What is Parasitism?

Parasitism is generally defined as a symbiotic relationship between the two living species. In this relationship, the parasites gain complete benefits from the host cell in which they are living by causing harm to the host’s cells. The word parasite is derived from the Latin form of the Greek word, meaning “one who eats at the table of another”.

A few examples of parasites are tapeworms, fleas, and barnacles. Tapeworms are segmented flatworms that attach themselves to the insides of the intestines of animals such as cows, pigs, and humans. They get food by eating the host’s partly digested food, depriving the host of nutrients.

Types of Parasitism

There are various types of parasitism and are classifications based on their size, characteristics, interactions with their hosts and on their life cycles.

  • Based on Interaction with host, these are the following types of Parasites.

Endoparasites: Parasites that live inside the body of the host are called endoparasites.

Ectoparasites: Parasites that live outside are called ectoparasites.

Epiparasite: Parasites that feed on other parasites are called epiparasite.

Meso Parasites: Parasites living in an intermediate position, being half-ectoparasites and half-endoparasites, are called meso parasites. 

  • Based on their Life Cycle

Obligate Parasite: Parasites which are completely dependent on the host to complete its life cycle.

Facultative Parasite: Parasites which are dependent but not completely on the host to complete its life cycle.

Social parasites do not directly feed on the tissue of their hosts like true parasites instead they gain benefit from their host by convincing the host to provide food or other benefits.

A good example of a social parasite occurs when there are generalised non-specific mutualisms between classes of organisms. For example, some plants can behave as “mycorrhizal cheaters”, establishing mycorrhiza-like interactions with a fungal symbiont, but taking carbon from the fungus (which the fungus, in turn, gets from other plants) rather than donating carbon. Another example is the cuckoo bird which leaves its young with a host to raise. This type of parasitism is often called brood parasitism.

Parasitism Dynamics: Due to the nature of the interaction between a host and a parasite many host populations will develop some form of immunity. The development of host population immunity causes either a decline in the parasite population or a genetic mutation in the parasite population to overcome the immunity. This dynamic tends to form a cycle in the parasite population where there are periods of population increases and periods of population decreases.

Advantages and Disadvantages of Parasitism

The host of a parasite gets no advantages. If it did, then the relationship would be mutualistic not parasitic. If one gets advantage and the other is relatively unaffected then the relationship is commensal. Some plants are parasitic (i.e. Mistletoe) and other plants are parasitized.
Many human diseases are caused by parasites (malaria, sleeping sickness etc) so this is clearly a disadvantage but humans can use parasites to their benefit. Many biological controls involve the use of parasites. In short, a parasite is a disadvantage to its host but may play a number of other roles within the ecosystem.
Many parasites cause harmful effects on their host. Such effects comprise:

  1. Wasting
  2. Allergic reactions
  3. Mechanical damage
  4. Irritative reflexes (intestinal contractions: ascaris)

To conclude about parasitism, it is evident that parasitism has very little to offer in terms of benefits. But yes, It helps maintain biodiversity in the ecosystem and controls the population to a large extent. Parasite-host interactions may be important at times. For example, such as parasitoids controlling the body temperatures of their hosts in order to ensure the survival of their offspring, and host choice in fleas being controlled by the off-host environment.

Stay tuned with BYJU’S to know more about Parasitism, its types and other interesting topics @ BYJU’S Biology

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