Scientists at Texas A&M AgriLife Research and Baylor College of Medicine have mapped the DNA of a tick that can spread African swine fever (ASF), a deadly disease in pigs. Not only is the Ornithodoros turicata tick a potential vector of the ASF virus, but it also carries human relapsing fever — a severe bacterial infection.
Researchers say the sequenced genome will allow further study of chromosomes linked to specific biological functions. Co-author Pete Teel, AgriLife Research entomologist and Regents professor in the Texas A&M department of entomology, says this will create opportunities for researchers to develop novel tools to control the pest.
“Physiology, development and reproduction of these ticks is all based on their genetics, and this allows us to open the doors to those discoveries,” Teel says in a Texas A&M AgriLife release. “Those discoveries create opportunities for novel genetic tools we might use for surveillance and control measures against the tick and the pathogens it carries.”
A Mysterious Foe
The O. turicata ticks in this study originated from specimens collected in 1992 from an infested cave in Travis County, Texas, and have been maintained in a colony at the Tick Research Laboratory at Texas A&M AgriLife Research.
These secretive ticks are cavity dwellers that live in animal burrows, caves and root hollows, as well as under pier-and-beam buildings. They blood-feed on animals that visit those environments.
Experts say they can live longer than five years without a blood meal. Meanwhile, female ticks can transfer pathogens to their offspring — making them vectors of disease and pathogen reservoirs.
The mapped genome opens up a new avenue of research to study the tick, its life cycle and biology, as well as tick-pathogen interactions, explains Job Lopez, Ph.D., senior author of the study and associate professor in the National School of Tropical Medicine at Baylor College of Medicine.
“It’s one thing to generate a genome, but there’s a lot of postprocessing once you’re done with sequencing,” Lopez says. “Our goal was to generate a high-quality, chromosome-level genome instead of a highly fragmented genome that is challenging to work with.”
Many gaps in knowledge of this tick remain, Teel says. For example, very little is known about how they disperse from one cavity to another and how closely related they are across their wide geographical range.
“We have a basis now to really look at population genetics, and we are looking at the vast geography that we’re discovering for this species from Florida all the way through the High Plains, throughout the Southwest and down to Mexico,” Teel says. “This is a huge step toward the connection of surveillance and development of control.”
How Can This Help the Pork Industry?
Soft tick relapsing fever cases in the U.S. are rare, researchers say. Between 2012 and 2021, there were 251 confirmed cases. There have been four confirmed cases since — including one in Colorado last year. According to the Centers for Disease Control, most cases occurred in western states. Symptoms range from fever, headache, muscle aches and chills to joint pain, nausea, vomiting and rare instances of facial paralysis and vision changes.
“While soft tick relapsing fever poses a threat to human health, ASF represents a potential catastrophe for the U.S. pork industry,” Texas A&M AgriLife said in the release. “About a decade ago, ASF spread globally due to the trade of infected domestic swine that directly transmitted the virus to each other. The disease gets its name ‘African swine fever’ from the natural cycle involving ticks, the virus and warthogs — a cycle in which warthogs do not get sick but maintain the virus.”
Since O. turicata is a vector of ASF and has been shown to feed on wild pigs, this study suggests having this genome available could be critical if ASF were to be introduced in the U.S. or Mexico.
“Texas has all the puzzle pieces for the emergence of a natural cycle for the African swine fever virus,” Lopez says in the release. “We have the tick and African warthogs in Texas — and one of the largest populations of feral hogs on the continent. That’s where the significance of this tick vector comes into play.”
The team collaborated with the USDA Agricultural Research Service (USDA-ARS) SCINet project and Ag100Pest Initiative to develop the first complete genome assembly for this ectoparasite. Their findings were recently published in G3: Genes | Genomes | Genetics.
Researchers Alexander Kneubehl, Baylor College of Medicine, and Amanda Stahlke, Ph.D., Colorado Mesa University, as well as Mackenzie Tietjen, Ph.D.; David Luecke, Ph.D.; Perot Saelao, Ph.D.; Sheina Sim, Ph.D.; Scott Geib, Ph.D.; Brian Scheffler, Ph.D.; and Anna Childers, all with USDA-ARS, contributed to the study.
