S
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