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Risk assessment on Human T-lymphotropic Virus transmission, part 2

20 Jun 2012

Following a request from the European Commission in August 2010, ECDC assessed the epidemiological history of Human T-lymphotropic Virus (HTLV) across the world, possible risks of HTLV transmission through transplantation of human tissues and cells, and possible measures to prevent such transmission.

HTLV infects a type of white blood cell called a T-cell or T-lymphocyte and HTLV types I and II can be transmitted through blood contact, breast feeding, sexual contact (less common for HTLV-II) and injecting drug use.  Transplanted tissues and cells as well as organs have been shown to transmit HTLV-I infection, too.

Testing for HTLV-I/II infection among most tissue and cell donors was discontinued in the United States while testing for HTLV type I is required for certain donors in the European Union (EU). The change of testing requirements thus raised the question on safety of tissues and cells imported from the United States (US). One major difference in transmission risk compared to many other blood-borne infections is the exclusive association between transmission and the presence of infected cells of lymphocyte origin in blood and tissues.

ECDC’s ad hoc expert panel considered the US classification that was used to decide which cell and tissue types should be tested as insufficient to remove the risk of HTLV transmission. Likewise, claims that tissue and cell processing remove the risk were considered difficult to evaluate without clear validation.

The ECDC ad hoc expert panel concluded that donor selection by risk factor exclusion is an inefficient strategy for reducing transmission risks. Moreover, donor review should not replace HTLV-I/II testing, particularly in the case of donors originating from endemic regions.

The literature review shows that tests are available which, if they received approval by the US Food and Drug Administration (FDA), would be technically suitable for testing tissue donations. This is illustrated by the fact that they are used in Europe and other parts of the world.

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