Life Cycle of a Parasite
There are many types of parasites, and each one has variations to its life cycle. There are, however, similarities among the life cycles of all parasites. The one thing that all parasites have in common is that they are opportunistic organisms that live off the blood of other living organisms. Parasites are dangerous for two reasons. The first is that they can infiltrate the host to the point of consuming all of the body's food, clogging vessels or organs and killing the host, and the other is that they can pass deadly diseases to host organisms.
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Types of Parasitic Life Cycles
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There are two main types of parasitic life cycle: direct and indirect. A direct life cycle parasite can reinfect the same type of host it came from. For instance, a hookworm can infest the intestines of a dog, and then larvae from the same hookworms can reinfest that dog. Indirect parasites require different types of hosts for various stages of their life cycle.
Hosts
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The host is the organism that gives a parasite "a ride." Parasites infect other organisms in one of two ways: ingestion and injection. Ingestion occurs when food or other matter containing eggs or parasite larvae are eaten or inhaled. The parasite then attaches itself to the host or moves through its system to the target area (heart, lungs, stomach, intestines, etc.) and attaches itself. Injection occurs when a different host bites a new organism and parasites are transferred via saliva to the new host.
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Unusual Hosts
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Accidental hosts are organisms that may accidentally come in contact with a parasite that cannot complete its life cycle on it. A flea may jump on a human being and bite, but it does not infest humans and cannot complete its life cycle on a human being.
Life Cycle Differences and Similarities
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Of the millions of types of parasites that exist today, there are two stages of life where they may differ in development: the larval stage and the pupae stage. However, they all have similarities in that the cycle consists of a pattern that is common to all parasites: egg, larvae, pupae and adult.
Types of Parasites
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Periodic parasites are those that only live part of their life cycle on one or more host(s). During some portion of their life cycle, these types of parasites must live on their own. Such is the case of a flea who lays eggs in a carpet and hatches to then jump on a passing host.
A hookworm begins its life as an egg passed in the stool of an animal that is inhaled or ingested by another animal to hatch inside that host. A hookworm is an obligatory parasite that must live on a host at all times.
Finally, there is a type of parasite that can live its complete life on its own without a host at all, but if a host passes by it will take advantage of the situation and attach itself to that host, feeding off the supplies there. This is called a facultative parasite.
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References
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