Inferring within‐flock transmission dynamics of highly pathogenic avian influenza H5N8 virus in France, 2020

Abstract

Following the emergence of highly pathogenic avian influenza (H5N8) in France in early December 2020, we used duck mortality data from the index farm to investigate within-flock transmission dynamics. A stochastic epidemic model was fitted to the daily mortality data and model parameters were estimated using an approximate Bayesian computation sequential Monte Carlo (ABC-SMC) algorithm. The model predicted that the first bird in the flock was infected 5 days (95% credible interval, CI: 3-6) prior to the day of suspicion and that the transmission rate was 4.1 new infections per day (95% CI: 2.8-5.8). On average, ducks became infectious 4.1 h (95% CI: 0.7-9.1) after infection and remained infectious for 4.3 days (95% CI: 2.8-5.7). The model also predicted that 34% (50% prediction interval: 8%-76%) of birds would already be infectious by the day of suspicion, emphasizing the substantial latent threat this virus could pose to other poultry farms and to neighbouring wild birds. This study illustrates how mechanistic models can help provide rapid relevant insights that contribute to the management of infectious disease outbreaks of farmed animals. These methods can be applied to future outbreaks and the resulting parameter estimates made available to veterinary services within a few hours.

Unravelling direct and indirect contact patterns between duck farms in France and their association with the 2016–2017 epidemic of Highly Pathogenic Avian Influenza (H5N8)

“…Similarly, for the sTN, an infectious contact was defined as a specific indirect contact (through the transit of transport vehicle but without live-animal exchange) occurring between two outbreak farms within t days before the date of suspicion of the most recent outbreak of the two. Because recent epidemiological findings suggest that duck mortality is likely to increase rapidly after HPAI (H5N8) virus introduction (Vergne et al, 2021), we considered a time-window of t = 7 days, but also tested longer periods of 14 and 21 days, similar to Guinat et al (2020). The rationale behind the k-test approach was that if the virus spread through the networks, the number of infectious contacts would be significantly greater than expected under the null hypothesis, i.e.…”

Highly Pathogenic Avian Influenza A(H5N8) Clade 2.3.4.4b Virus in Dust Samples from Poultry Farms, France, 2021

“…The higher sensitivity of environmental sampling methods for early detection is likely because of infection dynamics at the flock level. During the early phases of infection, only a few animals are infectious, making the probability of detecting virus during individual swab-based sampling low ( 6 ). Swab sampling also is time consuming, labor-intensive, and expensive, whereas dust wiping is inexpensive, fast, easy to perform, and noninvasive.…”

“…Epidemiologic modeling of this outbreak suggested within-farm viral transmission was extremely fast, and the environment was a major source of contamination for neighboring farms ( 6 ). HPAI viruses disperse in aerosols, in fomites carried by human and animal vectors, and via feathers, fecal particles, and to a great extent, dust ( 7 – 9 ).…”

Highly pathogenic avian influenza A H5 virus outbreaks in broiler farms in the Netherlands – Clinical signs, transmission and identification of reporting thresholds

“…This information is relevant to understand how transmissible these H5 HPAIV are in broiler flocks and how fast infection spreads in an infected flock. This information is relevant to guide tracing activities during outbreak response (13, 14).…”