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Ectoparasites - Damage To Host


Skin Lesions

Arthropods damage their hosts in a variety of ways. Their feeding on the host´s skin may cause intense itching, especially characteristic of lice and mites. Damage by mites results in the skin disease called mange, characterised by raw, thickened skin that has lost its hair. Much of the damage is actually inflicted as a result of the horses responding to the very intense itching caused by mites. Rubbing, licking, and scratching irritate the skin, which becomes raw. Fluid oozes onto the surface, coagulates, and dries to form a crust. This damaged area expands as mites travel to the edges of the lesions seeking fresh skin upon which to lay their eggs.

The entire lesion is susceptible to secondary bacterial infections which cause even more damage to the skin. Infestations of lice are less harmful than are those of mites but are serious in some geographical locations.

Animals plagued by external parasites become anxious and do not feed or rest well. The result of parasite worry may be loss of weight, condition, and stamina.

Skin Lesions image
Skin lesions caused by mite infestation

Life cycle of 1 host tick (not in New Zealand)

Life cycle of 2 host tick (not in New Zealand)

Life cycle of 3 host tick






Loss of Blood

Sucking of blood by lice and ticks can be a serious drain on animals, which must continually replace the lost blood. When the tick population is sufficiently high and these parasites feed for considerable lengths of time, iron stores, which are used for blood elements, become depleted and anaemia occurs. Animals may be forced to use ingested nutrients to replace losses rather than to build lean body mass or muscle.



Transmission of Disease

One of the most damaging aspects of ticks is their ability to transmit disease-carrying organisms to their host. These diseases are often serious and may be fatal. Equine viral encephalitis and piroplasmosis are transmitted by ticks although neither disease is found in New Zealand. Adult female ticks harbouring these organisms may infect the horses via their eggs; the resulting new generation of ticks will also carry the organism. This phenomenon, called transovarian transmission, aids the spread of a disease by increasing the number of ticks carrying the disease agent. Some ticks appear capable of releasing certain intrinsic elements into the blood of horses to cause sickness in the animals. A syndrome of paralysis occurs, with hind limbs being affected first and forward regions following. Animals may die. However, paralysis is relieved if ticks are removed in time. Ixodes and Dermacentor in particular are capable of causing tick paralysis but these ticks are not found in New Zealand.

Examples of tick-carried disease are listed in Table 1

Equine Tick Information



Most ectoparasites irritate horses. This annoyance can lead to a loss of condition.


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