Module 10: Veterinary Ectoparasites

Module 10.3: Hard Ticks

Common hard ticks

The next few sections will guide you through some of the common hard ticks found in the United States.

Common Hard Ticks

Ixodes spp.

In the United States, there are two Ixodes spp. of veterinary and public health importanceThese include Ixodes scapularis (deer tick or black-legged tick) and Ixodes pacificus (Western black-legged tick).  These ticks use 3 hosts (require 3 separate hosts to take a blood meal for maturation) for their life cycle and prefer to live in wooded areas.  Ixodes spp. are hard ticks that are inornate (no pattern on scutum).

What differentiates Ixodes ticks from other hard ticks are their long palps and the prominent anal grove on the ventrum. The adult ticks are also the smallest of the common ticks we find in the United States. The body of an unengorged (not full of blood) is approximately the size of a 1/4 carat diamond stud. Larvae are the size of a poppy seed!

Ixodes scapularis (deer tick or black-legged tick) and Ixodes pacificus (Western black-legged tick)
Ixodes scapularis (deer tick or black-legged tick) and Ixodes pacificus (Western black-legged tick)

Disease Transmitted by Ixodes spp. Ticks

Ixodes ticks are important vectors for disease transmission in animals and humans. Here are a few examples.

Table 10.3: Disease transmitted by Ixodes spp. ticks

Disease

Species affected

Type of disease transmitted

Lyme Disease (Borrelia burgdorferi) dogs and humans bacteria
Human and Canine Granulocytic Anaplasmosis (Anaplasma phagocytophilum) dogs, humans, horses bacteria

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Dermacentor spp.

There are several species of Dermacentor of veterinary importance. These ticks vary on the number of hosts required to complete their life cycle. Overall, Dermacentor spp. tend to prefer to live in tall grassy areas or grassy wooded areas.  These ticks are hard ticks that are ornate (white or iridescent pattern on scutum).  Species of veterinary importance are D. variabilis (American dog tick or Wood tick), D. andersoni (Rocky Mountain Wood Tick), and D. albipictus (Winter tick).

While there are several species in this genus one of their most distinctive traits is the incredibly ornate pattern easily visualized on their scutum, specifically the males. In comparison to Ixodes scapularis (Deer tick), aside from being ornate, their mouthparts, specifically the palps, are much shorter than the Deer tick. In Minnesota, D. variabilis, I. scapularis, and Rhiphacephalus sanguines are the most common hard ticks observed on people and domestic animals.

3 types of Dermacentor ticks
D. variabilis (American dog tick or Wood tick), D. andersoni (Rocky Mountain Wood Tick), and D. albipictus (Winter tick)

Disease Transmitted by Dermacentor spp. Ticks

Dermacentor spp. are important vectors for disease in people and animals. Here are a few of the common diseases transmitted.

 

Table 10.4: Disease transmitted by Dermacentor spp. ticks

Disease

Species affected

Type of disease transmitted

Tularemia (Francisella tularensis) humans, cats, small mammals bacteria
Rocky Mountain Spotted Fever (Rickettsia rickettsii) Dogs and humans bacteria

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Amblyomma americanum (Lone Star Tick)

Of the ticks found in North America, Amblyomma americanum ticks have the greatest impact on disease transmission in both people and domestic animals. These ticks are aggressive , have a wide host range they will take blood meals from (not picky eaters), and transmit the majority of fatal diseases of veterinary and public health importance. In general, these ticks require 3 hosts to complete their life cycle, but the host range is quite diverse.

Similar to Dermacentor, Lone star ticks are ornate hard ticks. They live in deep leaves and foliage mainly in the Southeastern USA, with the heaviest concentration in Missouri and Oklahoma, but also found as far north as southern Iowa. Most recently, these ticks have been found in Austin, MN so they are moving northward as a result of global warming. The female tick displays a single or “lone”  star on their scutum, while the males have small, white ticked lines on the festoons (the ridges on the “skirt” of the scutum).

Amblyomma americanum (Lone Star Tick)
Amblyomma americanum (Lone Star Tick) Male and Female

Disease Transmitted by Amblyomma americanum Ticks

Table 10.5: Disease transmitted by Amblyomma americanum ticks

Disease

Species affected

Type of disease transmitted

Granulocytic ehrlichiosis (Ehrlichia chaffeensis, E. ewingii) humans, dogs, cats bacteria
Tularemia (Francisella tularensis) humans, cats, small mammals bacteria
Cyatuxzoon felis wild and domestic cats protozoan

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Rhipicephalus sanguineus – “Brown dog tick” or “kennel tick”

The brown dog tick is the most common tick in Minnesota, United States, and worldwide.  This is a cosmopolitan tick and prefers to live indoors on dogs and humans.  Rhipicephalus sanguineus requires 3 hosts to complete its life cycle. Different than the other hard ticks, each of these “hosts” is usually a dog. It can be the same dog,  but following a blood meal, the tick will fall off the dog, molt in the environment, and quest for a new meal, that may be the same dog or a different dog (or human!).

Similar to the Ixodes ticks, these ticks are inornate (no pattern on scutum). However, it is fairly easy to tell the difference between Ixodes and Rhipicephalus, as the capitulum of the Rhipicephaus is hexagonal with short stumpy palps. If you remember, Ixodes has a rectangular capitulum and long palps. Lastly, the size can be a giveaway. Adult Rhipicephalus are generally larger than adult Ixodes ticks. Unengorged Rhipicephalus sanguineus are approximately the same size as a shucked sunflower seed.

Rhipicephalus sanguineus (Brown dog tick) as larva, nymph, adult male, and adult female
Rhipicephalus sanguineus (Brown dog tick)

Disease Transmitted by Rhipicephalus sanguineus Ticks

Table 10.6: Disease transmitted by Rhipicephalus sanguineus ticks

Disease

Species affected

Type of disease transmitted

Canine monocytic ehrlichiosis (Ehrlichia canis) Dogs bacteria
Rocky Mountain Spotted Fever (Rickettsia rickettsii) Dogs and humans bacteria

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