CHAPTER 36 Tick Removal and Prevention of Infection
Persons frequenting outdoor areas may be exposed to ticks. Ticks often lurk in tall grasses or in overhead branches, and will attach themselves to persons passing by them in search of a blood meal. Although most tick bites are harmless, ticks may be the vectors of several significant diseases. Because it is impossible to identify in the field whether a tick carries an infectious disease, it is good medical practice to remove all ticks found on human skin promptly. Ticks feed slowly, and several hours of attachment are thought to be required for transmission of tick-borne illnesses.
Ticks have eight legs and are members of the class Arachnida. Ticks belonging to the families Argasidae (soft ticks) and Ixodidae (hard ticks) are able to act as disease vectors to humans. The ixodid ticks Dermacentor and Ixodes are most likely to be encountered by humans in North America, and they can transmit microorganisms hematogenously during all phases of their development. See Box 36-1 for a list of tick-borne diseases.
Box 36-1 Tick-borne Diseases
Ticks have powerful mouthparts to break the skin of their hosts and enable a blood meal. The saliva of the tick has anticoagulant properties to keep blood flowing. Pathogens in the gut of the tick migrate to the tick’s salivary glands, and thus are transmitted parenterally to the host during feeding. Generally, a tick must be attached for longer than 8 hours for successful transmission of disease.
Two of the tick-borne diseases bear special mention. Tick-bite paralysis is a serious illness that presents as an ascending neuromuscular paralysis, similar to Guillain-Barré syndrome. The paralysis is caused by envenomation of the host with a salivary neurotoxin secreted in the saliva of certain gravid Dermacentor ticks. Resolution of the paralysis occurs after removal of the often-overlooked tick.
Lyme disease is a fairly common illness affecting the cardiovascular, musculoskeletal, neurologic, and dermatologic systems. It is often seen in children and adults who spend time outdoors. Lyme disease is caused by the spirochete Borrelia burgdorferi, and is transmitted to humans by the bite of the hard Ixodes tick. White-footed mice and white-tailed deer are the major reservoirs for B. burgdorferi. This disease is becoming prevalent throughout northeastern North America, and is worth including in the differential diagnosis of unusual rashes, fevers, myalgias, and arthralgias. It is best diagnosed by enzyme-linked immunosorbent assay (ELISA) testing of serum for specific antibodies to B. burgdorferi. A Lyme disease preventative vaccine is now commercially available (LYMErix), and may be appropriate for those individuals living in high-prevalence locations who spend a great deal of time outdoors. Treatment of Lyme disease is discussed in the section on Complications and Disease Prevention. See Table 36-1 for a synopsis of presenting features of other tick-borne diseases.