Current Advice on Parasite Control:
Vector-Borne Diseases - Ixodes scapularis and Ixodes pacificus
- 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 and in the environment will provide the most comprehensive protection against the many diseases transmitted by black-legged ticks.
- Ixodes scapularis (black-legged tick, also known as deer tick) (Link to image)
- Ixodes pacificus (western black-legged tick)
- Ixodes scapularis (black-legged tick, also known as deer tick) (Link to Image)
- Ixodes pacificus (western black-legged tick)
*Other Ixodes spp. may on occasion parasitize dogs and cats.
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 for 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.
Table 1: Peak activity of larval, nymphal, and adult Ixodes pacificus and Ixodes scapularis (phenology, or timing of activity, varies with local climatic factors)
Tick species Peak Larval Activity Peak Nymphal Activity Peak Adult Activity Ixodes pacificus Late spring
Early winter to late spring
Ixodes scapularis Northeast Late summer and early fall (Year 1) Summer (Year 2) Fall through winter (Year 2) South Spring and summer (Year 1) Spring and summer (Year 2) Fall through winter (Year 2)
- 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 several fold 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 all three feeding stages (lava, nymph and adult), which is visible under low magnification.
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.
- 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.
Table 2: Pathogens transmitted by I. pacificus and I. scapularis
Tick Species Common Name Pathogens Transmitted Disease Name Ixodes pacificus Western black-legged tick or deer tick Borrelia burgdorferi Lyme disease Borrelia miyamotoi Relapsing fever borreliosis Anaplasma phagocytophilum Anaplasmosis Ixodes scapularis Eastern black-legged tick or deer tick Babesia microti Human babesiosis Borrelia burgdorferi Lyme disease Borrelia miyamotoi Relapsing fever borreliosis Anaplasma phagocytophilum Anaplasmosis Ehrlichia muris / EML agent Ehrlichiosis Powassan virus Enchephalitis
- Ixodes scapularis is found throughout the eastern United States as far west as Texas and South 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.
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.
Table 3: Preferred hosts for Ixodes pacificus and Ixodes scapularis
Tick species Preferred Hosts for Immature Stages Preferred Hosts for Adults Ixodes pacificus Lizards, birds and less commonly small mammals Columbian black-tailed deer and other large/medium-sized mammals Ixodes scapularis North Small rodents, such as mice, shrews, and chipmunks, and birds White-tailed deer and other large/medium-sized mammals South Lizards, birds and less commonly small mammals
- 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 is made on physical examination of host, when attached ticks are recognized and recovered.
- Key features for identifying 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. (Link to image)
- 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.
- See general tick recommendations. (Click here to access treatment recommendations)
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. Detailed outdoor tick habitat management advice can be found here.
- 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 preventing 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.
- 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.