SIVagm incidence over two decades in a natural population of Ethiopian grivet monkeys (Cercopithecus aethiops aethiops).

The incidence of SIVagm seropositivity in a natural population of Ethiopian grivet monkeys (Cercopithecus aethiops aethiops) is investigated using plasma samples collected in 1973, and shown to be similar to that reported from the same population in 1990-91. Results tend to support our previous conclusions: endemic SIVagm has little or no impact on the survival of wild grivet monkeys, and the virus is transmitted almost always by sexual contact, occasionally by trauma, and rarely if ever maternally. Small differences between 1973 and 1990-93 suggest that the stress of drought years may raise the incidence of traumatic transmission, and temporarily depress transmission by sexual activity, in this population.