The Lone Star Tick (Amblyomma americanum) was the first tick to be described in the United States, in 1754 (Childs and Paddock 2003). Female Lone Star Ticks have a conspicuous whitish spot (usually just one) on the back near the posterior end of the scutum (the scutum is the hard shield extending over roughly the anterior third of a female hard tick's dorsal surface and may be obscured in an engorged tick) (Cooley and Kohls 1944). Males lack this conspicuous white spot and, as in other male hard ticks, the scutum extends over most of the dorsal surface.
Because of its aggressive and mostly non-specific feeding habits and its high population densities, the Lone Star Tick is one of the most annoying and economically important ticks in the United States. Adults parasitize medium and large mammals (including cattle), and the larvae and nymphs feed on a wide variety of small to large mammals and ground-feeding birds (a large number of known hosts are listed in Cooley and Kohls 1944 and Bishopp and Trembley 1945), although availability of large mammalian hosts such as White-tailed Deer is likely essential to maintain large populations (Childs and Paddock 2003). Bishopp and Trembley (1945) counted around 4800 ticks, mainly Lone Star nymphs, on a single ear of a deer.
The Lone Star Tick is a three-host species, and is a general feeder in all its active stages (Bishopp and Trembley 1945). All three motile life stages will bite people (Cooley and Kohls 1944; Bishopp and Trembley 1945; Goddard and Varela-Stokes 2009), but it was not until the early 1990s that this tick was shown to be the principal vector for any human disease. Since the late 1980s, researchers have come to view this tick as more than just a nuisance (from a human perspective), but in fact an important vector of several diseases affecting humans (Childs and Paddock 2003). Although these diseases--human monocytic (or monocytotropic) ehrlichiosis (HME), Ehrlichia ewingii ehrlichiosis, and southern tick-associated rash illness (STARI)--were presumably present in the United States prior to their recognition, it is very likely that the prevalence of both these three diseases and the Lone Star Tick itself increased as a result of exploding populations of their keystone host, the White-tailed Deer, during the 20th century (Paddock and Yabsley 2007).
An innovative effort to control populations of ticks relying heavily on deer hosts has involved the "4-poster" topical treatment device, which passively applies acaricide (i.e., mite-killing chemicals) to the head, neck, and ears of deer as they feed from the device. Pound et al. (2000), for example, applied the acaricide amitraz to White-tailed Deer through free-choice interaction with a "4-poster" device and observed a significantly reduced abundance of free-living Lone Star Ticks.
Lone Star Ticks are active from early spring until fall; adults appear in February, and population numbers peak in May or June and diminish by the end of July. Nymphs may appear as early as March after overwintering as flat nymphs and are active until August or September with two peaks of activity, one in May or June and one again in August representing the in-year population. Larvae are generally active from June through October, with numbers peaking in August. In the southern part of its range, the activity of the Lone Star Tick begins in February and declines by July, while in the northern part of the range, activity may begin later with peak activity in June and July. (Goddard and Varela-Stokes 2009 and references therein) Lonestar Ticks overwinter as replete larvae, unfed or replete nymphs, or unfed adults.
The lone star tick is endemic to the United States, occurring from west-central Texas north to the lower Midwest, east to the Atlantic Coast and northward all the way to Maine. This range represents a significant range expansion for this species, which was regarded as an essentially southern species well into the latter half of the 20th century (Good 1972; Cooley and Kohls 1944; Goddard and Varela-Stokes 2009 and references therein).
Although the time it spends feeding on a host is a critical period in a tick's life cycle, ticks spend most of their lives off-host. Between blood meals, nutrient reserves must be used economically and body water content must be maintained or desiccation and ultimately death results. Body water homeostasis is among the most important processes that influences off-host survival. Ticks as a group can survive longer without food or drinking water than any other arthropod. Needham and Teel (1991) review the physiological challenges and coping mechanisms associated with the "gorging-fasting" life history characteristic of ticks.
The Lone Star Tick inhabits meadows, woodlands, and hardwood forests. Its primary hosts are diverse wild and domestic mammals, although deer are considered to be definitive hosts (hosts upon which the reproductive stage depends) (Parola et al. 2005).
The Lone Star Tick is a known or suspected vector for several diseases affecting humans. Transmission of a number of diseases caused by rickettsiae has been attributed to the Lone Star Tick at one time or another. Although in the past this tick was believed to carry and transmit the bacterium Rickettsia rickettsii, the cause of Rocky Mountain Spotted Fever, much evidence now suggests that this rarely, if ever occurs, although a normally non-pathogenic rickettsia that has been referred to as Rickettsia amblyommii may cause mild disease in some individuals (Goddard and Varela-Stokes 2009 and references therein). In the early 1940s, a mysterious disease characterized by low white blood cell counts, fever, and severe occipital headache affected many (>1000) soldiers at Camp Bullis, Texas, near San Antonio. Investigations indicated that this disease was caused by an unidentified rickettsia transmitted by Lone Star Ticks, but Bullis Fever has not been reported since the late 1940s. (Childs and Paddock 2003; Goddard and Varela-Stokes 2009 and references therein) Based on current knowledge, the likelihood of Lone Star Ticks being important vectors for any rickettsial diseases of humans appears to be low.
Since first being recognized in 1986, a disease known as human monocytotropic ehrlichiosis (HME) has become an important public health issue in the southeastern and south-central United States. HME may cause morbidity and can result in severe illness, and even death, if left untreated or if treatment is delayed. In contrast to Rocky Mountain Spotted Fever, an associated rash is relatively uncommon in HME patients. Hundreds of cases a year are now reported and it is possible that many cases go unreported. At least one author has suggested that Bullis Fever (see above) may actually have been HME. The causative agent of HME, Ehrlichia chaffeensis, was not isolated until 1991. Considerable evidence indicates that the Lone Star Tick is an important vector for E. chaffeensis and that White-tailed Deer and other wild and domestic mammals (including dogs) are important hosts. The greatest influence on the emergence of ehrlichioses associated with Lone Star Ticks has been the explosive growth of White-tailed Deer populations in the United States. Other pathogenic Ehrlichia may also be transmitted by the Lone Star Tick. (Childs and Paddock 2003; Goddard and Varela-Stokes 2009 and references therein)
Several diseases caused by non-rickettsial bacteria can be transmitted by Lone Star Ticks. Tularemia is caused by infection with Francisella tularensis, which can be transmitted by Lone Star Ticks (as well as by other routes), often via cottontail rabbits. Lyme Disease, caused by the spirochete bacterium Borrelia burgdorferi, is apparently not transmitted by the Lone Star Tick, but only by the Ixodes ticks I. scapularis in the eastern United States and I. pacificus in the western United States. However, a Lyme Disease-like illness has been reported in the southern United States that has been referred to as ‘‘southern tick-associated rash illness’’ (STARI) or Master’s disease and this illness appears to be associated with the Lone Star Tick. Inconclusive data suggest the possibility that STARI may be caused by a recently discovered Borrelia, B. lonestari, isolated from the Lone Star Tick. (Goddard and Varela-Stokes 2009 and references therein)
There is evidence that Lone Star Ticks are capable of transmitting pathogenic viruses to humans, but so far no indication that this is a common or widespread phenomenon. The same can be said regarding transmission by Lone Star Ticks of pathogenic protozoans. Although much has been learned about the role of the Lone Star Tick (and ticks in general) in transmitting disease organisms to humans, many questions and uncertainties remain, making investigation of the ecology of tick-borne diseases an exciting and dynamic area of research (Goddard and Varela-Stokes 2009 and references therein)
Amblyomma americanum, also known as the lone star tick, the northeastern water tick, or the turkey tick, is a type of tick indigenous to much of the eastern United States and Mexico, that bites painlessly and commonly goes unnoticed, remaining attached to its host for as long as seven days until it is fully engorged with blood. It is a member of the phylum Arthropoda, class Arachnida.[2] The adult lone star tick is sexually dimorphic, named for a silvery-white, star-shaped spot or "lone star" present near the center of the posterior portion of the adult female shield (scutum); adult males conversely have varied white streaks or spots around the margins of their shields.[3][4]
A. americanum is also referred to as the turkey tick in some Midwestern U.S. states, where wild turkeys are a common host for immature ticks.[4] It is the primary vector of Ehrlichia chaffeensis, which causes human monocytic ehrlichiosis, and Ehrlichia ewingii, which causes human and canine granulocytic ehrlichiosis.[5] Other disease-causing bacterial agents isolated from lone star ticks include Francisella tularensis, Rickettsia amblyommii, and Coxiella burnetti.[6]
The lone star tick is widely distributed across the East, Southeast, and Midwest United States.[3][7] It lives in wooded areas, particularly in second-growth forests with thick underbrush, where white-tailed deer (the primary host of mature ticks) reside.[4][7][8] Lone star ticks can also be found in ecotonal areas (transition zones between different biomes) such as those between forest and grassland ecosystems.[7][8] The lone star tick uses thick underbrush or high grass to attach to its host by way of questing. Questing is an activity in which the tick climbs up a blade of grass or to the edges of leaves and stretches its front legs forward, in response to stimuli from biochemicals such as carbon dioxide or heat and vibration from movement, and mounts the passing host as it brushes against the tick's legs.[9] Once attached to its host, the tick is able to move around and select a preferred feeding site.[4]
The tick has also been reported, outside of its range in Canada, in areas of Southern Ontario, including in London, Wellington County and the Region of Waterloo.[10]
The tick follows the normal developmental stages of egg, larva, nymph, and adult. It is known as a three-host tick, meaning that it feeds from a different host during each of the larval, nymphal, and adult stages. The lone star tick attaches itself to a host by way of questing.[11] The eggs are laid on the ground, hatch, and the larvae wait for or actively seek a host (questing behavior). A larva feeds, detaches from its host, molts into a nymph when on the ground, and quests by crawling on the ground or waiting on vegetation. The nymph feeds and repeats the same process as the larva, but emerges having developed the anatomy of either an adult female or male. Adults quest similarly to nymphs. The female attaches only to a species of host for reproduction. The female engorges on much blood, expanding greatly, then detaches and converts the blood meal into eggs, which are laid on the ground. Females of large species of Amblyomma engorge to a weight of 5 g and lay 20,000 eggs. The female dies after this single egg-laying. The male takes repeated small meals of blood and attempts to mate repeatedly whilst on the same host. Feeding times for larvae last 4–7 days, nymphs for 5–10 days, and adults for 8 to 20 days. The time spent molting and questing off the host can occupy the remainder of 6 to 18 months for a single tick to complete its lifecycle. The lifecycle timing is often expanded by diapause (delayed or inactivated development or activity) in adaptation to seasonal variation of moisture and heat. Ticks are highly adapted for long-term survival off the host without feeding and can extract moisture directly from humid air. However, survival is greatly reduced by excess heat, dryness, and lack of suitable hosts to which to attach. Survival on the host is also greatly reduced by grooming and by hypersensitive immune reactions in the skin against the feeding of the ticks.[12]
The lone star tick is an aggressive, generalist feeder; it actively pursues blood meals and is not specific about the species of host upon which it feeds.[4] As already mentioned, A. americanum requires a separate animal or human host to complete each stage of its life cycle.[6] The lifecycle begins when the blood-engorged adult female tick drops from her host, depositing around 5,000 eggs a few days later, once she has reached a safe and suitable location, such as in mulch or leaf litter.[4] After an incubation period, larvae hatch from their eggs and undergo a quiescent (resting) period; this is followed by the pursuit of a host via questing.[4] After feeding for one to three days, the blood-engorged larva dislodges from its host to digest its blood meal and molt into a nymph. The nymph follows this same pattern, attaching to a new host via questing and dropping from the host after its blood meal to molt into an adult tick. The female adult tick dies shortly after depositing her eggs.[4]
Larval lone star ticks have been found attached to birds and small mammals, and nymphal ticks have been found on these two groups, as well as on small rodents.[4] Adult lone star ticks usually feed on medium and large mammals,[6] and are very frequently found on white-tailed deer.[2] Lone star ticks also feed on humans at any stage of development.[2]
Like all ticks, it can be a vector of diseases including human monocytotropic ehrlichiosis (Ehrlichia chaffeensis), canine and human granulocytic ehrlichiosis (Ehrlichia ewingii), tularemia (Francisella tularensis), and southern tick-associated rash illness (STARI, possibly caused by the spirochete Borrelia lonestari).[13] STARI exhibits a rash similar to that caused by Lyme disease, but is generally considered to be less severe.
Though the primary bacterium responsible for Lyme disease, Borrelia burgdorferi, has occasionally been isolated from lone star ticks, numerous vector competency tests have demonstrated that this tick is extremely unlikely to be capable of transmitting Lyme disease. Some evidence indicates A. americanum saliva inactivates B. burgdorferi more quickly than the saliva of Ixodes scapularis.[14] Recently the bacteria Borrelia andersonii and Borrelia americana have been linked to A. americanum.[15][16]
In 2013, in response to two cases of severe febrile illness occurring in two farmers in northwestern Missouri, researchers determined the lone star tick can transmit the heartland virus.[17] Six more cases were identified in 2012–2013 in Missouri and Tennessee.[18]
The bite of the lone star tick can cause a person to develop alpha-gal meat allergy, a delayed response to nonprimate mammalian meat and meat products.[19][20] The allergy manifests as anaphylaxis—a life-threatening allergic reaction characterized by constriction of airways and a drop in blood pressure.[19] This response is triggered by an IgE antibody to the mammalian oligosaccharide galactose-alpha-1,3-galactose (alpha-gal).[21] A study published in 2019 discovered alpha-gal in the saliva of the lone star tick.[22] As well as occurring in non-primate mammals, alpha-gal is also found in cat dander and in the drug cetuximab.[23][21] Allergic reactions to alpha-gal usually occur 3–6 hours after consuming red meat, unlike allergic reactions to other foods, whose onset following consumption is more or less immediate, making it more difficult to identify what caused the reaction.[19] Skin tests with standard meat test solutions are unreliable when testing for alpha-gal allergy, whereas skin tests with raw meat and/or pork kidney are more sensitive. Specific tests for determination of IgE to alpha-gal are available.[24]
Amblyomma americanum, also known as the lone star tick, the northeastern water tick, or the turkey tick, is a type of tick indigenous to much of the eastern United States and Mexico, that bites painlessly and commonly goes unnoticed, remaining attached to its host for as long as seven days until it is fully engorged with blood. It is a member of the phylum Arthropoda, class Arachnida. The adult lone star tick is sexually dimorphic, named for a silvery-white, star-shaped spot or "lone star" present near the center of the posterior portion of the adult female shield (scutum); adult males conversely have varied white streaks or spots around the margins of their shields.
A. americanum is also referred to as the turkey tick in some Midwestern U.S. states, where wild turkeys are a common host for immature ticks. It is the primary vector of Ehrlichia chaffeensis, which causes human monocytic ehrlichiosis, and Ehrlichia ewingii, which causes human and canine granulocytic ehrlichiosis. Other disease-causing bacterial agents isolated from lone star ticks include Francisella tularensis, Rickettsia amblyommii, and Coxiella burnetti.
The distribution of the lone star tick (Amblyomma americanum) in the United States
