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Increased cVi988 vaccine use credited with decline in Marek's disease

Increased use of CVI988/Rispens vaccines is credited with declines in the incidence of Marek's disease3 (MD), according to investigators from USDA's Agricultural Research Service.

A questionnaire was widely distributed in 2011 to estimate the global prevalence of MD. Responses representing 116 countries were obtained from numerous sources, including national branch secretaries of the World Veterinary Poultry Association, Marek's disease researchers and vaccine, breeder and production companies.

All flock types in nearly 50% of countries reportedly experienced an increased incidence of MD during the last 10 years, according to at least one respondent, with most of these countries located within French-speaking Africa, Eastern Europe, East Asia and South America. The most common explanation for the increased incidence was the presence of other immunosuppressive diseases, say John Dunn and I.M. Gimeno in the June 2013 issue of Avian Diseases.

"Increased use of CVI988/Rispens was cited as the most likely reason for [the] decreasing MD incidence in 49 countries," the scientists concluded.

In the US, the incidence of MD has decreased over the past 10 years, reaching a record low in 2007 of 0.0008% as measured by leukosis-condemnation rates in broilers at slaughter, the investigators say. They note, however, that there was a recent increase in leukosis condemnations in North Carolina and Pennsylvania that needs to be closely monitored.