Recent developments in the diagnosis of rinderpest and peste des petits ruminants

Effective implementation of control measures for rinderpest and peste des petits ruminants requires that a proper and rapid diagnosis of the disease is made. Peste de petits ruminants (PPR) can be confused clinically with other infections such as pasteurellosis or contagious ecthyma. Rinderpest, in its classical form, is easy to identify clinically; however, mass vaccination in many countries and also the emergence of mild strains of the virus have made clinical diagnosis more difficult. Clinical observations for both diseases should always be confirmed by a laboratory. Diagnostic techniques used in the past were virus neutralization, agar gel immunodiffusion and virus isolation in cell culture, followed sometimes by reproducing the disease in susceptible animals. All these techniques are either time-consuming, labour intensive, insensitive, or expensive to perform. With the advent of hybridoma and molecular biological techniques, new reagents to assist diagnosis have become available and have led to the development of specific and rapid tests for the diagnosis of each disease. The present article reviews the diagnostic techniques currently available. An indirect ELISA was used successfully to evaluate the status of cattle following the Pan African Rinderpest Campaign. More recently competitive or blocking ELISAs have been developed based on monoclonal antibodies specific for the N or H proteins of the viruses, and which enable differential diagnosis between rinderpest and PPR. This is particularly important in sheep and goats, which may be infected with either virus. In future, improved standardization and reduced costs may be expected with the introduction of ELISAs based on purified antigens expressed in gene vector systems such as baculovirus. ELISA may also be adapted to antigen detection. Nucleic acid technology has also been applied to virus detection procedures. Hybridization probes showed a disappointing sensitivity for diagnostic applications, but more recently the polymerase chain reaction method has shown great promise, providing the potential of high sensitivity combined with specificity.