Lapinised rinderpest virus and a vaccine: Some observations in East Africa: I. Laboratory experiments

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Summary The findings of Cheng and Fischman (1948) have been confirmed at Kabete. The Nakamura strain III of lapinised rinderpest virus was also “fixed” for the local breeds of rabbits and during 21 passages at Kabete there was no increase in virulence for rabbits, or attenuation of the antigenic properties for cattle. Freeze-drying of the major virus-containing tissues of rabbits ensured the maintenance of the virus and dried material or “seed-virus” remained viable for long periods when kept under optimum conditions. The symptoms and post-mortem findings of infected rabbits at Kabete have closely simulated those reported by other workers. It was noted that the temperatures of normal rabbits kept under laboratory conditions were slightly lower than those generally accepted. Rabbits below the age of 4 1/2 months did not react thermally when injected with the virus, but showed lesions typical of rinderpest; pregnant does were also unsuitable subjects for the propagation of the virus. Alternate passage of the virus in cattle and rabbits appeared to alter the character of the virus, which showed a decreased virulence for rabbits with an irregular and somewhat increased virulence for cattle. Co-habitation of infected rabbits with non-infected rabbits and infected cattle with susceptible cattle, did not result in passage of the virus by contact to the susceptible animals. In contra-distinction to goat-adapted virus, lapinised virus provoked a very mild reaction in high and medium grade cattle at Kabete which could not be readily recognised. The development of an immunity in cattle so inoculated could not be determined until challenged with virulent rinderpest virus. The immunity induced by the injection of lapinised virus in susceptible cattle was sufficient to prevent clinical symptoms of rinderpest after challenge with Kabete bovine virus. Lapinised virus induced a serviceable protection in cattle challenged 84 hours and at 108 hours respectively, after inoculation.