Lyme disease is a bacterial infection caused by the spirochete Borrelia burgdorferi. It is transmitted to humans through the bite of an infected tick. As the geographic range of the tick vector expands, this illness has garnered increasing public attention across the United States. Understanding the presence of this infection in Missouri requires reviewing confirmed case data and considering the challenges presented by other tick-borne illnesses that share similar symptoms.
Presence and Geographic Risk in Missouri
Lyme disease is reported in Missouri, but the state is generally considered a low-incidence area compared to regions in the Northeast and Upper Midwest. Missouri reports cases annually that meet the Centers for Disease Control and Prevention (CDC) surveillance criteria. Public health data indicates a relatively small number of formally confirmed cases, with a total of 372 cases reported between 2000 and 2020.
The Missouri Department of Health and Senior Services often characterizes local infections as “Lyme or a lyme-like disease.” This is because the causative bacteria, Borrelia burgdorferi, has not been consistently isolated from patients within the state. However, the clinical syndrome observed in Missouri patients, including the characteristic rash, appears similar to Lyme disease seen elsewhere. Geographic risk within Missouri is not uniform. Data suggests that the highest concentration of reported cases has historically been observed near the Kansas City metropolitan area. Specific eastern and central counties, such as Lewis, Clark, and Pike, have also reported confirmed cases.
The Primary Vector and Transmission Cycle
The organism that transmits Borrelia burgdorferi is the Blacklegged Tick (Ixodes scapularis), often referred to as the deer tick. Ticks acquire the Lyme bacteria by feeding on infected reservoir hosts, primarily small wild rodents like mice. The tick then carries the bacteria throughout its three-stage life cycle: larva, nymph, and adult.
The nymph stage is the most common source of human infection. Nymphs are extremely small, roughly the size of a poppy seed, making them difficult to detect. They are active during the spring and summer months, which coincides with increased human outdoor activity.
Transmission of the Borrelia bacteria does not happen instantly upon a bite. The tick must remain attached and feeding for a period of at least 24 hours to successfully transmit the infectious agent to the human host. Adult ticks are more noticeable and are less likely to transmit the disease because they are usually found and removed sooner. The tick’s habitat is generally wooded and brushy areas, tall grasses, and leaf litter.
Recognizing the Stages of Infection
Lyme disease manifests in three progressive clinical phases, though not every patient will experience every stage.
Early Localized Disease
This phase typically appears days to weeks following the tick bite. The hallmark symptom is the erythema migrans (EM) rash, a red, expanding lesion that often develops a partial central clearing, giving it a classic “bullseye” appearance. While the rash is considered the most specific sign, 20 to 40% of patients may not develop the EM rash. Other symptoms during this early phase resemble the flu, including fatigue, headache, muscle and joint pain, and fever.
Early Disseminated Disease
If the infection is not treated early, it may progress as the bacteria spreads to other body systems. This stage can involve neurological issues, such as facial palsy or pain radiating along nerve pathways, or cardiac involvement, which may present as heart block.
Late Disseminated Disease
This final phase can occur months to years after the initial infection. It is often characterized by intermittent or chronic arthritis, particularly in the large joints, and may also involve persistent nervous system issues. Diagnosis in Missouri is complicated by the prevalence of other tick-borne diseases, such as ehrlichiosis and Rocky Mountain spotted fever, which share symptoms like fever and headache.
Essential Prevention Strategies
Prevention is the most effective defense against contracting Lyme disease and other tick-borne illnesses in Missouri’s outdoor environments.
Chemical Repellents and Clothing Treatment
When venturing into tick habitats, use chemical repellents. For exposed skin, products containing 20% to 50% DEET offer effective protection against tick bites. Treating clothing and gear with products containing 0.5% permethrin is also recommended. Permethrin is an insecticide that kills ticks upon contact and should never be applied directly to the skin.
Post-Activity Checks and Laundry
After returning from outdoor activities, perform a thorough tick check on yourself, children, and pets. Ticks often seek concealed areas like the hair, behind the knees, and under the arms, requiring a full-body inspection using a mirror. Clothes worn outdoors should be tumbled in a dryer on high heat for at least an hour to kill any attached ticks.
Landscaping Practices
Landscaping can reduce the tick population around a home. Creating a three-foot-wide barrier of wood chips or gravel between the lawn and the surrounding woods can discourage tick migration. Ticks prefer moist, shady environments, so keeping the grass mowed short and pruning trees and shrubs to allow more sunlight into the yard makes the area less hospitable. Removing leaf litter and wood piles eliminates the debris where ticks typically hide and overwinter.