Ticks can transmit long list of diseases to humans and other animals, including Rocky Mountain spotted fever, Anaplasmosis, and Lyme disease. More are emerging all the time, like Borrelia mayonii, which was first observed in patients in 2013. Ticks are also seriously detrimental to agriculture. Controlling these diseases would be easier if we could get rid of ticks, but insecticides often contaminate milk and meat and ticks can gain resistance to their effects, for example.
Researchers are now presenting a new approach at the American Chemical Society (ACS) Fall 2019 National Meeting & Exposition. In this method (outlined in the video above), chemical compounds are used to dry out tick saliva by disrupting the ion balance in their salivary glands. It reduces their feeding behaviors, and might limit the spread of the pathogens they carry.
"Lyme disease is exploding in the northeastern U.S.," says Daniel Swale, Ph.D., the principal investigator of the study, of Louisiana State University. "Most methods to kill ticks in the agricultural sector involve the use of neurotoxic insecticides, but it's difficult to effectively use these insecticides to control ticks in residential areas. So we wanted to identify a new way to control these disease-carrying ticks."
The research team hypothesized that if ticks didn’t have enough saliva, they wouldn’t consume as much food, and their survival rates would drop. They zeroed in on a channel that moves potassium ions called Kir; it’s been shown to play a role in excretion in arthropods, a class that includes ticks. Potassium ions use Kir channels to move through cells of the salivary gland and other structures, and help maintain a balance of ions, which is important to the secretion of saliva and tick health.
"We knew that the salivary gland is critical to the biological success of ticks, suggesting it had potential as a target for a pesticide that works through a new mechanism," said graduate student Zhilin Li, who is presenting the work.
The researchers tested chemicals that target Kir channels by adding them to blood that ticks were then exposed to. VU0071063 and pinacidil were both able to reduce the secretion of tick saliva by 95 percent or more, and reduced the amount of blood the ticks took in about 15-fold. When ticks ingested bovine blood laced with these compounds, they died within twelve hours - the minimum amount of time it can take for a pathogen to be transmitted to humans though tick saliva (it can take as many as forty hours). The ticks also showed signs of sickness before they died.
"We think their nervous system wasn't working normally, and we suspect that's why we saw high mortality in the treated ticks," Li said.
In this study, an artificial system was used to feed the ticks, but the scientists are now planning to test the compound in a rodent model. The researchers are also working to learn more about the ion channel, which seems to appear in the salivary gland only when ticks are feeding on blood. They also want to know more about the cells expressing the channel, which might help in the creation of tick bite prevention or insecticides.
Sources: AAAS/Eurekalert! Via American Chemical Society