Key Difference – Obligate vs Facultative Parasite
Parasitism is a kind symbiotic relationship between two organisms in which one is benefited while the other is not. The parasite is an organism which lives on or within another living organism (host) and obtains nutrients for its nourishment. Parasites include single-celled and multi-celled animals, fungi, bacteria and viruses. This relationship is beneficial for the parasite while the host is often adversely affected. Some parasites are very harmful to the host organism. It can even lead to the death of the host organism. There are different types of parasites. Obligate parasite and facultative parasite are two such types. The key difference between obligate and facultative parasite is that obligate parasite is unable to complete its life cycle without the host organism while facultative parasite is able to continue its life cycle even without a host organism. Obligate parasite fails to reproduce when the host is absent while facultative parasite does not rely on the host for reproduction.
CONTENTS
1. Overview and Key Difference
2. What is an Obligate Parasite
3. What is a Facultative Parasite
4. Side by Side Comparison – Obligate vs Facultative Parasite
5. Summary
What is an Obligate Parasite?
Obligate parasite, also known as holoparasite, is an organism which fails to complete or continue its life cycle without a host. The presence of the host organism is essential for an obligate parasite for the reproduction and survival. If the obligate parasite cannot reach a host organism, it affects its growth and reproduction. Since an obligate parasite requires a host, this type of a parasitic relationship often does not cause the death of host organism. An obligate parasite is capable of preserving the health of its host until transmitting into a new host. During the transmission to a new host, it causes the death of the host organism as it is necessary for their survival.
Most obligate parasites die due to the absence of their specific host organisms. Therefore obligate parasites have a variety of different parasitic strategies to find a suitable host for their survival. Rickettsia, Trichomonas, Taenia, Trichinella, and Chlamydia are examples of obligate parasites. Viruses are also considered as obligate parasites since they are not capable of reproducing and increasing in number without a host organism.
Figure 01: Obligate Parasite Mycobacterium spp.
What is a Facultative Parasite?
The facultative parasite is a kind of parasite which is able to complete its life cycle even without a host organism. It can either live independently from the host or dependently with the host in contrast to an obligate parasite. The presence of the host is not an essential factor for the survival of a facultative parasite. Most of the facultative parasites are free-living organisms, and they infect the host very rarely. Naegleria, Acanthamoeba, Candida are examples of facultative parasites. Certain fungal species are facultative parasites in nature. Sometimes they behave like facultative parasites and the other times as saprophytes in the absence of a host.
Figure 02: Facultative parasite – A fungus
What is the difference between Obligate and Facultative Parasite?
Obligate vs Facultative Parasite |
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| A parasitic organism which requires the host organism to complete its life cycle is known as an obligate parasite. | A parasitic organism which is able to complete and continue its life cycle even with the absence of the host is known as a facultative parasite. |
| Life Cycle | |
| Obligate parasites have complex life cycles. | Facultative parasites have comparatively simple life cycles. |
| Presence of the Host | |
| Obligate parasite can survive only with the presence of its host. | Facultative parasites can survive even with the absence of the host. |
| Transmission through Host Organisms | |
| Obligate parasites travel directly from one host to another host. | Facultative parasites can pass important stages of their life cycle even without a host. They do not travel directly from one host to another. |
| Free-living Nature | |
| Obligate parasites do not have free-living stages. | Facultative parasites are free living when the host is absent. |
Summary – Obligate vs Facultative Parasite
Parasitism is a symbiotic relationship between two organisms called a parasite and a host. In this relationship, a parasite gets advantages at the expense of the host. The parasite can be totally dependent on the host or partially dependent on the host for nutritional and reproductive requirements. An obligate parasite is strictly dependent on a host organism to complete its life cycle and survival. A facultative parasite does not strictly depend on a host to complete its life cycle. Even with the absence of the host, facultative parasites are able to complete their life cycles. This is the difference between an obligate parasite and a facultative parasite.
References:
1.Poisot, T., M. Stanko, D. Miklisová, and S. Morand. “Facultative and obligate parasite communities exhibit different network properties.” Parasitology. U.S. National Library of Medicine, Sept. 2013. Web. 17 Apr. 2017.
2.”Parasite.” Parasite – New World Encyclopedia. N.p., n.d. Web. 17 Apr. 2017
Image Courtesy:
1. “Mycobacterium tuberculosis Bacteria (1684398146) By NIAID – Mycobacterium tuberculosis Bacteria (CC BY 2.0) via Commons Wikimedia
2. “Armillaria mellea, Honey Fungus, UK 1” By Stu’s Images (CC BY-SA 3.0) via Commons Wikimedia