Ixodes scapularis and Ixodes pacificus

Synopsis

CAPC Recommends

• Year-round use of tick control for dogs is particularly important for black-legged ticks (also known as deer ticks) because the adults are most active and likely to feed on dogs and cats in the cooler months.
• Keeping pets treated with acaricides creates a safer environment for pets and people. Pets not maintained on acaricides may bring ticks into the home which can then move to people and other pets, creating a risk of infection.
• Vaccinating dogs for Lyme disease in areas where disease is endemic or emerging, in addition to diligent attention to tick control on pets, will provide the most comprehensive protection against infection

Species

Canine

Ixodes scapularis (black-legged tick, also known as deer tick)

Click here to view a video on the deer tick

Ixodes pacificus (western black-legged tick)

Click here to view a video on the western black-legged tick

Feline

Ixodes scapularis (black-legged tick, also known as deer tick)

Ixodes pacificus (western black-legged tick)

*Other Ixodes spp. may on occasion parasitize dogs and cats.

Ixodes scapularis adult male

Ixodes scapularis adult female

Overview of Life Cycle

• Ixodes scapularis and I. pacificus are ‘three-host’ ticks, which means that each feeding stage (larva, nymph, and adult) will molt off the host between their requisite blood meals, and then seek another host after molting to the subsequent stage.
• The life cycle of I. scapularis and I. pacificus can take two years to completion depending on environmental conditions. Females deposit a single clutch of approximately 1,500-3,000 eggs in the environment and the six-legged larval stage hatches from the egg.
• The larva must then find a host, feed for several days, and then drop to the ground and molt to an eight-legged nymph.
• The nymph then finds an appropriate host and feeds for several days to a week. Once the nymph has engorged, it drops to the ground and molts to the eight-legged adult, which then must find a third host.
• Adults may mate on or off a host, and once mated and fully engorged, the female will detach, crawl to a suitable environmental location, oviposit a clutch of several thousand eggs, and then die.

Peak activity of larval, nymphal, and adult Ixodes pacificus and Ixodes scapularis (phenology or timing of activity) varies with local climatic factors

Ixodes pacificus

• Peak Larval Activity: Late spring (Year 1)
• Peak Nymphal Activity: Late spring (Year 2)
• Peak Adult Activity: Early winter to late spring (Year 2)

Ixodes scapularis

Northeast

• Peak Larval Activity: Late summer and early fall (Year 1)
• Peak Nymphal Activity: Summer (Year 2)
• Peak Adult Activity: Fall through winter (Year 2) often with bimodal peaks in the late fall and late winter

South

• Peak Larval Activity: Spring and summer (Year 1)
• Peak Nymphal Activity: Spring and summer (Year 2)
• Peak Adult Activity: Fall through winter (Year 2) often with bimodal peaks in the late fall and late winter

Stages

• Adults are approximately 3mm and are characterized by a highly sclerotized dorsal shield (a “scutum”) that is dark brown to black with no white markings and mouthparts that are longer than the basis capitulum. The scutum extends part way across the dorsum on the female, allowing expansion with feeding, and completely covers the dorsum of the male.
• Nymphs are less than 2mm and have 8 legs, while larvae are tiny (less than 1 mm) and have 6 legs.
• Both larvae and nymphs have a scutum that only extends part way across the dorsum, allowing them to expand severalfold in size as they engorge on host blood before they detach to molt to the next stage. Immature stages also possess an anal pore but not a genital pore on the ventral surface.
• All Ixodes spp. have an anterior anal groove present on the three feeding stages (lava, nymph and adult), which is visible under low magnification.

Disease

Direct disease caused by tick bite

• Like any ticks, Ixodes spp. may cause irritation and pruritus around attachment sites. Secondary infections can develop at tick attachment sites, leading to sepsis.
• In Australia, tick paralysis caused by Ixodes holocyclus is commonly reported, but this phenomenon is more commonly associated with Dermacentor spp. in North America.

Pathogen transmission

• The feeding time required to allow disease transmission varies between ticks and disease agents. Borrelia burgdorferi transmission generally requires 24-48 hours or more of feeding before a host is infected, although transmission in less than 24 hours has been occasionally documented. Other tick-borne disease agents, including rickettsial organisms, may be transmitted in less than 24 hours.
• Many tick-borne pathogens are acquired by immature ticks when feeding as larvae or nymphs, and then transmitted by nymphs or adults in subsequent feedings after molting because the infections are maintained through developmental stages. This process is referred to as transstadial transmission.

Pathogens transmitted by I. pacificus and I. scapularis

Ixodes pacificus

• Common Name: Western black-legged tick or deer tick
• Pathogens Transmitted (Disease Name)
  • Borrelia burgdorferi (Lyme disease)
  • Borrelia miyamotoi (hard tick relapsing fever)*
  • Anaplasma phagocytophilum (anaplasmosis)

*Disease reported in humans only. Not considered to be pathogens of dogs and/or cats.

Ixodes scapularis

• Common Name: Eastern black-legged tick or deer tick
• Pathogens Transmitted (Disease Name)
  • Babesia microti (human babesiosis)*
  • Borrelia burgdorferi (Lyme disease)
  • Borrelia mayonii (Lyme disease)*
  • Borrelia miyamotoi (hard tick relapsing fever)*
  • Anaplasma phagocytophilum (anaplasmosis)
  • Ehrlichia muris eauclairensis (ehrlichiosis)*
  • Powassan virus (Powassan virus disease)*

*Disease reported in humans only. Not considered to be pathogens of dogs and/or cats.

Prevalence

• Ixodes scapularis is found throughout the eastern United States as far west as Texas and North Dakota. In recent years, this tick has expanded its geographic range into southern Canada.
• Ixodes pacificus is found west of the Rocky Mountains in a more limited, primarily coastal distribution.
• Ixodes scapularis and I. pacificus are most commonly found in the understory or leaf litter associated with natural wooded areas frequented by wildlife. The forest edge often found surrounding a home, yard, or public recreation area provides ample habitat to support these ticks.
• Tick abundance is based on the seasonal activity of the ticks in specific regions. Because different stages are active at different times, Ixodes spp. activity extends to include most of the year.

Maps showing the general distribution of the most common pet-biting species of ticks. These maps are courtesy of the CDC (https://www.cdc.gov/ticks/about/where-ticks-live.html) . Note that these tick species may occur outside of these shaded areas due to range expansion or movement on people or animals.

Host Associations and Transmission Between Hosts

• Ixodes scapularis populations in the eastern United States appear to adapt their phenology to local environmental conditions, shifting host preferences and timing of activity depending on geography. General patterns for host preferences and transmission between hosts are listed below.

Preferred hosts for Ixodes pacificus and Ixodes scapularis

Ixodes pacificus

• Preferred Hosts for Immature Stages: Lizards, birds and less commonly small mammals
• Preferred Hosts for Adults: Columbian black-tailed deer and other large/medium-sized mammals

*Only adults commonly reported on dogs and cats.

Ixodes scapularis

North

• Preferred Hosts for Immature Stages: Small rodents, such as mice, shrews, chipmunks, and birds
• Preferred Hosts for Adults: White-tailed deer and other large/medium-sized mammals

South

• Preferred Hosts for Immature Stages: Lizards, birds and less commonly small mammals
• Preferred Hosts for Adults: White-tailed deer and other large/medium-sized mammals

*Adults and nymphs commonly reported on dogs and cats.

Environmental Factors

• Seasonal tick activity varies widely by geographic region and climatic cues, and tick populations can vary dramatically within a given area due to local vegetation and wildlife host abundance.
• Deciduous forests consisting of oak and maple trees are ideal habitats for I. scapularis and I. pacificus as the leaf litter provides shelter for the ticks from harsh environmental conditions. These forests also support a robust wildlife population that serve as a reservoir for the ticks and their associated pathogens.
• In recent years, the range of I. scapularis has apparently expanded into areas of higher latitude and higher altitude than previously documented.
• Stages of Ixodes spp. in the environment require protection from desiccation to survive, and populations tend to thrive in years with higher humidity and precipitation.

Diagnosis

• Diagnosis is made on physical examination of host, when attached ticks are recognized and recovered.
• Key features for identifying adult Ixodes spp. are the dark brown to black scutum lacking any white ornamentation, relatively long mouthparts, and the presence of a distinct anal groove arching anterior to the anus on the ventral surface.
• Identification of larval and nymphal ticks is more challenging; however, the presence of an anal groove arching anterior to the anus allows confirmation that the immature tick is an Ixodes spp.
• For submission to a diagnostic laboratory, ticks should be secured in specimen tubes with or without alcohol.

Treatment

• See general tick recommendations.
• Products may only be labeled against I. scapularis for dogs and cats, but those products can be assumed to be effective against other Ixodes spp.

Control and Prevention

• Because substantial annual, seasonal, and geographic differences occur in prevalence and activity of Ixodes spp. in North America, CAPC supports year-round use of tick-control products on pets.
• Limited or “seasonal” use of tick control can permit transmission of disease agents, particularly when use of tick control products is discontinued in the cooler months, just as Ixodes spp. adults become most active.
• Ixodes spp. are acquired from outdoors. However, the habitat around the home can be modified to render it less supportive of ticks and wildlife hosts that can amplify tick populations.
• Bait boxes and permethrin-impregnated cotton has been used to limit Ixodes spp. ticks on rodents, and four-poster corn feeders can be used to apply acaricides to deer. Deer are the primary host for the reproductive adult stages and thus key for maintaining tick populations in nature.

Public Health Considerations

• Ixodes spp. that infest dogs and cats also feed on people and can transmit numerous zoonotic agents (described in Disease section).
• People become infested in the same way as their pets, i.e., by encountering questing ticks in tick-infested habitats.
• Pets not maintained on acaricides may bring ticks into the home which can then move to people and other pets, creating a risk of infection. Keeping pets treated with acaricides creates a safer environment for pets and people.
• The following measures are recommended to prevent human infestation with ticks and infection with tick-borne disease agents. These recommendations are applicable to prevent infestations with Ixodes spp. and many other tick species from natural environments.
  • Maintain pets on tick-control products year-round.
  • Avoid tick-infested areas whenever possible.
  • Wear light-colored clothing when entering infested areas to facilitate visualization of ticks as they crawl on clothing.
  • Tuck pant cuffs into socks to limit tick access to legs.
  • Walk in the center of trails; avoid vegetation at trail margins.
  • Use a chemical repellent such as DEET, picaridin, or permethrin.
  • Perform frequent tick checks when vacationing or visiting tick-infested areas. It is especially important that such checks be performed on children.
  • Shower, shampoo, and put on clean clothes after visiting areas where ticks might be present.
  • When a tick is found on a person, remove it with fine forceps. Prompt removal is necessary; some rickettsial infections can be transmitted after as little as 3-6 hours of tick feeding.
  • Save the removed tick, wrapped in cellophane tape or in a vial with alcohol, for future identification if needed. The tape or vial can be sealed in a plastic bag, labeled with the date found, and frozen. If illness develops, identification of the tick and the day it was discovered may aid the physician in recognizing which infection was most likely transmitted and allow prompt, appropriate treatment.

Selected References

• Nagamori Y, Reichard MV. 2015. Feline tick-borne diseases. Today’s Veterinary Practice. 5(3): 69-73.
• Ogden NH, Lindsay LR, Morshed M, Dockett PN, Artsob H. 2009. The emergence of Lyme disease in Canada. CMAJ 180:1221–4.
• Oliver JH. 1996. Lyme borreliosis in the southern United States: a review. J Parasitol 82:926–35.
• Piesman J, Eisen L. 2008. Prevention of tick borne diseases. Annu. Rev. Entomol. 53:323–43.
• Saleh MN, Sundstrom KD, Duncan KT, Ientile MM, Jordy J, Ghosh P, Little SE. Show us your ticks: a survey of ticks infesting dogs and cats across the USA. Parasit Vectors. 2019 Dec 19;12(1):595. doi: 10.1186/s13071-019-3847-3. Erratum in: Parasit Vectors. 2021 Feb 22;14(1):117. doi: 10.1186/s13071-021-04599-4. PMID: 31856893; PMCID: PMC6923977.
• Ghosh P, Saleh MN, Sundstrom KD, Ientile M, Little SE. Ixodes spp. from Dogs and Cats in the United States: Diversity, Seasonality, and Prevalence of Borrelia burgdorferi and Anaplasma phagocytophilum. Vector Borne Zoonotic Dis. 2021 Jan;21(1):11-19. doi: 10.1089/vbz.2020.2637. Epub 2020 Sep 28. PMID: 32986535; PMCID: PMC9469741.
• Saleh MN, Allen KE, Lineberry MW, Little SE, Reichard MV. Ticks infesting dogs and cats in North America: Biology, geographic distribution, and pathogen transmission. Vet Parasitol. 2021 Jun;294:109392. doi: 10.1016/j.vetpar.2021.109392. Epub 2021 Feb 19. PMID: 33971481; PMCID: PMC9235321.