Lizards May Help Protect People from Lyme Disease
By Ethan Estabrook, BCE, Research Entomologist and Product Support at Insects Limited, Inc.
Lyme disease is caused by the bacterium, Borrelia burgdorferi, and is the most common vector-bone disease infecting 476,000 people in the United States each year.
Early symptoms can be mild and include fever, headache, fatigue, and skin rash. If left untreated, Lyme disease can spread to joints, heart, and nervous system and cause more serious symptoms like facial palsy, severe joint and muscle pain, heart palpitations, episodes of dizziness, and nerve pain.
Blacklegged ticks (Ixodes scapularis), also known as deer ticks, become a carrier of Lyme disease from feeding on the blood of an infected animal host like mice, deer, and lizards.
Lyme disease is then transmitted to humans through the bite of an infected tick. Blacklegged ticks are found throughout the country, but positive Lyme disease cases are found more frequently in northern states, particularly in the Northeast.
So why is there a geographic discrepancy? New research suggests that lizards, particularly skinks, may be part of the answer.
Figure 1. Estimated distribution of the blacklegged tick, lxodes scapularis, in the United States. Imaged obtained from the CDC (https://www.cdc.gov/ticks/geographic_distribution.html).
According to a paper published from Ginsberg et al. in 2021, there are two reasons why Lyme disease is more common in the north and less common in the south.
First, fewer people are bitten by blacklegged ticks in the south because ticks tend to stay under forest leaf litter to avoid dehydration from higher temperatures. Whereas in the north, cooler temperatures allow ticks to venture further on top of leaf litter, leaf tops, and twigs, where ticks would encounter people more frequently.
Figure 2. 2019 map of confirmed Lyme disease cases in the United States. Image obtained from the CDC (https://www.cdc.gov/lyme/datasurveillance/maps-recent.html).
Second, blacklegged ticks in the south have a lower prevalence of the Lyme disease bacterium because they feed primarily on skinks, compared to blacklegged ticks in the north who feed primarily on rodents. The Lyme disease bacterium does not survive as well in reptiles as it does in mammal hosts, so when a tick feeds on a skink it is less likely to become infected and transmit Lyme disease to people.
Figure 3. Life stages of the Blacklegged tick, lxodes scapularis. Starting from the left is the larvae, nymph, adult male, and adult female. Imaged obtained from the CDC (https://www.cdc.gov/lyme/index.html).
This brings about some interesting questions as our climate changes. Currently, black-legged ticks are moving further northward into Canada with the increased prevalence of Lyme disease. Will climate change alter tick behavior? If skink populations move northward will the prevalence of Lyme disease decrease in states like Virginia? If skink populations decrease will the prevalence of Lyme disease increase?
References:
Ginsberg HS, Hickling GJ, Burke RL, Ogden NH, Beati L, LeBrun RA, et al. (2021) Why Lyme disease is common in the northern US, but rare in the south: The roles of host choice, host-seeking behavior, and tick density. PLoS Biol 19(1): e3001066. https://doi.org/10.1371/journal.pbio.3001066
Centers for Disease Control and Prevention. Available from: https://www.cdc.gov/lyme/datasurveillance/maps-recent.html
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