(02/25/19) BATON ROUGE, La. — Populations of ticks and the diseases they spread have exploded in recent years in the United States. Yet there are few ways to control the insects, and no vaccine is available to protect people from tick-borne diseases.
To try to curb increasing rates of Lyme disease and other sicknesses caused by tick bites, LSU AgCenter entomologist Daniel Swale is taking a closer look at the insects’ salivary glands.
When ticks bite someone, they spit out proteins that affect the human immune system and enable them to feed on that person’s blood. Tick saliva also carries disease-causing pathogens.
Scientists have tried over the years to develop vaccines for tick-borne diseases that target the proteins in tick saliva, but the products are only marginally effective and not commercially available for humans, Swale said.
He is taking a different approach.
“To eat, you need spit, and ticks are no different,” he said. “So instead of developing products to inhibit proteins in the saliva once they are secreted, why don’t we just prevent the tick from spitting in the first place? It’s like giving the tick dry mouth. If we can stop the tick from being able to spit, then we would stop the tick from being able to feed and transmit a pathogen.”
Swale is working on the research with doctoral student Zhilin Li, AgCenter entomologist Lane Foil and LSU School of Veterinary Medicine professor Kevin Macaluso. Their goal is to come up with a product that can stop ticks from salivating and, ultimately, interrupt the life cycle of the pathogens they transmit.
They are focusing on Kir channels, which transport potassium ions.
“Kir channels are known to be critical for salivary gland function in mammals and are also an exploited drug target to reduce the morbidity of hypertension and diabetes, but this channel is severely understudied in insect systems,” Swale said.
“This current study has shown that changing the function of Kir channels in tick salivary glands reduces the ability of the tick to secrete saliva, which leads to reduced blood feeding capabilities and eventual death of the tick. This suggests these Kir channels may represent a novel target site for insecticide or vaccine development to reduce the burden of tick-vectored pathogens,” he said.
A solution to the outbreak of tick-borne diseases — which is worst in Northeastern states — is urgently needed, Swale said. The U.S. Centers for Disease Control reported 59,349 cases of illnesses resulting from tick bites in 2017 — an increase of more than 10,000 from the year before.
“Right now, the most effective way we have to control them is to spray yards with insecticides,” which simply is not eliminating enough ticks, Swale said. People also can use insect repellents and wear protective clothing.
In addition to Lyme disease, tick bites can sicken humans as well as pets and livestock with anaplasmosis, spotted fever rickettsiosis and babesiosis. The ailments can cause fever, rashes, nausea, joint pain, muscle weakness and, less commonly, death.
LSU AgCenter entomologist Daniel Swale, left, points out secreted saliva on an image of a tick salivary gland as doctoral student Zhilin Li, right, watches. Swale and Li, along with AgCenter entomologist Lane Foil and LSU School of Veterinary Medicine professor Kevin Macaluso, are studying how ticks’ salivary glands work in an effort to find new ways to control populations of the insects, which spread harmful diseases. Photo by Olivia McClure/LSU AgCenter