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Kuru (disease)

2007 Schools Wikipedia Selection. Related subjects: Health and medicine

   CAPTION: Kuru (disease)
   Classifications and external resources

     ICD- 10   A81.8
     ICD- 9    046.0
   DiseasesDB  31861
   MedlinePlus 001379
    eMedicine  med/1248

   Kuru (also known as laughing sickness due to the outbursts of laughter
   that mark its second phase) was first noted in New Guinea in the early
   1900s. By the 1950s, anthropologists and Australian government
   officials reported that kuru ("shaking death" in the language of the
   Fore) was rampant among the South Fore, a single census division of
   approximately 8,000 individuals within the Okapa subdistrict. This
   particular group partook in ritual acts of mortuary cannibalism, a
   tradition later determined to be responsible for the epidemic
   transmission of the disease.

   Kuru is now known to be a prion disease, one of several known
   transmissible spongiform encephalopathies. Understanding the structure
   and replication of the prion is crucial to interpreting the dynamics of
   kuru and the several other prion diseases which exist today.

   Knowledge of the dynamics of the disease has continued to grow, even
   though the disease all but disappeared with the termination of
   cannibalism in New Guinea. The onset of kuru led to a five-decade study
   of an unfamiliar disease. This particular disease serves as an example
   of the procedures scientists undergo in order to understand and
   appreciate all of the aspects of a disease and how potential therapies
   and solutions can be found.

Kuru among the South Fore

   Upon the death of an individual, the maternal kin were responsible for
   the dismemberment of the corpse. The women would remove the arms and
   feet, strip the limbs of muscle, remove the brains and cut open the
   chest in order to remove internal organs. Shirley Lindenbaum, one of
   the early kuru researchers, states that kuru victims were highly
   regarded as sources of food, because the layer of fat on victims who
   died resembled pork. Women also were known to feed morsels, such as
   human brains and various parts of organs, to their children and the
   elderly (Lindenbaum, 1979). It is currently believed that kuru was
   transmitted among the South Fore through participation in such
   cannibalism, although opportunistic infection through wounds when
   removing infectious tissue from the corpse can be assumed to be another
   cause, as not all cases can be explained by ingestion of infectious
   tissue.

   The kuru epidemic reached its height in the 1960s. Between 1957 and
   1968, over 1,100 of the South Fore died from kuru. The vast majority of
   victims among the South Fore were women. In fact, eight times more
   women than men contracted the disease. It later affected small children
   and the elderly at a high rate as well. The disproportion was later
   traced to the distribution of the corpse's remains between the sexes.
   The males got the "good" parts of the corpse, which usually consisted
   of the muscles and fatty organs. The females and children got the "bad"
   parts, which included the brain and the other less desirable parts.
   Thus, the women and children directly ingested the prion, leading to a
   much higher occurrence rate of Kuru.

   Lindenbaum and Vincent Zigas worked among the South Fore in New Guinea
   trying to identify and catalog the symptoms and possible behaviour
   causing the disease. Daniel Carleton Gajdusek also traveled there in
   1957, to study disease patterns in traditional and isolated populations
   (Gajdusek, 1996). Lindenbaum, Zigas, and Gajdusek were all crucial to
   explaining the specifics of kuru to the rest of the world.

Symptoms of kuru

   In Daniel Gajdusek's studies of kuru, he found the condition of kuru
   victims to be an upsetting sight. "To see them, however, regularly
   progress to neurological degeneration in three to six months (usually
   three) and to death is another matter and cannot be shrugged off."
   (Gajdusek, 1996:10) Gajdusek reported three main stages in the
   progression of symptoms:
    1. The ambulant stage, with unsteadiness of stance, gait, voice,
       hands, and eyes; deterioration of speech; tremor; shivering; loss
       of coordination in lower extremities that moves slowly upward; and
       dysarthria (slurring of speech).
    2. The sedentary stage: patient can no longer walk without support,
       more severe tremors and ataxia (loss of coordination of the
       muscles), shock-like muscle jerks, emotional lability, outbursts of
       laughter, depression, and mental slowing. It is important to note
       that muscle degeneration has not occurred in this stage, and tendon
       reflexes are usually still normal.
    3. The terminal stage, which is marked by inability to sit up without
       support; more severe ataxia, tremor and dysarthria (slurring of
       speech); urinary and fecal incontinence; difficulty swallowing (
       dysphagia); and deep ulcerations appear. Cerebellar dysfunction is
       the cause of these conditions.

   These symptoms are common among prion diseases, such as
   Creutzfeldt-Jakob disease (CJD).

Misinterpretations of kuru

   Scholars who first studied the disease had two major misconceptions
   concerning its nature. They first incorrectly postulated that it was a
   genetic disorder, as it had a tendency to occur among family members.
   This possibility was eventually ruled out because kuru was too common
   and too fatal (Lindenbaum, 1979) — such a lethal genetic disorder would
   drastically reduce the fitness of a population and soon die out of the
   gene pool.

   Gajdusek conducted studies on chimpanzees injected with brain material
   from a victim. These studies led scientists to hypothesise that the
   agent was a slow virus, because the chimps developed a very similar
   condition after a long incubation period. Gajdusek defined a slow virus
   as a viral disease with an abnormally long incubation period. In
   humans, kuru had an incubation period with a minimum of two years and
   maximum of twenty-three (Gajdusek et al., 1966). Later studies showed
   the slow virus hypothesis to be a misinterpretation as well. Gajdusek’s
   results, however, confirmed the infectious, transmissible nature of the
   prion.

The prion protein

   All known prion diseases are fatal. Such diseases are often called
   spongiform encephalopathies, because they frequently cause the brain to
   become spongy, that is, riddled with holes (Prusiner, 1995). Well known
   prion diseases include scrapie, bovine spongiform encephalopathy (BSE
   or mad cow disease) and Creutzfeldt-Jakob disease (CJD). Less
   well-known prion diseases include the transmissible mink
   encephalopathy, chronic wasting disease, feline spongiform
   encephalopathy, exotic ungulate encephalopathy,
   Gerstmann-Sträussler-Scheinker syndrome (GSS) and fatal familial
   insomnia (Krakauer et al., 1997). Five of these affect humans:
   Creutzfeldt-Jakob disease, Gerstmann-Strässler-Scheinker syndrome,
   fatal familial insomnia, mad cow disease, and kuru. The most common
   form of prion disease is scrapie, expressed in sheep and goats
   (Prusiner, 1995). According to Cohen et al. ( 1994), prions cause a
   variety of degenerative neurologic diseases that can be infectious,
   inherited or sporadic in origin. The cause of the sporadic forms is
   unknown; inherited forms are caused by up to twenty different mutations
   of the human PRNP gene; and the infectious forms are transmitted
   through contact with or consumption of previously infected tissues
   (Prusiner, 1997).

   The exact nature of kuru perplexed scholars for decades after the
   discovery of the ailment, until Stanley B. Prusiner identified and
   defined prion diseases in 1982 (Prusiner, 1995). Prusiner ( 1991)
   classified a prion as an infectious particle composed of a protein that
   causes neurodegenerative disorders. According to Cashman (1997), prions
   are infectious agents by biological and medical criteria. However, they
   are also fairly unique, and properties of prions differ from those of
   conventional microbes.

   Scientists have worked on the prion puzzle since the 1950s, with
   microbiologists and epidemiologists having been confused by them.
   Advancements have been made, particularly in the 1990s, as evidenced by
   Prusiner receiving the Nobel Prize for Physiology or Medicine in 1997.
   However, it is still difficult to detect prion infection, track its
   transmission and type the different strains (Cashman, 1997). The Fore's
   long struggle with kuru serves as a poignant example.

Acknowledgements

     * This article was adapted with permission from a report "Kuru: The
       dynamics of a prion disease", authored by Stacy McGrath.

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