15.6 Parasitism
Parasitology is a science of human and animal parasites. In a wider sense, some
authors consider parasitology to be a part of microbiology. It deals with protozoa,
worms, and insects parasitizing on humans or on animals. Furthermore, it describes
the life cycles of parasitic organisms, diseases caused by them, and also proposes the
pertinent treatment. There are two branches of parasitology, human and veterinary.
15.6.1 Definition of a Parasitic Organism
Parasite is a word derivation from the Greek word parasitos. In parasitism very often
a tiny parasite attacks a much larger organism, the host. The parasite lives at the
expense of its host, but in general, it does not kill it. On the other hand, predators first
kill their victim and only then devour it. Depending on the host, the parasites are
classified either as zooparasites or as phytoparasites. Intracellular parasites live in
somatic cells or in phagocytes, often causing chronical infections (for instance,
bacillar dysentery, brucellosis, and tuberculosis). On the other hand, extracellular
parasites are quickly destroyed by phagocytosis and they harm the host only as long
as they are outside of phagocytes.
However, there does not exist any clear cut distinction between parasitism and
predation, because there are many intermediary forms. The same is true for commensalism and parasitism, where a commensal microorganism can convert to a
parasitic relationship.
15.6.2 Ectoparasite and Endoparasite
There are plant parasites as well as animal parasites, and microbial parasites. An
equal term for an ectoparasite is an exoparasite. Generally, it represents every
organism that parasitizes on the surface of a host’s body. On the other hand, an
endoparasite lives inside the body of the host. Parasites can be classified as either
facultative or obligate. As the name suggests, a facultative parasite can live even
beyond its perhaps customary existence with a host organism. However, under
certain conditions, it will enter into a parasitic relationship with its specific host.
Obligate parasites are absolutely unable to live and multiply without nutrition
received from the host organism. Obligate parasitism exists among plants and
animals. Also, viruses belong to the category of obligate parasites. Each parasite
has a certain spectrum of hosts. That means a parasite always seeks a host, which
suits it based upon the parasite’s nutritional requirements. Some parasites are highly
specialized and therefore they can have just one type of a host. These cases exist,
especially with viruses, including phages and also with fungal parasites.
252
V. Klaban
Parasitology is a science of human and animal parasites. In a wider sense, some
authors consider parasitology to be a part of microbiology. It deals with protozoa,
worms, and insects parasitizing on humans or on animals. Furthermore, it describes
the life cycles of parasitic organisms, diseases caused by them, and also proposes the
pertinent treatment. There are two branches of parasitology, human and veterinary.
15.6.1 Definition of a Parasitic Organism
Parasite is a word derivation from the Greek word parasitos. In parasitism very often
a tiny parasite attacks a much larger organism, the host. The parasite lives at the
expense of its host, but in general, it does not kill it. On the other hand, predators first
kill their victim and only then devour it. Depending on the host, the parasites are
classified either as zooparasites or as phytoparasites. Intracellular parasites live in
somatic cells or in phagocytes, often causing chronical infections (for instance,
bacillar dysentery, brucellosis, and tuberculosis). On the other hand, extracellular
parasites are quickly destroyed by phagocytosis and they harm the host only as long
as they are outside of phagocytes.
However, there does not exist any clear cut distinction between parasitism and
predation, because there are many intermediary forms. The same is true for commensalism and parasitism, where a commensal microorganism can convert to a
parasitic relationship.
15.6.2 Ectoparasite and Endoparasite
There are plant parasites as well as animal parasites, and microbial parasites. An
equal term for an ectoparasite is an exoparasite. Generally, it represents every
organism that parasitizes on the surface of a host’s body. On the other hand, an
endoparasite lives inside the body of the host. Parasites can be classified as either
facultative or obligate. As the name suggests, a facultative parasite can live even
beyond its perhaps customary existence with a host organism. However, under
certain conditions, it will enter into a parasitic relationship with its specific host.
Obligate parasites are absolutely unable to live and multiply without nutrition
received from the host organism. Obligate parasitism exists among plants and
animals. Also, viruses belong to the category of obligate parasites. Each parasite
has a certain spectrum of hosts. That means a parasite always seeks a host, which
suits it based upon the parasite’s nutritional requirements. Some parasites are highly
specialized and therefore they can have just one type of a host. These cases exist,
especially with viruses, including phages and also with fungal parasites.
252
V. Klaban