. It is caused by a virus of the genus Aphthovirus, family Picornaviridae
. Seven serotypes have been known to infect cloven-hoofed animals: O, A, C, SAT 1, SAT 2, SAT 3, and Asia-1. Importantly, each serotype infection does not grant immunity to another infection [1
]. Over the last 40 years, different genetic subtypes of this disease have persisted in Thailand within a limited range of the bordering countries. However, the disease is known to spread periodically and temporarily beyond these boundaries [2
]. Recently, six serotypes of the FMD virus (O, A, SAT 1, SAT 2, SAT 3, and Asia-1) have been circulating globally [4
] and remain a persistent threat of incursions in large parts of Africa, the Middle East, and Asia [1
For the development of an effective FMD control program, several regional challenges persist, including uncontrolled animal movements, difficulties in supplying vaccines and establishing their efficacy, limited technical skills in the field, insufficient biosecurity networks, low levels of involvement of local disease control programs, and the inherent complexities of integrating national and international control programs [6
]. However, an universal strategy for FMD control was endorsed in 2012 at the global level [7
]. The Food and Agriculture Organization of the United Nations (FAO) and the World Organization for Animal Health (OIE) launched the Progressive Control Pathway for FMD control (PCP-FMD) with the goal of eradicating FMD worldwide in 2014 [8
]. The initial measures outlined in this strategy include early detection and alert systems and the implementation of successful surveillance programs, as has been stated in the OIE Terrestrial Code guidelinesThe global FMD control strategies include improving global FMD control by the enhancement of field and laboratory technical capabilities and the expansion and implementation of effective disease control measures. These measures would include vaccines, surveillance, biosecurity, compliance with movement regulations and public awareness campaigns to regulate FMD, strengthening veterinary services, as well as improving the prevention and control of other major diseases known to affect cattle [6
Disease surveillance is an important epidemiological tool used to monitor the health of a population. The goals of an effective disease surveillance program are mainly to describe the current burden and epidemiology of the disease, to monitor current trends and to identify outbreaks and new pathogens [9
]. Examples of successful FMD eradication programs that have been implemented in some countries of Southeast Asia, which include effective surveillance programs, have revealed that intensive epidemiological surveillance can be undertaken to track the potential reappearance of FMD cases. One of these successful programs was utilized in Indonesia [10
]. Additionally, the Philippines established a method to strengthen their disease monitoring and surveillance activities in order to eliminate cases of the disease that reemerged in high risk areas during implementation of an FMD eradication program [11
Thailand has been recognized as an endemic area of FMD for more than 60 years [12
]. FMD serotype O and A are common serotypes that are found in this country [13
]; however, serotype Asia-1 FMD has not been observed since 1998 [12
]. Cattle, buffalo, and pigs were identified as the main FMD affected species during the outbreak over the previous decades [13
]. To effectively control FMD and eradicate it from the country, the FMD National Strategic Plan of 2008–2015 [17
] and the national FMD control program of 2016–2023 [18
] were implemented by the Department of Livestock Development of Thailand (DLD).
The aims of this study were: (1) to analyze the distribution of FMD in Thailand from 2008 to 2019; (2) to describe a national surveillance approach; and (3) to identify the existing knowledge gap with regard to the disease in terms of cattle production.
Although the national strategic plan and control measures have been implemented, FMD still remains a critical problem for cattle farmers in Thailand. Several important points and the existing knowledge gaps regarding FMD are discussed in this study.
The number of FMD outbreaks has increased in the last six years (Table 1
). Both FMD serotype O and A were spatially distributed across Thailand (Figure 3
). This finding may reflect the true outbreak situation, wherein more outbreaks may have occurred or, with high certainty, this upward trend may be the result of an enhancement in the reporting system implemented. As the new system supports both passive and active surveillance systems, more reports of outbreaks would be expected. Most outbreaks occurred in the northern region from 2014 to 2016, but after 2016, a high number of outbreaks were reported in the southern region (Figure 2
). Since the massive outbreak that occurred in northern Thailand in 2015–2016, the DLD has implemented a rigid set of FMD control measures [24
], which could lead to a decrease in the number of outbreaks. Specifically, FMD serotype O was the predominant type causing numerous outbreaks (Figure 1
). This finding raises a question for future studies as to why the FMD serotype O has been the main cause of FMD for a long period of time in Thailand and what factors contribute to the spread of the FMD virus.
Evaluation of the surveillance programs is a critical component for the success of any system [56
]. Appropriate surveillance assessment plays a vital role in the establishment and maintenance of international confidence [61
]. Based on this study and our knowledge, there has been no country-wide evaluation of FMD surveillance in Thailand. Thus, the evaluation of the national FMD surveillance system should be set as a priority.
As the FMD outbreak is highly contagious and the spread of the disease can occur via direct and indirect contact [62
], early detection and early warning systems are essential for the investigation of FMD outbreaks and the control of the disease. For case detection, we have recommended that the education of cattle farmers is strictly needed. Prompt responses from local veterinary officers would be a remarkable component of enhancing an early detection system. In addition, the outbreak investigation program should then be carried out by well-trained staff. A systematic and organized investigation of the outbreak will help stakeholders to understand the outbreak characteristics and identify potential risk factors of an outbreak [63
]. The implementation of a risk-based surveillance system should be strengthened and enhanced, as it can be very supportive of an active surveillance system. Moreover, participatory livestock disease surveillance should be implemented to develop better animal health programs and more successful surveillance and control strategies [64
Vaccinations are the primary preventive measure in protecting cattle against FMD. While vaccinations are typically conducted 2 to 3 times a year, FMD outbreaks still occur in areas where vaccinations have been administered [39
]. The following practices could be a possible reason for unsuccessful vaccination programs. First, there is the tendency for some animals to be exempt from receiving vaccinations (e.g., pregnant animals, animals sent out for grazing at a distance, and sick animals) as was found in Sri Lanka [65
]. Second, if vaccinations were administered by less experienced farmers, it is possible that the handling of the vaccine and vaccination techniques may not be appropriate. Third, inadequate storage of vaccines may also reduce the efficacy of the vaccines. Last, there is a chance that the spread of the FMD virus could have occurred before the vaccine protective titer was achieved. Thus, practical training for the vaccinator would be necessary. Future research on an effective vaccination policy needs to be carried out to provide information on strengthening the current vaccination program.
A better understanding of the epidemiology of FMD will support an effective surveillance system. Most epidemiological studies report important epidemiological information such as prevalence and risk factors of FMD outbreaks that are useful for formulating control strategies but more future studies are needed. For instance, several studies have indicated that the movement of new cattle into farms without quarantine is the significant risk factor for FMD outbreaks [39
]. However, a recent study found that most of the farmers in FMD endemic areas do not conduct such quarantine [39
]. Thus, it is interesting to determine whether the current control strategies are well-adopted by farmers since this practice has been implemented through 2008–2015 national strategic plan. Moreover, it is important to determine the effectiveness of the national control strategies in the future study, as it will provide essential knowledge to strengthen the existing control strategies. Additionally, since the application of advanced epidemiological methods such as spatial statistics and network analysis to epidemiological studies with provincial datasets [20
] provides a better understanding of FMD epidemiology, such methods should be applied for the analysis of larger datasets, such as regional and national data for future studies.
The relevant data related to the FMD situation in Thailand could be useful for future studies that will focus on improving an FMD surveillance system and the associated control measures. More epidemiological studies using other advanced methods are needed. Similar to other countries [66
], one of the circumstances of concern is the under-reporting of incidences of FMD, which can result in an underestimation of the true disease situation [68
]. With the capture-recapture method using two or more data sources [69
], the true status of FMD could be estimated. Moreover, a hierarchical Bayesian model should be used to create a spatial risk map that would be very useful for risk communication [72
]. Additionally, the application of mathematical models for disease transmission and control could provide information relevant to the policy decision-making process. Furthermore, we have determined that it would be imperative to conduct more studies on measuring the subclinical infection status of cattle. This could impact FMD transmission along with field vaccine trial studies implemented to determine the efficiency of vaccines and an effective vaccination strategy.