What are a vector and a reservoir host?

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Concept understanding — Parasitism and Host-Parasite Relationships

Parasitism is a biological relationship in which one organism, the parasite, lives on or inside another organism, the host, deriving nourishment from it and generally causing it harm without necessarily killing it. This concept lays the vocabulary foundation for every life cycle studied later in the chapter.

Facultative vs obligate parasites. A facultative parasite can live a completely independent, free existence but will adopt a parasitic habit opportunistically if it enters a suitable host — parasitism is optional for it. An obligate parasite, however, must spend at least one stage of its life cycle in or on a host to survive and reproduce; it cannot complete its life cycle any other way. Entamoeba histolytica, Plasmodium vivax, Ascaris lumbricoides and Wuchereria bancrofti are all obligate parasites.

Host types. A definitive host is where a parasite attains sexual maturity or reproduces sexually (e.g., the mosquito for Plasmodium). An intermediate host is where the parasite's larval stages or asexual multiplication occur (e.g., humans for Plasmodium). A vector, usually an arthropod, actively transmits the parasite between hosts; a reservoir host is an alternative (often animal) host that keeps the parasite circulating in nature and can re-infect humans.

Mechanical vs biological vectors. In a mechanical vector, the pathogen is simply carried passively on the vector's body without any development inside it (e.g., houseflies carrying bacteria on their legs). In a biological vector, the pathogen actually develops or multiplies inside the vector's body before it becomes infective again (e.g., Anopheles mosquitoes for Plasmodium).

Hyperparasites and parasitic castration. A hyperparasite is a parasite that itself parasitises another parasite. Parasitic castration is a phenomenon where a parasite damages or destroys a host's reproductive organs (functionally sterilising it) without killing the host, redirecting the host's reproductive energy toward growth and toward supporting the parasite instead. …

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A vector is an organism — typically a blood-feeding arthropod such as a mosquito or housefly — that actively carries a parasite or pathogen from an infected host to a healthy, susceptible one, and so is directly responsible for transmission. A reservoir host, on the other hand, is not necessarily involved in transmission at all; it is simply an alternative host species (often a wild or domestic animal) in which the parasite can survive and multiply even when there are no active human cases, so that it continues to be available in nature as a source from which humans can later become infected. Both concepts matter for disease control: controlling a vector (e.g. mosquito control) can break transmission, while a reservoir ho …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2022Set ANNUAL2 marks
$Q. What is a hyper-parasite? Mention the name of one hyper-parasite.$
›Reveal solutionSolution

A hyperparasite (secondary parasite) parasitises another organism that is itself a parasite, rather than parasitising a free-living host directly.

Parasites are usually classified by which host they infect. An ectoparasite lives on the host's body surface, an endoparasite lives inside the host's body, and a parasite that requires more than one host during its life cycle needs a primary (definitive) host and one or more intermediate hosts. A special category is the hyperparasite (or secondary/tertiary parasite): an organism that parasitises another parasite, rather than a free-living organism.

This relationship can occur at several removes — a hyperparasite may itself become the host of a further hyperparasite. Hyperparasitism is common in the animal kingdom, especially among protozoan and helminth (fluke/tapeworm) life cycles, and is of biological-control interest because a hyperparasite can reduce the effectiveness of a parasite being used to control a pest.

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CBSE 2020Set ANNUAL2 marks
$Q. What do you mean by parasitic castration? Give one example.$
›Reveal solutionSolution

Parasitic castration is a parasitic strategy in which the parasite disables the host's reproductive system so that the host's energy is redirected to feeding the parasite instead of producing offspring.

Definition: Some parasites, rather than (or in addition to) drawing nutrients from the host, interfere with or destroy the host's gonads/reproductive organs. This is called parasitic castration. Because the castrated host no longer expends energy on producing eggs/sperm, courtship or brooding, more of the host's resources become available for the parasite's growth and reproduction — and the host, unable to reproduce, effectively becomes a long-term resource for the parasite rather than dying quickly.

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Q.What are a vector and a reservoir host?

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