A multitude of environmental and human factors has created a near “perfect storm” over the past 20 years leading to a population explosion of ticks throughout North America.
There are two families of ticks found in the United States: Ixodidae (hard ticks) and Argasidae (soft ticks). Of the 700 species of hard ticks and 200 species of soft ticks found throughout the world, only a few are known to bite and transmit disease to humans.
Hard ticks and soft ticks have very different life cycles appearing different at each stage.
Hard ticks (Ixodidae) begin as an egg that is laid by an adult female tick. Once the egg hatches a larvae emerges that must then find and feed on a small mammal or bird (host). After feeding they will drop to the ground from their host and go through a molting process emerging as a nymph. The nymphs will then seek larger hosts, and after feeding will drop, then molt into adults. The life cycle of hard ticks lasts one to two years depending on the species. The bite of a hard tick is generally painless, with a feeding process lasting several hours, to days, even weeks.
Soft ticks (Argasidae), like hard ticks begin as an egg, hatching into a larvae, feeding then molting into a nymph. Nymphal Argasid ticks may go through several phases as nymphs, requiring a blood meal at each stage. Soft ticks life cycle lasts from months to years depending on the species. The bite is typically painless only lasting 15-30 minutes making it harder to detect.
While both hard and soft adult ticks are easiest to identify, it is important to note nymphal ticks are equally capable of transmitting disease.
The following is a list of types of ticks found in the United States that are known to bite and transmit disease to humans.
Types of Ticks
American Dog Tick (Dermacentor variabilis)
The American dog tick is the primary vector of the bacterium that causes Rocky Mountain spotted fever (Rickettsia rickettsii). It also transmits the agents of tularemia (Francisella tularensis), ehrlichiosis (Ehrlichia spp.), and anaplasmosis (Anaplasma phagocytophilum), and can cause tick paralysis. This tick has a broad distribution east of the Rocky Mountains, throughout the East and Gulf Coast, along the Pacific Coast, into Canada and parts of Alaska. The greatest risk of being bitten is from the adult females during the spring and summer months. American dog ticks are mostly found in areas with little or no tree cover, such as tall grassy fields and low lying brush and twigs, as well as along walkways and trails.
Blacklegged or Deer Tick (Ixodes scapularis)
The deer tick is widely distributed across the eastern United States and is known to transmit Borrelia burgdorferi and B. mayonii (Lyme disease), Borrelia miyamotoi (Borrelia miyamotoi disease, aka hard tick-borne relapsing fever), Ehrlichia muris (ehrlichiosis), A. phagocytophilum, Babesia microti (babesiosis), multiple species of Rickettsia, deer tick virus, and Powassan virus. This tick is also suspected of transmitting Bartonella spp. to humans. Over the last two decades, the distribution of blacklegged ticks has expanded. They are now found throughout the eastern U.S., large areas in the north and central U.S., and in the South. The northern distribution of the blacklegged tick continues to spread in all directions from major endemic areas in the Northeast and Upper Midwest. It’s important to note that adult ticks will search for a host any time that temperatures are above freezing. These ticks are found in a wide variety of habitats that are suitable for birds, small and large mammals such as mice, squirrels, coyotes, deer and livestock. All life stages can bite humans, but nymphs and adult females are most commonly found on people after coming in contact with grass, brush, leaves, logs or pets that have been outdoors. In humans, most disease is transmitted by the nymphal ticks.
Brown Dog Tick (Rhipicephalus sanguineus)
Dogs are the primary host for the brown dog tick, which is found throughout the world. This tick can survive and breed in nature, but lives primarily in and around homes with dogs. These ticks are capable of spending their entire life cycle indoors. All of its life stages can transmit Rocky Mountain spotted fever (R. rickettsii), Q Fever (Coxiella burnetii), and other rickettsial agents to humans. They can also transmit several pathogens specific to dogs. To eradicate brown dog tick infestations, experts suggest treating all pets, their bedding areas, and the interiors of homes, kennels and yards with commercially approved acaricides (pesticides which target ticks). This process may take repeated applications over a period of several months.
Groundhog Tick (Ixodes cookei)
The groundhog tick, also known as the woodchuck tick, is found throughout the eastern half of the U.S., and is known to transmit Powassan virus. All life stages feed on a variety of warm-blooded animals, including groundhogs, skunks, squirrels, raccoons, foxes, weasels, and occasionally humans and domestic animals.
Lone Star Tick (Amblyomma americanum)
The lone star tick is widely distributed throughout the Eastern U.S., but is most prevalent in the South. Nymphal and adult ticks can transmit the agents of human monocytotropic ehrlichiosis (HME), ehrlichiosis (Ehrlichia chaffeensis, Ehrlichia ewingii, and Panola Mountain ehrlichiosis), rickettsioses (Rickettsia spp.), Rocky Mountain spotted fever (R. rickettsii), tularemia (F. tularensis), Heartland virus, Bourbon virus, Q fever and tick paralysis, as well as Borrelia lonestari, the cause of Southern tick-associated rash illness, “STARI,” which is similar to Lyme disease. These ticks are notoriously aggressive biters, with the greatest risk of being bitten from early Spring through late Fall. The adult female has a white dot or “lone star” on her back. The bite of this tick can cause a condition known as alpha-gallergy, also called alpha-gal syndrome (AGS). It causes a person to become seriously allergic to meat and products that contain mammalian ingredients, such as glue, gelatin capsules, and natural flavorings. AGS is not thought to be a tick-borne infection per se, but rather an immune response to a substance carried in the tick’s gut.
Pacific Coast Tick (Dermacentor occidentalis)
The Pacific Coast tick occurs in California), Oregon and northern Baja California. It can transmit Colorado fever virus, the unclassified spotted fever group Rickettsia 364 that causes Pacific Coast tick fever, C. burnettii (Q fever) and F. tularensis (tularemia).
Rocky Mountain Wood Tick (Dermacentor andersoni)
The Rocky Mountain wood tick is found primarily in shrublands, lightly wooded areas, open grasslands, and along trails. It occupies the vast area between the eastern and western distribution of the American dog tick and extends into Canada. It is mostly found at higher elevations. This tick is the primary vector of Colorado tick fever virus, as well as the agents of Rocky Mountain spotted fever, Q fever and tularemia. The saliva of the Rocky Mountain wood tick contains a neurotoxin that can cause tick paralysis in humans, pets, livestock and wildlife. The paralysis takes anywhere from 24-72 hours to dissipate after tick removal. These ticks are active from January through November, with diminished activity during the hot and dry mid-summer period. Adult wood ticks can be found questing about knee-high on the tips of vegetation and prefer to feed on medium to large mammals.
Soft Ticks (Ornithodoros spp.)
Soft ticks do not have a hard outer shell, and some are shaped like a large raisin. Ornithodoros hermsi and O. turicata are the primary vectors of the principal North American agents of tick-borne relapsing fever (TBRF), i.e., Borrelia hermsii and Borrelia turicatae, respectively. Of these, B. hermsii causes most cases of TBRF in the U.S., which are mostly limited to coniferous forests at elevations between 900 – 2,000 meters above sea level. People usually are bitten as they sleep in rustic mountain cabins that have been previously infested with rodents. In Texas, where TBRF is caused by B. turicatae, cases may be associated with the exploration of caves. Documented outbreaks of TBRF caused by B. hermsii have occurred at national parks and vacation cabins in Arizona, Colorado and the Lake Tahoe and Big Bear Lake areas in California.
Western Blacklegged Tick (Ixodes pacificus)
While the western blacklegged tick is most prevalent in California, it also has been found in Oregon, Washington, Arizona, Idaho, Nevada and Utah. This tick transmits the agents of Lyme disease, Borrelia miyamotoi disease, ehrlichiosis and human granulocytic anaplasmosis. It also has been found to be naturally infected with Bartonella in California. Most pathogens are transmitted by adult females and nymphs.
This tick can be found in chaparral, grasslands and woodland-grass habitats in coastal regions, as well as in dense woodlands, amongst fallen leaves or fir needles, and on fallen logs or branches. Lizards, birds, rodents, rabbits, coyotes, foxes, dogs and deer are common hosts for these ticks.