ANIMAL SPONGIFORM ENCEPHALOPATHIES - AN UPDATE .1. SCRAPIE AND LESSERKNOWN ANIMAL SPONGIFORM ENCEPHALOPATHIES

The present article (part I) reviews recent developments in animal spo ngiform encephalopathies (SEs), with the exception of bovine spongifor m encephalopathy (BSE), which is dealt with in part II. The article fo cuses on scrapie and describes epidemiological aspects and the prospec ts for a preclinical diagnosis. Up to now, confirmatory diagnosis of s crapie depended on histological examination of the brain, collected du ring post-mortem examination from sheep with clinical signs of the dis ease. An altered protein, PrPSC, can be detected in the brain of disea sed animals. The demonstration of the same protein in the spleen and i n peripheral lymph nodes of infected animals seems to offer interestin g possibilities of arriving at a method for a preclinical diagnosis, a nd thus a diagnosis in the live animal. Progress has also been made in our understanding of the relationship between the genetic constitutio n and susceptibility of the host. Susceptibility is expressed as the s urvival time of sheep inoculated with scrapie. This was thought to be determined by a single genetic locus designated the Sip gene (scrapie incubation period gene). Putative markers for the two alleles of the S ip gene, sA and pA, have been discovered, consisting of restriction fr agment length polymorphisms (RFLPs). In field tests, however, the link between these markers and the length of incubation time was far from consistent. These RFLPs were found to be situated outside the prion-pr otein-coding region of the ovine gene. In later studies, RFLPs were de tected inside this region. These markers appear to be more informative , i.e. they correspond with a difference in the length of the scrapie incubation period. Finally, the article briefly describes recent devel opments in other, lesser known, animal spongiform encephalopathies: ch ronic wasting disease and other spongiform encephalopathies in exotic ungulates, transmissible mink encephalopathy, and feline spongiform en cephalopathy, focusing on their possible links with scrapie or bovine spongiform encephalopathy.