What’s Eating You? Lone Star Tick (Amblyomma americanum)
Amblyomma americanum, also known as the lone star tick, is found in much of the eastern United States. Since the mid-20th century, the lone star tick has been implicated in human disease. Today, A americanum remains an important vector for tick-borne illness. In addition to others, species of Rickettsia, Ehrlichia, and Borrelia are all transmitted by the lone star tick. Recently described conditions such as Southern tick–associated rash illness and anaphylaxis to red meat following tick bites have been attributed to the lone star tick. Impressive local reactions also can result after bites from A americanum. Early treatment of tick-borne illness is crucial to ensure good patient outcomes. Tick-control measures also are an important part of disease management in endemic areas. We discuss the tick’s biology, human illnesses associated with A americanum, and methods to control tick numbers and eliminate disease in local reservoirs.
Practice Points
- Amblyomma americanum (lone star tick) is widely distributed throughout the United States and is an important cause of several tick-borne illnesses.
- Prompt diagnosis and treatment of tick-borne disease improves patient outcomes.
- In some cases, tick bites may cause the human host to develop certain IgE antibodies that result in a delayed-onset anaphylaxis after ingestion of red meat.
Disease Hosts
At Little Rock Air Force Base in Arkansas, A americanum has been a source of Ehrlichia infection. During one outbreak, deer in the area were found to have as many as 2550 ticks per ear,19 which demonstrates the magnitude of tick infestation in some areas of the United States. Tick infestation is not merely of concern to the US military. Ticks are ubiquitous and can be found on neatly trimmed suburban lawns as well as in rough thickets.
More recently, bites from A americanum have been found to induce allergies to red meat in some patients.1 IgE antibodies directed against galactose-alpha-1,3-galactose (alpha gal) have been implicated as the cause of this reaction. These antibodies cause delayed-onset anaphylaxis occurring 3 to 6 hours after ingestion of red meat. Tick bites appear to be the most important and perhaps the only cause of IgE antibodies to alpha gal in the United States.1
Wild white-tailed deer serve as reservoir hosts for several diseases transmitted by A americanum, including HME, human ehrlichiosis ewingii, and Southern tick–associated rash illness.12,20 Communities located close to wildlife reserves may have higher rates of infection.21 Application of acaricides to corn contained in deer feeders has been shown to be an effective method of decreasing local tick populations, which is a potential method for disease control in at-risk areas, though it is costly and time consuming.22
Tick-Control Measures
Hard ticks produce little urine. Instead, excess water is eliminated via salivation back into the host. Loss of water also occurs through spiracles. Absorption of water from the atmosphere is important for the tick to maintain hydration. The tick produces intensely hygroscopic saliva that absorbs water from surrounding moist air. The humidified saliva is then reingested by the tick. In hot climates, ticks are prone to dehydration unless they can find a source of moist air, usually within a layer of leaf debris.23 When the leaf debris is stirred by a human walking through the area, the tick can make contact with the human. Therefore, removal of leaf debris is a critical part of tick-control efforts, as it reduces tick numbers by means of dehydration. Tick eggs also require sufficient humidity to hatch. Leaf removal increases the effectiveness of insecticide applications, which would otherwise do little harm to the ticks below if sprayed on top of leaf debris.
Some lone star ticks attach to birds and disseminate widely. Attachments to animal hosts with long-range migration patterns complicate tick-control efforts.24 Animal migration may contribute to the spread of disease from one geographic region to another.
Imported fire ants are voracious eaters that gather and consume ticks eggs. Fire ants provide an excellent natural means of tick control. Tick numbers in places such as Camp Bullis have declined dramatically since the introduction of imported fire ants.25
