Rinderpest was one of the first diseases to be recognized as being caused by a filterable virus. It is now classified as a paramyxovirus in the genus Morbillivirus , whose terrestrial members - bovine rinderpest, canine distemper and human measles viruses - have been chronicled for centuries as virulent plagues of their host species.

In contrast, the fourth terrestrial morbillivirus - peste des petits ruminants (PPR) virus - was only recognized in the 1940s. At first the PPR virus was thought to be a variant of rinderpest virus, but it has now been identified as a distinct member of the genus (Gibbs et al ., 1979). Since 1987 a clutch of previously unknown morbilliviruses has emerged and plagued populations of marine mammals such as seals, porpoises and dolphins in the Northern Hemisphere. More recently, morbillivirus antibodies - although not disease - have been detected in the sera of Atlantic pinniped and many cetacean species (Duignan et al ., 1994).

The most-studied and best-known morbilliviruses not only look alike but they also have similar physico-chemical properties, produce similar cytopathic effects in cell cultures and share antigens. They are all negative single-stranded, non-segmented ribonucleic acid (RNA) viruses possessing six structural proteins and two non-structural proteins (Diallo, 1990). Sequence analyses of parts of the F protein gene of rinderpest virus have revealed distinct lineages of the virus that reflect the geographical location of then-isolation in Africa and Asia.

Disease is most commonly observed in domestic ungulates, particularly buffaloes and cattle. Sheep are reported to contract mortal rinderpest in India, but elsewhere the disease has been recognized in this species only sporadically; the common rinderpest-like disease of sheep in southern India may be PPR.

In contrast, in northern equatorial Africa and the Near East, overt disease from PPR is more frequently observed in goats. The Asian domestic sway-backed pig suffers from and succumbs to rinderpest, while European pigs experience inapparent infections when exposed experimentally.

The first demonstration of natural infection in European-type pigs was belatedly reported from Egypt in 1991; blood samples were collected from 128 pigs slaughtered in 1982, when severe outbreaks of rinderpest were affecting Egyptian buffaloes and cattle. Rinderpest neutralizing antibodies were detected in the sera of 36 (28 percent) pigs (Youssef et al ., 1991).

Fulminating peracute infections occur in free-ranging African buffalo, eland, kudu and warthog. Acute infections that usually end fatally have been observed in Africa in bongo, bushbuck, bush pig, chevrotain, dik-dik, duiker, giant forest hog, giraffe, sitatunga and wildebeest, and in Asia in banteng, blackbuck, gaur, nilgai and sambar.