Parasitism
Parasitism is the relationship between a parasite and its host.
The parasite benefits by gaining nutrients and/or energy from the host.
The host is harmed by losing energy and/or nutrients.
Parasites often have a very limited metabolism and cannot survive out of contact with a host. For example, a tapeworm lacks a digestive system since it lives within its host digestive system.
The most effective parasite is one that does not kill its host completely. This helps ensure a continues supply of nutrients or energy.
Parasites need to spread from host to host in order to survive. They can be transmitted in a variety of ways:
- Direct contact 鈥 head and body lice are passed from person to person during physical contact.
- Release of resistant stages 鈥 some parasites use resistant larvae and pupae, which can survive adverse environmental conditions until a new host comes in contact with them.
- Use of a vector - some parasites use another species to transfer them from one host to another - the Plasmodium parasite (commonly known as malaria) is carried by mosquitoes (the vector) from one human to another.
Some parasites require the use of a secondary host within its life cycle. This can be seen in tape worms. Larvae form cysts in the organs of secondary hosts (such as fish for the fish tapeworm (Diphyllobothrium latum) or pigs in the pork tapeworm (Taenia solium).