Parasitism

Different species interact in an ecosystem for their sustenance of life. It is not possible for a species to live completely isolated from another species. When species interact with each other, it is called population interactions. These interactions could be beneficial for both species or beneficial for one of these species. It is a population interaction among  two species in which one member drives benefits from the other. The benefiting species are regarded as parasites, while the host usually faces loss in form of diseases or even death in some cases.

Parasitism

Parasitism is a kind of interaction among two species for sustaining life. In parasitism, parasites are the benefiting species, and the other which is not benefited is the host. The host is larger than the parasite which attacks it.

Mostly every parasite derives food from its host by living on it or, in some cases, inside it.

Types of Parasites

Parasites can be broadly classified into six categories based on their location of occurrence, type of dependency, the period for which they act as a parasite, their location, etc.

Ectoparasites

These parasites live outside the host’s body, mainly on its surface. They can either be temporarily or permanently attached to the host. As they are present outside the host, active parasites undergo aerobic respiration. They derive their food from the host by sucking their blood when the host is an animal and juice when the host is a plant. These parasites can either feed on living tissue like scab mites or can even derive nutrition from dead tissue like bird lice.Cuscuta is also an example.

Endoparasites

These parasites occur inside their host’s body and lives permanently inside it. Endoparasites have anaerobic respiration. Based on the location, these can be intracellular like the malarial parasite or found in the body tissues, such as Trichinella. Some even occur in the body fluid of the host, like Trypanosoma. However, a majority of endoparasites are found in the gut cavity of the host, like the Ascaris and Taenia solium. Endoparasites get digested food in the host’s gut cavity, so their major digestive organs are reduced.

Temporary and permanent parasites

Temporary parasites attach to their host for a smaller time period only when they derive nutrition, for example, leech. Permanent parasites live throughout their life cycle with the host and transfer their progeny to other hosts by cysts or eggs, for example, Entamoeba histolytica.

Hollow parasites and hemiparasites

Hollow parasites are dependent on their host for every process they perform, for example, Rafflesia. Family Convolvulaceae of Angiospermic plants that are parasites receive phytohormones from their host.

Hemiparasites only depend on their host for nutrition and carry out the rest of the processes independently, for example, Rhinanthus

Phytoparasites

There are a number of parasites that only live on plant species. These parasites attack on stem or root. The Lac insect or aphids attack on the stem region of the plant, and root nematodes attack on the root of the host plant. However, several microbial parasites, which can be bacteria, fungi, or viruses, also attack plants as parasites.

Pathogenicity of a parasite

Parasites such as bird lice are non-pathogenic as they feed only on dead tissues.

However parasites like Ustilago tritici or Erysiphe cichoracearum  are pathogenic in nature as they cause loose smut of wheat and powdery mildew of cucurbits, etc.

Parasitism seen in birds

Parasitism in birds can be seen in the spring season in birds . The cuckoo bird does not  provide parental care to its young ones as it lays its egg in the host’s nest. In this kind of interaction, the cuckoo bird’s eggs act as parasites, and the crow serves as a host. Evolution caused great similarity between the cuckoo and crow’s eggs and are, therefore, hard to detect by the host. This kind of parasitism is regarded as brood parasitism

How do parasites cause infection?

There can be a variety of ways through which parasites get attached to their host

• In ectoparasites, some parasites may stick to the host’s surface, for example, leech.
•  Some parasites pierce through the skin surface and enter into their host. 
• Lice gets transferred to another host simply when the new host is in the vicinity of the infected person. 
• Biting can also be a mechanism by which a parasite can enter a host, for example sleeping sickness caused by the bite of the tsetse fly or malarial parasite that enters its host by the bite of a mosquito. 
• Some parasites adapt oral routes to infect their hosts, for example Ascaris and Entamoeba.

Conclusion

Parasitism is a way of interaction between two species. In this interaction, one species feeds on another. Parasites, though smaller in size than the host, use the host for its beneficial purpose. Both plants and animals have parasites located in different segments of their body. Most parasites do not kill their host; however, they make their host weaker by deriving its nutrition. Parasites often modify themselves to adapt to their host; some develop suckers while others eliminate their digestive tracts. Parasites are host-specific; all parasites have a certain host through which they can derive their nutrition.