Canadian Poultry Magazine

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Novel Marek’s Disease Vaccine

PIC Update: March 2011

November 30, 1999


Marek’s disease (MD) is a viral disease of chickens often associated with the formation of tumours and immunosuppression. Based on some estimates, the annual losses to the global poultry industry due to this disease are between $1 and 2 billion. These losses are mostly due to condemnation and, more importantly, suppression of the chick’s immune system, a condition that predisposes the bird to secondary infections.

Vaccines are available to control this disease and almost all broilers, layers and breeders in North America are vaccinated against MD. However, Marek’s disease virus (MDV) is ubiquitous and there is evidence that it is increasingly gaining virulence, which may lead to breakdown of immunity generated by vaccines in vaccinated flocks. The challenge for the poultry industry is that there are no vaccines available to protect against new virulent strains of the virus. More importantly, it is thought that vaccines act as a driving force for evolution of MDV because vaccines, although protective against clinical disease, are not able to prevent shedding of the virus. When virus is shed to the environment, other birds may contract the virus from the environment and become infected.

Dr. Shayan Sharif and his research team at the University of Guelph have been developing new vaccine formulations that are able to control virus shedding and, at the same time, protect against virulent strains of MDV. From feathers, the team dissected out cellular and molecular mechanisms of immune response to the virus, since feather tissue is the main site for development and shedding of infectious viral particles.

Their findings? It was clearly demonstrated that both field and vaccine viruses elicited a robust immune response in feathers. However, despite the fact that cells of the immune system could enter the feather in order to fight off the virulent viruses present in the tissue, these cells were not able to eliminate the virus. This may be the root cause of the inability of the chicken’s immune system to prevent virus shedding.

It was also discovered that an immunological molecular mediator was present in feathers of vaccinated or infected chickens. When added to vaccine formulations, this molecular mediator conferred high protection against Marek’s disease. Protection of birds was also associated with a reduction in virus load in their tissues. Therefore, although this vaccine formulation is still experimental, it provides another line of defence against highly virulent strains of MDV. Finally, in collaboration with Dr. Robert Silva of the USDA’sAvian Disease and Oncology laboratory, USDA in Michigan, the team developed an assay that is able to distinguish a widely used vaccine strain, called CVI988/Rispens, from virulent strains of MDV. This will be a useful test for determining if vaccinated flocks have been infected with virulent MDV.

PIC’s Picks
By Tim Nelson, Executive Director

2011 is off to a flying start!
This year we’ve already seen an increased interest in the producer updates. Check out the PIC website ( for venues and dates for the next producer updates, and please register early online or call us to make sure we have numbers for catering early on.

This year’s Innovations Conference is moving to London (previously held in Niagara Falls), and will also bring a terrific learning opportunity back in front of farmers. With the new location comes a new format with an exciting lineup of hands-on practical workshops to start the proceedings and an excellent lineup of speakers to round off what promises to be an excellent couple of days – look out for details in Canadian Poultry magazine and on the PIC website.

PIC is involved in some exciting projects this year: developing a PAACO-certified poultry welfare auditing course, investigating the real cost of biosecurity, and looking into the effectiveness of electronic monitoring technology which, in the event of a disease outbreak, will aid in tracking farm service vehicles that may be carrying the disease and help to control it more quickly. We’re also working with students in the two poultry clubs at the University of Guelph to develop a video on planning and implementing a biosecurity management system on your farm.  

In late January, a group of decision makers from the four feather boards met to consider our long-term poultry research needs. It was clear from the meeting that a strategic investment in personnel and infrastructure is needed and we need to start soon if we are to keep abreast of the emerging issues that will challenge our industry over time. Industry is taking investment in scientific research seriously, which is why it’s all the more disappointing to read a recent National Scientific and Engineering Research Council (NSERC) media release stating that agriculture is no longer a priority for research investment. Please contact Tim Nelson at PIC for more information on this troubling development.

Finally, we’re always looking for farmers to get involved in our projects – those who have taken part in the past report that they learn a lot by being involved and generally have a lot of fun. For details of any of the above, or simply to find out how you can join PIC activities, call us at 519-837-0284 or e-mail