Gulf Coast Tick
Gulf Coast ticks (Amblyomma maculatum) normally inhabit grassland prairies and the edges of wooded areas where the shade of canopy cover provides optimal micro-climate off-host survival. The range of the Gulf Coast tick is historically described as a region approximately 100-150 miles inland along the Gulf of Mexico and southern Atlantic coast, extending from Texas to South Carolina.
Gulf Coast ticks are found in grass prairies and coastal uplands throughout much of the western hemisphere. The ticks are ectoparasites that feed on a variety of birds and mammals, and will readily bite humans. Gulf Coast ticks are of increasing concern because of their ability to transmit several pathogens of veterinary and medical importance.
A three-host tick, the Gulf Coast tick is an arthropod of veterinary and medical importance throughout its range. Adult ticks attach and concentrate feeding primarily in the ears of their hosts. This clustered feeding habit concentrates tissue damage and can cause “gotch ear” in young calves, a condition that negatively effects their sale value at market. Seasonal activity of Gulf Coast ticks varies among life stage and population locality.
Gulf Coast ticks are considered three-host ticks because each active life stage feeds on a different host. In general, Gulf Coast tick larvae and nymphs feed on small animals, such as birds, rodents and rabbits, while adults feed on larger animals including dogs, coyotes, skunks, panthers, and bears. Gulf Coast ticks preferentially infest the ears of host animals and feed by inserting their barbed mouthparts, called a hypostome, into the host’s skin.
Feeding and mating occur in succession on the host. After eight days of blood feeding on a host and completion of spermatogenesis, male Gulf Coast ticks release a pheromone which alerts female ticks, also located on the host, that they are ready to mate. Thereafter, female Gulf Coast ticks aggregate near the male and attach to the host to blood feed. Males move to the females and complete the mating process. After the blood meal and mating have been completed, the females drop off the host and find suitable microhabitats to lay their egg clutch, which typically takes up to 26 days; males remain on the host and mate with additional females.
Following an incubation period of up to three weeks in optimum temperatures (~80°F at 70-98% humidity), larvae hatch and aggregate on the lower surface of vegetation before ascending the foliage in search for their first host through a behavior called questing.
Gulf Coast ticks are xerophilic, which means that they love drier environments, and can quest for an extended period of time in peak temperature environments to find suitable hosts. Once on the host, immature Gulf Coast ticks remain attached until fully engorged, which can take up to 10 days. Replete ticks drop from their host and stay hidden in the environment as they undergo a molt to the next active life stage.
Seasonal peaks in Gulf Coast tick populations vary based on their geographic location. Coastal populations found in Texas are active from May through March, whereas inland populations in Oklahoma and Kansas are active from February through October.
In Texas, adult activity peaks in August, followed by larvae in December and nymphs in January. In Oklahoma and Kansas, adult activity peaks in April, followed by larvae in June and nymphs in July. Gulf Coast ticks in Mississippi have been collected from March through November, with adults peaking during late July to early August. Seasonal activity of Gulf Coast ticks in northern Florida occurs from February to September.
Rickettsia rickettsii, the causative agent of Rocky Mountain Spotted Fever, was the only known tick-borne spotted fever to occur in the United States. This changed in 2002 when a rickettsial species, identified 60 years earlier, was implicated as the causative agent of Rickettsiosis in a middle-aged man from Virginia. This newly recognized pathogen, Rickettsia parkeri, is primarily transmitted by Gulf Coast ticks and is now recognized as a human pathogen of increasing public health concern in the southeastern United States. Gulf Coast tick Rickettsia parkeri infection rates in some areas have been recorded as high as 55%. These ticks also transmit the pathogen Rickettsia parkeri to humans, another type of Spotted Fever. Recent studies (2018) report infection rates of greater than 20% in Gulf Coast ticks.
The historical importance of Gulf Coast ticks has centered on the impact due to livestock infestations. Gulf Coast tick bites can cause severe inflammation, abscesses, and predispose livestock hosts to the primary screwworm, Cochliomyia hominivorax, where this pest occurs and can cause other tissue damage. Additionally, severe infestations on livestock have been shown to cause lethargy, debilitation, and altered body composition. Livestock infested with Gulf Coast ticks were often recognized by drooping “gotch ears,” which reduced market value at sale. Today, the importance of the Gulf Coast tick is more profound because of the recognition of the impacts of pathogenic organisms transmitted by this tick that result in serious medical conditions and diseases affecting humans and their domesticated and companion animals.
Gulf Coast ticks are recognized as the principal vector of Hepatozoon americanum, the causative agent of American canine hepatozoonosis in the southern United States . Interestingly, the protozoan pathogen is not transmitted through the bite of an infected tick; rather, transmission occurs when dogs consume infected ticks while grooming. In wild canines, transmission often occurs through predation of infected prey.
Laboratory experiments have shown Gulf Coast ticks are capable of transmitting the causative agent of Leptospirosis in livestock, Leptospira pomona. Burgdorfer used capillary tubes filled with concentrated infected blood to artificially feed ticks. The ticks were then allowed to feed on naïve guinea pigs approximately two weeks later and some of the guinea pigs became ill with infection caused by the spirochete pathogen. However, the role of Gulf Coast ticks in natural transmission of Leptospira in the United States is unclear.
In the laboratory, Gulf Coast ticks have been shown to be competent vectors of Ehrlichia (formerly Cowdria) ruminantium, the Heartwater pathogen. Heartwater is a fatal disease of wild and domestic ruminants (i.e. cattle, deer, sheep) and is transmitted by ticks in the genus Amblyomma. Heartwater occurs in sub-Saharan Africa and on some islands in the Caribbean, but has not been detected in the United States. However, two of the principal vectors, Amblyomma variegatum and Amblyomma hebraeum, have been reported on imported wildlife in Florida and could introduce Ehrlichia ruminantium to naïve host species. If introduced, Ehrlichia ruminantium potentially could be maintained in animal disease cycles by the Gulf Coast tick.
Tick paralysis is a potentially fatal medical condition caused by tick toxins released during feeding that affect the host’s motor neurons, leading to paralysis and respiratory failure. Once the tick is removed or voluntarily detaches, full recovery is usually observed within 24 hours. Gulf Coast ticks have been responsible for paralysis in dogs and humans, although these incidents are uncommon.
Gulf Coast ticks are found in grass prairies and coastal uplands throughout much of the western hemisphere. The ticks are ectoparasites that feed on a variety of birds and mammals, and will readily bite humans.
The range of the Gulf Coast tick is historically described as a region approximately 100-150 miles inland along the Gulf of Mexico and southern Atlantic coast, extending from Texas to South Carolina.
Resident populations of Gulf Coast ticks are established in Oklahoma, Kansas, and Arkansas, where their distributions appear to be expanding. Incidental introductions of these ticks beyond endemic regions occurs with increasing frequency; likely due to the feeding of immature ticks on migrating birds, and the transportation of tick infested livestock and wildlife into new areas.
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