Obligate Parasites: What Is It, Their Life Cycle And Development

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Obligate Parasites: What Is It, Their Life Cycle And Development
Obligate Parasites: What Is It, Their Life Cycle And Development
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Video: Parasites: Protozoa (classification, structure, life cycle) 2023, February

Parasites are creatures that live off other organisms. They are divided into two types - obligate and optional. Obligate parasites cannot exist outside the limits of their host's organism - they die in the external environment. Under favorable conditions, parasitic creatures begin to actively reproduce, laying up to a million eggs per day. Facultative parasites are characterized by a free lifestyle, they are not attached to their breadwinner.


  • 1 Characteristics of the obligate species
  • 2 Life cycle
  • 3 Intracellular
  • 4 Endoparasites
  • 5 Ectoparasites

Characteristics of the obligate type

Once outside the body, the parasitic creatures die or do not reproduce. In contrast, facultative parasites lead a free lifestyle. Nevertheless, the parasitic lifestyle is not alien to them. Obligatory parasitism is more common.

Infection routes:

  1. contact;
  2. airborne;
  3. animal bites;
  4. sexual.

Permanent parasites have a well-developed reproductive system, capable of laying from several thousand to several million eggs per day per day.

Life cycle

Obligate parasites are able to live only in the body of their host - leaving it, they immediately perish. In this case, the owner may not be one, but two creatures. One organism is called the intermediate, the other the final host.


Obligate parasites can live in:

  • cells in which viruses and chlamydia settle - they are called intracellular parasites;
  • human body cavity - this group of endoparasites includes worms (tape, round, flat);
  • external integuments where fungi and lice settle are ectoparasites.

More than a million obligate parasites are known, many of which are dangerous to humans.


Obligate intracellular parasites are bacteria that infect the cells of a living organism. They are toxic. The most popular representatives of intracellular obligate parasites are:

  • chlamydia;
  • rickettsia;
  • viruses.

Rickettsiae are intracellular bacteria that infect the cells of chicken embryos and the lungs of mice. Human infection occurs through a chicken egg, which is consumed raw.

Mice are also dangerous - with their bite, the disease can pass to humans. After infection, he begins to develop rickettsiosis, which manifests itself in two types - typhus and spotted fever.


Viruses begin to progress once they enter a living cell. They affect plants, animals and people. Thus, the influenza virus is an obligate parasite that can develop only at the expense of a living cell. Everything that is necessary for life, he receives from the cell, and multiplies in it. Viruses cause different types of diseases, which in most cases can be successfully treated.

It is quite simple to protect yourself from obligate intracellular parasites - you need to be vaccinated and strengthen the immune system


Obligate endoparasites represent a rather impressive list, which includes different types of worms:

  • intracellular - plasmodium and toxoplasma;
  • tissue - dysentery amoeba and itch itching;
  • intraorgan - opisthorchis, fasciola;
  • cavity worms - roundworm, pinworm, tapeworms.

Pinworms are part of the group of obligate worms that are localized in the intestines. This type of helminth lives exclusively in the human body.

Pig tapeworm needs an intermediate and permanent owner. The permanent owner is a person, and intermediate development is carried out in the body of a pig or wild boar.

Roundworms are very common. They can affect the body of almost any animal, they are dangerous to humans. These worms primarily affect the gastrointestinal tract. Ascaris larvae can migrate throughout the body.


Endoparasites can be:

  • monoxenous, which live in the body of one host (ascaris, pinworm, whipworm);
  • heteroxenous - for full development, two or more hosts are needed, their development is carried out in stages (flukes, tapeworms, plasmodium).

Obligate endoparasites are very common in nature. In total, there are more than 50,000 species, of which 500 varieties of helminths can affect the human body


Obligate ectoparasites are organisms that infect the external organs. They fall into two groups:

  • permanent ones that live and reproduce on the skin of an animal or person;
  • temporary ones, which use blood, skin scales, wool for food, do not live and multiply on the surface of a living organism.

The scabies mite is also a persistent parasite. His place of residence is human skin. In the course of its life, it causes itching and rash in a person. The scabies mite usually affects areas where the skin is thin (between the fingers, wrists, armpits).

All types of parasites provoke diseases and pose a danger to human health. Therefore, it is necessary to know the ways of their distribution, to observe the rules of personal hygiene and other preventive measures. This is the only way to avoid infection.

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