Can routinely recorded reproductive events be used as indicators of disease emergence in dairy cattle? An evaluation of 5 indicators during the emergence of bluetongue virus in France in 2007 and 2008

Abstract

In response to increasing risks of emerging infectious diseases, syndromic surveillance can be a suitable approach to detect outbreaks of such diseases across a large territory in an early phase. To implement a syndromic surveillance system, the primary challenge is to find appropriate health-related data. The objective of this study was to evaluate whether routinely collected dates of reproductive events in dairy cattle could be used to build indicators of health anomalies for syndromic surveillance. The evaluation was performed on data collected in France between 2003 and 2009. First, a set of 5 indicators was proposed to assess several types of reproductive disorders. For each indicator, the demographic coverage over the total number of cattle at risk was analyzed in time and space. Second, the ability to detect an emerging disease in an early phase was retrospectively evaluated during epidemics of bluetongue serotypes 1 and 8 (BTV-1, BTV-8) in France in 2007 and 2008. Reproductive indicators were analyzed weekly during these epidemics for each indicator in each infected French district (16 in 2007 and 50 in 2008 out of 94 districts). The indicators were able to detect the BTV epidemics despite their low demographic coverage on a weekly basis relatively to total number of cattle (median=1.21%; range=0-11.7%). Four indicators related to abortions, late embryonic death, and short gestations were abnormally elevated during both BTV epidemics. Median times to abnormal elevations in these indicators were 20 to 71 d after the first notification of clinical signs of BTV by veterinarians. These results demonstrate that reproduction data can be used as indicators of disease emergences, whereas in the specific case of these BTV epidemics, detection via these indicators was later than clinical detection by veterinarians. The emergence of bluetongue in 2007 in France was associated with gestations that were a few days shorter than expected. A short gestation indicator underwent high elevations relative to prior random fluctuations and was the earliest (out of the 4 indicators) to show abnormal elevations, making it possible to detect this emergence.

Quantification of the increase in the frequency of early calving associated with late exposure to bluetongue virus serotype 8 in dairy cows: implications for syndromic surveillance

“…The dates were expressed as a number of days since the first clinical case herd during the 2007 epizootic in France (31 st July 2007), and location of reported case herds (black crosses). The hatched areas correspond to regions with no data (from [ 15 ]). …”

“…A recent study evaluated whether reproduction data could be used to build indicators suitable for syndromic surveillance [ 15 ]. This study showed an increased frequency of early calving (after a pregnancy length still within a normal range) in cows located in BTV infected areas, concomitant with the BTV notifications.…”

Using big data in cattle practice

“…A classic example is the use of frequency of search engine queries for early detection of human influenza outbreaks (Ginsberg and others 2009). As syndromic surveillance represents a relatively low-cost method compared to many conventional approaches; it has attracted some interest at national level, for example in detection of exotic disease incursion (Marceau and others 2014, Dórea and Vial 2016). However, this approach could also be taken at veterinary practice level; for example, by identifying farms where measured outcomes (such as conception rate or milk yield) deviate from what would be expected based on previous data both from that individual herd and from others in the practice.…”

Improving the Utility of Voluntary Ovine Fallen Stock Collection and Laboratory Diagnostic Submission Data for Animal Health Surveillance Purposes: A Development Cycle

“…They found that, in 2013, although there were 27 veterinary syndromic surveillance systems in 12 European countries, most of these did not yet have the statistical wherewithal to adequately analyse the data. Subsequently, there have been additional studies [e.g., (16)(17)(18)(19)(20)(21)(22)] and increased momentum within the animal health surveillance sector. Although there is evidence of further development of digital surveillance systems for animal populations (23), they have not yet matured into fully functional, digital, automated biosurveillance systems providing outbreak detection, syndromic surveillance, monitoring of trends and situational awareness in animal populations.…”