3)

Mink. TME occurs as a result of mink being fed scrapie-infected

sheep or goat tissues.8 The most important contribution of the mink

model of scrapie disease has been to further our knowledge on the de-

velopment of spongiform degeneration in the brain. These diseases are

all characterized pathologically by microvacuolation of the neuropil

(Figure 1A) accompanied by reactive astrocytic hypertrophy (Figure 1B).

Ultrastructurally, the vacuolation is produced by dilations in axons and

nerve cell bodies (Figure 1C). However, studies on TME in mink homo-

zygous for the Aleutian gene have shown conclusively that the spongi-

form degeneration is a secondary effect of the disease process and prob-

ably produced by lysosomal enzymes.’° Therefore, the only primary le-

sion remaining is neuronal degeneration (Figure 2), but the method of

cell injury remains unknown.

Significance to Creutzfeldt-Jakob Disease

Studies on the animal models of scrapie and TME will provide critical

information on the biophysical nature of these pathogens and on their

mechanisms of infection and progression in the host. These results can

then be applied to animal models of the human disease and, eventually,

to infected human tissues.

References

1.

Sigurdsson B: Observations on three slow infections of sheep. I. Maedi, slow pro-

gressive pneumonia of sheep: Epizootiological and pathological study. II. Para-

tuberculosis (Johne’s disease) of sheep in Iceland: Immunological studies and ob-

servations on its mode of spread. III. Rida, chronic encephalitis of sheep, with

general remarks on infections which develop slowly and some of their special char-

acteristics. Brit Vet J 110:7-9, 225-270, 307-322, 341-354, 1954

2.

Williams E S, Young S: Chronic wasting disease of captive mule deer: A spongi-

form encephalopathy. J Wildi Dis, 16:89-98, 1980

3.

Kimberlin R H, Walker C A: Characteristics of a short incubation model of scrapie

in the hamster. J Gen Virol 34:295-304, 1977

Fig 2— Neuronal degeneration in brain stem of a mink with transmissible mink enceph-

alopathy. (H&E, x 800.)