A new 15-year study by the University of Toronto indicates that Lyme disease rates are increasing in northern states and decreasing in southern ones. While the researchers found Lyme disease rates to be largely stagnant in 15 states, they found significant declines in 14 states and equally significant increases in 21 other states. The study was conducted from 1992 until 2007. If you live in a state affected by Lyme disease, it’s important to take the proper precautions before (and after) heading outdoors with your family this spring and summer.

Early symptoms of Lyme disease include things that might initially look like flu – chills, fever, stiff neck, headaches, fatigue, muscle aches and joint pain. Advanced cases can involve nerve issues and even arthritis. The giveaway symptom in the early stages is a large, ring-like rash.

Shifts in Lyme Disease Prevalence by State

The majority of the states that have experienced increases in Lyme disease prevalence are located in the northern region of the country, according to the study. These states include North Dakota, Minnesota, Wisconsin, Ohio, Illinois, Michigan, Pennsylvania, Virginia, and most New England states.

Meanwhile, decreases in Lyme disease prevalence were mainly detected in southern states such as Kentucky, Tennessee, Mississippi, Louisiana and Georgia. However, states in the western region of the country such as Wyoming, Oregon and California enjoyed declines in Lyme disease rates as well.

In order to carry out their study, the researchers analyzed data from the Centers for Disease Control and Prevention pertaining to rates of Lyme disease incidence. The researchers were careful to account for factors that could have influenced the data, including the percentage of each state’s population living in rural areas, where Ixodes ticks are found almost exclusively.

Why the Geographical Shift in Lyme Disease Prevalence?

The researchers behind the study believe that Lyme disease has shifted north largely as a result of climate change. Lyme disease is carried by Ixodes ticks. According to recent studies, increasing temperatures in northern regions have caused these types of ticks to move to the north.

However, the southern states are rising in temperature as well, so why have we seen a decrease in the prevalence of Lyme disease there? The researchers believe that the increasingly hot climate in the south has also caused increases in the lizard population there. Ixodes ticks infect the lizards with Lyme disease, but the transmission of the disease stops there because lizards are unable to infect humans with Lyme disease.

Adding credence to the beliefs of the researchers is the fact that some regions of Canada are now experiencing cases of Lyme disease. These particular regions were once thought to be too frigid to allow for the survival of Ixodes ticks.

Preventing Lyme Disease

Obviously, you’re not going to relocate simply because cases of Lyme disease are becoming more common in your state. But you can take certain steps to greatly reduce the risk of you or someone in your family being infected. The CDC offers the following tips:

• Avoid outdoor areas with tall grass
• Wear an insect repellant with at least 20% DEET
• Shower immediately after getting home from a trip to the outdoors

It’s also a good idea to check inside your clothes, especially your socks and pantlegs, periodically as you hike through areas known for ticks, especially when encountering tall grass and denser foliage.

The Bottom Line

A recent study by the University of Toronto indicates that Lyme disease is moving north, at least partly as a result of climate change. The full text of the study can be found online in CMAJ Open.