Effect of different vaccination strategies on IBV QX population dynamics and clinical outbreaks

Abstract

The extreme variability and rapid evolution of Infectious bronchitis virus (IBV) has always represented the key challenge for its control because of the limited cross-protection among different strains. Several experimental trials have proven a broadening of the protection spectrum when animals are vaccinated with multiple genotypes. Nevertheless, the conditions of vaccine administration in field are so different that the generalization of experimental results is, at least, questionable. In the present study a large scale epidemiological-phylodynamic approach was used to reconstruct the demographic history of the major field genotype (i.e. the QX one) circulating in Italy and Spain. These two countries were selected because, even if they share a comparable epidemiological scenario, the implemented vaccination protocols did not vary in Spain while changed dramatically in Italy over the time period considered. One hundred and ninety-five Italian and 98 Spanish non-recombinant sequences of the hyper-variable region of the S1 gene obtained between 2012 and 2016 were analyzed using a serial coalescent-based approach to reconstruct viral population history over time. While the IBV QX population dynamics remained constant in Spain, a much more complex pattern was evidenced in Italy; both in terms of viral population size and clinical outbreak frequency. Remarkably, a strong association with changes in vaccination strategies was recognized. This allowed demonstrating, by accomplishing all Hill's criteria for causation, the cause-effect relationship between the vaccine administration/withdrawal and the variation in viral population dynamics and, above all, IBV related outbreaks. Thus, a robust confirmation about the efficacy of IBV vaccination in field conditions was provided. Additionally, the history herein reported testifies the primary importance of rigorously planning not only the intervention strategies but also their monitoring and evaluation.

Phylodynamic analysis and evaluation of the balance between anthropic and environmental factors affecting IBV spreading among Italian poultry farms

“…2). A previous study has ascribed this episode to a change in the vaccination scheme adopted by this company, which moved from a heterologous Mass+793B based vaccination to a Mass only vaccination leading to an increased viral circulation and clinical outbreaks number 4 . Moreover, experimental studies demonstrated a significant reduction in R 0 in vaccinated groups compared to unvaccinated ones 28 .…”

“…Currently, the most effective control measure is vaccine application, which proved to effectively reduce clinical signs emergence, infectious pressure and viral population size, at least when properly performed 4,5 . However, this approach cannot be considered a panacea, and some drawbacks cannot be denied.…”

Think globally, act locally: Phylodynamic reconstruction of infectious bronchitis virus (IBV) QX genotype (GI-19 lineage) reveals different population dynamics and spreading patterns when evaluated on different epidemiological scales

“…Several experimental [ 29 ] and field [ 21 ] studies confirmed the efficacy of vaccination schemes based on the protectotype concept [ 30 ]. However, the rapid spread and high virulence [ 27 ] of this new variant challenged the previously established control strategies and has forced their re-assessment and the development of new homologous vaccines.…”

“…To cover this lack of information, a large scale phylodynamic study has been performed based on the S1 protein hypervariable region analysis of strains sampled all over the world, from the first GI-19 lineage (alias QX genotype) detection to the end of 2015. Additionally, to better understand the GI-19 lineage fate after its introduction in a previously naïve county, the spreading and population variation patterns were evaluated with reference to Italy, a major poultry producing country, where, after the first description in 2005, this lineage established itself as the predominant one [ 21 ].…”

Genotyping of Avian infectious bronchitis viruses in Iran (2015–2017) reveals domination of IS-1494 like virus

“…QX type IBV was first isolated by Bozorgmehri-Fard et al in Iran, the incidence was 9.6% from 2010 to 2014 and 10% from 2014 to 2015 (Najafi et al, 2016).The present study shows a reduction in the frequency of occurrence rate of QX IBV, which may reflect the efficacy of combined Massachusetts and 793/B type IB vaccines. Epidemiological analysis of IBV in Italy and Spain indicated a causal relationship between Massachusetts plus 793/B vaccination and a decreased prevalence of QX (Franzo et al, 2016). Kahya et al detected IS-1494-06 like IBV strain in turkey, 2011 (Kahya et al, 2013).…”