Sheep strain hosts

Viruses replicate only in living cells so the first viral vaccines were necessarily made in animals smallpox vaccine in the dermis of calves and sheep and rabies vaccines in the spinal cords of rabbits and the brains of mice. Such methods are no longer used in advanced vaccine production and the only intact animal hosts that are used are embryonated hens eggs. Almost all of the vims that is needed for viral vaccine production is obtained from cell cultures infected with vims of the appropriate strain. 

Heath, D.D., Zhang, L.H. and McManus, D.P. (2005) Short report inadequacy of yaks as hosts for the sheep-dog strain of Echinococcus granulosus or E. multilocularis. American journal of Tropical Medicine and Hygiene 72, 2 89-2 90. 

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