Abstract
Many pathogens of humans are blood borne, including HIV, Malaria, Hepatitis B and C, West Nile virus, Dengue, and other viral hemorrhagic fevers. Although several of these pathogens are transmitted by blood-feeding arthropods, HIV is not. A number of properties of HIV and its life cycle have been identified as proximate explanations for the absence of arthropod transmission, but little consideration has been given to why HIV has not evolved this form of transmission. We consider the empirical evidence for arthropod transmission, and suggest that mechanical transmission has not evolved in HIV because such strains would induce a faster onset of AIDS during infection, which would thereby limit their ability to spread. On the other hand, it is not as clear why biological transmission has not occurred. Available data suggests that a lack of appropriate genetic variation in HIV is one explanation, but it is also possible that a conflict between natural selection occurring within and between infected individuals has prevented its evolution instead. We discuss the potential significance of these ideas, and argue that taking such an evolutionary perspective broadens our understanding of infectious diseases and the potential consequences of public health interventions.
Highlights
40 million people are infected with the human immunodeficiency virus (HIV) worldwide (UNAIDS 2006)
HIV transmission via arthropods was a serious concern upon the discovery of this virus
Experiments and epidemiological data have unequivocally demonstrated, that such vector transmission does not occur at any significant level, and various aspects of HIV biology have been implicated as proximate reasons (Bockarie and Paru 1996)
Summary
40 million people are infected with the human immunodeficiency virus (HIV) worldwide (UNAIDS 2006). It has been suggested that some Hepatitis viruses can be transmitted mechanically by arthropods (Jupp et al 1983), this has been controversial (Kuno 2004) Even if this does occur, the viral levels of HIV in humans are thought to be about 10 to 100 times lower than that of some hepatitis viruses (Foil and Issel 1991), again implicating HIVs low titre during infection a 2008 The Authors Journal compilation a 2008 Blackwell Publishing Ltd 1 (2008) 17–27 of humans as the primary reason that mechanical transmission does not occur in this virus. The calculations in Appendix 2 demonstrate that the factor by which vectors must increase the overall transmission rate of HIV, in order for the relative frequency of the mutant, p/(1 ) p), to increase by a factor of K over a period of T years, is given by
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