The American Dog Tick (Dermacentor variabilis) is one of the most common tick species encountered across the United States. It is a known vector for several serious diseases, making it a significant public health concern. Lyme disease, caused by the bacterium Borrelia burgdorferi, is the most frequently reported tick-borne illness in the country. Scientific evidence indicates that while this species can transmit other pathogens, it is generally not considered a competent vector for transmitting the Lyme disease bacterium to humans.
The American Dog Tick and Lyme Disease
The American Dog Tick (ADT) is not an efficient carrier of Lyme disease due to biological limitations. Although the tick can acquire the Borrelia burgdorferi bacterium, it rarely transmits the pathogen effectively during a subsequent blood meal. This lack of vector competence means the bacteria struggle to survive or migrate from the tick’s midgut to its salivary glands, a necessary step for transmission.
Identifying this species helps assess risk, as the adult ADT is noticeably larger than the true Lyme vectors, measuring about one-quarter of an inch when unfed. The female ADT has a reddish-brown body with a distinct creamy-white or silver-gray shield (scutum) behind its head. Adult males exhibit a mottled pattern of silver-gray markings covering their entire back. This tick prefers grassy areas, scrubland, and trails, and its adult stage is most active from spring through mid-summer.
The True Vector: Blacklegged Ticks
The responsibility for Lyme disease transmission falls almost entirely on the Blacklegged Tick, Ixodes scapularis, in the Eastern and Midwestern United States. The Western Blacklegged Tick, Ixodes pacificus, fulfills this role on the Pacific Coast. These Ixodes species possess the biological mechanisms necessary for the Borrelia spirochete to migrate and be injected into the host during feeding.
The nymph stage is most often responsible for infecting humans, as it is about the size of a poppy seed and difficult to spot. Nymphs are active during late spring and summer, feeding undetected for the required attachment time, which typically needs to exceed 24 hours for transmission. Adult Blacklegged Ticks are also capable of transmission, but they are larger and more likely to be removed sooner. Unlike the American Dog Tick, the Blacklegged Tick has a solid dark-colored scutum and favors heavily wooded areas and leaf litter.
Other Health Threats from American Dog Ticks
While the American Dog Tick is not the vector for Lyme disease, it is a carrier for other serious tick-borne illnesses. The most concerning is Rocky Mountain Spotted Fever (RMSF), caused by the bacterium Rickettsia rickettsii. RMSF is a rapidly progressing disease that can be fatal if not treated promptly within the first five days of symptoms.
Symptoms of RMSF typically begin three to twelve days after the tick bite, often starting with a sudden high fever and a severe headache. Other early signs include myalgia (muscle pain) and gastrointestinal issues like nausea, vomiting, or abdominal pain. A rash often develops two to four days after the fever begins, usually starting on the wrists and ankles before spreading. The American Dog Tick is also a confirmed vector for Tularemia (rabbit fever), a rare but serious bacterial infection that can cause fever, skin ulcers, and swollen lymph glands.
Prevention and Safe Removal
Protecting against tick bites involves consistent preventative measures, especially when spending time in wooded or grassy habitats.
Prevention Measures
- Wearing light-colored clothing makes it easier to spot ticks crawling on the fabric.
- Tucking pants into socks minimizes entry points.
- Using an EPA-registered repellent containing DEET on the skin.
- Treating clothing and gear with products containing permethrin can reduce the risk of attachment.
After outdoor activity, perform a thorough full-body tick check, paying special attention to hair, ears, armpits, and the groin area. If a tick is found attached, remove it immediately using fine-tipped tweezers. Grasp the tick as close to the skin’s surface as possible and pull upward with steady, even pressure. Avoid twisting or jerking, and do not crush the tick’s body during removal, as this can force infectious fluids into the bite site.