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Isolation of highly cytolytic MDV strains from Germany and Spain
I Kross1, P J Davis, R W Shilleto
1Intervet UK Ltd, Houghton, Huntingdon, UK.
Abstract:
Four serotype 1 Marek's disease virus (MDV) strains were isolated from Marek's disease (MD) outbreaks in Germany and Spain and their virulence was tested in SPF White Leghorn chickens. Two of the isolates from Germany (MR48/1-2 and /2-8) induced early mortality from cytolytic MD in 25% of the chickens whereas one isolate from Germany (MR48/3-16) caused early mortality in 58% of the inoculated chickens. Histological examination showed severe depletion of the lymphoid tissue of the bursa of Fabricius and the thymus, consistent with the cytolytic phase of MD. AH surviving chickens later developed acute MD in the form of multiple visceral tumours. Inoculation of SPF chickens with various doses of the isolate MR36 8/1C (Spain) caused early mortality in up to 69% of the chickens and acute MD in 92 to 100% of the chickens surviving the cytolytic phase of the disease.
Insights
Marek
Area of Science:
- Veterinary Virology
- Avian Pathology
Background:
- Marek's disease (MD) is a significant lymphoproliferative disease in poultry.
- Serotype 1 Marek's disease virus (MDV) is the etiological agent responsible for MD outbreaks.
Purpose of the Study:
- To assess the virulence of newly isolated serotype 1 MDV strains from European outbreaks.
- To characterize the pathological effects of these MDV strains in specific-pathogen-free (SPF) chickens.
Main Methods:
- Isolation of four serotype 1 MDV strains from MD outbreaks in Germany and Spain.
- Virulence testing through inoculation of SPF White Leghorn chickens with different MDV isolates.
- Histological examination of lymphoid tissues (bursa of Fabricius, thymus) and assessment of mortality and tumor development.
Main Results:
- Two German MDV isolates caused 25% early mortality due to cytolytic MD.
- One German isolate induced 58% early mortality, with lymphoid depletion observed.
- A Spanish isolate caused up to 69% early mortality and acute MD in 92-100% of survivors.
Conclusions:
- The tested serotype 1 MDV strains exhibit varying degrees of virulence.
- These isolates can cause both cytolytic disease and subsequent tumor formation in chickens.
- Understanding MDV virulence is crucial for effective disease control strategies in poultry farming.
