A stride in combating tick-borne illnesses

Ticks present a significant threat to public health, with nearly half a million instances of Lyme disease caused by ticks treated annually in the United States.

Young nymphs and mature females are generally the most hazardous in transmitting infections to humans. However, scientists indicate that there remains much to be learned about tick sexual biology, insight that would be beneficial for management initiatives.

A recent study published in the Journal of Medical Entomology signifies a substantial advancement, documenting a revolutionary molecular method that distinguishes male and female blacklegged ticks (commonly known as deer ticks) while also indicating whether these arachnids have copulated.

Lyme is arguably the most recognized ailment transmitted by ticks, but the pathogen responsible for this condition is just one of various diseases associated with these creatures, noted Isobel Ronai, an HHMI postdoctoral researcher in the Department of Organismic and Evolutionary Biology and a primary author of the study.

Referring to other tick-associated illnesses, such as babesiosis, Ronai emphasized that “ticks hold significant public health relevance here in the United States with respect to the disease burden.”

The threat, as per the Centers for Disease Control, is escalating. 

“The number of cases of diseases conveyed by ticks and mosquitoes has risen markedly in the U.S. over the past 25 years, with tick-borne diseases now comprising over 80 percent of all reported vector-borne disease cases each year,” stated C. Ben Beard, principal deputy director of the CDC’s division of vector-borne diseases, who advocated for enhanced “research aimed at improving our understanding of tick reproductive biology.”

Ronai collaborated with her long-time partners at the University of Georgia, who possessed “a unique dataset of tick genomes” encompassing DNA sequences of blacklegged ticks nationwide. Together, they created a molecular assay to ascertain whether individual ticks were male or female.

In addition to determining the sex of the ticks, Ronai explored “fascinating findings” in females collected in New York that exhibited the marker for male DNA. By mating other ticks in the laboratory, she discovered that the marker could also be utilized to identify female ticks that had mated.

Ticks undergo a complex life cycle.

“They feed at multiple life stages,” Ronai explained. “In mosquitoes, only the adult stages consume blood, whereas in ticks, they feed at three stages during their life cycle.”

Ticks initiate their life as eggs, from which larvae are hatched. These larvae feed on a host before evolving into their subsequent stage, known as nymphs. The nymphs also feed on a host.

“They take a blood meal to advance to the adult stage,” Ronai elaborated. “Then, in the adult stage, female ticks feed to produce their egg clutch and initiate the next generation.”

A great deal remains unclear.

“I am very keen on utilizing our sexing assay to examine whether there is any correlation between the gender of a larva or nymph and the hosts they are feeding on,” said Ronai. From observing this behavior, we can infer “which potential microbes that lead to disease male and female ticks are acquiring from hosts and transmitting to humans.”

In her own research within the Extavour lab group at Harvard, the path forward is evident.

“I’m eager to investigate what is transpiring with the biology at these immature stages,” expressed Ronai. “The overall sexual biology of ticks is an area where we have much to explore at the molecular level.”

Furthermore, Ronai added, “we can progress toward establishing new control methods for ticks that target them specifically.”