In recent years, infectious diseases has jumped from the animal kingdom onto human terrain with higher prevalence and lethal consequences, prompting the science world to investigate causes for this terrible outbreak. Emerging infectious diseases are those which occur in new populations or places, are reintroduced or newly introduced, or become highly virulent or resistant to certain treatments. Typically, emerging infectious diseases arise for multiple reasons, spanning from deforestation to human behavior, and entail certain harm for their host species, or the species which contains the infectious pathogen.
Jonathan Davies, a scientist at UCSB’s National Center for Ecological Analysis and Synthesis (NCEAS) and Amy Pederson, a research fellow at the University of Sheffield addressed the growing risk of emerging infectious disease in an analysis showing how both the proximity and similarities between species can determine the communicability of a pathogen between various hosts. “Infectious diseases crossing species barriers pose a huge and increasing threat to human health and the conservation of wild species,” said Davies. “The critical question we investigated is what determines the breadth of host species that a pathogen can infect.”
Published in this week’s Proceedings of the Royal Society B, the team’s research explains that “host shifts” from animal reservoirs to humans typically occur between closely related species with similar biological make-ups and immune responses. Such was the case with Simian Immunodeficiency Virus (SIV) in primates which crossed over to humans as Human Immunodeficiency Virus (HIV), theoretically during the preparation of chimpanzee meat, or “bush meat.”
However, Davies and Pederson said pathogens traverse genetic borders with astounding ease, suggesting that location rather than genetics plays a greater role in host shifts. “Viruses are more adept at jumping between distantly related host species, so that geographical proximity rather than evolutionary relatedness determines the spread of viral diseases,” said Davies.
Viral disease like Bird Flu, West Nile Virus, and Hendra Virus, which affect birds and bats, respectively, now affect humans and - as Pederson predicts - may only be the tip of the iceberg. Because of urban expansion, humans are more exposed to wild animals and their pathogens.
“We suggest hotspots of future emerging diseases may be found where humans come into close proximity with wild primates, as is increasingly the case in the forests of Central and West Africa due to rapidly growing human populations and scarcity of resources in this region,” said Pederson. “In addition, we are likely to see an increase in outbreaks of novel viral diseases as humans invade previously isolated habitats, and these may be just as likely to jump from a rat or a bat, as an ape.”
Fortunately, the ability to predict host shifts can help limit the incidence of outbreaks and/or minimize the resulting mortality, morbidity and financial expenses.