Allocating limited surveillance effort for outbreak detection of endemic foot and mouth disease

TL;DR

This study explores efficient ways to detect foot and mouth disease outbreaks in regions with limited resources by comparing different surveillance strategies using cattle shipment and outbreak data.

Contribution

The study evaluates three data-informed surveillance allocation methods for detecting FMD outbreaks in resource-limited settings.

Findings

All three surveillance methods detected 2.5-4 times more outbreaks than random sampling.

Network Proximity did not outperform the less data-intensive Network Connectivity and Spatial Proximity methods.

Spatial Proximity found the fewest outbreaks among the three methods.

Abstract

Foot and Mouth Disease (FMD) affects cloven-hoofed animals globally and has become a major economic burden for many countries around the world. Countries that have had recent FMD outbreaks are prohibited from exporting most meat products; this has major economic consequences for farmers in those countries, particularly farmers that experience outbreaks or are near outbreaks. Reducing the number of FMD outbreaks in countries where the disease is endemic is an important challenge that could drastically improve the livelihoods of millions of people. As a result, significant effort is expended on surveillance; but there is a concern that uninformative surveillance strategies may waste resources that could be better used on control management. Rapid detection through sentinel surveillance may be a useful tool to reduce the scale and burden of outbreaks. In this study, we use an extensive outbreak and cattle shipment network dataset from the Republic of Türkiye to retrospectively test three possible strategies for sentinel surveillance allocation in countries with endemic FMD and minimal existing FMD surveillance infrastructure that differ in their data requirements: ranging from low to high data needs, we allocate limited surveillance to [1] farms that frequently send and receive shipments of animals (Network Connectivity), [2] farms near other farms with past outbreaks (Spatial Proximity) and [3] farms that receive many shipments from other farms with past outbreaks (Network Proximity). We determine that all of these surveillance methods find a similar number of outbreaks – 2-4.5 times more outbreaks than were detected by surveying farms at random. On average across surveillance efforts, the Network Proximity and Network Connectivity methods each find a similar number of outbreaks and the Spatial Proximity method always finds the fewest outbreaks. Since the Network Proximity method does not outperform the other methods, these results indicate that incorporating both cattle shipment data and outbreak data provides only marginal benefit over the less data-intensive surveillance allocation methods for this objective. We also find that these methods all find more outbreaks when outbreaks are rare. This is encouraging, as early detection is critical for outbreak management. Overall, since the Spatial Proximity and Network Connectivity methods find a similar proportion of outbreaks, and are less data-intensive than the Network Proximity method, countries with endemic FMD whose resources are constrained could prioritize allocating sentinels based on whichever of those two methods requires less additional data collection.

Foot and Mouth Disease (FMD) poses a significant economic burden in countries where it is endemic. Developing surveillance systems that are efficient at detecting outbreaks is essential for managing and mitigating its impact in these countries. In this study, we use detailed outbreak and cattle shipment data from the Republic of Türkiye as a retrospective case study of endemic FMD. We use these data to evaluate the effectiveness of three data-informed surveillance allocation methods across a range of surveillance effort: 1) searching farms that frequently send and receive shipments, 2) searching farms near other farms with outbreaks, and 3) searching farms that receive many shipments from other farms with past outbreaks. We find that all three data-informed methods find 2.5-4 times more outbreaks than non-data informed methods but similar numbers of outbreaks to each other, even though some methods used more data than others. From this, we conclude that countries with endemic FMD and limited surveillance resources should consider developing surveillance systems based on either outbreak data or cattle shipment network data, whichever data requires less effort to collect.

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