Risk factors for human disease emergence

A comprehensive literature review identifies 1415 species of infectious org anism known to be pathogenic to humans, including 217 viruses and prions, 5 38 bacteria and rickettsia, 307 fungi, 66 protozoa and 287 helminths. Out o f these, 868 (61%) are zoonotic, that is, they can be transmitted between h umans and animals, and 175 pathogenic species are associated with diseases considered to be 'emerging'. We test the hypothesis that zoonotic pathogens are more likely to be associated with emerging diseases than nonemerging o nes. Out of the emerging pathogens, 132 (75%) are zoonotic, and overall, zo onotic pathogens are twice as likely to be associated with emerging disease s than non-zoonotic pathogens. However, the result varies among taxa, with protozoa and viruses particularly likely to emerge, and helminths particula rly unlikely to do so, irrespective of their zoonotic status. No associatio n between transmission route and emergence was found. This study represents the first quantitative analysis identifying risk factors for human disease emergence.