Limiting Lyme Disease - Naturally?
In the last few years, cases of Lyme disease in Virginia have nearly doubled. According to Fairfax County’s Disease Carrying Insect Program almost 200 cases of the disease are now reported in the county annually. On July 22, Supervisors Herrity (Springfield District) and Frey (Sully District) hosted a highly attended town hall meeting about the disease and its prevention, evidence of both the public and political concern about this alarming new trend.
Air and water conservation initiatives resulting in decreased landscape maintenance or meadow or woodland habitat creation often encounter opposition from citizens concerned about Lyme disease. Are such efforts truly counter to public health measures aimed at decreasing Lyme disease? Can we protect ourselves and our children and still pursue our environmental objectives?
Lyme Disease Facts
Lyme disease is a bacterial disease transmitted in our area through the bite of the black-legged tick, Ixodes scapularis, known more commonly as the deer tick. Lyme disease is not contagious and if detected promptly, often by the tell-tale bull’s eye rash, is typically easily cured with antibiotics. However, in a fraction of patients - particularly in adult patients whose disease remains undiagnosed for some period - Lyme disease can cause serious lingering symptoms including joint pain and arthritis, fatigue, memory loss, other neurologic symptoms or heart trouble.
Black-legged ticks are ubiquitous and pernicious pests. They inhabit humid woody areas such as wooded parklands, but also flourish in the edge areas between forest and lawn that are common in suburban and residential settings. They wait in leaf litter and on the tips of leaves and grasses for an appropriate mammal host to brush against them. At 3/8-inch long or less, they are easy to overlook, and although they are less prevalent in the winter, they can be active in periods of warm weather year-round.
Black-legged ticks have a rather complex two-year life cycle involving several life stages: larvae, nymphs and adults. Ticks can feed on humans in any life stage, but the majority of Lyme disease cases, up to 98 percent, are caused by bites from nymphs. Black-legged tick nymphs, which may be 2 mm in size or less, are active from spring through mid-summer, transforming into adults in late summer or fall.
Ticks ingest the Lyme disease-causing bacteria, Borrelia burgdorferi, as larvae or nymphs during blood meals from small, infected mammals or birds. The white-footed mouse is the predominant carrier, although chipmunks and common suburban birds such as robins, grackles and house wrens may also carry the disease-causing bacteria. Black-legged ticks are also called deer ticks because the deer is another important host, particularly for adult ticks. Deer do not transmit the bacterium that causes Lyme-disease, but up to 90 percent of adult ticks feed exclusively on deer! Black-legged tick populations and distribution have been conclusively linked to the size of the deer herd.
Basic Lyme Disease Prevention
Particularly for families with young children, Lyme disease prevention is of utmost concern. Unfortunately, most cases of Lyme disease in children can be traced to normal outdoor play. Adult cases are often also related to typical outdoor activities such as walking the dog and yard work.
The best way to prevent Lyme disease is to make checking for ticks a habit; check yourself and your children thoroughly including the armpits, scalp and groin. If you do find a tick, remove it immediately with fine-tipped tweezers to reduce the chances of contracting Lyme disease. Black-legged ticks are slow eaters; they typically must be attached for 24-36 hours to spread the Lyme disease-causing bacteria to their host.
If you know you will be in tick territory, take additional precautions. Since most ticks hang out close to the ground, wear or dress your children in light-colored long pants for trips to woodlands and natural areas. Tucking your pants into your socks may look ridiculous, but can help to further limit access points to your skin. For older children and adults, spray shoe tops, pant legs and socks with insect repellent containing 20-30 percent DEET. (Increasing the concentration of DEET is not noticeably more effective at preventing tick bites.) Stay on paved or mulched trails and avoid contact with adjacent vegetation to further limit your exposure to the pests. Outdoor clothing and gear can also be dosed with a product containing the pesticide permethrin, which will kill ticks on contact.
“Tick Safe” Landscapes?
Integrated pest management (IPM) for ticks involves a combination of landscaping changes, control of host populations and pesticide use if necessary. The approach incorporates official public health recommendations for creating “tick safe zones” in landscapes, but is more flexible allowing each property owner or manager to balance ecological concerns with tick eradication efforts.
In controlled studies, reduction of deer populations has been demonstrated to be at least if not more effective than pesticide use and more effective than landscape changes in reducing cases of Lyme disease. Fencing out deer from your yard, planting deer resistant plants and encouraging public programs that reduce deer populations can reduce the number of ticks around your home. Research has also linked removal of thick non-native groundcovers like pachysandra and invasive understory with decreases in tick populations. These types of landscape cover provide habitat for the white-footed mouse, a primary tick host. Out of control deer populations and rampant invasive plants are two of the most pressing concerns for urban natural resource managers. Using a variety of deer-resistant native vegetation around your home can limit tick hosts and also support natural resource management strategies to encourage biodiversity and conserve habitat.
Public concerns about Lyme disease and ‘messy’ landscapes should be recognized and addressed. However, no-mow zones and habitat areas can be part of a “tick-safe” home or public landscape. Sunny, upland meadows and butterfly gardens, for example, are typically too hot and dry for ticks to proliferate. Establishing dry, sunny gardens or mulch areas around play, outdoor eating, storage and vegetable gardens will reduce contact with ticks. Outside recreation areas can also be separated from habitat areas, stonewalls and woodpiles with 3-foot wide mulched perennial borders or mulch or gravel pathways. Creating or widening paths through meadows, woodlands and other natural areas and pruning vegetation encroaching on walkways will allow for intimate connections with natural areas and also make both children and adults less likely tick hosts.
A single landscape-wide application of a pyrethroid pesticide in late May or early June targets tick nymphs and is often recommended by public health entities to reduce Lyme disease cases. However, pyrethroids are highly toxic to bees as well as to fish and other aquatic organisms. In fact, the U.S Environmental Protection Agency limits use of these chemicals on or within 100 feet of wetlands, streams and other water bodies. An alternative to landscape-wide pesticide use is targeted use of pyrethroids at the margins of outdoor recreation zones. Techniques also exist to treat hosts, particularly white-footed mice, with pesticides. These techniques include using bait-boxes containing the pesticide Fipronil (often used for flea and tick control on pets) or tubes filled with permethrin-coated cotton balls that mice harvest as nesting material.
Lyme disease can be a serious illness and keeping families safe is a primary concern. Environmental projects can take public health risks related to Lyme disease into account while still resulting in increased habitat, more diverse ecosystems and cleaner air and water. At the same time, home and public property owners and managers can undertake a balanced, ecologically sound approach to reducing Lyme disease risks. An extremely thorough guide to tick management has been published by the Connecticut Agricultural Experiment Station and is on-line at http://www.cdc.gov/ncidod/dvbid/lyme/resources/handbook.pdf. For local information, visit the Fairfax County Disease Carrying Insects program web site at http://www.fairfaxcounty.gov/hd/westnile/.