Lizards Potentially Protect People From Lyme Disease in Southeastern United States Science

By Harini Barath5 February 2021, 11:00

Lyme disease is one of the most devastating tick-borne infections in the United States, affecting more than 300,000 people annually. It is also one of the most mysterious: the creature that spreads it – the black-footed tick – lives throughout the country. Yet the northeastern United States is home to many more cases than elsewhere. Now researchers have identified an unexpected reason: lizards.

Black-footed Ticks (Ixodes scapularis), also known as deer, carry corkscrew-shaped bacteria that cause Lyme disease. The ticks pick up the pathogens – spirochete belonging to the genus Borrelia—When they suck the blood of animals such as mice, deer and lizards. In the next phase of their life cycle, the ticks can cling to an unhappy human being. But each host transmits the microbes differently. Reptiles are worse transmitters than mammals, so ticks that have lived on reptiles are less likely to make people sick.

The north-south separation in Lyme cases is a fairly sharp line right along the border of Virginia and North Carolina. Researchers have suspected that the difference in cases stems from ticks feeding different hosts in the two regions.

To test the idea, Jean Tsao, a pathologist at Michigan State University, and colleagues spent more than two years conducting an extensive study of eastern ticks – their abundance, behavior, and host – on eight field sites across the United States. They found a clear gap in ticks’ preferred hosts and behaviors south of Virginia, consistent with the pattern of both tick infections and Lyme disease.

Mark a tracker

Black-legged ticks (eastern USA) without record of infection Western black-footed ticks without infection Ticks infected with spirochete bacteria No records

It seems that the strong difference is especially linked to one host. In the northeast, black-footed ticks cling to small mammals such as the white-footed mouse, notorious for transmitting the Lyme disease bacteria to the bugs. But in the south, the ticks prefer to feed lizards, especially skink. These slender, smooth-scale reptiles often live in leaves and twigs that have fallen to the ground – so-called leaf litter – and are particularly weak carriers of the Lyme pathogens. So fewer southern ticks are infected and fewer people get sick – the team reported last week PLOS Biology.

The researchers followed the right approach to solve the mystery, says Andrea Swei, a disease ecologist at San Francisco State University who was not involved in the study. “They compare apples to apples here, and that allows them to say a lot about host association patterns in a large geographic area.”

In a previous study, Tsao and her colleagues noted that ticks in the northeast and southeast also look for hosts differently. In the south, the bugs remained under the forest debris to prevent drying out of the heat. Northern ticks were more outgoing and climbed on leaves and twigs, where they were more likely to encounter and bite people. This, coupled with fewer lizards, makes ticks a double whammy in the northeast, Tsao says.

“The peculiarities of tick ecology have implications for human health,” said co-author Howard Ginsberg, an ecologist at the U.S. Geological Survey’s Patuxent Wildlife Research Center. He hopes the work will share efforts to detect and reduce the spread of Lyme disease.

Climate change could change these patterns, says Swei. Observations show that northeastern ticks have already expanded their range. At the same time, the researchers speculate that a hot climate may alter the behavior of ticks and the presence of particular hosts, which may increase the patterns of Lyme disease. It is important to keep an eye on the regions around the north-south divide, says Swei. “As the zone shifts,” she will really change the disease risk for people living right on the border. ‘