KERRVILLE, Texas – Researchers have recently identified the genetic markers for sex determination in the tick species Rhipicephalus microplus, one of two invasive cattle fever tick species. This discovery lays the foundation for future genetic tools to control cattle fever ticks.

Cattle fever ticks carry and spread microscopic parasites that cause the disease often known as Texas Cattle Fever. The disease destroys animals’ red blood cells, causing anemia, high fever, and spleen and liver enlargement. When infected, 70-90 percent of previously unexposed cattle die from the disease.

Jason Tidwell, microbiologist at the USDA’s Cattle Fever Tick Research Unit in Kerrville, said the work was inspired by similar research on mosquitoes.

“(Researchers studying mosquitoes) have identified the sex-determining genes, and they’re utilizing that research to develop genetic control methods so that when you introduce a genetically modified mosquito, it will crash that species of mosquito out of the population,” he said.

There are a few ways that researchers can use sex-determining genes to control insect populations. One, researchers can modify male individuals so they are sterile but still able to mate, resulting in no offspring, which gradually reduces the population over time. Another strategy is to use genetic engineering tools to spread specific genetic modifications rapidly through a population, such as a modification that forces all offspring to be male or sterile, leading to population collapse because females are required for reproduction. Similarly, researchers could design a genetic modification that causes female offspring to die early or never develop.

For example, in recent years, researchers genetically modified a species of mosquitoes that spread viruses, including dengue, Zika, and chikungunya, to release into the wild to lower the population size and reduce the spread of disease. Genetically modified mosquitoes were mass-produced in a laboratory carrying two types of genes: a self-limiting gene that prevents female mosquito offspring from surviving to adulthood and a fluorescent marker gene that glows under a special light, helping researchers identify genetically modified mosquitoes in the wild. These mosquitoes were first released in the U.S. in 2021.

“In some ways, (genetic tools) are a more environmentally friendly option. We could possibly control a specific species of tick and wipe out that population and not harm the rest of the environment. (In contrast), chemical methods could be toxic to animals or the environment,” Tidwell said.

Although cattle fever was declared eradicated in the U.S. in 1943, the U.S.-Mexico border remains a key zone for potential tick introduction, especially along Texas. The USDA and Texas Animal Health Commission enforce strict quarantine and treatment measures in border regions to detect and eliminate infestations. Still, the combination of wildlife movement, border dynamics, and environmental changes means that the ticks remain an ongoing challenge.

Currently, cattle fever is prevented and controlled by monitoring tick infestations along the Texas-Mexico border, inspecting livestock entering or moving through the quarantine zone, and monitoring wildlife to detect tick presence. Additionally, cattle undergo acaracide treatment, chemicals specifically designed to kill ticks. However, Tidwell said that ticks captured and tested demonstrate resistance to almost all classes of acaricides,

“(There are) still outbreaks along the border, but we have a good handle on protecting cattle right now,” he said. “We’re trying to be ahead of the curve and come up with new (control) methods that are not specifically chemical control.”

Tidwell added that the benefit of using genetic control is that genetic controls target the specific species spreading disease without affecting other species in the surrounding environment.

There are no approved vaccines or drugs to prevent and treat cattle fever. Tidwell said some vaccines are under development, and other researchers are investigating using essential oils to control ticks. Moving forward, researchers developing a genetic tool to control cattle fever ticks will build genomes of ticks of local reference from Texas and Mexico to examine genetic variation.