Difference Between Definitive Host and Intermediate Host

Main Difference

The main difference between definitive host and the intermediate host is that definitive host includes the maturation and sexual reproduction of the parasite, whereas the intermediate host includes the immaturities and persistence of the parasite.

Definitive Host vs. Intermediate Host

The definitive host is an organism that supports the sexual reproductive form of parasites, whereas the intermediate host is an organism that supports the non-reproductive and immature form of parasites. The definitive host is also known as the primary host, while the intermediate host is also known as the secondary host. Sexual reproduction occurs inside the definitive host of the parasite; on the other hand, asexual reproduction occurs inside the intermediate host of the parasite. Inside the definitive host, the formation of zygote occurs; on the contrary, inside the intermediate host, sexual differentiation of the parasite occurs. The example of the definitive host of plasmodium is female Anopheles; conversely, the example of the intermediate host of plasmodium is human.

Comparison Chart

Definitive HostIntermediate Host
Definitive host that normally includes the sexual reproductive forms of parasites.An intermediate host that usually supports the non-reproductive or immature forms of parasites.
Alternative Names
Also known as the primary hostAlso known as a secondary host
Types of Reproduction
Sexual reproduction occurs inside the definitive host of the parasiteAsexual reproduction occurs inside the intermediate host of the parasite
Stages of Sexual Reproduction
The formation of zygote occursSexual differentiation of the parasite occurs
Examples
The definitive host of plasmodium is female AnophelesThe intermediate host of plasmodium is human

What is the Definitive Host?

The definitive host usually refers to the organism that supports the sexual reproductive form of a parasite. The definitive host is also called a primary host. Tapeworms and some other parasites only use the definitive host to complete their sexual reproduction cycles. Normally, tapeworms lay eggs on grasses and these eggs unintentionally move into the intestine of animals when they eat that grass, and then the larva grows to an adult tapeworm inside the host. There they complete their life cycles and sexual reproduction, lay eggs inside the host which then come to the environment with feces of animals. Other parasites live their complete life inside the different hosts. To complete their sexual reproduction, they use the definitive host to complete that. Plasmodium completes its sexual reproduction inside the female Anopheles mosquito. The mosquito generally picks blood-stage parasites during the blood meal called gametocytes. The types of gametocytes are microgametocytes (male) and macro-gametocytes (females). The gametocytes multiplication cycle occurs inside the sporogonic cycle. The penetration of macro-gametocytes in the stomach by microgametocytes, producing the zygote. The formed zygote is motile, and to become the oocyst; it invades the midgut wall. The breakdown of the oocyst produces sporozoites that travel into the salivary glands of the mosquito.

What is an Intermediate Host?

The intermediate host normally refers to the organism in which the parasite grows but not to the point of sexual maturity. The intermediate host is also called a secondary host. The intermediate host is a host in which a parasite usually designated as first and second host when parasite passes one or more of its asexual stages if there is more than one. More frequently, the intermediate host acts as the vector of the parasite to reach its definite host which means the parasite spends only a particular developmental stage inside the intermediate host and then the remaining as a definitive host. Sporozoites which produced by the breakdown of oocyst are inoculated into the bloodstream of the human. Therefore, the human is the intermediate host of the plasmodium. The liver cells of human are infected by sporozoites where they mature into schizonts, and then the rupture of the schizonts releases merozoites that infect red blood cells of human. The clinical manifestation of malaria disease is caused by blood-stage parasites.

Example

Some tapeworms make use of pigs, goats, cows, and fish as their intermediate host.

Key Differences

  1. The definitive host usually supports the sexual reproductive form of parasites, whereas intermediate host supports the non-reproductive and immature form of parasites.
  2. The definitive host is also known as the primary host, while the intermediate host is also known as a secondary host.
  3. Inside the definitive host, the formation of zygote occurs; on the contrary, inside the intermediate host, sexual differentiation of the parasite occurs.
  4. Sexual reproduction occurs inside the definitive host; on the other hand, asexual reproduction occurs inside the intermediate host of the parasite.
  5. The example of the definitive host of plasmodium is female Anopheles; conversely, the example of an intermediate host of plasmodium is human.

Conclusion

Above discussion concludes that both the definitive host and intermediate host are obligate to parasites and the stage of the life cycle of the parasites that take place inside each type of host.

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