Vaccination and Reduced Cohort Duration Can Drive Virulence Evolution: Marek’s Disease Virus and Industrialized Agriculture

Atkins, Katherine E.; Read, Andrew F.; Savill, Nicholas J.; Renz, Katrin; Islam, Aminul; Walkden‐Brown, Stephen W.; Woolhouse, Mark E. J.

doi:10.1111/j.1558-5646.2012.01803.x

Cited by 81 publications

(99 citation statements)

References 59 publications

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“…Atkins et al. (2012), in a study of MDV evolution, found that fitness was maximized at intermediate virulence levels, also in accord with the standard virulence–transmission trade‐off (Atkins et al., 2012). We should note that alternative assumptions on life‐history traits could have been made.…”

Section: Discussionmentioning

confidence: 61%

“…We found that increasing the cohort duration can select for lower virulence strains of MDV, a result also found by Atkins et al. (2012), and supported by the historical trend towards greater virulence as cohort durations have shortened (Atkins et al., 2012). As the cohort duration increases, the lifespan of the chicken increases, and so too does the lifespan of the parasites exploiting the host.…”

Section: Discussionmentioning

confidence: 86%

“…The emergence of more virulent strains since the 1970s has largely been attributed to the widespread use of vaccinations (Davison & Nair, 2005), and this has been supported by empirical and theoretical work (Atkins et al., 2012; Read et al., 2015). Atkins et al.…”

Section: Introductionmentioning

confidence: 99%

“…Atkins et al. (2012) constructed a model of MDV fitness for a range of vaccination treatments and cohort durations. They used an individual‐based approach in deriving an expression for pathogen fitness and with it found that the reduced lifespan of poultry on industrial farms (reduced cohort duration) and the introduction of vaccination can lead to an increase in virulence.…”

Section: Introductionmentioning

confidence: 99%

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The industrialization of farming may be driving virulence evolution

Rozins

Day

2016

Evolutionary Applications

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Farming practices have changed dramatically over the years. The industrialization of farming has provided parasites with an abundance of hosts and is thought to have influenced parasite evolution. For example, the parasite that causes the highly contagious poultry disease, Marek's disease, has evolved over the past 60 years into a highly virulent pathogen. It is assumed that the industrialization of the industry and vaccination have selected for more virulent strains of the virus. Here, with the use of an impulsive differential equation model, we investigate how modern broiler farm practices could independently lead to virulence evolution. Our model suggests that longer cohort durations and more densely stocked barns both select for less virulent strains of the virus. Our model also suggests that if intensive cleaning between cohorts does not rid the barn of disease, it may drive evolution and cause the disease to become more virulent.

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Section: Discussionmentioning

confidence: 61%

Section: Discussionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The industrialization of farming may be driving virulence evolution

Rozins

Day

2016

Evolutionary Applications

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“…Unfortunately, MD vaccines are incapable of inducing a sterile immunity and allow the virulent virus strains to replicate and be transmitted into the environment through the vaccinated host (Zhang et al 2015). It is believed, that keeping host alive, vaccination prolongs the infection time of virulent strains and may cause evolution of MDV with increased virulence (Witter 1997, Atkins et al 2013, Hunt and Dunn 2013. This is why more virulent MDV pathotypes emerge, reducing the effectiveness of existing vaccines (Davison and Nair 2005, Hunt and Dunn 2015, Zhang et al 2015.…”

Section: Introductionmentioning

confidence: 99%

Morphology of immune organs after very virulent plus strain of Marek’s disease virus infection in vaccinated hens

Madej¹,

Woźniakowski²,

Gaweł³

2016

Polish Journal of Veterinary Sciences

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Marek's disease (MD) outbreaks in poultry flocks may be associated with overriding of vaccine immune protection by very virulent (vvMDV) or very virulent plus (vv+MDV) strains. This paper presents the study on lymphoid organ morphology in the latent phase of MD caused by vv+MDV which break post-vaccinal protection in hens. We also immunohistochemically examined B and T populations as well as B/T and CD4 + /CD8+ ratio of lymphocytes in lymphatic organs and, as a background, in MD lymphomas from non-lymphatic organs. The number of antigen expressed cells was evaluated as a percentage of positive cells in the one power field. Organ samples were collected from 24 dead reproductive hens (Ross 308 line) in age between 35-56 weeks, infected with vv+MDV. The hens originated from farms with MD outbreaks, despite earlier routine vaccination with CVI988/Rispens + HVT. The control organ samples originated from 15 clinically healthy hens at the same age and line, subjected to the same vaccination schedule. The number of CD3 + , CD8 + and TCRγδ + cells was significantly lower in MDV infected thymus, spleen and cecal tonsils in comparison to that found in the control organs. The proportion of CD4 + was also distinctly reduced in the thymus and limited in the spleen of MDV infected hens. This study revealed that infection with field vv+MDV isolates might break post-vaccinal protection and influence the central and peripheral immune system. The decrease in CD8 + and TCRγδ + cell number in the thymus, spleen and cecal tonsils suggests that primarily these cells are involved in cell-mediated cytotoxicity against MDV transformed cells during latency.

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Impact of Vaccination and Pathogen Exposure Dosage on Shedding Kinetics of Infectious Hematopoietic Necrosis Virus (IHNV) in Rainbow Trout

2020

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Vaccine efficacy in preventing clinical disease has been well characterized. However, vaccine impacts on transmission under diverse field conditions, such as variable pathogen exposure dosages, are not fully understood. We evaluated the impacts of vaccination on disease‐induced host mortality and shedding of infectious hematopoietic necrosis virus (IHNV) in Rainbow Trout Oncorhynchus mykiss. Fish, in up to three different genetic lines, were exposed to different dosages of IHNV to simulate field variability. Mortality and viral shedding of each individual fish were quantified over the course of infection. As the exposure dosage increased, mortality, number of fish shedding virus, daily virus quantity shed, and total amount of virus shed also increased. Vaccination significantly reduced mortality but had a much smaller impact on shedding, such that vaccinated fish still shed significant amounts of virus, particularly at higher viral exposure dosages. These studies demonstrate that the consideration of pathogen exposure dosage and transmission are critical for robust inference of vaccine efficacy.

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Vaccination and Reduced Cohort Duration Can Drive Virulence Evolution: Marek’s Disease Virus and Industrialized Agriculture

Abstract: Marek's disease virus (MDV),

Cited by 81 publications

References 59 publications

The industrialization of farming may be driving virulence evolution

The industrialization of farming may be driving virulence evolution

Morphology of immune organs after very virulent plus strain of Marek’s disease virus infection in vaccinated hens

Impact of Vaccination and Pathogen Exposure Dosage on Shedding Kinetics of Infectious Hematopoietic Necrosis Virus (IHNV) in Rainbow Trout

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