Coinfection of Schistosoma (Trematoda) with Bacteria, Protozoa and Helminths

This review examines coinfection of selected species of Schistosoma with bacteria, protozoa and helminths and focuses on the effects of the coinfection on the hosts. The review is based mainly on tables that contain the salient information on the coinfecting organisms in vertebrate hosts. Further explanation and clarification of the tables are given in the text. A table is also provided that gives synoptic information on the 37 species in the 19 genera considered in this review. Coinfection studies with Schistosoma species and the other organisms were considered in six tables plus the accompanying text. Considerations of the Schistosoma interactions with another species of organism include studies on coinfection with Plasmodium, with protozoa other than Plasmodium; with Salmonella, with bacteria other than Salmonella; and with Fasciola, with helminths other than Fasciola. Numerous factors were found to influence the effects of coinfection on the vertebrate host, including organisms and hosts used in the studies, order and time interval between the first and the second infection, studies on natural versus experimental hosts, dosage of the infectious agents, strains and pedigrees of the parasites, age of hosts at time of exposure to the infectious agents and age of hosts at the time of necropsy. Overall, a prior infection with Schistosoma, particularly a patent infection, often has an effect on the subsequent infection by a protozoan, bacterium or other helminth. In relatively few cases, a prior infection with Schistosoma decreased the severity of the subsequent infection as with Helicobacter pylori, Fasciola hepatica, Echinostoma or Plasmodium, the latter only exhibiting this behaviour when coinfected with Schistosoma haematobium. More often, however, a prior infection with Schistosoma increased the severity of the second infection as with Leishmania, Toxoplasma gondii, Entamoeba histolytica, Staphylococcus aureus or Salmonella. In some of these coinfection studies, the increased severity of the subsequent infection was associated with a specific, prolonged form of the disease in humans, which has implications for patient treatment and recovery. Additional research is needed, particularly on Schistosoma coinfections which currently have a small body of research and are current problems in human populations. Examples of such Schistosoma interactions include the genera of Mycobacteria, Leishmania, Staphylococcus, Necator and Strongyloides. Hopefully, future studies will elucidate valuable new information on the interesting subject of coinfection of Schistosoma with other organisms.