Parasitic diseases are those diseases caused by parasites and a parasite is a small organism that lives on or in and at the expense of a larger organism called a host. The parasite benefits from the relationship while the host suffers.

The parasites that cause diseases in ruminants include those that are found in the blood (Protoazoan and Rickettsial parasites), digestive system (helminthes) and on the skin (ticks, mites, flies and lice).

1. Protozoan Diseases

Protozoan diseases of livestock include the following;

a. Trypanosomosis

Animal Trypanosomosis is a severe parasitic disease affecting cattle, sheep, goats, camels, antelopes, dogs and humans. The disease is caused by different species of Trypanosomes which are transmitted by biting flies (tse tse flies or Glossina).

The disease is characterized by intermittent fever, anaemia, loss of condition and death. The species that cause disease include T.brucei brucei (Cattle, sheep, goats, camel), T. brucei evansi (Cattle, goats, camel), T. congolense (Cattle, sheep, goats, camel), T. vivax (Cattle, sheep, goats, camel), T. theileri (Cattle T. simiae (Sheep, goats, camel) and T. melophagium (Sheep and goats). The disease can occur in acute, subacute, or chronic form.

Diagnosis is usually based on demonstration of trypanosomes in blood smears. However, more specific test such as indirect fluorescent antibody test (IFA) and the enzyme-linked immunospecific assay (ELISA) test are used for diagnosis.

Treatment is by use of trypanocidal drugs such as Diminazene aceturate, Homidium bromide etc. Vector control can help to control or prevent trypanosomosis.

b. Babesiosis

Babesiosis also known as piroplasmosis, redwtaer, tick fever is tick-borne disease of ruminants characterised by fever, anemia, haemoglobinuria (reddish dark-brown urine) and weakness.

In cattle, the disease is caused B. bigemina and B. bovis which are transmitted by ticks (Boophilus species). In sheep and goats the disease is associated with B. ovis and B. motası which is trans- mitted by ticks of the genus Haemaphysalis and Rhipicephalus.

Diagnosis is based on demonstration of Babesia parasites in blood smears. Control of the disease is by proper tick control and quarantine. Animals should be routinely treated with acaricides. Tick vaccines are also available in addition to acaricides.

c. Coccidiosis

Coccidiosis is a serious disease affecting mainly young animals (calves, lambs and kids) causing important economic losses.

Coccidiosis in sheep and goats is caused by protozoa of the genus Eimeria (E. parva, E. arloingi, etc) and is characterized by diarrhea which can be bloody or mu- coid, anorexia, tenesmus (straining) and weight loss.

The temperature may be normal. Diagnosis is based on history, clinical and necropsy findings, and microscopic examination of feces.

Treatment is by the use drugs (coccidiostats) and usually all animal in the herd or flock is treated.

Preventive measures include good hygienic practices such as removal of animal manure, avoid- ing overcrowding of animals and pasture management to control parasites.

d. Theileriosis (East CoastFever)

Theileriosis is a haemoparasitic disease of cattle, goats, and sheep caused by the protozoan para- site of the genus Theileria and transmitted by ticks. In cattle the disease is caused by Theileriaparva, T. mutans, T. velifera, T. taurotragi, and transmitted by the tick.

In sheep and goats the causative parasite is T. ovis and T. hirci. The tick vectors of this disease are Rhipicephalus ap-pendiculatus Ambylomma variegatum, Haemaphysalis spp.

Affected animals show anorexia, decreased milk production, loses condition, ceases rumination, rapid heartbeat petechial haemor- rhages under the tongue and on the vulva.

Diagnosis is by demonstration of parasites in blood and schizonts in lymphocytes. The disease is controlled by good hygiene and used of appropriate drugs for treatment.

Other Protozoan Diseases

Parasitic Diseases of Livestock and Control Measures

There are several other protozoan diseases that affect ruminants. These include Toxoplasmosis, Cryptosporidiosis, Besnoitiosis, Neopsorosis, Giardiasis and Sarcocytosis.

2. Rickettsial Diseases

a. Anaplasmosis

This is an infectious disease of cattle, sheep and goats caused by intraerythrocytic parasites of the genus Anaplasma.

The disease is characterized by fever, depression, progressive anaemia, inappetance, labored breathing, jaundice, constipation, abortion and death.

In cattle the disease is caused Anaplasma marginale which is transmitted by tick (Dermacentor species) and A. boviswhich is carried by Hyalomma species of ticks. In sheep and goats, the A.marginaleis transmitted by Dermacentor species of ticks.

Control measures are keeping tick vectors off the animals and use of vaccination.

b. Heartwater

This is a noncontagious infectious disease of cattle, sheep and goats caused by the previously thought rickettsial organism now a bacterium Ehrlichia ruminantum (formerly called Cowdriaruminantium).

The disease is transmitted by the ticks of the genus Amblyomma variegatum. The symptoms of the disease include chewing movements, protrusion of the tongue, twitching of eyelids and circling.

Neurologic signs become apparent as the disease progresses and the animal can go into convulsions, lateral recumbency with paddling movements, twisting of the neck (opisthotonos) and frothing at the mouth. Prevention is by tick control and vaccination.

3. Diseases Caused by Helminthes

Helminthes, otherwise known as worms are mostly endoparasites though some live externally. The helminthes that cause disease in ruminants are round worms (Nematodes), flukes (Trematodes) and tapeworms (Cestodes).

The deleterious effect of diseases caused by helminthes on ruminants depends on the type of helminthes, location within the host, degree of parasitism and the nutritional status of the animal.

The major diseases in ruminants caused by helminthes are Haemonchosis and Fasciolosis. Haemonchosis is caused by the nematode, Haemonchuscontortus is characterized by weakness, pale mucous membrane and inflammed mandibular region (bottle jaw).

Fasciolosis on the other hand is caused by Fasciola gigantic and Fasciolahepatica and is characterized by weakness, pale mucous membrane, enlargement of the liver and abdominal distension.

In addition to these other species of helminthes which cause disease in ruminants are Paramphistomum, Bunostumum, Oeasophagostomum and Trichostrongyloids among others. Diagnosis is usually based demonstration of eggs, larvae or adult in appropriate samples from affected animals depending on the helminth in question.

Samples usually collected from sick animals include faeces, blood, sputum, urine, lacrimal fluid and skin snips depending on the helminth in question.

Prevention helminthosis is by proper grazing management and use of resistant animals. Treatment is achieved by the use of appropriate anthelmintics for deworming.

4. Diseases Caused by External Parasites

The ectoparasites cause diseases in ruminants either by serving as vectors or transmitters of other disease-causing agents, by feeding on blood or cells of the host animal or by secreting toxins in their saliva.

Ectoparasites also constitute a biting nuisance in ruminants and distract animals from feeding thereby affecting productivity. These ectoparasites are ticks, mites, lice, fleas and flies.

A major disease is Mange, which is caused by several species of mites (Sarcoptes, Psoroptes, chrioptes and Demodex), Tick paralysis is also another disease caused by Ixodes species while severe anaemia in the young can be caused by flea and lice infestation.

Control of Ectoparasites

Control of ectoparasites is achieved by use of appropriate insecticides to spray the pens and immediate surroundings of where ruminants are kept. Regular spraying of animal sheds, pens etc with appropriate insecticides is a good management practice.

It is also be necessary to regularly clean animal pens in addition to raking and burning of infested litter where ectoparasites are resident. However, care must be taken when doing this to avoid uncontrolled fire outbreak.

Treatment of animals with ectoparasite infestation include, dipping animals or spraying animals with appropriate acaricides and the use of formulations which are used as pour-on.

Use of insecticide impregnated eartags is also another method of control of ectoparasites in ruminants. Chemotherapy as a means of control involves the use systemic drugs like Ivermectin, Doramectin etc. The specific control measure applied will depend on the ruminant species, resources available and the purpose for which they are kept.

In summary, we have discussed selected protozoan, rickettsial and helminthic diseases as well as diseases caused by external parasites that affect ruminants.

We have also seen that most of these are transmitted by a vector, ticks and it is therefore important to keep animals free of parasites. Preventive and/or control measures for these diseases have also been mentioned.