Parasitic nutrition

Parasitic nutrition is a mode of heterotrophic nutrition where an organism (known as a parasite) lives on the body surface or inside the body of another type of organism (known as a host). The parasite obtains nutrition directly from the body of the host. Since these parasites derive their nourishment from their host, this symbiotic interaction is often described as harmful to the host. Parasites are dependent on their host for survival, since the host provides nutrition and protection. As a result of this dependence, parasites have considerable modifications to optimise parasitic nutrition and therefore their survival.

Parasites are divided into two groups: endoparasites and ectoparasites. Endoparasites are parasites that live inside the body of the host, whereas ectoparasites are parasites that live on the outer surface of the host and generally attach themselves during feeding. Due to the different strategies of endoparasites and ectoparasites they require different adaptations in order to acquire nutrients from their host.

Parasites require nutrients to carry out essential functions including reproduction and growth. Essentially, the nutrients required from the host are carbohydrates, amino acids and lipids. Carbohydrates are utilised to generate energy, whilst amino acids and fatty acids are involved in the synthesis of macromolecules and the production of eggs. Most parasites are heterotrophs, so they therefore are unable to synthesise their own 'food' i.e. organic compounds and must acquire these from their host.

enderoparasite is parasites which live inside the body of the host. This group includes helminths, trematodes and cestodes. Endoparasites are two groups of parasites: intercellular and intracellular parasites. Intercellular parasites live in spaces within the host e.g. the alimentary canal, whereas intracellular parasites live in cells within the host e.g. erythrocytes. Intracellular parasites typically rely on a third organism, a vector, to transmit the parasite between hosts. Rather than requiring adaptations to penetrate the host, as ectoparasites do, endoparasites are in a nutrient-rich location so they instead have adaptations to maximise nutrient absorption. Endoparasites have a readily available and renewable supply of nutrients inside the host, which in some cases is pre-digested by the host, so mechanisms of nutrient absorption across their body surface is a common feature. As part of their life cycle strategy, endoparasites must also be able to transmit from within the host body and survive the hostile environment within the host. Only by achieving this can they benefit from acquiring nutrition in this way.

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