Perhaps the greatest facet of Cultural Perspectives is the opportunity it has given me to plunge into the infinitely dimensional field of science and as such my eyes were opened to, through the ‘Parasite Biology’ CP, the evolution and clever predation of one of the most dangerous microorganisms on Earth: parasites.
By definition, a parasite is “an organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense” but this, like any other scientific definition, places an oversimplified veil of which history, adaptation & evolution, among many other aspects are absent. The elaborate world of parasites is composed of those in all their adapted, twisted, and unclassifiable forms.
Parasitism presents the least favourable (or most favourable for the parasite) form of biological interaction, in which the parasite benefits at the expense of its host. This is a relationship which has profound social and economical effects in the human world and the global economy, inflicting billions of dollars’ worth of damage through the likes of neglected tropical diseases, bringing a narrative of social inequality into science, which some may wish to explore. The extent to which the parasite benefits, and the host is harmed, exists on a continuum of parasitic severity that I intend to focus on.
Parasites have evolved to maximise spread of infection through development in morphology, medium of reproduction i.e. whether they are hermaphrodites (organisms with both female and male reproductive organs and hence can undergo asexual reproduction) or not, their life cycles and medium of transmission among many other factors. There are three main classes of parasites: ectoparasites, helminths and protozoa.
Probably the least deadly are ectoparasites. These are parasites which act outside of the “host” body hence inflicting limited damage, common examples are lice, fleas and ticks. Ectoparasites can become more (indirectly) lethal when they act as vectors of disease, such as those of other parasites.
Helminths are parasitic worms, some of which have evolved incredible adaptations to compromise their primary hosts. Exciting examples include the lancet liver fluke (Dicrocoelium dendriticum) and the horsehair worm (Spinochordodes tellinii) which both ultimately lead to the death of their hosts (at a certain stage in its life cycle).
The lancet liver fluke is a trematode flat worm which is hermaphroditic as well as sexually active. Their life cycle consists of the infection of ants which, through what is infamously known as ‘parasitic mind control’, are made to migrate to the top of blades of grass where they can be eaten by the lancet liver fluke’s true host: cows. After successful transmission, an attraction to bile causes migration of the parasite towards the liver where its oral suckers attach, and feeding can begin (and mating if other lancet liver flukes are present). This parasite will then be spread to its intermediate hosts via cow faeces.
The horsehair worm Spinochordodes tellinii is a parasitic nematomorph hairworm which targets insects as its definitive host. Adult forms of this parasite live in aquatic environments such as puddles and damp soils. Upon transmission, this parasite has the ability to rewire the brains of insects – forcing them to jump into water where mating of the worm occurs, and the life cycle can repeat. These two parasites are prime examples of how awesome evolution can be and how science is yet to explain the intricacy of these organisms.
Parasitic protozoa are unicellular, eukaryotic organisms which have significant reproductive potential- allowing them to be highly infectious agents. The most well-known example is malaria (a plasmodium parasite of which 5 species are infectious to humans), which consists of multiple strains of human-infecting plasmodium species. Malaria parasites are mainly spread through mosquito vectors, agents which carry & transmit infectious pathogens to another live organism. When these infected mosquitos bite a human, they transmit the parasite into the bloodstream where they migrate to the liver and replication occurs. Once the malaria parasites have replicated sufficiently at the liver, they begin to attack red blood cells where they replicate and burst out via cell lysis. The death of these red blood cells is the cause of the symptoms of malaria, and as this occurs- the parasites will then develop into an infectious form which can be transferred to other hosts such that the life cycle of the parasite repeats.
The purpose of this article is to present a different perspective on what is a stigmatic attitude towards parasites and explore a world as elaborate as parasitology- to show that there is a way to appreciate and revel in the diversity and complexity of these organisms in a scientific and technical manner.
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