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Foreign Sources of Infection

To−Vi Nguyen

Foreign Infection

Preventable environmental source of infection Remove infectious material, epidemic outbreaks

disappear Ex. BSE & Kuru

Infectious Forms of Prion Diseases in Humans

Kuru Iatrogenic CJD ddVariant CJD

Kuru

Fore tribe from Papua New Guinea transmitted kuru through ritualistic cannibalism

Ate dead relatives Only exposed to infectious agent if they consumed

or came in contact with brain tissue or spinal fluid

Iatrogenic

Prion tainted human growth hormone and gonadotropin

Dura mater grafts Transplants of corneas obtained from people who

died of CJD Neurosurgical procedures in which ineffectively

sterilized depth electrodes or instruments were used

vCJD

Results from prions being transmitted from cattle with BSE to humans through consumption of contaminated beef products

All vCJD individuals were identified to express methionine methionine homozygously at codon 129 Except a single case of vCJD in a patient who was

heterozygous at codon 129 Raised possibility of a second wave of BSE related

deaths

Spread of BSE

Late 1970s, hydrocarbon solvent extraction method used in rendering offal was abandoned

Resulted in meat and bone meal with a much higher fat content Fed to cattle, sheep, pigs, and chickens

Allowed scrapie prions from sheep or low levels of bovine prions generated sporadically to survive the rendering process Resulted in widespread infection of cattle

CWD

White tailed deer and elk have developed CWD Only prion disease known in free ranging animals

Genetics vs. Environment

1930 High incidence of familial CJD in some families was known 60 more years would pass before significance was

appreciated Once shown to be an infectious disease, little attention

was paid to the familial form of the disease How do you think the course of scientific

investigation might have proceeded had transmission studies not been performed until after the molecular genetic lesion was discovered?

If we discovered the molecular genetic lesion before the transmission studies were performed, the prion concept may have been more readily accepted

Prion concept explains how a single disease can have a genetic or infectious etiology

Because the transmissibility was discovered first, there was more skepticism as to whether prions were a whole new infectious agent