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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 cattle 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 lesion 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 geographic locations.

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

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, thereby reducing weight gain.

Transmission of Disease

One of the most damaging aspects of ticks is their ability to transmit disease-producing organisms to their host. These diseases are often serious and may be fatal. East Coast fever (Theileria parva), bovine babesiosis (Bebesia bigemina and B. bovis), and anaplasmosis (Anaplasma marginale) are transmitted in this fashion. Adult female ticks harbouring Babes spp. may pass them on to the next generation of ticks via the eggs. This phenomenon, called transovarian transmission, aids the spread of a disease by increasing the number of ticks carrying the disease agent. Heartwater Cowdria ruminantium is another serious disease of cattle spread by ticks. Transovarian transmission of Cowdria ruminantium does not occur.

Loss of Hides

Valuable hides are often damaged by ectoparasites. The irritation and trauma to the skin reduce the hide quality. Some ectoparasite larvae, notably warbles (Hypoderma), migrate through the body and eventually penetrate the skin, leaving large holes. This invasion of the body by larvae is called myiasis. The resultant damage to hides may render them worthless.

Annoyance

Most ectoparasites inflict damage through annoyance of the cattle. This can lead to loss of condition and poor weight gains.

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