SUMMARY

Movement and land application of manure is a known risk factor for secondary spread of avian influenza viruses. During an outbreak of highly pathogenic avian influenza (HPAI), movement of untreated (i.e., fresh) manure from premises known to be infected is prohibited. However, moving manure from apparently healthy (i.e., clinically normal) flocks may be critical, because some egg-layer facilities have limited on-site storage capacity. The objective of this analysis was to evaluate targeted dead-bird active surveillance real-time reverse transcriptase polymerase chain reaction (rRT-PCR) testing protocols that could be used for the managed movement of manure from apparently healthy egg-layer flocks located in an HPAI control area. We also evaluated sequestration, which is the removal of manure from any contact with chickens, or with manure from other flocks, for a period of time, while the flock of origin is actively monitored for the presence of HPAI virus. We used stochastic simulation models to predict the chances of moving a load of contaminated manure, and the quantity of HPAI virus in an 8 metric ton (8000 kg) load of manure moved, before HPAI infection could be detected in the flock. We show that the likelihood of moving contaminated manure decreases as the length of the sequestration period increases from 3 to 10 days (e.g., for a typical contact rate, with a sample pool size of 11 swabs, the likelihood decreased from 48% to <1%). The total quantity of feces from HPAI-infectious birds in a manure load moved also decreases. Results also indicate that active surveillance protocols using 11 swabs per pool result in a lower likelihood of moving contaminated manure relative to protocols using five swabs per pool. Simulation model results from this study are useful to inform further risk evaluation of HPAI spread through pathways associated with manure movement and further evaluation of biosecurity measures intended to reduce those risks.

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