PROTECTION OF MICE AND LAMBS AGAINST PANTROPIC RIFT VALLEY FEVER VIRUS WITH IMMUNE SERUM

Immune serum was used prophylactically and therapeutically in mice and lambs infected with Rift Valley fever virus. One-tenth milliliter of immune serum was effective in protecting mice against challenge with Rift Valley fever virus for a period of two weeks but not three weeks. A high percentage of mice receiving immune serum within 15 hours after the inoculation of 10 to the 4th power MIPLD50 of virus were protected. When serotherapy was administered to mice 11 to 25 hours after challenge, pathogenesis was altered so that the usual pantropic nature of the virus was masked and a neurotropic propensity appeared. This was demonstrated by delayed deaths, symptoms involving the central nervous system, and high titers of virus in the brain of the mice. Serotherapy was also effective in one- to three-day-old lambs infected with Rift Valley fever virus. Protection was demonstrated when immune serum was administered after the appearance of viremias and clinical signs of illness. All surviving lambs that received serotherapy were immune to a challenge infection approximately 30 days later.