As the world continues to become more connected through travel, technology, and infrastructure, it is becoming easier for transmissible diseases to spread across countries rapidly. Controlling the spread of disease at the local level is highly difficult and the majority of the world is not prepared to combat outbreaks.
An important component to prepare for and prevent disease outbreaks is an understanding of the risk factors that impact disease spread. Most modern outbreaks can be traced back to animals, where a zoonotic spillover event occurred. A zoonotic spillover event is when another species transmits a disease to a human.
CEID member Maxwell Farrell worked with a research team to use a novel link-prediction method to analyze existing gaps in global disease preparedness and undocumented parasites that both humans and non-human primates share. Non-human primates (NHPs) include animals such as monkeys, apes, and lemurs.
Due to genetic similarities between humans and NHPs, there is a higher risk of humans being infected by these NHP hosts with many transmission opportunities for disease spread occurring when humans and NHPs come into contact: tourist areas, urban areas, or when humans rely on NHPs as a food source.
Additionally, for a parasite to be successfully transmitted into the human population the parasite must be able to infect human cells and be able to spread to other hosts before a person’s immune system can flush the parasite out. Parasite species can spread via close contact, by sharing an environment, sexual contact, vectors (such as mosquitoes or ticks), and by hosts that a parasite can survive in throughout their life cycles.
The research team examined data from the Global Mammal Parasite Database and the Global Infectious Disease and Epidemiology Network in order to predict parasites shared between humans and non-human primates. The study assessed NHP hosts that a parasite typically infects, how genetically related these hosts are to humans, and geographic overlap with humans.
A total of 1136 parasite species and 98 primate species were deemed high risk of transmitting parasites to humans were analyzed in China, Brazil, Colombia, Congo DRC, Indonesia, and Madagascar. Out of these parasites, 899 have documented cases in humans. From these 899 human parasites, 12.2% were shared with at least one other non-human primate. The link prediction model implicated 54 parasites infecting humans that are not documented in GIDEON (a resource that tracks infectious disease information globally) across the six countries. These parasites were predicted to have high spillover risk, with 47% having already naturally infected humans. The remaining 53% have either been shown to infect human cells in an experimental setting or have not been confirmed to infect humans, so there is unclear risk of spillover potential. While around two-thirds of the parasites predicted to infect humans were helminths and protozoans, there is low risk of humans spreading these parasites to other humans and host immunity prevents outbreaks originating from these types of parasites. Viruses are able to mutate quickly and evade immunity, making these parasites the target for future surveillance measures to prevent outbreaks.
Future link-prediction models could build upon these findings and include more extensive research on patterns in host behavior, human and wildlife contact probabilities, and parasite distributions. More widespread efforts to identify NHP parasites with a high spillover risk to humans would be beneficial to global preparedness for emerging disease.
To read more about this study, click here.
By: Brenna Daly