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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, mites, and keds. Damage by mites results in the skin disease called mange, characterised by raw, thickened skin that has lost its wool. Much of the damage is actually inflicted as a result of the sheep responding to the very intense itching caused by mites. Rubbing, licking, and scratching irritate the skin, which becomes raw. The fleece may also be damaged. 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. Wool becomes loose and falls out easily. This is known as a wool break.

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. This is particularly true in the case of sheep blowfly strike. The result of parasite worry may be reduced gains and possibly even weight loss.

  

Loss of Blood

Sucking of blood by keds 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 anemia occurs. Infested animals may be forced to use ingested nutrients to replace losses rather than to build lean body mass or muscle, thereby reducing weight gain. Death may eventually result.


Wool break due to mite infestation

  

Myiasis

Adult female blowflies deposit their eggs near damaged skin. Larvae that hatch out then migrate into the skin, liquefying it with enzymes in order to feed. Larval infestation is called myiasis. The damage that occurs attracts more flies which lay eggs. Feeding fly maggots expand the lesions. The open, putrid areas that result are ideal for bacterial growth, and death of sheep often results from these secondary infections.

 

Transmission of Disease

A serious problem results from the ability of ticks to transmit disease-carrying organisms to their host. Although this does not routinely occur in NZ, many of these diseases are serious.

   

Tick Paralysis

Some ticks release toxins into the blood of sheep. 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 are particularly capable of causing tick paralysis.

 

Annoyance

Most ectoparasites inflict damage through annoyance of the sheep. This can lead to loss of condition.

 

Hide Damage

        A major ectoparasite-caused problem in New Zealand is significant hide damage affecting leather quality.

       

Back to Sheep Disease Information 

 

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