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AssigneesUsda, Boehringer Ingelheim GmbH
InventorsWilliam L. Mengeling, Ann Vorwald, Kelly Lager, Mike Roof, Kelly Burkhart, David E. Gorcyca
Estimating the term…
Substantially avirulent forms of atypical porcine reproductive and respiratory syndrome (PRRS) virus and corresponding vaccines are provided which result from cell culture passaging of virulent forms of PRRS. The resultant avirulent atypical PRRS virus is useful as a vaccine in that PRRS specific antibody response is elicited by inoculation of host animals, thereby conferring effective immunity against both previously known strains of PRRS virus and newly isolated atypical PRRS virus strains. The preferred passaging technique ensures that the virus remains in a logarithmic growth phase substantially throughout the process, which minimizes the time required to achieve attenuation.
In a method for attenuating a virus, said virus being culturable in cell culture, said method including the steps of successively replicating said virus through inoculation and replication of the virus in respective individual cell cultures until attenuation is achieved, each of said successive inoculations occurring after cytopathic effect is observed in a previously inoculated cell culture of said respective individual cell cultures, the improvement which comprises removing virus-containing samples from at least certain of said cell cultures while the virus is replicating at a logarithmic rate and prior to induction of cytopathic effects in said certain cell cultures, and inoculating the next respective cell culture passages with said samples, wherein said logarithmic rate refers to the time period in which the virus is replicating exponentially.
In a method for attenuating a virus, said virus being culturable in cell culture, said method including the steps of successively replicating said virus through inoculation and replication of the virus in respective individual cell cultures until attenuation is achieved, each of said successive inoculations occurring after cytopathic effect is observed in a previously inoculated cell culture of said respective individual cell cultures, the improvement which comprises removing virus-containing samples from at least certain of said cell cultures while the virus is replicating at a logarithmic rate and prior to induction of cytopathic effects in said certain cell cultures, and inoculating the next respective cell culture passages with said samples, wherein the period in which said virus is replicating at said logarithmic rate is determinable by the portion of a one-step growth curve in which the virus is replicating exponentially.
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