Florida Medical Entomology Laboratory
Florida Medical Entomology Laboratory
Ticks in Florida
Many mosquito control districts also confront issues with ticks. There are likely to be inquiries from the public about ticks and tick-borne diseases, since the local MCD may be perceived as the appropriate place for help regarding any insect which bites humans. Ticks aren't insects, but this is a subtlety often missed by those whose reaction to animals with more than 4 legs or that feed on blood is "go away"! MCD's may also confront ticks while carrying out their own operations; mosquito habitat may also be tick habitat and personnel may be bitten during the course of their activities. Besides the aggravation, this is a concern because of tick-borne disease.
There are numerous tick species in Florida, many of which never bother humans or domestic animals. Ticks are related to spiders and mites; essentially, ticks are giant mites. There are three families of ticks, two of which are in Florida. The Argasidae, or soft ticks, are primarily nest parasites and are generally not pests in Florida. Most of the species of concern in Florida are members of the Ixodidae, or hard ticks. There are five species which frequently bite humans or domestic animals, and a few others that may be of interest. They vary in their host usage, habitat preferences, and disease transmission, and thus in the risk they present to the public and MCD workers.
Hard ticks are obligate parasites, requiring a blood meal once in each stage (larva, nymph and adult). All of the species of concern in Florida are 3-host ticks, so named because they use 3 separate hosts for each meal (Fig. 1). The hosts may be of the same species, but the tick will attach, feed, and then drop off the host each time. Ticks seek hosts by climbing up vegetation (questing) and waiting for a host to contact them. The preferred height and type of vegetation depends on the preferred host, but is typically less than 1 meter high. While questing, ticks alternate between host seeking in the vegetation and rehydrating on the ground. Contrary to popular opinion, ticks are not found up in trees! Ticks found on your head got there by climbing up after they were on you.
Ixodes scapularis - the black-legged tick. This is also called the deer tick, particularly in northern areas. It is one of the smaller ticks, with the females being red and black and other stages plain brown to black, with no ornamentation. This tick prefers small to medium sized mammals, birds and lizards as larvae and nymphs and larger mammals, such as deer, dogs and humans, as adults (see Fig. 1). This is the vector of the Lyme disease agent, Borrelia burgdorferi. The ecology of this species is very different in southern areas than in the north, where many studies have been located. In Florida, the immatures rarely are found on humans or domestic animals. The adults are active from October to May and are the biggest threat to humans. The black-legged tick is found throughout Florida, but typically does not have large populations. It is most commonly found in wooded areas or along the edge of forest patches.
Fig. 1. Life cycle of Ixodes scapularis, as an example of a 3-host tick. Note that each stage of the tick uses a different host, but there is substantial overlap in the species fed upon in each stage.
Dermacentor variabilis - the American dog Tick. Found primarily on small rodents as immatures and on larger mammals, including dogs and humans as adults. This is one of the larger ticks in Florida, and the adults are typically brown with white markings. It is a vector of Rocky Mountain spotted fever, Rickettsia rickettsi. It is found throughout Florida, most often in open habitats and grassy areas, but also along the edge of wooded areas.
Amblyomma americanum - The Lone Star Tick. This tick is named for the ornamentation on the adult female, which is golden brown with a prominent white spot on the back. All stages of this tick will readily bite humans and domestic animals, and populations can be large enough to be a pest. It has been found throughout Florida, but large populations are generally found in the north and central areas. Its vector status is uncertain, but it has been implicated in the transmission of Ehrlichia and Anaplasma species, the causative agents of ehrlichiosis in humans and animals, and in Rocky Mountain spotted fever. The lone star tick has a broad host range, feeding on most mammals in all stages and also on birds as immatures. It has broad habitat use as well, and can be found in woods and open areas.
Amblyomma maculatum - the Gulf Coast Tick. This tick is generally only noticed in the adult stages, when it will attach to humans and domestic animals. It prefers large animals such as cattle and deer. It is a very striking tick, gold-brown with white ornamentation. It is not known to vector any disease agents in Florida, but there is concern that it could be an effective vector of heartwater (a severe disease of cattle) if the bacteria became established. It can be found statewide, but generally is rare.
Rhipicephalus sanguineus - the brown dog tick. This tick is cosmopolitan, found throughout the world, and is a specialist on dogs in all stages. It can be occasionally found on wildlife, but this is rare in Florida. All stages will bite humans, but usually only when there is an infestation and then the dogs are removed. This is one of the few, and only one in Florida, hard ticks that will establish a population indoors, in a house or kennel. The ticks will seek out cracks and crevices and retreat deep into the walls between feeding, and are very difficult to control once a population has become established. This species is known to vector Ehrlichia species, particularly to dogs, and has been implicated in transmission of Rocky Mountain spotted fever.
A note on taxonomy: as with mosquitoes, the taxonomy of ticks and bacteria is always undergoing revision. Therefore, you will often see different names for ticks and bacteria. Tick phyologeny was revised in 2004 (Barker & Murrell 2004), changing the cattle tick from Boophilus microplus to Rhipicephalus (Boophilus) microplus. Similarly, the genera Anaplasma and Ehrlichia were revised (Dumler et al. 2001); this moved Ehrlichia phagocytophila, the agent of human granulocytic ehrlichiosis, into the genus Anaplasma. The taxonomy of the bacteria which causes Lyme disease, Borrelia burgdorferi, is complex. There are several genospecies, and they cause differing pathology in humans. In the US, B. burgdorferi sensu strictu is the agent of Lyme disease. However, as we understand this complex interaction between ticks and bacteria more completely, other Borrelia species may be shown to cause human disease.
Minimizing tick contact is the best way to reduce the risk of tick-borne disease. Using repellents (those containing DEET are effective), wearing long pants, tucked into boots or socks if necessary, and thorough tick checks after returning from tick-infested habitat are effective methods. Most ticks do not bite immediately, and some, but not all, pathogens are not transmitted until the tick has been attached for 24-48 hours. For attached ticks, the best removal method is to grasp the tick as close to the skin as possible using tweezers or forceps and pull straight back. Do not grab the abdomen of the tick since this injects the gut contents into the host! The wide ranges of folk remedies (Vaseline, oils, heat, twisting) are ineffective at best and can be dangerous.
This is just a quick overview of ticks in Florida. For more information, there will be a tick identification course at the Dodd short courses and there are several EDIS fact sheets available (link: Brown dog ticks, Lyme in Florida, Ehrlichia, Koehler & Castner Fleas & Ticks IN009). Some primary references of interest are:
- Barker, SC, Murrell, A. 2004. Systematics and evolution of ticks with a list of valid genus and species names. Parasitology 129: S15-S36.
- Clark, K. 2004. Borrelia species in host-seeking ticks and small mammals in northern Florida. J Clin Microbiol 42: 5076-5086.
- Dumler, J. S., A. F. Barbet, C. P. J. Bekker, G. A. Dasch, G. H. Palmer, S. C. Ray, Y. Rikihisa, and F. R. Rurangirwa. 2001. Reorganization of genera in the families Rickettsiaceae and Anaplasmataceae in the order Rickettsiales: unification of some species of Ehrlichia with Anaplasma, Cowdria with Ehrlichia and Ehrlichia with Neorickettsia, descriptions of six new species combinations and designation of Ehrlichia equi and 'HGE agent' as subjective synonyms of Ehrlichia phagocytophila. Int J Syst Evol Microbiol 51:2145-2165.
- Keirans, J. E. and T. R. Litwak. 1989. Pictorial key to the adults of hard ticks, family Ixodidae (Ixodida: Ixodoidea) east of the Mississippi River. J. Med. Entomol. 26:435-448.
Cynthia C. Lord, Associate Professor
Florida Medical Entomology Laboratory
University of Florida/IFAS
Vero Beach, FL
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