Ticks are more than just troublesome pests encountered on a hike. While the fear of their bite and the diseases they carry is well-founded – tick-borne illnesses are the most common vector-borne diseases in the U.S. – each tiny tick also holds a surprising amount of history. Environmental historians like me see ticks not just as parasites, but as products of their environment, an environment profoundly shaped by human actions over centuries.
Contained within every tick bite is a trove of social, environmental, and epidemiological history. Our past decisions about how we use land, where we settle, and how we interact with livestock have inadvertently created conditions where ticks and the pathogens they carry can thrive and spread more easily.
Let’s explore how human history paved the way for today’s tick risks.
Shifting Forests & Rising Lyme Disease in the Northeast
Consider the black-legged tick, or deer tick (Ixodes scapularis), the primary vector for Lyme disease. Centuries ago, during the 18th and 19th centuries, vast stretches of forest across the northeastern U.S. were cleared for timber, farms, towns, and mining. This large-scale deforestation drastically reduced wildlife populations, including both deer and their natural predators like bears and wolves.
As farming moved westward, millions of acres in the Northeast returned to forest. Plant-eaters like deer rebounded, but their apex predators did not return in significant numbers. The result? Deer populations exploded. With the deer came deer ticks carrying the Borrelia burgdorferi bacterium, the cause of Lyme disease. Ticks feeding on infected animals pick up the bacteria and can then transmit it to their next host – including humans.
By the 1970s, the eastern U.S. had become a global hot spot for tick-borne Lyme disease. While reported cases fluctuate, estimates based on insurance claims suggest nearly half a million Americans are diagnosed and treated for Lyme annually. This demonstrates a clear link between historical land use changes and the modern prevalence of this debilitating illness.
Fragmented California Landscapes Increase Tick Risks
Human settlement patterns also play a critical role. In California, areas like the Northern Inner Coast and Santa Cruz mountains retained large forest preserves and predators like mountain lions. However, increasing demand for housing pushes development into wildland areas, often creating a fragmented, checkerboard pattern of homes rather than large, connected communities.
This fragmentation breaks up natural habitats into small, isolated patches of greenery. These patches become havens for rodents and other small tick hosts, safe from predators that require larger territories. However, isolation and lower biodiversity in these small patches can lead to infections spreading more easily among hosts. Fewer, more tightly packed hosts often mean a higher proportion of infected animals, and consequently, more dangerous ticks for humans living nearby.
This pattern has tangible consequences: Six counties around San Francisco, where this type of fragmented settlement occurs, account for 44% of California’s recorded tick-borne illnesses.
Lessons from Texas Cattle Fever
Domesticated livestock management also offers historical insights into tick-borne disease control. In the late 19th century, Texas cattle fever devastated herds, but how it spread was a mystery. In 1892, Dr. B.A. Rogers proposed that ticks were the culprits – a theory initially met with ridicule.
Fortunately, the U.S. Department of Agriculture supported Rogers’ idea. Their cattle fever tick program, launched in 1906, focused on controlling cattle movement in tick-dense areas. By 1938, they established a quarantine zone along the U.S.-Mexico border. This innovative use of natural space and understanding the tick’s environment as a public health tool helped functionally eradicate cattle fever from 14 Southern states by 1943.
Global Patterns: Hunter Ticks and Settlement in the Mediterranean
This connection between human actions and tick risks isn’t unique to the U.S. The hunter tick (Hyalomma spp.) in the Mediterranean and Asia historically bothered nomadic shepherds only occasionally. These ticks feed on small forest animals as juveniles and livestock as adults.
However, in the 1850s, Ottoman Empire policies forced nomadic tribes to settle as farmers, often on previously forested, unclaimed land. This shift brought domesticated livestock into environments favored by the hunter tick and altered the landscape through farming. These changes created ideal conditions for the ticks, leading to spikes in tick-borne diseases, including Crimean-Congo hemorrhagic fever, among settled farmers in areas now part of Turkey.
The Growing Threat: Beyond Lyme Disease
While Lyme disease is the most well-known, tickborne diseases overall are significantly increasing in the U.S. The annual number of reported cases has more than doubled over the past two decades. This rise is linked to expanding tick populations, warmer and more humid weather allowing ticks to spread and stay active longer, and improved disease tracking.
Other tick-borne illnesses carried by black-legged ticks include Babesiosis (a parasitic disease on the rise in the Northeast) and the rare but dangerous Powassan virus, for which no specific treatments exist. Other tick species, like the American dog tick and Lonestar tick found across different U.S. regions, transmit diseases like Rocky Mountain spotted fever, Tularemia, Heartland virus, STARI, and Bourbon virus.
Symptoms of many tick-borne illnesses are often non-specific, resembling flu-like symptoms (fever, headache, malaise), making diagnosis challenging. Early treatment is critical for diseases like Lyme and Rocky Mountain spotted fever, though diagnosing Lyme can be difficult due to the tick’s small size, non-specific symptoms, and the bull’s-eye rash not always appearing.
Prevention and Future Solutions
Since ticks are active from spring through fall, inhabiting wooded and grassy areas, prevention remains the most crucial tool. Simple steps can significantly reduce risk:
Wear long pants and sleeves when in tick-prone areas.
Tuck pants into socks and wear a hat.
Apply EPA-registered insect repellents.
Consider treating clothing and gear with 0.5% permethrin insecticide.
Shower within two hours of being outdoors to wash off potential ticks.
Perform thorough tick checks on yourself, children, and pets, paying close attention to warm areas like armpits, groin, behind knees, ears, and scalp.
- Promptly and correctly remove any attached ticks using fine-tipped tweezers.
- theconversation.com
- www.aamc.org
- publichealth.jhu.edu
The increasing burden of tickborne diseases has also spurred research into new preventative measures, particularly for Lyme disease. While a previous human Lyme vaccine (LYMErix) was withdrawn in 2002 due to factors like limited market, lukewarm reception, and negative publicity (despite FDA findings), promising new approaches are underway. These include traditional vaccines in Phase 3 trials, monoclonal antibody shots offering immediate immunity, and mRNA vaccines targeting tick saliva proteins to make bites noticeable sooner. While these offer hope, they primarily target Lyme, reinforcing the need for broader tick bite prevention against the array of diseases ticks carry.
Ultimately, ticks are indeed products of their environment. Their ability to trouble us with disease isn’t inherent malevolence but a consequence of ecological conditions – conditions that human history has profoundly shaped through deforestation, reforestation, settlement patterns, livestock management, and more. Understanding this deep historical connection is key to developing effective strategies to coexist with ticks and mitigate the risks they pose today and in the future.
