SUPPLEMENTAL UPDATE, 1980

Model Number 20

Slow Infection by Unconventional Viruses

Human Disease: Creutzfeldt-Jakob

Disease, Kuru

Animal Model: Scrapie, Transmissible

Mink Encephalopathy

Contributed by: R. F. Marsh, DVM, Department of Veterinary Science,

University of Wisconsin, Madison, WI 53706

Biologic Features

Since Sigurdsson’s original description of slow infections,’ it has been

recognized that these types of diseases which are produced by viruses

may be subdivided into two general groups depending on whether they

are caused by conventional or unconventional agents. The latter group

of slow virus infections comprise two which affect humans: Creutzfeldt-

Jakob disease and kuru; and three affecting animals: scrapie, transmis-

sible mink encephalopathy (TME), and the newly recognized chronic

wasting disease of captive mule deer.2 Although the human diseases have

been transmitted to several animal models, scrapie remains the animal

model of choice for the study of the spongiform encephalopathies be-

cause its models are better characterized and represent a lesser human

health hazard. Additionally, one of the advantages of the study of scra-

pie is the availability of several choices of models, each offering indi-

vidual features which can be manipulated to examine different aspects

of the disease:

1)

Hamster. The major strengths of this model are the short incuba-

tion periods (8 weeks) and high brain titers of infectivity (l0’°LD50/

gram) which allow for faster endpoint titrations measuring the trans-

missible agent.3’4 This remains necessary because of the lack of a cell

culture assay and the absence of any specific immune response in in-

fected animals. The hamster has also been found to be a useful model

for the study of scrapie-induced retinopathy.5

2)

Mouse. Although the hamster has for the most part replaced the

mouse bioassay, the mouse model remains important for the study of

agent-host interactions. By evaluating the responses of different inbred

strains of mice to inoculation with various sources of scrapie, it has been

For reference citation — Marsh, R. F.: Slow viral Infections, Model No. 20, Supplemental Update,

1980. In Handbook: Animal Models of Human Disease. Fasc. 2. Edited by C. C. Capen, D. B.

Hackel, T. C. Jones and 0. Migaki. Registry of Comparative Pathology, Armed Forces Institute of

Pathology, Washington, DC (1980).