Effects of Rispens CVI988 vaccination followed by challenge with Marek’s disease viruses of differing virulence on the replication kinetics and shedding of the vaccine and challenge viruses

Ralapanawe, Sithara; Walkden‐Brown, Stephen W.; Islam, Aminul; Renz, Katrin

doi:10.1016/j.vetmic.2015.11.025

Cited by 16 publications

(12 citation statements)

References 33 publications

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“…Although vaccinated birds can still be infected with MDV and can still shed MDV (Witter et al, 1971; Islam et al, 2008; Ralapanawe et al, 2016), vaccination greatly reduces clinical signs of disease (Witter et al, 1971). This, along with other measures to ensure bird health, means that total mortality from hatch to processing is typically minimal (≈3% and ≈8% in the two farms used for model inference below – in line with the national average of 4.8%, National Chicken Council, 2016).…”

Section: Methodsmentioning

confidence: 99%

Modeling Marek's disease virus transmission: A framework for evaluating the impact of farming practices and evolution

2018

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Marek’s disease virus (MDV) is a pathogen of chickens whose control has twice been undermined by pathogen evolution. Disease ecology is believed to be the main driver of this evolution, yet mathematical models of MDV disease ecology have never been confronted with data to test their reliability. Here, we develop a suite of MDV models that differ in the ecological mechanisms they include. We fit these models with maximum likelihood using iterated filtering in ‘pomp’ to data on MDV concentration in dust collected from two commercial broiler farms. We find that virus dynamics are influenced by between-flock variation in host susceptibility to virus, shedding rate from infectious birds, and cleanout efficiency. We also find evidence that virus is reintroduced to farms approximately once per month, but we do not find evidence that virus sanitization rates vary between flocks. Of the models that survive model selection, we find agreement between parameter estimates and previous experimental data, as well as agreement between field data and the predictions of these models. Using the set of surviving models, we explore how changes to farming practices are predicted to influence MDV-associated condemnation risk (production losses at slaughter). By quantitatively capturing the mechanisms of disease ecology, we have laid the groundwork to explore the future trajectory of virus evolution.

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Section: Methodsmentioning

confidence: 99%

Modeling Marek's disease virus transmission: A framework for evaluating the impact of farming practices and evolution

2018

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“…To quantify the impact of management scenario on mitigating the effects of MDV infection on egg production, we use a mathematical model for MDV transmission in industrial poultry farms of laying-hens (Rozins and Day, 2016). As the vast majority of laying-hens are vaccinated (Payne, 1985), our model assumes full vaccination coverage with the current gold standard vaccine Rispen CVI988 (Ralapanawe et al, 2016a). We also assume two distinct mechanisms of MDV transmission: 1) transmission within a cohort of laying hens (those sharing a barn), and 2) transmission between consecutive cohorts of laying-hens occupying a barn (i.e.…”

Section: Methodsmentioning

confidence: 99%

“…All model parameters were extracted from available data (Atkins et al, 2013a, 2011a; Cui et al, 2016; Kennedy et al, 2018; Ralapanawe et al, 2016b, 2016a; Zhang et al, 2015). Parameters associated to barn characteristics where obtained from communication with Burnbrae Farms in Ontario Canada, or the literature.…”

Section: Methodsmentioning

confidence: 99%

“…Parameters associated to barn characteristics where obtained from communication with Burnbrae Farms in Ontario Canada, or the literature. We assume dust shed by MDV infected laying-hens contain viral particles proportional to the virulence level of the MDV strain (Ralapanawe et al, 2016a). To obtain the viral shedding rate, we took Atkins et al (2011) model of daily dander shedding for a typical broiler bird and arameterized it according to a recent study on dust shed from MDV infected layer chickens vaccinated with Rispen CVI988 (Atkins et al, 2011a; Ralapanawe et al, 2016b, 2016a).…”

Section: Methodsmentioning

confidence: 99%

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Managing Marek’s disease in the egg industry

Rozins

Day

Greenhalgh

2018

Preprint

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The industrialization of farming has had an enormous impact. To most, this impact is viewed solely in the context of productivity, but the denser living conditions and shorter rearing periods of industrial livestock farms provide pathogens with an ideal opportunity to spread and evolve. For example, the industrialization of poultry farms drove the Marek’s disease virus (MDV) to evolve from causing a mild paralytic syndrome to causing a highly contagious, globally prevalent, disease that can have up to a 100% mortality rate. Fortunately, the economic catastrophe that would occur from MDV evolution has been prevented through widespread use of live imperfect vaccines that limit disease symptoms, but fail to prevent transmission. Unfortunately, the continued rollout of such imperfect vaccines is steering the evolution of MDV towards an even greater virulence and an ability to evade vaccine protection. Thus, there is a need to investigate alternative economically viable control measures for their ability to inhibit MDV spread and evolution. In what follows we examine the economic viability of standard husbandry practices for their ability to inhibit the spread of both virulent MDV and very virulent MDV throughout an industrialized egg farm. To do this, we parameterized a dynamic MDV transmission model and calculate the loss in egg production due to disease. We find that the MDV strain as well as the cohort duration had the greatest influence on disease burden and hence egg production. Additionally, we find that the standard husbandry practice involving conventional cages, often referred to as “battery cages”, results in the least per capita loss in egg production due to MDV infection when compared to alternative enriched or aviary (free-run) systems for virulent MDV, but not very virulent MDV, in which case the Aviary system performs the best. These results highlight an important cost that managers will face when implementing new hen husbandry practices.

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“…Marek's disease virus is sufficiently pervasive that it should be considered ubiquitous (15,31,34). This idea came from observations that the virus is highly stable in the environment (26), that problems with Marek's disease can occur quickly and without warning when there are issues with vaccine administration, and that vaccination does not preclude infection with and transmission of the virus (24,36,39). It was further supported by the historical ubiquity of antibody detection in production flocks (5,11,22,47).…”

Section: Conventional Wisdom Is Thatmentioning

confidence: 99%