A parasite is an organism living in or on another organism called the host. The host is usually bigger and stronger than the parasite. The parasite derives benefits (food) from the host while the host is harmed or injured during the association. Parasite which lives inside its host is called endoparasite, which include tapeworm, ascaris or roundworm and liverfluke. Parasite which lives on or outside the host is called ectoparasite, e.g ., ticks, lice and mites.
a) Tapeworm (Taenia solium): Tapeworm is a long endoparasite flatworm with a very small head, neck and long segmented body. It belongs to the group called platyhelminthes. Taenia solium is found in pigs while Taenia saginata is found in cattle. The head, also known as scolex has suckers and hooks with which it holds firmly to the intestinal wall of its primary host (man). Pig is the secondary host. The body segments known as proglottides are arranged in long row formed from the neck. At the neck region, the proglottides are small and young while those far from the neck are the largest and the oldest.
Life Cycle of Tapeworm: Tapeworm is a hermaphrodite, that is, it has both male and female reproductive organs and as such, it can fertilise itself.
When a matured and fertilised proglottide pulls off the body of the adult tapeworm, it drops or passes out with the faeces of man to the ground from where pigs can pick it up during feeding.
It eventually gets to the intestine of the pig where an enzyme acts on the egg and liberates the embryo which can find its way into the blood stream by passing through the intestinal wall and is finally deposited in the muscle or heart of the pig. Each embryo forms a cyst round itself to become bladderworm with the head turned inside out, so that its sucker lies on the inside. When raw or under-cooked pork of beef containing the bladderworm is eaten, the digestive enzymes of man dissolve the bladderworm and the young tapeworm with its head turned inside out emerges.
Economic Importance of Tapeworm on Man
- Abdominal pain or discomfort.
- Indigestion and vomiting.
The combined effects of these symptoms are called taeniasis.
Control of Tapeworm
- All meat should be examined for bladderworm before selling to the public.
- Meat should be properly cooked before eating.
- Practise good sanitary measures so that it will not be possible for animals to come in contact with or eat human faeces.
- Infected people should be treated by regular deworming.
b) Liverfluke: The liverfluke is a flattened, leaf-like organism. It is brown in colour, about 2cm long. It is an endoparasite of farm animals like cattle, sheep and goat. Farm animals are the primary host while the snail (Limnaea truncatula) is the secondary host.
Life Cycle of Liverfluke: Fertilised eggs are passed out together with faeces. During favourable conditions, the eggs hatch into small ciliated larvae called miracidia. Each miracidium swims in water and is usually attracted to water snail, which is its secondary host. It enters the body of the snail during which it loses its cilia and changes to a sporocyst and reproduces asexually to give rise to new larvae called rediae. The redia comes out of the sporocyst and goes to the digestive gland where it develops into a minute worm called cercariae. The cercaria leaves the body of the snail and swims about in water until it finds a suitable host when the animal drinks contaminated water. At times, the larvae leave the host snail and encyst on vegetation. From there, it is ingested by grazing animals. The cercaria penetrates the skin and tissue to enter the blood stream; then, to the liver tissue and finally gets to the bile duct where they finally settle down and develop into adult liverfluke.
How to prevent liverfluke from completing its life cycle in the field
The life cycle of the fluke can be disrupted by:
- Eliminating all the snails which are their secondary hosts in the waters /pastures where the ruminant animals drink/feed by spraying copper sulphate solution on them.
- Provide clear, uninfested water and feed for the animals.
- Control weeds along river sides.
- Periodic burning of pasture to kill eggs in faeces.
- Economic Importance of Liverfluke Liverfluke causes a disease called bilharzia or schistosomiasis.
- It leads to loss of blood (physical loss as parasite is sucking blood).
- It causes anaemia, i.e, inability to produce blood.
- It obstructs the bile duct.
- It leads to digestive disturbance.
- It may result in death.
- It causes liver rot.
- Drain pasture properly since wet pasture can harbour snails.
- Introduce ducks and geese to eat up the snails.
- Use lime on pasture because eggs of livefluke do not hatch in water containing high level of alkaline.
c) Roundworm (Ascaris lumbricoides): Roundworm is an elongated, cylindrical, white worm which is pointed at both ends. The body is smooth and is covered by thick, tough cuticle of few centimetres long.
Life Cycle of Roundworm: The eggs are fertilised in the female worm and the larva developed within the egg shell. The eggs are deposited in the intestine of pig from where they are passed out with the host’s faeces into soil where it can remain for many years. When the eggs are picked up by pigs, either through feeding or drinking, the egg shells are dissolved by digestive enzymes and the young larvae emerge.
The larvae then pierce through intestine wall to the blood, then to the liver, the heart and then to the lungs. From the lungs, they pierce into the mouth and throat of the pig. From the throat, the larvae are swallowed through the gullet into the intestine. Here the larvae develop into mature worms and the life cycle is repeated all over again.
Economic Importance of Round-worm
- They reduce the growth of host animals.
- High infestation can affect the respiration of host animals.
- It causes indigestion and constipation.
- It results in loss of appetite, weakness and may result in death.
- It destroys many of the organs during the migration of the young worms.
- The pigs should be dewormed with piperazine drugs regularly.
- Good sanitation of the environment should be maintained.
- Clean and uncontaminated water and feed should be provided for animals.
Tick is an ectoparasite of cattle, sheep and goat.
The body of tick is divided into two segments – head region and abdomen. It has four pairs of tough leathery integument and possesses a toothed hypostome – a piercing organ for sucking blood of the host.
Life Cycle of Tick: The life cycle of most ticks occurs in four stages. These include the egg, the larvae, the nymphs and the adult stages. Each stage requires a separate host.
Egg: A mature female tick, after sucking blood from its host, drops down and lays her eggs in the ground under grass and then dies.
Larvae: The egg hatches into a larva with six legs. The larva crawls into the grass and attaches itself to the skin of any animal passing by. The larva feeds on the blood of the host and then falls to the ground.
Nymphs: The larva now on the ground moults into a nymph with eight legs. The nymph also crawls and attaches itself to a second host. It feeds on the host and later drops to the ground.
Adult: The nymph now on the ground finally moults into an adult tick, which crawls into the grass and attaches itself onto a third host. If the adult tick is a female, it inserts its mouth parts immediately into the skin of the host and sucks blood. But if the adult tick is a male, it does not fix itself to the host but crawls on the skin in search of a female tick to mate with. After mating with the female, the male dies. When the female has sucked enough blood it falls on the ground and lays its eggs and the whole cycle is repeated.
Economic Importance or Effects of Ticks
- They cause great annoyance and irritation to their hosts.
- They act as vectors of diseases, e.g ., tick fever and heart water diseases.
- Injuries from their bites may become ulcerated wounds.
- Injuries or wounds caused may become sources of secondary infection.
- Damage of the skin by tick on host reduces the quality of skin or hides.
- They suck the blood of the host, thus leading to anaemia in host animal.
- The loss of blood may lead to loss of weight and death of host animal.
- Animals should be kept in clean surroundings.
- Animals should be dipped in insecticide solutions regularly to destroy ticks or spray them with ascaricide solution.
- Practise rotational grazing or paddlocking.
- New stocks are to be isolated to ensure that they are free from infection.
- Animal bedding should be changed regularly.
- Ticks should be hand-picked from the body of the host animals.
b) Lice: Lice are wingless insects with flattened bodies. They have three pairs of legs. The body is divided into three – head, thorax and abdomen. Their bodies are made up of exoskeleton with mouthpart used for biting and sucking. They attack cattle, sheep, goat and poultry birds.
Life Cycle of Lice: All lice pass their life cycles on the surface of the host and they cannot live long, away from their host. They lay their eggs called nits and attach them to the hair or feather of the host. The young ones, called nymphs, emerge from the hatched eggs. This is an incomplete metamorphosis.
The nymph leaves the egg and after a series of moulting of its skin, it becomes the adult male or female louse. The life cycle takes about three to four weeks. Transmission from host to host is by body contact.
Effects or Economic Importance of Lice
- Their bites cause irritation which result in scratching and restlessness.
- Scratching results in sores which become sources of secondary infection.
- Restlessness results in low productivity of animals.
- They act as vectors of diseases.
- They suck the blood of the host, thus leading to aneamia, loss of weight and death.
- Animals should be kept in a clean surrounding.
- Ensure regular dipping of animals in ascaricide solution to destroy lice.
- Overcrowding of birds should be avoided.
METHODS OF PREVENTING DISEASES
- Quarantine: New stock being brought to the farm should be separated from the animals orignally on the farm to enable the farmer to know whether the new stock possess diseases or not.
- Vaccination: Farm animals should be vaccinated or immunised at the right time and given right doses to enable them to acquire immunity in them so as to resist the invasion of pathogenic organisms.
- Hygiene: Good hygiene or sanitary measures must be taken to prevent infection of farm animals. This involves cleaning of pens, watering and feeding equipment, disposal of waste and regular disinfection.
- Good Feeding: Animals should be properly fed in order to resist disease attacks.
- Breeding: Disease-resistant stocks should be bred in the farm.
- Rotational Grazing: This should be practised so that the build-up of parasites will be avoided. This ensures the death of the infective stages of the parasites.
- Isolation: All sick animals should be isolated from healthy ones to pens where they will be treated separately.