Ebola Zaire virus from the 1976 outbreak (EBO-Z) was recently adapted to the stage of lethal virulence in BALB/c mice through serial passage. In the present study, various parameters were examined in groups of mice and guinea-pigs and in three rhesus monkeys after infection with mouse-adapted EBO-Z. The virus caused fatal disease not only in mice but also in guinea-pigs, in which the course of illness resembled that produced by guinea-pig-adapted EBO-Z. Mice, guinea-pigs and monkeys showed similar haematological and biochemical disturbances, but coagulopathy was less striking in mice than in the other two species. The virus caused severe illness in all three monkeys, one of which died. In the lethally infected monkey the degree of viraemia and the haematological, serum biochemical and coagulation changes were greater than in the other two animals, an observation that may prove to be of value in predicting fatal outcome. All three monkeys developed disseminated intravascular coagulation. The two survivors were completely resistant to challenge one year later with non-adapted EBO-Z. In general, the clinical and pathological changes produced in the three species resembled those previously described in guinea-pigs and non-human primates infected with non-mouse-adapted EBO-Z. It was noteworthy, however, that mouse-adaptation appeared to have resulted in a degree of attenuation for monkeys.
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