Cessation of Breeding and Burnout

If a virus possesses the ability to induce an immune response in the host animal strong enough to eliminate the virus and protect against reinfection as well as an infectivity that high, that a prevalence of 100% can be reached in the colony, the virus may be eliminated from breeding colonies by a time break in all breeding procedures. The principle is that all animals gets infected and develop protective immunity, and until this has happened, no naive animals are introduced. This has been successful for especially coronaviruses in rats223 and mice.224 The period from the last births before the break until the first matings after the break should be at least 6 weeks. This method is definitely not applicable for immune-deficient rodents, such as nude or SCID mice, and in relation to transgenic animals, caution should be taken, as viruses may behave abnormally in these animals and, e.g., develop persistent states or immunity may not develop.225 The same principles may eventually be applied in experimental facilities by not taking in new animals for a period of 6 weeks. This is called burnout. None of these methods are applicable for bacterial infections, as these are generally persistent.

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