Experimental infection with Murray Valley encephalitis virus: galahs, sulphur-crested cockatoos, corellas, black ducks and wild mice.

Abstract

Orally infected Culex annulirostris or intravenous injections were used to infect 10 Galahs, 15 Sulphur-crested cockatoos, 12 Corellas, 4 Black ducks and 10 wild mice with Murray Valley encephalitis (MVE) virus. The birds produced moderate viraemias of titres of log 10(2.0)-10(6.0) suckling mouse intracerebral (SMIC) LD50/ml for durations of 1-9 d. However, the wild mice developed low grade viraemia for 1-4 d. Recipient Cx annulirostris feeding on viraemic birds sustained infection rates of 0-10% but, by extrapolation from vector competence data, some titres were capable of infecting greater than or equal to 50% of recipient Cx annulirostris. HI antibody responses were moderately high for most birds (reciprocal titres of 1 in 640-2560) by 14 d and usually persisted at detectable levels for 140 d and, in some individuals, for 6 months. However, 6 of 12 Corellas and 1 of 4 Black ducks became seronegative after 42 and 56 d, respectively. As with previously tested animals, any IgM response was absent 4 wks post-infection. The viraemias attained indicate that these bird species may be considered as potential hosts of MVE, but the limited viraemic response of wild mice suggests that they might play only a minor role.