WHO Guidelines on Tissue Infectivity Distribution in TSEs (2006) and WHO Tables (2010)

This is WHO guidance, not law. The 2006 guidelines come from a WHO consultation of experts and regulators held in Geneva on 14 to 16 September 2005, which revised the 2003 TSE guidelines for biological and pharmaceutical products. Their purpose is to give national regulators, especially where BSE has not been reported and surveillance is weak, evidence for assessing the risk of transmitting variant CJD through blood, plasma products and other medicines. The core of the document is a sorting of tissues and fluids into three categories: high infectivity (IA), lower infectivity (IB) and no detectable infectivity (IC). The WHO Tables of 2010 update that sorting and add chronic wasting disease for the first time, while stating that the 2006 guidelines remain valid. The categories describe where infectious agent or abnormal prion protein has been found, not the size of the risk to a person. Information only, not regulatory or clinical advice.

Key facts

  • The 2006 guidelines were produced after a WHO consultation in Geneva on 14 to 16 September 2005 and carry a 2006 WHO copyright and ISBN.
  • Stated audience and aim: national regulatory authorities of WHO Member States, so they can carry out risk assessments and choose measures to reduce vCJD transmission through human blood, plasma products and other biologicals.
  • Three categories: IA high-infectivity tissues (central nervous system tissue that reaches high levels late in all TSEs, plus tissues anatomically tied to it), IB lower-infectivity tissues (peripheral tissues positive for infectivity or abnormal prion protein in at least one TSE), IC tissues examined with negative results.
  • The 2010 Table IA lists brain, spinal cord, retina, optic nerve, spinal and trigeminal ganglia, pituitary gland and dura mater; pituitary and dura mater are kept in the high category because contaminated cadaver-derived products have transmitted disease to many people.
  • Both documents say categories of infectivity are not categories of risk: risk also depends on the amount of tissue and the route. Tissue level matters most for instrument contamination in surgery, but is only one factor for transfusion (large volume of low-infectivity material into the circulation) and for food (inefficient oral route).
  • The tables rely only on naturally occurring disease or primary oral infection in ruminants, not laboratory-adapted strains, and show abnormal prion protein results alongside bioassay results.
  • For medicines, the 2006 text asks for a product-level risk assessment covering source of starting materials, manufacturing process and clinical use, and prefers avoiding ruminant materials, or using sources from countries with negligible BSE risk.
  • Its conclusion declines to set one global policy on blood donor measures; each country should analyse its own situation and weigh effects on blood supply.
  • The 2010 Tables (WHO/EMP/QSM/2010.1, 21 pages) cover human sporadic and variant CJD, cattle with typical and atypical BSE, sheep with scrapie, and deer and elk with chronic wasting disease.
  • Since the 2006 Annex 1, ovary, uterus, mammary gland/udder, skin, adipose tissue, heart/pericardium, saliva, milk, urine and feces were moved from no detectable infectivity to lower infectivity.
  • The 2010 text warns that results from amplification assays or over-expressing transgenic mice may fall below the level that transmits to normal animals and humans, and expects more tissues to move from IC to IB but probably none into IA.
  • Downstream, national tissue-risk tables for infection control cite the 2006 categories (Canadian and Australian examples seen in search excerpts only, not verified in full).

Timeline

  1. 2003First of three probable transfusion-transmitted vCJD infections identified, cited in 2006 as a reason for revision.
  2. 2005WHO consultation in Geneva, 14 to 16 September, revises the 2003 guidelines.
  3. 2006Guidelines published (WHO copyright 2006); WHO web page lists 16 September 2006.
  4. 2010WHO Tables on Tissue Infectivity Distribution listed on 30 October 2010, adding chronic wasting disease and moving several tissues to lower infectivity.

Last checked 1 November 2026

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