Using egg production data to quantify within-flock transmission of low pathogenic avian influenza virus in commercial layer chickens

Abstract

Even though low pathogenic avian influenza viruses (LPAIv) affect the poultry industry of several countries in the world, information about their transmission characteristics in poultry is sparse. Outbreak reports of LPAIv in layer chickens have described drops in egg production that appear to be correlated with the virus transmission dynamics. The objective of this study was to use egg production data from LPAIv infected layer flocks to quantify the within-flock transmission parameters of the virus. Egg production data from two commercial layer chicken flocks which were infected with an H7N3 LPAIv were used for this study. In addition, an isolate of the H7N3 LPAIv causing these outbreaks was used in a transmission experiment. The field and experimental estimates showed that this is a virus with high transmission characteristics. Furthermore, with the field method, the day of introduction of the virus into the flock was estimated. The method here presented uses compartmental models that assume homogeneous mixing. This method is, therefore, best suited to study transmission in commercial flocks with a litter (floor-reared) housing system. It would also perform better, when used to study transmission retrospectively, after the outbreak has finished and there is egg production data from recovered chickens. This method cannot be used when a flock was affected with a LPAIv with low transmission characteristics (R(0)<2), since the drop in egg production would be low and likely to be confounded with the expected decrease in production due to aging of the flock. Because only two flocks were used for this analysis, this study is a preliminary basis for a proof of principle that transmission parameters of LPAIv infections in layer chicken flocks could be quantified using the egg production data from affected flocks.

Risk based surveillance for early detection of low pathogenic avian influenza outbreaks in layer chickens

“…An example of the latter is the LPAIV H7N3 outbreak in 2003 in the Netherlands (de Wit et al, 2004). Despite its high transmission characteristics (Gonzales et al, 2012b), this virus affected only three flocks, which were located in an area of low flock density (R f < 1).…”

“…The differential equations describing the transition rates in this model have been described elsewhere (Keeling and Rohani, 2008). To account for the variation in the within-flock transmission characteristics of various LPAIV strains, the model was parameterised using data from various transmission experiments (van der Goot et al, 2003;Gonzales et al, 2011Gonzales et al, , 2012a and from outbreaks (Gonzales et al, 2012b) (Table 1). With these data, the dynamics of LPAIV of low and high transmission characteristics were considered in the analysis (Table 1).…”

“…The latter describes how the transmission rate scales with distance. We examined different kernel functions (Table 2), and, on the basis of the Akaike's Information (Gonzales et al, 2012b) aˇ, transmission rate; T, infectious period; R0, basic reproduction ratio. Parameters of LPAIV of low transmission characteristics are those with R0 ≤ 1.5 and LPAIV of high transmission characteristics are those with R0 > 1.…”

“…A total of 27 outbreaks were selected for analysis, based on sufficient information about antibody and/or virus (PCR) prevalence, egg production data and tracing. This information was used to reconstruct the within-flock infection dynamic (Comin et al, 2011a;Gonzales et al, 2012b) and the between-flock transmission events in case of secondary spread. Twenty out of these 27 outbreaks were primary introductions; the remaining seven were secondary cases.…”

LPAI detection in wild birds and LPAI spread between European holdings in the period 2005‐2015

“…Experimental trials (two groups of ten birds, five contact and five inoculated) showed the infectious period was significantly greater in inoculated chickens compared to contact-infected chickens (Gonzales et al, 2012a). …”