title: Difficulties in demonstrating long term immunity in FeLV vaccinated cats due to increasing age-related resistance to infection.
abstract: BACKGROUND
  Feline leukaemia virus (FeLV) is a pathogen causing fatal illness in cats worldwide, and as such there is a high demand for products to protect against disease. The duration of immunity provided by an inactivated FeLV vaccine, Versifel FeLV, when administered to cats of the target age was determined. Kittens received two vaccinations when aged 7 to 9 weeks old, and were subsequently challenged up to 36 months later with the FeLV-A Glasgow isolate.
  
  
  RESULTS
  In all studies, all of the younger aged control kittens showed persistent FeLV p27 antigenaemia confirming that the challenge virus was severe and efficacious. In contrast, the control cats did not show the required level of persistent antigenaemia, with a maximum of 45% cats affected in the middle duration study and only 10% in the longer study. However, apart from one animal in the short duration study, all of the cats vaccinated with Versifel FeLV were negative for persistent antigenaemia and can be considered treatment successes.
  
  
  CONCLUSIONS
  In conclusion, we have shown that although age-related resistance to infection with a virulent FeLV challenge is evident from as early as 10 months of age, vaccination with Versifel FeLV may aid in the protection of cats from FeLV related disease up to three years after primary vaccination as kittens.
authors: Veterinary Medicine Research and Development, Pfizer Animal Health, Pfizer European Service Centre, Zaventem, Belgium. Stephen.wilson@pfizer.com
authors: Stephen
authors: S
authors: Wilson
authors: Juliet
authors: J
authors: Greenslade
authors: Gillian
authors: G
authors: Saunders
authors: Catherine
authors: C
authors: Holcroft
authors: Lynn
authors: L
authors: Bruce
authors: Andy
authors: A
authors: Scobey
authors: Tedd
authors: T
authors: Childers
authors: Gordon
authors: G
authors: Sture
authors: James
authors: J
authors: Thompson
mesh_terms: D000375:Aging / Q000276:immunology*; D000818:Animals; D000956:Antigens, Viral; D002415:Cats; D005256:Leukemia Virus, Feline / Q000276:immunology*; D016582:Leukemia, Feline / Q000517:prevention & control*; D018809:Proliferating Cell Nuclear Antigen / Q000097:blood; D015164:Vaccines, Inactivated / Q000276:immunology; D014765:Viral Vaccines / Q000276:immunology*
chemical_list: D000956:Antigens, Viral; D018809:Proliferating Cell Nuclear Antigen; D015164:Vaccines, Inactivated; D014765:Viral Vaccines; C413374:p27 antigen