Difference Between Parasite and Host

Parasitism is an acquired, secondary type of hostile symbiosis characterised by mutual metabolic dependency between host and parasite. Parasites live off of and feed off of members of different species (called hosts) for extended periods of time. Parasitism serves the parasite but harms the host.

What are Parasites?

The term "parasite" comes from the Greek words para, which means "alongside," and sitos, which means "meal"; "parasitos" means "eating at another person's table." A parasite is another organism which receives nourishment from another organism, termed the host. Parasites may or may not cause harm to their hosts, but they never gain anything from the parasitic connection.

Certain endoparasites that reside inside the host are among the 70% of parasites that cannot be seen with the naked eye. Endoparasites need a third creature, termed a vector or carrier to be able to be transmitted to a host. On the other hand, those that live outside the body are termed ectoparasites.

Protozoa, helminths, and ectoparasites are the three primary categories of parasites that may infect people and cause illness (Centers for Disease Control and Prevention, 2016).

• Protozoa − are minute and unicellular organisms which can proliferate in people; those that dwell in the intestines are often found in contaminated food or water. For instance, the parasite Entamoeba histolytica is responsible for the symptoms of amebiasis, which include diarrhoea and stomach discomfort. Vectors spread protozoa that may replicate in human cells or circulate in the blood. The protozoan parasites of the genus Trypanosoma, which are transmitted to humans by the bites of tsetse flies, are one example of the cause of sleeping sickness.

• Helminths − are large, multicellular organisms that, in their adult form, cannot reproduce in humans. These include flatworms (e.g. flukes and tapeworms), thorny-headed worms or spiny-headed worms (thought to seldom infect humans), and roundworms (e.g. Ascaris lumbricoides which cause ascariasis, an infection of the small intestines) (e.g. Ascaris lumbricoides which cause ascariasis, an infection of the small intestines).

• Ectoparasites − are creatures that burrow into the skin; for example, ticks, lice, and fleas infest the skin and its appendages. They spread pathogens.

What are Hosts?

A host is an organism that serves as a source of food and habitat to a parasite. Depending on their role in the development and existence of the parasites, hosts can be divided into obligate, paratenic, and potential.

Obligate are hosts without which the parasite cannot complete its development cycle and ensure its existence as a species. Depending on the stage of development of the parasite, obligate hosts are divided into −

• End host − Here the parasite reaches sexual maturity and reproduces sexually. For single-host parasites, this is the only host;

• Intermediate host − Here the parasite develops part of the larval stages of two-host and three-host parasites. In some parasites is observed asexual reproduction of larval stages in the intermediate host;

• Additional host − Takes place the second phase of larval development of the three-host parasites.

Depending on the living conditions offered by obligatory hosts, they are divided into −

• Specific (typical) host − The parasite finds the most favorable living conditions;

• Non-specific (atypical) host − Conditions are not optimal and the survival rate is low.

A paratenic host can host a particular phase of the development of a parasite but does not provide all the necessary conditions for its entire development. The parasite can exist without this host. Depending on the development of the parasite within the paratenic host, they are divided into −

• Euparatenic host − The parasite does not develop in this host;

• Paraparatenic host − Partial development begins;

• Metaparatenic host − Partial development ends.

Depending on the further development of the parasite, paratenic hosts are −

• Tank host − A paratenic host that can transmit the parasite to an obligatory host.

• Abortive host − A paratenic host that releases the parasites in the stage that they have entered it and cannot transmit the invasion to an obligatory host;

• Captive host − A paratenic host in which the larval form of a parasite enters without being able to be transmitted to an obligatory host.

The potential hosts can provide a favorable environment for the development of a parasite, but cannot naturally be infected due to the lack of ecological connection.

Parasites have a negative effect on the survival and the physical condition of the hosts. They are an important factor influencing the dynamics of hosts’ populations and their evolution. Parasites can harm the host by using it as a source of nutrients or with the excreted metabolites. Indirect impacts include adverse effects on certain reproductive parameters, transmission of various diseases, etc. In some cases, parasites can cause the death of the hosts.

The factors that determine the course of the parasitosis are the condition of the immune system, protective reflexes, immunopathological reactions, hosts’ nutrition, concomitant diseases, etc. If the host is human important factors are the lifestyle, culture, level of health care, etc.

Differences: Parasite and Host

The following table highlights the major differences between Parasites and Hosts −

Characteristics	Parasite	Host
Definition	Parasite is an organism that lives on the surface or inside another organism and feeds on it.	Host is an organism that serves as a source of food and habitat to a parasite.
Types	According to their localization, parasites are endoparasites or ectoparasites. According to their ontogenesis and way of life, parasites are obligate, facultative or pseudoparasites. According to the time span of the parasitism, parasites are temporary, permanent or transit.	Depending on their role in the development and existence of the parasites, hosts can be divided into obligate, paratenic, and potential. Depending on the stage of development of the parasite, obligate hosts are divided into end, intermediate, and additional host. Depending on the development of the parasite within the paratenic host, they are divided into euparatenic, paraparatenic, and metaparatenic hosts.
Impact	The parasite benefits from the host, using it as a source of food and habitat.	Parasites have a negative effect on the survival and the physical condition of the hosts. In some cases, parasites can cause the death of the hosts.
Influencing factors	The factors that determine the course of the parasitosis are the pathogenicity, species characteristics, adaptations, quantity, reproductive potential, localization of the parasites, etc.	The factors that determine the course of the parasitosis are the condition of the immune system, protective reflexes, immunopathological reactions, hosts’ nutrition, concomitant diseases, etc. If the host is human important factors are the lifestyle, culture, level of health care, etc.

Conclusion

The relationship between a parasite and a host is complex and can vary from mutualistic to parasitic. The key differences between parasites and hosts include their physical and behavioral characteristics, their impact on each other, and their ability to survive and reproduce independently.

Understanding the differences between parasites and hosts is important for understanding the dynamics of this unique relationship and for developing strategies for controlling or mitigating the negative impact of parasites on hosts.