Ten years ago, a group of scientists argued that unsterile injections played a role in the emergence of HIV in Africa (and that serial passage of the virus within syringes altered it in a way that made it more virulent and/or more transmissible, something which remains debated among virologists until now). As mentioned in the introduction, after studying this question for some time I came to the conclusion that they were right, that a substantial part of the early amplification of HIV-1 in central Africa occurred through the re-use of improperly sterilised syringes and needles, and that this mechanism was probably as important as the sexual amplification which we just reviewed. It will be impossible to prove this directly. But like a crown prosecutor who has not found the exact gun used in a crime, in the next three chapters we will assemble circumstantial evidence that would ultimately convince any jury. We will first examine how HIV but also HBV and HCV can be transmitted through injections.

Parenteral or iatrogenic

Parenteral is synonymous with injectable; it literally means to bypass the gut, by administering a drug (therapeutic or recreational) or blood product as an injection, either into a vein (IV), muscle (IM), the tissues underneath the skin (SC) or the skin itself (intradermal (ID)). Iatrogenic means during health care; the transmission of pathogens between intravenous drug users is not included in this latter definition, but non-injection modes of healthcare transmission are (for example, during an organ transplant or some other invasive procedure). In sub-Saharan Africa, there is much overlap between these two terms, parenteral and iatrogenic, because the continent has few drug addicts (such a habit is far too expensive) and few patients undergo invasive medical procedures during which a virus could be transmitted.