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Parasite, any organism living on or in another living organism, and deriving part or all of its nutrients from the host without contributing anything to the host. In most cases, parasites damage or cause disease in the host. Such parasites as lice, which live on the surface of the host, are known as ectoparasites. Parasites that live within the body of the host—threadworms, for example—are known as endoparasites. Permanent parasites pass most of their life cycle in or on a host; temporary parasites spend a brief period of time in or on a host and are free-living organisms for the remainder of the life cycle. Parasites that cannot survive without a host are called obligate parasites; facultative parasites are those able to feed either on a living host or on dead material. Heteroecious parasites, such as the liver fluke, require different organisms for various stages of the life cycle. Autoecious parasites, such as the pinworm, pass the parasitic stage of their life cycle in only one host. The scientific study of parasites is known as parasitology.

PARASITES OF HUMANS

Life Cycle of Human Blood Flukes Flukes of the genus Schistosoma parasitize two hosts. The young hatch from their eggs in rivers and lakes and enter a specific kind of aquatic snail, where they develop into tadpolelike larva called cercariae. When the cercariae leave the snail, they burrow through the skin of a human host swimming or wading in infested water. Adult flukes mature in the host’s bloodstream and settle in the veins of the gut. Their eggs, deposited in the lining of the human intestine and bladder, pass back into water via the excretory system, and the cycle begins again. More than 200 million people worldwide suffer from schistosomiasis (bilharzia), a disease characterized by the abscesses and bleeding caused by the flukes’ infestation.

Helminth Worm Helminths are a heterogeneous group of parasitic worms that attack the digestive tract and other internal organs of the vertebrate body. They include such diverse forms as the roundworms (nematodes), flukes (trematodes), tapeworms (cestodes), thorny-headed worms (acanthocephalans), and tongue worms (linguatulids).

Human parasites include viruses, rickettsias, bacteria, fungi, protozoans, worms, and flukes. Viruses and rickettsias are not usually considered living organisms, but they have parasite-like methods of transmission between hosts and obtain all their nourishment from the host. In humans, bacteria and fungi cause the most common infectious diseases. Protozoans also cause disease. The lethal human disease sleeping sickness, for example, is caused by the one-celled organism Trypanosoma; a similar organism causes malaria. The debilitating disease schistosomiasis is caused by a liver parasite .Other human parasites include various species of worms

III PARASITIC PLANTS

Mistletoe Plant Growing in a Tree A variety of small, parasitic, evergreen shrubs called mistletoe are native to Europe and the United States. These plants infest trees such as pine, fir, apple, and juniper. Some mistletoes are hemiparasites, relying on their host tree for some, but not all, of their nourishment.

All parasitic plants feed on other plants. They may be either partial parasites, deriving some of their nutrients from the host, or total parasites, completely dependent on the host for food. Partial parasites have green leaves and are capable of synthesizing carbohydrates, proteins, and fats by the process of photosynthesis; however, they derive all their water, nitrogen, and mineral salts from the host.

Common examples of such parasites are the painted cup, parasitic on roots, and mistletoe, parasitic on branches. The mistletoe is typical of a group of parasitic plants that never form roots of their own; the seeds of these plants are carried from tree to tree by birds, and develop penetrating outgrowths, known as haustoria, that pierce the host and enter the conducting system. Total parasites have vestigial leaves without chlorophyll and never have functioning roots. In dodder, the seed germinates in the ground, forming a small root attaching the plant to the soil but deriving no food from the soil; a long, thin, pliable stem grows above the ground until it contacts a green plant, which it then climbs up.

The ultimate in total parasitism is exhibited by certain tropical plants of the family Rafflesiaceae, which have neither stems nor leaves; they grow only on specific species of green plants. The germinated seed sends haustoria directly into the host; the only other organs of the parasite are nonpetalled flowers, composed of five huge, fleshy sepals that give off the odour of decaying meat. Insects, attracted by this distinct odour, carry the pollen of the parasite from flower to flower.

Worms are in pig and fish mostly cod fish.Seriously Cod is infested.If you pour coke over raw pork and wait the worms show up.Also try lamb it tastes better than pig.Turkey is great and also sometimes you can get it from eggs or the bird if chicken ate worm but it's rare.

Pinworms are from uncleanness.

You can also get worms from contaminated/ unfiltered water.

You can get worm from an actual worm in ground or mosquito bite because it has bug which becomes worm and grow 12 inches inside