Recent Articles from BRMC Newsletters

Ticks & Lyme

Spring is a time of rejuvenation. Life surges with new vigor after the winter. Unfortunately for all who like to revel in the woods and backyards, so do ticks.

Ticks are members of the phylum Arthropoda, animals with jointed legs and hard outer skeletons. More specifically, ticks belong to the subphylum Chelicerata, which includes horseshoe crabs, sea spiders, scorpions, spiders, mites, and harvestmen. Cheliceratae are characterized by their six pairs of appendages -- a pair of chelicerae, a pair of pedipalps, and four pairs of walking legs -- and by their lack of mandibles and antennae.

Within the subphylum Chelicerata there are three main classes. Ticks belong to the class Arachnida, along with scorpions, spiders, mites, and harvestmen. Arachnids are arthropods with only two body regions -- a cephalothorax and an abdomen. Ticks and mites differ from all other arachnids in having their cephalothorax and abdomen completely fused; they are classified together in the order Acarina.

Ticks pierce the skin of vertebrates and feed on their blood until enormously distended, then drop off to digest the meal. After molting, they wait on the tips of leaves, forelegs outstretched, ready to attach to any vertebrate that brushes past. Because of this mode of feeding, ticks are important disease carriers. Wood ticks, Dermacentor spp., carry Rocky Mountain spotted fever, caused by a bacteria-like organism, rickettsia. The tick Boophilus annulatus transmits a protozoan parasite that causes Texas cattle fever. Blacklegged ticks, more often called deer ticks, Ixodes scapularis, transmit the Lyme disease bacterium, Borrelia burgdorferi.

Lyme disease was named in 1977 after a group of children living around Lyme, Connecticut, began suffering from arthritis. Investigation of clinical symptoms and environmental conditions determined that Lyme disease is caused by a bacterial infection. The bacterium enters the human body through an intermediate vector, usually a deer tick. Ixodes ticks are much smaller than common wood, dog, and cattle ticks. As larva and nymphs, Ixodes are no larger than a pinhead. B. burgdorferi is believed to be endemic to Europe and to have been transferred from Europe to the United States in the early 1900s.

There are three ingredients that must all be present for Lyme disease to spread in an area. There must be the spirochete bacteria, Borrelia burgdorferi. There must be Ixodes ticks that can transmit the bacteria. Finally, there must be mammals such as mice and deer to provide the meals for the ticks as they move through their lifecycle. The northeast, mid-Atlantic, and north-central regions of the U.S., along with northwestern California, have these interrelated elements. In Northern Virginia alone, Lyme disease is reaching epidemic proportions, according to regional infectious disease specialists.

Knowledge of the deer tick lifecycle is key to understanding your risk of acquiring Lyme disease as well as to finding ways to reduce the risk. The deer tick's lifecycle takes two years to complete. In spring, adult females lay eggs on the ground that hatch into larvae by summer. Larvae feed on mice, small mammals, deer, and birds, and by the fall, these larvae molt into nymphs that remain dormant throughout the winter. In the following spring, nymphs begin to feed on small mammals, including rodents, birds, and humans. In late summer or early fall, the nymphs molt into adults. The adults feed and mate on large mammals, especially deer, and pass through the winter on their host. In the spring, adult females drop off the host and lay their eggs, completing the lifecycle.

Ticks, small rodents, and other nonhuman vertebrates serve as natural reservoirs to B. burgdorferi and the bacteria can live and grow within these hosts without killing them. Larval ticks rarely carry B. burgdorferi when feeding and thus are not important as Lyme disease vectors. Nymphal ticks, because of their small size, are the usual transmitters of B. burgdorferi to humans through natural feeding behaviors. Transmission of the bacteria usually occurs after two or more days of feeding by the nymph. Adults are larger and are usually noticed and removed by the human host before they have transmitted the Lyme bacterium.

Avoiding deer ticks is the most effective way to prevent Lyme disease. Deer ticks are present in woodlands, nearby grasslands, and forest edges. When walking through these environments it is best to remain on trails and limit contact with vegetation that may have clinging ticks. Humans are most susceptible in the spring and summer when nymphs are most active. There is a chemical, permethrin, which can be sprayed on clothing and is effective at killing most insects, especially small ticks. Wearing permethrin-coated clothing that fits snuggly at the wrists and ankles when entering tick-infested areas is the most prudent control. In many areas, as few as

1 percent of ticks will be carrying the B. burgdorferi bacteria, but in some heavily infected areas 20 to 30 percent of ticks have been found to be vectors. Light-colored clothing is advisable to aid in seeing these small organisms.

Lyme disease is a serious health threat. Infected people show great variability in symptoms including rashes, muscle and joint aches, headaches, fevers, fatigue, arthritis, facial paralysis, etc. Early treatment usually results in a complete recovery, but chronic infections are much harder to treat. Take caution and pay attention to your body.

Today, we often hear how nature is out of balance, leading one, understandably, to imagine that the natural world thousands of years ago was in balance. In truth, nature is in constant flux, but the constant changes have tended to balance out. We humans have greatly altered our environment. Ticks have been a part of the landscape for millennia and have probably always been vectors for various smaller organisms. Deer were present in much greater numbers, as far as we can tell, in pre-Columbian times. The reality is, we manage our landscape for our needs and we reap the benefits and the costs.