Introduction
- A parasite is an organism that obtains its livelihood from another organism (host), which suffers damage as a result.
- Parasitism is the association between a parasite and a host.
The Effects of Parasites on the Host Animal
- Depriving the host of its food.
- Sucking blood.
- Damaging the organs of the host.
- Causing irritation on the skin of the host.
- Destruction of hides and skins.
- Transmission of diseases.
- Causing obstruction in body passages.
General Symptoms of Parasite Infestation
- Emaciation.
- Pot-bellied condition.
- Swellings in the jaw or other areas.
- Rough hair or rough coat.
- Anaemia.
- Diarrhoea.
- Presence of worm segments and blood stains in the defecation.
Types of Parasites
There are two types of parasites:
- External (ecto-parasites)
- Internal (endo-parasites)
External Parasites
- 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 type 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 type requires two different hosts to complete its life cycle.
- Example: The red-legged tick (Rhipicephalus evertsi).
- 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 type 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 transmits heartwater (Amblyomma spp.).
Control of Ticks
- Dipping, spraying, or hand dressing with acaricides.
- Rotational grazing.
- Ploughing the land to break the life cycle.
- Hand picking and killing ticks.
- Fencing grazing fields to keep off other animals, including wild game.
- Burning grass to kill ticks 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 that fouls the anal and tail region.
- Dullness.
- Anaemia.
- Big stomach (pot-bellied condition).
- Presence of worm segments in faeces.
- Coughing.
Trematodes (Liver Flukes)
- There are two species of flukes:
- Fasciola gigantica
- Fasciola hepatica (more common)
- They are 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 (freshwater snails).
- In the snail, it develops through sporocyst, redia, and cercaria stages.
- 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 as it matures.
Control of Liver Fluke
- Keep livestock off marshy areas near rivers, streams, lakes, and dams.
- Drench affected animals with appropriate medication.
- Drain swampy areas to reduce snail habitats.
- Eradicate the intermediate host by using molluscicides.
- Provide water to livestock in elevated troughs to prevent access to contaminated water.
Tapeworms
- There are many species of tapeworms.
Examples:
- Taenia solium
- Taenia saginata
The adults live in the small intestines of humans (the primary host).
- The intermediate host of Taenia solium is the pig.
- The intermediate host of Taenia saginata is cattle.
Life Cycle of Tapeworm
- Adult tapeworms live in human intestines where they lay eggs.
- Eggs are passed out with faeces.
- They develop an outer covering known as the onchosphere.
- The eggs are swallowed by intermediate hosts.
- 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, and thigh muscles.
- It develops into an encysted form called the bladder-worm.
- When the animal is killed and meat is eaten raw or inadequately cooked, humans get infected by the bladder-worm.
- In humans, 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 the primary host.
- Meat inspection by meat inspectors or veterinary officers.
- Use of pit latrines by humans to prevent contamination.
Nematodes (Roundworms)
Common nematodes include:
- Ascaris suum (pig roundworms)
- Ascaris lumbricoides found in humans and sheep
- Haemonchus contortus found in sheep, cattle, and goats
- Roundworms are common in warm areas, especially where standards of hygiene and sanitation are low.
Nature of Damage
- Damage is done to the liver and lung tissues as the worms migrate through the body.
- Suck out blood from the host.
- Deprive the host of food.
Control of Roundworms
- Use of appropriate anthelmintic drugs.
- Rotational grazing to reduce parasite load.
- Use of proper stocking rates to avoid overgrazing and reduce parasite transmission.
- Practicing high standards of cleanliness and hygiene, such as the use of latrines.
