Conversations about Lyme disease ticks often revolve around the deer tick, also known as the blacklegged tick, or Ixodes scapularis. But did you know the western U.S. has its own species of blacklegged tick? Ixodes pacificus, or the Western blacklegged tick, is widespread along the Pacific coast, transmitting Lyme and other tick-borne diseases in California, Oregon, Washington, and parts of Nevada, Arizona, and Utah.
Keep reading to learn more about the Western blacklegged tick.
Ixodes pacificus basics
Ixodes pacificus is a species of hard-bodied tick similar to Ixodes scapularis, the tick responsible for Lyme disease in the Eastern and upper Midwestern United States. Like Ixodes scapularis, Ixodes pacificus is an important vector for several tick-borne pathogens besides the Borreliae that cause Lyme disease. Also like Ixodes scapularis, Ixodes pacificus has a lifecycle comprised of three stages: the larval stage, the nymph stage, and the adult stage. At each stage, the tick feeds on a different host and can both ingest and transmit disease pathogens.
The Ixodes pacificus lifecycle
An adult female Western blacklegged tick typically lays an egg mass in mid to late May before dying. In mid- to late July, the larvae emerge and feed on lizards, birds, or small mammals such as mice and squirrels. At this stage, larvae can become infected with pathogens in the host animal’s blood. Larval ticks are most active from mid-July to September before overwintering until the following summer.
From May to August, larval ticks that have survived to the nymph stage emerge to feed on larger mammal hosts, including cats, dogs, and humans. At this stage, ticks that have ingested pathogens from their previous host can transmit disease to their new hosts. The vast majority of human Lyme disease and other tick-borne disease cases are spread by nymphs, since they are often too small to be detected – typically no bigger than a poppyseed.
After molting into adults, female ticks feed one last time between October and May before laying an egg mass and dying.
Ixodes pacificus can be active in the winter
Adult female blacklegged ticks can remain active throughout the winter as long as no snow is present. This is especially important to note in the case of the Western blacklegged tick, since the western U.S. has milder winters in which snow is extremely rare.
Ixodes pacificus has been found on California beaches
As mentioned, the Western blacklegged tick is widespread in coastal counties in California, Oregon, and Washington. Though it is most common in Northern California and the Pacific Northwest, it has also been found in parts of Arizona, Utah, and Nevada, and is believed to be spreading geographically as climate change leads to longer summers and milder winters.
In fact, a recent study found populations of Ixodes pacificus on beaches in Northern California – an atypical habitat since their preferred host meals of mice and squirrels do not frequent beach scrub. However, researchers say it is not surprising that ticks are spreading in coastal areas including beaches, since they require warm weather and moisture to survive.
You can use LivLyme’s Tick Tracker app to report and track ticks in real-time whenever you’re outdoors where ticks may be found.
Diseases spread by Ixodes pacificus
The Western blacklegged tick is a known vector of the following tick-borne diseases:
- Lyme disease: One of the fastest growing infectious diseases in the U.S. and Western Europe, with an estimated 400,000 cases per year in the U.S. It is caused by over a dozen distinct species and sub-species of bacteria from the genus Borrelia, most commonly Borrelia burgdorferi.
- Borrelia miyamotoi disease: A type of bacteria that causes Tick-Borne Relapsing Fever (TBRF). It is currently the only type of TBRF Borrelia known to be spread by hard ticks.
- Babesiosis: A tick-borne illness caused by a parasite that infects the red blood cells, similar to the parasite that causes malaria.
- Ehrlichiosis & Anaplasmosis: Though also associated with the lone star tick, Ehrlichiosis and Anaplasmosis can both be spread by Ixodes scapularis and Ixodes pacificus.
- Rickettsiosis: Commonly called Rocky Mountain Spotted Fever (RMSF), Rickettsiosis is the deadliest tick-borne disease in the world. It is most commonly spread by the American dog tick, Rocky Mountain wood tick, and brown dog tick, but Rickettsial diseases can also be spread by the lone star tick and the Western blacklegged tick.
- Powassan virus: This rare but deadly viral infection, also known as tick-borne encephalitis, is most commonly associated with Ixodes scapularis but can also be spread by Ixodes pacificus. It’s important to note that this virus can be transmitted much more quickly than the other pathogens in this list, underscoring the importance of careful tick prevention.
Note that it is possible to be infected with multiple diseases from the same tick bite. This makes it even more important to get tested at a reputable lab with the most accurate diagnostic testing available if experiencing symptoms of a tick-borne illness.
Get tested with IGeneX
Based in the San Francisco Bay Area, IGeneX is at the forefront of diagnostic testing for tick-borne diseases both in and outside of Northern California. Learn more about what sets our tests apart or order a kit today.
