Wildlife to human transmission of viruses has caused some of the world’s most notorious pandemics, from severe acute respiratory syndrome, also known as SARS to H1N1 swine flu and Ebola, and now COVID-19. New Mexico State University post-doctoral fellow Katie Young spent a year in the tropical rainforests of Malaysian Borneo studying the mosquito-borne virus Dengue, to better understand the cross talk between viruses and hosts.
“Almost all arboviruses (group of viruses transmitted by arthropod insects including mosquitoes) we know about, like dengue and Zika, originated from transmission cycles in wildlife and eventually completely emerged into the human population, similar to the coronavirus that is causing a massive pandemic now,” Young said. “One of the big questions is how these host contacts can influence spillover which would be a virus “jumping” from one host to a novel host, like a monkey or bat to a human.”
Borneo is a large island in the Maylay Archipelago, the largest group of islands in the world. Borneo is known for its beaches and bio-diverse rainforest, which is home to wildlife such as orangutans and clouded leopards. Young’s mentor Kathryn Hanley, Regents Professor of Biology in the College of Arts and Sciences, has extensive experience researching infectious diseases transmitted via mosquitoes. Young and other members of Hanley’s team collected thousands of mosquitoes through a backpack aspirator in the tropical rain forest of Borneo.
“It was really intense, back-breaking work at some points,” Young said. “We sampled thousands of mosquitoes. Out of those we got 134 that were blood-fed and out of that we were only able to identify hosts from 116 of them.”
Young collected the blood-fed mosquitoes and used molecular techniques to identify the host species using the blood that was still in the mosquito.
“We took the DNA from the blood, and, with it, identified the host,” she said. “We looked at the interactions between mosquitoes and hosts and where they were occurring in the context of land cover and land use change which is thought to influence spillover. We identified over 21 different types of host species that covered mammals, birds, reptiles and amphibians.”
With the data Young gathered, she created graphs to plot the frequency of host/mosquito connections.
“That gives us some information on what types of hosts mosquitoes are using, if they are specialists, in that we only see them using one host type, or if they are generalists, which means they use many host types and are thought to be better at transmitting novel viruses to novel hosts and creating spillover.”
Of the nearly 400 emerging infectious diseases identified globally since 1940, over 60% are zoonotic, meaning the infection can jump from animals to humans. For spillover of a zoonotic disease to happen and become established in humans resulting in the level of community spread seen with COVID-19, a number of conditions need to occur.
“First, you need to have a reservoir host, which in the case of coronavirus is potentially bats. Those reservoir hosts need to have the virus replicating within them and they also need to shed the virus,” Young said. “Then, there needs to be human hosts in the vicinity of those bats and typically you see close contact between them. These are some of the shared conditions needed for spillover to happen no matter what virus you’re looking at.”
According to the National Institutes of Health, more than two-thirds of human viruses are passed from animals to humans. But most result in limited cases, with no further human-to-human transmission.
“Spillover in itself is rare but we are seeing an increasing trend of spillover and emergence events of new pathogens. This is likely to continue to increase with climate change and land cover and land use change, and increases in human travel and trade. These are things that many scientists think are drivers for spillovers to occur.”
Scientists in more than a dozen countries now are racing to address the COVID-19 pandemic, while others are working to develop systems to predict the occurrence and persistence for emerging infectious diseases.
Of the more than 1,700 known viruses, bacteria, and other pathogens that infect people, more than half either originated in or now come directly from animals; the rest come from the environment, such as soil, water and air.
“We don't have great tools in place as of right now to identify how often spillover is happening because we're lacking surveillance which makes it hard to predict disease emergence,” Young said. “But, scientists all over the world are working on this, including my mentors Debra Peters of USDA ARS (U.S. Department of Agriculture Agricultural Research Service) and Kathryn Hanley here at NMSU with advanced tools like artificial intelligence."
“This has been a really big push in our scientific community and hopefully we can take this and learn from it. To really see how we can be better prepared for the future.”
“EYE ON RESEARCH” is provided by New Mexico State University. This week’s feature was written by Amanda Adame of University Communications. Amanda Adame can be reached at email@example.com.