Tick Identification for Public Health and Medical Professionals in Wisconsin

This page will provide more detailed information concerning tick identification for public health and medical professionals in Wisconsin. We will identify species if the specimen or a digital image is provided (contact paskewit@entomology.wisc.edu for identifications).

IXO SCA F & M and DER VAR F & MFigure 1.  Adult deer ticks on the top (female on left, male on right) and adult wood ticks on the bottom (female on left, male on right).

IXO SCA 4 STAGESFigure 2.  All 3 life stages of Ixodes scapularis.  Upper Left, Nymph.  Upper right, larva.  Lower left, Adult female.  Lower right, adult male.

 cropped-all-3-with-nymph-1000pixel.jpg

 Figure 3.  From the left:  Wood (dog) tick, lone star tick, deer tick (all adult females) and a nymph of the deer tick (far right).

Note to Readers: 

In 1993 Ixodes dammini was shown to be the same species as Ixodes scapularis and and taxonomists decided to retain the older name, I. scapularis. Those who read peer-reviewed papers or utilize keys with references to I. dammini, should make note of this (Oliver et al. 1993).

Ticks belong to the class Arachnida, which also includes spiders and mites. Hard ticks belong to the family Ixodidae while soft ticks belong to the family Argasidae. Hard ticks have a scutum or dorsal shield while soft ticks do not.  In males hard ticks, the scutum completely covers the dorsal surface while in females the scutum covers only the anterior portion of the dorsal surface. The capitulum of hard ticks is visible or extends forward from the anterior end of the body. In soft ticks, the capitulum is found on the ventral side, does not extend beyond the anterior margin of the body and is usually not visible from a dorsal view of the tick. Male and female soft ticks are similar in appearance and lack a scutum or dorsal shield which can be used to distinguish the sexes in hard ticks. Some species of soft ticks do feed on humans but are more commonly found on birds and small mammals. There are no tick species within the Argasidae or soft tick species family which transmit tick-borne diseases of concern to humans in Wisconsin. The ticks of most importance to humans and domestic animals in North America and Wisconsin belong to the family Ixodidae. 

 

Anatomy of hard and soft ticks
Source: http://www.ticktexas.org/ticks/ticks101_anatomy.htm

1. Blacklegged or Deer Tick 

Common Name: blacklegged or deer tick

Scientific Name: Ixodes scapularis Say (Arachnida: Acari: Ixodidae)

Description and Identification: 

Adult female deer ticks are dark brown to reddish in appearance and are less than 1/8 inch (3.12mm) long. Adults exhibit sexual dimorphism with females being slightly larger than males. Nymphs are tiny (< 2 mm in size) and very difficult to see while larvae are even smaller at approximately less than 1 mm in size or about the size of a period at the end of a sentence. Adults and nymphs have four pairs of legs that are dark in coloration while larvae have 3 pairs of legs. Adult blacklegged ticks have no distinguishing markings or ornamentation on the dorsal area, are eyeless and lack festoons. The scutum, or dorsal shield just behind the mouth parts in hard-bodied ticks, covers the entire dorsal area in males while only covers the anterior portion of the dorsum in females. Unfed females also typically have orange to red coloration behind the scutum as seen in the photo to the right. Coloration of blood fed females can vary depending on the degree of engorgement from light yellowish or gray to darker brown. The scutum is also broadly rounded in comparison to other less common Ixodes species found in Wisconsin. Ixodes species also have a distinctive anal groove on the ventral side which extends anteriorly around the anus and helps distinguish Ixodes species from other species of ticks in Wisconsin (Patnaude and Mather, 2000; Keirans and Litwak 1989). 

Distribution in Wisconsin: See the section titled “Ixodes scapularis Maps.”  http://labs.russell.wisc.edu/wisconsin-ticks/presence-of-ixodes-scapularis-on-hunter-killed-deer-in-wisconsin-2008-09/

Life Cycle: see the sub-section titled “Ixodes scapularis Life Cycle” for more detailed information.

Medical and Veterinary Significance: 

The blacklegged tick is a vector of three bacterial diseases, one protozoan disease and one arboviral disease in humans in Wisconsin. Here is a link to a chart “Characteristic of Tick-borne Diseases in Wisconsin” by the Wisconsin Division of Public Health with more detailed information on diseases, etiologic agents, animal reservoirs, vectors, incubation range, clinical symptoms, available tests, treatment (ISDA guidelines). 

http://www.dhs.wisconsin.gov/communicable/tickborne/PDFfiles/Tickborne%20chart_04%2013%202012_final.pdf

Bacterial diseases:

  1. Lyme disease (Borrelia burgdorferi)- see the section on Lyme disease under tick-borne diseases for more detailed information on this pathogen.
  2. Anaplasma phagocytophilum (HGA or human granulocytic anaplasmosis) – see the section under tick-borne diseases on Anaplasmosis for more detailed information concerning this pathogen.
  3. Ehrlichia muris-like (EML)- see the section on Ehrlichia muris-like (EML) under tick-borne diseases for more detailed information concerning this pathogen. 

Protozoal disease:

  1. Most commonly Babesia microti- see the section on Human babesiosis under tick-borne diseases for more detailed information concerning this pathogen. 

Arboviral disease:

  1. Powassan virus (Flavivirus)- see the section on Powassan virus under tick-borne diseases for more detailed information concerning this pathogen. 
Diseases of Veterinary Significance associated with Ixodes scapularis as a vector:
 
  1. Lyme disease (Borrelia burgdorferi)
  2. Canine granulocytic anaplasmosis (Anaplasma phagocytophlium)

Management: See the section on Integrated Tick Management for more information on  tick-borne disease prevention and control on humans, pets and in your yard. 

 

2. Wood tick or American dog tick

Common Name: wood tick or American dog tick

Scientific Name: Dermacentor variabilis (Say) (Arachnida: Ixodida: Ixodidae)

Description and Identification: American dog tick adult females generally are about 1/4 inch (6.35mm) in length when unfed and are reddish brown in color. Adult females have a scutum or dorsal shield that covers only the anterior portion of the dorsum that has creamy-white to silvery-gray markings or striations. Females will vary in size depending on whether they have taken a blood meal. Blood fed or engorged females can enlarge to up to 15 mm long and 10 mm wide (Chan & Kaufman 2008). Adult male ticks are slightly smaller in size (3.6 mm in length) than females, and are also reddish brown with similar cream to silvery-gray colored vertical markings or striations on the dorsal scutal surface. The scutum or dorsal shield covers the entire dorsum on the males. The anal groove never extends anteriorly around the anus as does in Ixodes species. Adults have eleven festoons along the posterior edge of the abdomen and also have “eyes” along the dorsal anterior marginal edges bilaterally. The basis capituli is rectangular in shape with the palpi about as long as the basis capituli (Keirans and Litwak 1989). Adult and nymphal stage Dermacentor variabilis have eight legs while larval stages have six legs (Chan & Kaufman 2008).

Nymphs are approximately 0.9 mm long and pale, yellowish brown before taking a blood meal. Nymphs become light gray in color when engorged. Larvae are smaller than nymphs (~0.6 mm in length), also yellowish brown in color before a blood  mealand then turn grey in color when engorged (Smith and Whitman 1992). Both immature larval and nymphal stages have red markings near their eyes and lack any coloration or markings on the scutum. Nymphs can also be distinguished from adults because they lack a genital opening (Chan & Kaufman 2008).

Life stages of Dermacentor variabilis the American dog tick
Source: http://hardinmd.lib.uiowa.edu/cdc/5472.html

Distribution in United States and Wisconsin: The American dog tick is widely distributed east of the Rocky Mountains and is also found in Canada east of Saskatchewan and in limited areas along the Pacific coast (west of the Cascade and Sierra Nevada Mountain ranges) (Chan & Kaufman 2008). In Wisconsin the American dog tick can be found distributed throughout the entire state particularly associated with woodland, shrubby or tall grass habitats.  

Seasonality: In Wisconsin, all life stages of Dermacentor variabilis are most active throughout the warmer months (May-August). Peak abundance and activity of D. variabilis varies within North America with adults being most abundant in June and July in temperate zones and July and August in sub-tropical zones (Cilek & Olson 2000).

Hosts: Dermacentor variabilis larvae typically feed on small mammals, and nymphs feed on small-to medium-sized mammals. Adults will occasionally feed on humans but are more commonly found on domestic dogs and other medium-sized mammals (Merten and Durden 2000; Campbell & MacKay 1979). A study examining how host-related and environmental stimuli factors affect D. variabilis activity and questing behaviors found ticks were attracted to heat sources within close proximity but were not responsive to light or odor stimuli. These data suggest D. variabilis utilizes more of an ambush strategy to locate and make contact with the host, ticks were most active within an optimal temperature range and activity decreased at upper and lower temperature thresholds (Hranac 2011).

Medical and Veterinary Significance: 

The American dog tick is capable of transmitting the organism that causes Rocky Mountain spotted fever, Rickettsia rickettsii, (Azad & Beard, 1998) but this disease is rare in Wisconsin (WI-DHS, 2012). Cases that are reported in Wisconsin residents are usually associated with travel to other states where Rocky Mountain spotted fever more commonly occurs.

Dermacentor variabilis, is also one of the main implicated vectors for the disease tularemia or rabbit fever caused by the bacterium Francisella tularensis. Other known tick vectors include Dermacentor andersoni and Amblyomma americanum as well as deer flies, (Chrysops spp.) (Goethert & Telford 2009). This disease is also rarely reported in Wisconsin. There were a total of three human cases of tularemia in Wisconsin from 2001-2010 reported to the Centers for Disease Control and Prevention (CDC, 2011).

Although the bacteria which causes Lyme disease, Borrelia burgdorferi, has been isolated from Dermacentor variabilis, it has not been proven to be a competent vector and Dermacentor variabilis does not transmit the Lyme disease bacterium (Piesman and Happ 1997; Mukolwe et al. 1992; Mather & Mather 1990; Soares et al. 2006). 

Surveillance & Management: See the section titled Integrated Tick Management for more information on tick and tick-borne disease surveillance, prevention and control on people, domestic animals and in your yard. 

3. The Brown Dog Tick (Rhipicephalus sanguineus)

Common Name: brown dog tick

Scientific Name: Rhipicephalus sanguineus Latreille (Arachnida: Acari: Ixodidae)

Description and Identification: The adult stage of Rhipicephalus sanguineus or the brown dog tick is red-brown in coloration, lacking any ornamentation with an elongated body shape, festoons and a hexagonal basis capituli (Lord 2011). Males are slightly smaller than females in size. Rhipicephalus annulatus(formerly Boophilus annulatus), also known as the American cattle tick, also has a hexagonal basis capituli but lacks any festoons and the palpi are shorter than the basis capituli whereas in R. sanguineus, the palpi are as long as or longer than the basis capituli (Keirans and Litwak 1989). Also, the American cattle tick has been eradicated from the United States but can sometimes be found in Texas or California or other states along the Mexican border (CFSPH 2007). 

Biology: The brown dog tick is an endophilic (adapted to indoor living), monotropic (all developmental stages feed on the same host species), and three-host (each life stage requires a new host to feed on) tick species. Although R. sanguineus is adapted to indoor living, it is able to survive in some outdoor environments and will occasionally feed on other hosts (e.g., humans), although it prefers dogs. R. sanguineus is a wide-ranging tick species, being able to adapt different strategies for survival when necessary (Dantas-Torres 2010). 

Distribution in the United States and Wisconsin: The brown dog tick is the most widespread tick in the world and a well-known vector of pathogens which affect both humans as well as domestic animals. This species is more commonly found in warmer climates and associated with human habitations and domestic dogs in urban, suburban and rural environments. The brown dog tick can be found throughout most populated areas in the United States, including Wisconsin, and is rarely associated with uninhabited wild or forested areas. 

Hosts: R. sanguineus will feed on a variety of hosts but domestic dogs are the preferred host in the United States, hence the common name, “brown dog tick.” They can attach anywhere on a dog, but particularly prefer the head, ears, interdigital spaces, back, inguinal region and axilla (Dantas-Torres 2010). 

When seeking a host, the brown dog tick is typically utilizes a hunting strategy or actively pursues hosts but has also been known to adopt the ambush strategy or “questing behavior” typical of other tick species such as Ixodes scapularis (Dantas-Torres 2010). 

Life Cycle:

Life cycle of the brown dog tick, (Rhipicephalus sanguineus)
Drawing by: James Newman and Leah LeFevre, University of Florida

R. sanguineusis unique among tick species as it can complete its entire life cycle indoors, therefore infestations in homes or kennels can occur rapidly (Lord 2011). This tick is a three-host tick and requires three blood meals to complete development. Dogs are the preferred primary host across all life stages (larva, nymph and adult) in North America. The brown dog tick attains sexual maturity and mates only on the host. A female may begin feeding without the presence of a male but will not become fully engorged unless she mates with a male since the ingestion of a blood meal is a stimulus for production of spermatocytes in males and oocytes in females. (Dantas-Torres 2010). 

An adult female typically feeds on a host for approximately one week and after mating, the engorged female detaches from the host and finds a safe area for egg development (typically cracks or crevices in or near a home, garage or dog kennel). A female may begin oviposition or egg-laying anywhere from as soon as four days to several weeks after detaching from the host (Lord 2011; Dantas-Torres 2010). The oviposition period can last for up to several weeks (Koch 1982). These ticks are very prolific– an individual fully blood-fed gravid female is capable of laying an average of 1500-4000 eggs (Dantas-Torres 2010; Koch 1982). The number of eggs deposited depends on a number of factors including the weight of the female, the amount of blood ingested and the length of the oviposition period (Koch 1982). The ambient temperature also influences the length of time each stage feeds and the time required for development and molting where feeding and development are generally faster at higher temperatures but survivability is greater at cooler temperatures and higher relative humidity (Lord 2011).

Medical and Veterinary Significance: 

The brown dog tick has been reported to transmit several pathogens of medical and veterinary significance.

R. sanguineus has been implicated in the transmission of several Ehrlichia species. The bacterial agent Ehrilichia canis, responsible for canine monocytic ehrlichiosis is transmitted transstadially, but not transovarially by R. sanguineus (Groves et al. 1975) and R. sanguineus acts as a competent reservoir for E. canis (Harrus et al. 1997). Other Ehrlichia agents associated with R. sanguineus include: E. ewingii, responsible for canine granulocytic ehrlichiosis in dogs and can also cause illness in humans; and E. chaffeensis, also known as human monocytic ehrlichiosis (HME) due to its predilection for monocytes (Murphy et al. 1998). The brown dog tick has also been reported to transmit the bacterium Rickettsia ricksettsii, causing Rocky Mountain Spotted Fever (RMSF) in humans in the United States (Dantas-Torres 2007; Demma et al. 2005) and Mexico (Mariotte et al. 1944; Bustamente and Varela 1947). In regions of southern Europe, Africa and Asia, the brown dog tick is the main vector for R. conorii responsible for Mediterranean spotted fever in humans as well as Rickettsia massiliae, recently implicated as a cause of human disease (Parola et al. 2005, Vitale et al. 2006). R. massiliae was also  recently isolated in R. sanguineus from Arizona (Eremeeva et al. 2006). R. sanguineus has also been reported to vector the parasite Hepatozoon canis (canine hepatozoonosis) (Baneth et al. 2001; Nordgren & Craig 1984) and Babesia canis (canine babesiosis) to dogs (Dantas-Torres 2008). Bartonella henselae, the causative agent for cat scratch disease and typically associated with fleas was recently detected in R. sanguineus ticks in California (Wikswo et al. 2007) but it is currently unknown whether it is a competent vector for B. hensaelaeR. sanguineus have also been experiementally infected with Bartonella vinsonii (Billeter et al  2012). Experimental acquisition of the protozoan parasites Leishmania chagasi has also been reported in brown dog ticks feeding on dogs with acute infections (Coutinho et al. 2005; Blanc & Caminopetros 1930). R. sanguineus is considered a competent vector for R. rickettsii (Rocky Mountain spotted fever), and possibly Anaplasma platys and Babesia gibsoni to canines as well (CAPC, 2012).

Management:  An integrated pest management approach may need to be considered for the control of infestations with R. sanguineus. If you have pets, speak with your veterinarian about tick control options for your pet (also see the section on integrated tick management: on pets). Implementing tick control and prevention methods for your pet will also help reduce attachment and feeding of other tick species such asDermacentor variabilis and Ixodes scapularis as well as other insects such as fleas. Be sure to follow your veterinarians instructions as well as the labeled instructions on any tick control product you may use for your pets. Be careful about which flea and tick control products you use on cats, certain products for dogs cannot be used for cats.

Once an infestation has started, thorough treatment of the dog is necessary and you may need to repeat treatments. You may also need to consider treating the house as well as the kennel (Lord 2011). Adults and children should also check for ticks, although this species does not prefer human hosts, they will bite humans.  

4. The Lone Star tick (Amblyomma americanum)

Important note: This tick is rarely found in Wisconsin and it is currently unknown whether there are established populations within the state. There are occasional reports every year, especially in the southern half of Wisconsin.

Common Name: Lone star tick

Scientific Name: Amblyomma americanum Linnaeus(Arachnida: Acari: Ixodida: Ixodidae)

Description and Identification: Amblyomma tick species are more rounded in shape versus Dermacentor and Ixodes species which have more of a tear-drop shape that tapers at the mouthparts. Adult females are reddish-brown in color and can be easily distinguished from other ticks by the presence of a distinctive white spot or “star” on the dorsum. The spot  may vary in color from whitish to cream or gold to bronze and is often iridescent in appearance upon closer inspection. The spot appears closer to the basis capitulum when the female is engorged. Females are generally larger than males and average 4-6 mm unfed and up to 16 mm or larger when fully fed. The basis capituli is rectangular in shape with the palpi much larger than the basis capituli and palpal segment two much longer than broad (Keirans & Litwak, 1989). Adult males average 2-5 mm in size with a scutum that is dark brown in coloration. A reticulated pattern or whitish ornamentations are usually apparent along the outer margins and festoons on the posterior dorsal body surface of males. Both males and females have eyes along the dorsal anterior margins of the back and festoons along the posterior dorsal margins. 

Distribution in the United States and Wisconsin: 

A. americanum is found west-central Texas, north to Iowa and eastward. It is most widely distributed in the eastern and southeastern United States (Childs & Paddock 2003; Means & White 1997). Over-wintering populations are established as far north as coastal Maine (Keirans & Lacombe 1998).

This tick is rarely found in Wisconsin and it is currently unknown whether there are established populations within the state. There are occasional reports every year, especially in the southern half of Wisconsin.

Hosts: A. americanum species are three-host ixodid ticks that are aggressive, generalist feeders at all three life stages. A. americanum larvae and nymphs tend to feed on small mammals, ground-feeding birds as well as white-tailed deer and domestic cattle.          A. americanum adults frequently parasitize white-tailed deer, domestic cattle, horses and sheep, feral swine and domestic dogs and humans (Allan et al. 2010; Childs & Paddock 2003; Kollars et al. 2000). 

Life Cycle:  Lone star ticks are most often found in woodland habitats, especially young, second-growth forests with dense understory (Childs & Paddock, 2003). The abundance of A. americanum is influenced by the availability of suitable hosts for all three life stages and the availability of appropriate habitat for both the tick as well as it’s potential hosts (ibid).

References:

Allan BF, Goessling LS, Storch GA, Thach RE. (2010). Blood meal analysis to identify reservoir hosts for Amblyomma americanum ticks. Emerg Infect Dis; 16(3): 433-440. http://wwwnc.cdc.gov/eid/article/16/3/09-0911.htm

Azad AF and Beard CB. (1998). Rickettsial pathogens and their arthropod vectors. Emerg. Inf. Dis; 4:179–186.

Baneth G, Samish M, Alekseev E, Aroch I, and Shkap V. (2001). Transmission of Hepatozoon canis to dogs by naturally-fed or percutaneously-injected Rhipicephalus sanguineus ticks. Journal of Parasitology; 87(3):606-611.

Billeter SA, Kasten RW, Killmaster LF, Breitschwerdt EB, Levin ML, Levy MG, Kosoy MY, Chomel BB. (2012). Experimental infection by capillary tube feeding of Rhipicephalus sanguineus with Bartonella vinsonii subspecies berkhoffi. Comp Immunol Microbiol Infec Dis; 35(1): 9-15. doi: 10.1016/j.cimid.2011.09.004. 
 
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Campbell A and MacKay PR. (1979). Distribution of the American dog tick. Dermacentor variabilis (Say), and its small-mammal hosts in relation to vegetation types in a study area in Nova Scotia. Can. J. Zool. 57: 1950- 1959.

Centers for Disease Control and Prevention. (2011). Reported tularemia cases by state, United States, 2001 – 2010. Accessed June 27, 2012. http://www.cdc.gov/tularemia/statistics/state.html

Center for Food Security and Public Health, Iowa State University, College of Veterinary Medicine. Rhipicephalus (Boophilus) annulatus: Cattle Tick, Cattle Fever Tick, American Cattle Tick. Content Update: February 19, 2007 Last Reviewed: July 3, 2007. http://www.cfsph.iastate.edu/Factsheets/pdfs/boophilus_annulatus.pdf 

Chan WH and Kaufman PE. (2008). American dog tick: Dermacentor variabilis (Say) (Arachnida: Ixodida: Ixodidae). Featured Creatures: University of Florida Institute of Food and Agricultural Sciences; Dept. of Entomology and Nematology. http://entnemdept.ufl.edu/creatures/urban/medical/american_dog_tick.htm                     Accessed June 27, 2012. 

Childs JE & Paddock CD (2003). “The ascendancy of Amblyomma americanum as a vector of pathogens affecting humans in the United States.” Annual Review of Entomology; 48 (1): 307–337. http://www.annualreviews.org/doi/pdf/10.1146/annurev.ento.48.091801.112728

Cilek, J.E. and M.A. Olson. (2000). Seasonal distribution and abundance of ticks (Acari: Ixodidae) in northwestern Florida. Journal of Medical Entomology 37:439-444.

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Demma LJ, Traeger MS, Nicholson WL, Paddock CD, Blau DM, Eremeeva ME, Dasch GA, Levin ML, Singleton J Jr., Zaki SR, Cheek JE, Swerdlow DL, and McQuiston JH. (2005). Rocky Mountain spotted fever from an unexpected tick vector in Arizona. New England J. Medicine 353: 587-594.

Eremeeva ME, Bosserman A, Demma LJ, M. L. Zambrano ML, Blau DM, and Dasch GA. 2006. Isolation and identification of Rickettsia massiliae in Rhipicephalus sanguineus ticks from Arizona. Appl. Environ. Microbiol; 72: 5569-5577.

Goethert HK and Telford SR III. (2009). Nonrandom Distribution of Vector Ticks (Dermacentor variabilis) Infected by Francisella tularensis. PLoS Pathog 5(2): e1000319. doi:10.1371/journal.ppat.1000319

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Keirans JE and Litwak TR. (1989). Pictorial Key to the Adults of Hard Ticks, Family Ixodidae (Ixodida: Ixodoidea), East of the Mississippi River. J. Med. Entomol. 26(5): 435-448. http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA233445

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Lord CC. April 2011. Brown dog tick, Rhipicephalus sanguineus Latreille (Arachnida: Acari: Ixodidae). Featured creatures, University of Florida Institute of Food and Agricultural Sciences, Department of Entomology and Nematology. Gainesville, FL. http://www.entnemdept.ufl.edu/creatures/urban/medical/brown_dog_tick.htm Accessed June 15, 2012. 

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