Amblyomma, Boophilus, Dermacentor, Ixodes, Rhipicephalus: Ticks

General Description: These five important genera of horse ticks may be differentiated on the basis of several characteristics. Amblyomma and Dermacentor ticks have ornate (patterned) upper body surfaces, whereas Boophilus, Ixodes, and Rhipicephalus are plain brown in colour. Rectangular divisions on the rear body edge are called festoons and are present only on Amblyomma, Dermacentor, and Rhipicephalus. Amblyomma ticks have long, prominent mouth parts, easily distinguished from the short mouth parts of Dermacentor. Of these ticks, only Ixodes is eyeless.

Life Cycle: Amblyomma species are three–host ticks. Their life cycle varies in length from 3 months to over 2 years, depending on species, climate, and host availability. Boophilus, a one–host tick genus, can complete its life cycle in 6 weeks under optimal conditions. Some species of Dermacentor are one–host ticks, while the rest are three–host species. Depending on species and climate, generation time ranges from 2 months to 3 years. Ixodes is a three–host tick genus with a life cycle that requires about 3 years. Unfed larvae, nymphs, and adult ticks each can survive for 1.5 to 2 years. Rhipicephalus ticks have two– or three–host life cycles depending on the tick species. The life cycle takes at least 2 months.

Location: Anywhere on the host body.

Geographical Distribution: Amblyomma parasitises all domestic livestock species in central and southern Africa, the southern United States, Mexico, and Central and South America to Brazil. Boophilus occurs on horses and cattle in warm climates throughout the world except the United States, where it has been eradicated. Species of Dermacentor are found in Asia, Europe, and North and South America, while Ixodes species occur on horses and other animals in Australia, Europe, North America, and South Africa. Rhipicephalus species are significant parasites of horses in Africa south of the equator.

Significance: Heavy tick infestation can cause great debilitation. Ticks are of most economic significance on horses in tropical and subtropical regions. Ticks transmit diseases, as listed in the overview. Equine babesiosis (piroplasmosis) can have high mortality rates.

Effect on Host: These parasites cause tick worry, blood loss, damage at feeding sites, and can transmit protozoal diseases. Wounds left from tick bites are susceptible to additional attacks by various biting flies and flesh–fly larvae. Infested horses itch, bite, scratch, causing self–inflicted skin trauma which can become infected. Heavy tick burdens may result in anaemia, loss of appetite, and weight loss. Amblyomma, Dermacentor, and Ixodes ticks are associated with tick paralysis, which can be fatal within several days if the parasites are not removed. The paralysis is caused by toxins injected by female ticks while they suck blood.

Diagnostic Information: Identification of adult ticks found on the host animal.

Control: Treatment of infested animals and their premises is an integral part of tick control. Chemical agents with residual action are most effective.

Amblyomma		Dermacentor		Rhipicephalus
Engorged female tick		Mouthparts – Boophilus