Key Difference – Intermediate Host vs Definitive Host
Parasites depend on another living organism for their nourishment. They spend important stages of their life cycles on or within one or more living organisms. The organism which provides nutrition and space for the parasite is known as the host organism. Some parasites are entirely dependent on the host while some parasites are partially dependent on the host. Based on the way parasite is living with the host organism and the stages of the parasitic life cycle inside the different hosts, host organisms can be classified into several categories. Intermediate host and definitive host are two such types. The key difference between intermediate host and definitive host is that intermediate host is the organism in which a parasite lives shortly and passes several asexual stages whereas definitive host is the organism in which a parasite becomes mature and reproduces sexually.
CONTENTS
1. Overview and Key Difference
2. What is an Intermediate Host
3. What is a Definitive Host
4. Side by Side Comparison – Intermediate Host vs Definitive Host
5. Summary
What is an Intermediate Host?
The intermediate host is a living organism in which a parasite spends short time period of its life cycle before exploiting a suitable host to become mature and reproduce sexually. Inside the intermediate host, parasite passes one or more asexual stages, mostly development stages. The intermediate host is also known as the secondary host. For example, for Trypanosoma (a parasite which causes sleeping sickness) intermediate host is the human.
Intermediate hosts are mostly considered as vectors since the parasite only shows development stages inside the intermediate host and the host does not get infected by the parasite.
Figure 01: Human – An intermediate host of malaria parasite
What is a Definitive Host?
Definitive host or the final host is an organism in which a parasite becomes sexually matured. The definitive host is also known as the primary host. Inside the definitive host, the parasite becomes an adult and reproduces sexually. For example, the female Anopheles mosquito serves as the definitive host for the malaria parasite. Humans also serve as definitive hosts for several parasites including pinworms, schistosomes and tapeworms.
Trypanosoma which causes sleeping sickness uses tsetse fly as its definitive host and shows sexual reproduction inside tsetse fly.
Figure 02: Mosquito – A definitive host for malaria parasite
What is the difference between Intermediate Host and Definitive Host?
Intermediate Host vs Definitive Host |
|
| Intermediate host is the organism in which parasite spends a transition period of its life cycle. | Definitive parasite is the organism in which parasite becomes matures and reproduces sexually. |
| Maturation of the Parasite | |
| Parasite does not become mature inside the intermediate host. | Parasite becomes matured inside the definitive host. |
| Time Spent | |
| Parasite spends a short time period inside the intermediate host. | Parasite spends more time inside the definitive host. |
| Stages of the Life Cycle | |
| Parasite completes several asexual stages inside the intermediate host. | Parasite sometimes completes sexual reproduction inside the definitive host. |
Summary – Intermediate Host vs Definitive Host
Host is an organism which harbors a parasite. Parasites use host organisms for their growth and reproduction. Some parasites use more than one host and complete their life cycles inside a sequence of several different hosts. Intermediate and definitive host are two such types. Inside the intermediate host, parasite passes asexual or the development stages while inside the definitive host it becomes matured for sexual reproduction. Intermediate host serves as a secondary host in which parasite spends a short transition period before reaching the definitive host to become matured. Parasites attain sexual maturity only inside the definitive or the final host. This is the difference between intermediate host and definitive host.
Reference:
1.”Themes of Parasitology.” Intermediate Host: The Delivery Boy of the Parasitic World. N.p., n.d. Web. 18 Apr. 2017
2.”Life Cycle.” Malaria Site. N.p., n.d. Web. 18 Apr. 2017
3. Penczykowski, Rachel M., Anna‐Liisa Laine, and Britt Koskella. “Understanding the ecology and evolution of host–parasite interactions across scales.” Evolutionary Applications. N.p., 21 Aug. 2015. Web. 18 Apr. 2017
Image Courtesy:
1. “Falciparum-life-cycle-final” By Le Roche Lab, UC Riverside – (CC BY 3.0) via Commons Wikimedia
2. “Anopheles stephensi”Por Jim Gathany – (Domínio público) via Commons Wikimedia