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Agricultural Science


What is a parasite? A Parasite is an organism which obtains its livelihood from another organism (host) which suffers damage. Parasitism is the association between a parasite and a host.


The effects of parasite on the host animal are:

  • Depriving the host of its food.
  • Sucking blood.
  • Damaging the organs of the host.
  • Cause irritation on the skin of the host.
  • Destruction of hides and skins.
  • Transmission of diseases.
  • Cause obstruction in body passages.


General Symptoms of Parasites infestation:

  • Potbellied condition.
  • Swellings in the jaw or other areas.
  • Rough hair or rough coat.
  • Presence of worm segments and blood stains in the defecation.


Types of Parasites

There are two types of parasites: (1) External (ecto-parasites) (2) Internal(endo-parasites)

External parasites are;

  • ticks,
  • tsetse flies,
  • mites,
  • lice,
  • fleas
  • keds

Life Cycle of ticks

  • Eggs are laid in cracks on the ground.
  • They hatch in 4-6 weeks into larvae which climb on the grass waiting for a passing animal.

One-Host Tick

  • This requires one host to complete its life cycle.
  • Example: blue tick (Boophilus decoloratus).
  • Preferred sites: face, neck, dewlap and side of the body.
  • Disease transmitted: Redwater and anaplasmosis.

Two-Host Tick

  • This requires two different hosts to complete its life cycle.
  • Example: The red legged tick (Rhipicephalus everts)
  • Preferred sites: Ears, anus, udder and the tail.
  • Disease transmitted: Redwater and east coast fever.
  • Example: Bont legged tick (amblyomma spp.)
  • Preferred sites: Udder, scrotum and tail switch.
  • Disease transmitted: Sweating sickness.

Three-Host Tick

  • This requires three hosts to complete its life cycle.
  • Example: The brown ear tick (Rhipicephalus appendiculatus)
  • Preferred sites: Ears, tail switch and around the eyes.
  • Disease transmitted: East coast fever and redwater.
  • Bont tick transmit heartwater (amblyomma spp.)

Control of Ticks

  • Dipping/spraying/hand dressing with acaricides.
  • Rotational grazing.
  • Ploughing the land to break the life cycle.
  • Hand picking and killing.
  • Fencing of the grazing fields to keep off other animals including wild game.
  • Burning of grass to kill them in various stages.


Endo-parasites ( internal Parasites)

Endoparasites are helminths.

They can be divided into:

Platyhelminthes/flatworms which include;

– Trematodes (flukes)

– Cestodes (tapeworms).

– Nemato-helminthes/nematodes. E.g Roundworms.


General Symptoms of Helminthiasis

  • Diarrhoea which foul the anal and tail region.
  • Big stomach (pot bellied condition).
  • Presence of worm segments in faeces.


Trematodes (Liver Fluke)

There are two species of flukes:

  • Fasciola gigantica
  • Fasciola hepatica.

Fasciola hepatica is more common.

It is commonly found in the liver and bile duct of cattle, sheep and goats.

Liver fluke is a problem in marshy and low lying wet areas.


Life Cycle of the Liver Fluke

  • Adult fluke in the liver of the primary host lays eggs.
  • Eggs pass through the bile duct into the small intestines and are passed out in faeces onto the pasture.
  • Under moist conditions, they hatch into a miracidium larva which swims about in search of a secondary host (fresh water snails).
  • In the snail, it develops through sporocyst, redia and cercaria.
  • When it leaves the snail, the cercaria gets encysted on vegetation and becomes metacercaria.
  • This is swallowed by the primary host with grass.
  • The young fluke migrates into the liver through blood vessels when it matures.


Control of Liver Fluke

  • Keep livestock off marshy areas near the rivers/streams/lakes and dams.
  • Drench af-fected animals.
  • Drainage of swampy areas.
  • Eradicate the intermediate host by use of molluscicides.
  • Provide water to livestock in elevated troughs.



There are many species of tapeworms


Taenia solium

Taenia saginata.

  • The adults live in the small intestines of man (the primary host).
  • The intermediate host of Taenia solium is pig .
  • The intermediate host of Taenia saginata is cattle.

Life Cycle of Tapeworm

  • Adult tapeworms live in man’s intestines where it lays eggs.
  • Eggs are passed out with faeces,
  • Then they develop an outer covering known as onchosphere.
  • The eggs are swallowed by intermediate host.
  • The outer covering is digested and the young worm emerges.
  • This bores into the blood vessels and is carried to specific muscles such as the tongue, heart, thigh muscles.
  • It develops into an encysted form called bladder-worm.
  • When the animal is killed and meat is eaten raw or in an inadequately cooked form, man gets infected by the bladder-worm.
  • In man, the bladder-worm evaginates and attaches itself onto the intestinal wall where it develops into an adult.

Control of Tapeworms

  • Meat should be well cooked before eating.
  • Use of drugs in primary host.
  • Meat inspection by meat inspectors] veterinary officers.
  • Use of pit latrines by man.


Nematodes (Roundworms)

Common ones are:

  • Ascaris suum (pig roundworms),
  • Ascaris lumbricoides found in man and sheep
  • Haemonchus contortus found in sheep, cattle and goats.
  • Roundworms are common in warm areas especially in areas where the standards of hygiene and sanitation are low.

Nature of Damage

  • Damage is done to the liver and lung tissues as they migrate in the body.
  • Suck out blood.
  • Deprive the host of food.

Control of Roundworms

  • Use of drugs.
  • Rotational grazing.
  • Use of proper stocking rates to avoid overgrazing.

Practicing high standards of cleanliness and hygiene such as use of latrines


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