Parasitology

Original Articles

HIV-1/parasite co-infection and the emergence of new parasite strains

JAMES O. LLOYD-SMITHa1 c1, MARY POSSa1 and BRYAN T. GRENFELLa1a2

a1 Center for Infectious Disease Dynamics, Pennsylvania State University, 208 Mueller Lab, University Park PA, 16802, USA

a2 Fogarty International Center, US National Institutes of Health, Bethesda MD, 20892, USA

SUMMARY

HIV-1 and parasitic infections co-circulate in many populations, and in a few well-studied examples HIV-1 co-infection is known to amplify parasite transmission. There are indications that HIV-1 interacts significantly with many other parasitic infections within individual hosts, but the population-level impacts of co-infection are not well-characterized. Here we consider how alteration of host immune status due to HIV-1 infection may influence the emergence of novel parasite strains. We review clinical and epidemiological evidence from five parasitic diseases (malaria, leishmaniasis, schistosomiasis, trypanosomiasis and strongyloidiasis) with emphasis on how HIV-1 co-infection alters individual susceptibility and infectiousness for the parasites. We then introduce a simple modelling framework that allows us to project how these individual-level properties might influence population-level dynamics. We find that HIV-1 can facilitate invasion by parasite strains in many circumstances and we identify threshold values of HIV-1 prevalence that allow otherwise unsustainable parasite strains to invade successfully. Definitive evidence to test these predicted effects is largely lacking, and we conclude by discussing challenges in interpreting available data and priorities for future studies.

(Received October 24 2007)

(Revised December 23 2007)

(Accepted January 10 2008)

(Online publication March 27 2008)

Correspondence:

c1 Corresponding author. Tel: +1-814-863-9545. Fax: +1-814-865-9131. E-mail: jlloydsmith@psu.edu

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