Download Foreign Sources of Infection

Foreign Sources of
Infection
To−Vi Nguyen
S
Foreign Infection
S Preventable environmental source of infection
S Remove infectious material, epidemic outbreaks disappear
S Ex. BSE & Kuru
Infectious Forms of Prion
Diseases in Humans
S Kuru
S Iatrogenic CJD
S ddVariant CJD
Kuru
S Fore tribe from Papua New Guinea transmitted kuru
through ritualistic cannibalism
S Ate dead relatives
S Only exposed to infectious agent if they consumed or came in
contact with brain tissue or spinal fluid
Iatrogenic
S Prion tainted human growth hormone and gonadotropin
S Dura mater grafts
S Transplants of corneas obtained from people who died of
CJD
S Neurosurgical procedures in which ineffectively sterilized
depth electrodes or instruments were used
vCJD
S Results from prions being transmitted from cattle with BSE
to humans through consumption of contaminated beef
products
S All vCJD individuals were identified to express methionine
methionine homozygously at codon 129
S Except a single case of vCJD in a patient who was
heterozygous at codon 129
S Raised possibility of a second wave of BSE related deaths
Spread of BSE
S Late 1970s, hydrocarbon solvent extraction method used in
rendering offal was abandoned
S Resulted in meat and bone meal with a much higher fat
content
S Fed to cattle, sheep, pigs, and chickens
S Allowed scrapie prions from sheep or low levels of bovine
prions generated sporadically to survive the rendering
process
S Resulted in widespread infection of cattle
CWD
S White tailed deer and elk have developed CWD
S Only prion disease known in free ranging animals
Genetics vs. Environment
S 1930 High incidence of familial CJD in some families was
known
S 60 more years would pass before significance was appreciated
S Once shown to be an infectious disease, little attention was
paid to the familial form of the disease
S 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?
S If we discovered the molecular genetic lesion before the
transmission studies were performed, the prion concept may
have been more readily accepted
S Prion concept explains how a single disease can have a
genetic or infectious etiology
S Because the transmissibility was discovered first, there was
more skepticism as to whether prions were a whole new
infectious agent