Global prevalence or incidence of coinfection among humans is unknown, but it is thought to be commonplace,[1] sometimes more common than single infection.[2] Coinfection with helminths affects around 800 million people worldwide.[3]
Coinfection is of particular human health importance because pathogen species can interact within the host. The net effect of coinfection on human health is thought to be negative.[4] Interactions can have either positive or negative effects on other parasites. Under positive parasite interactions, disease transmission and progression are enhanced and this is also known as syndemism. Negative parasite interactions include microbial interference when one bacterial species suppresses the virulence or colonisation of other bacteria, such as Pseudomonas aeruginosa suppressing pathogenic Staphylococcus aureuscolony formation.[5] The general patterns of ecological interactions between parasite species are unknown, even among common coinfections such as those between sexually transmitted infections.[6] However, network analysis of a food web of coinfection in humans suggests that there is greater potential for interactions via shared food sources than via the immune system.[7]
A globally common coinfection involves tuberculosis and HIV. In some countries, up to 80% of tuberculosis patients are also HIV-positive.[8] The potential for dynamics of these two infectious diseases to be linked has been known for decades.[9] Other common examples of coinfections are AIDS, which involves coinfection of end-stage HIV with opportunistic parasites[10] and polymicrobial infections like Lyme disease with other diseases.[11] Coinfections sometimes can epitomize a zero sum game of bodily resources, and precise viral quantitation demonstrates children co-infected with rhinovirus and respiratory syncytial virus, metapneumovirus or parainfluenza virus have lower nasal viral loads than those with rhinovirus alone.[12]
^Petney, TN; Andrews, RH (1998). "Multiparasite communities in animals and humans: frequency, structure and pathogenic significance". International Journal for Parasitology. 28 (3): 377–93. doi:10.1016/S0020-7519(97)00189-6. PMID9559357.
^Shrestha, S. (2011). "Influence of host genetic and ecological factors in complex concomitant infections – relevance to sexually transmitted infections". Journal of Reproductive Immunology. 92 (1–2): 27–32. doi:10.1016/j.jri.2011.09.001. PMID22019002.