Evaluating Surveillance Strategies for the Early Detection of Low Pathogenicity Avian Influenza Infections

Abstract

In recent years, the early detection of low pathogenicity avian influenza (LPAI) viruses in poultry has become increasingly important, given their potential to mutate into highly pathogenic viruses. However, evaluations of LPAI surveillance have mainly focused on prevalence and not on the ability to act as an early warning system. We used a simulation model based on data from Italian LPAI epidemics in turkeys to evaluate different surveillance strategies in terms of their performance as early warning systems. The strategies differed in terms of sample size, sampling frequency, diagnostic tests, and whether or not active surveillance (i.e., routine laboratory testing of farms) was performed, and were also tested under different epidemiological scenarios. We compared surveillance strategies by simulating within-farm outbreaks. The output measures were the proportion of infected farms that are detected and the farm reproduction number (Rh). The first one provides an indication of the sensitivity of the surveillance system to detect within-farm infections, whereas Rh reflects the effectiveness of outbreak detection (i.e., if detection occurs soon enough to bring an epidemic under control). Increasing the sampling frequency was the most effective means of improving the timeliness of detection (i.e., it occurs earlier), whereas increasing the sample size increased the likelihood of detection. Surveillance was only effective in preventing an epidemic if actions were taken within two days of sampling. The strategies were not affected by the quality of the diagnostic test, although performing both serological and virological assays increased the sensitivity of active surveillance. Early detection of LPAI outbreaks in turkeys can be achieved by increasing the sampling frequency for active surveillance, though very frequent sampling may not be sustainable in the long term. We suggest that, when no LPAI virus is circulating yet and there is a low risk of virus introduction, a less frequent sampling approach might be admitted, provided that the surveillance is intensified as soon as the first outbreak is detected.

Systematic review of surveillance systems and methods for early detection of exotic, new and re-emerging diseases in animal populations

“…Simulation models (n = 10) [30,41,97,107,[119][120][121][122][123][124] aimed to mimic disease transmission in a population in time, and sometimes in space, terms in specific circumstances. The outputs from the simulations could be used for estimating the risk of disease spread (n = 5).…”

Avian Influenza Risk Surveillance in North America with Online Media

“…The abundance of virus shed into lake water and wetlands can provide a way for ducks to spread the virus through migration onto other domestic or wild birds [11]In addition, introduction of LPAI viruses into a poultry population may not necessarily involve direct contact but rather the mechanical transfer of the virus through infective faeces from the waterfowl [13]. LPAI of subtypes H5 and H7 in wild birds can still be problematic as it can mutate when transmitted to poultry to the highly pathogenic type [14]. As was shown in February 2003 when an outbreak of pathogenic avian influenza (subtype H7N7) in the Netherlands is thought to have originated from free-living ducks that had evolved into a highly pathogenic variant after introduction into poultry farms [15].…”

“…Due to the inherent bias in samples of convenience, establishing valid estimates of disease absence or prevalence remains difficult [18]. HPAI detection has been traditionally based on passive surveillance since the infection induces clear clinical signs and high mortality in most poultry species [14]. In wild birds, dead bird collection limits the insights that can be made on the distribution, spread and the diversity of AIV strains, since death is rarely caused in wild birds [19].…”

“…Comin [14]used epidemiological data from Italian LPAI surveillance programs and simulated within-farm outbreaks using different surveillance strategies. They found that surveillance was only successful in preventing an epidemic in turkeys if action was taken within two days of sampling.…”

Influenza monitoring in Sardinia, Italy identifies H3 subtype in Mediterranean wild migratory birds

“…The new threat of a highly pathogenic transmissible strain of avian influenza has provoked the need for monitoring influenza strains circulating in wild migratory birds [31]. Furthermore, it is commonly thought that early detection of avian influenza is essential for economic security in the poultry industry and maintenance of public health [32]. Previously, avian influenza has been monitored in wild birds, including those in Italy and those crossing the Europe/North America land bridge [11,[33][34][35][36][37].…”