Life Cycles of Human and Animal Parasites: Types and Classifications

life cycle- This is the sum of all developmental stages "from egg to egg", and in the absence of eggs, from any stage to the closest similar stage. The primary biological aspect of the life of any organism is the adaptations that ensure the preservation of the individual and the species.In parasites (unlike in free-living animals), nutrients are provided uninterrupted, so the reproductive activity of the body increases. Due to the spatial and temporal limitations of the habitat, parasite reproduction increases, leading to rapid overpopulation in the area and the need to relocate the species for conservation.

The sum of all stages of a parasite's ontogeny and its route of transmission from one host to another is called its life cycle.

loop form

After discovering that parasites are organisms that use other organisms to develop, it is important to understand what options exist for the development of life. According to classification, there are simple loops and complex loops. The first case occurs without changing the owner. Examples include the development of roundworms, amoeba, whipworm, etc. Complex groups contain multiple hosts simultaneously. These can be vertebrates, fish, shellfish, etc. An example is worms.

The whipworm developmental cycle does not require an intermediate host.

After entering the final host, the parasite grows and reproduces. Depending on the type of pathogen, the larvae can remain in the body or leave the body. In most cases, excretion occurs through the intestines. This makes it possible to determine the type of pathogen with a simple test.

Characteristics of cycle stages

Each stage of development has its own characteristics. Even treatment is decided based on this factor alone. For example, not all drugs are effective against larvae, while it is much easier to remove mature parasites.

The intermediate and final vectors of the parasite depend on the type of helminthiasis.

In this regard, let's take a look at how the development cycle works:

• Dispersal – This cycle exists when an intermediate host (i. e. source rather than final stage) is considered to be the only option at the moment (i. e. no potential final host exists). In this case, an intermediate host is used for further development and nutrition.
• Active Growth - After reaching the most suitable conditions, the parasite will stop, repair itself if suitable equipment is available, and begin growing to sexual maturity.
• Migration to another habitat – After mature individuals lay eggs, they in most cases move to further develop. They can be distributed in different ways. Most commonly, parasites migrate through the digestive system along with food boluses. Others, due to their size, can easily penetrate the bloodstream and spread throughout the body.
• Asexual Reproduction – A characteristic of certain types of parasites is that they do not require a second partner to reproduce. The most striking example is the tapeworm, in which each coccidia has a uterus in which mature eggs can be produced.

important concepts

The first thing to emphasize in understanding parasites is the concept of "host". This is an organism in which parasites develop and reproduce. The "intermediate host" stands alone. In this case, the pathogen remains in the body until it has the opportunity to migrate to the most favorable environment provided by the final host.This cycle can occur after replacing 1-4 hosts. In this case, the first one is the middle and the rest are additional. The parasite enters the final host through direct contact or through an intermediate host. This is where development and sexual reproduction occur.

Parasite development begins when the parasite enters its final host.

There are also concepts such as host parasitism and host feeding. In the first case, we are talking about a situation where the parasite, after reaching the right conditions, can remain unchanged for a long time, waiting for a more favorable solution.provider-owneris an organism that is specialized for use as food. The easiest option is pliers. By figuring out how this parasite feeds, we can learn that they need human blood to exist, but they don't stay in or on the body for long.

The concepts of "parasite reservoir" or "reservoir host" are also distinguished. This is a host in which pathogens can survive for long periods of time, accumulate, multiply, and spread to surrounding areas.

parasite biology

Parasite carriage is considered separately - if the pathogenic parasite lives in the human body, but the development of the disease does not occur. However, such people pose a danger to others.Parasites interact with their hosts.Harmful effects of parasites on the host:

1. Mechanical;
2. poisonous;
3. food withdrawal;
4. Destroy tissue integrity.

Therefore, the host's body "reacts" to the parasite's influence.Infections caused by parasites can be classified according to the susceptibility of the pathogen to the host:

1. Humanization – humans serve as hosts;
2. Zoonoses – multiple animals serve as reservoirs;
3. Zoonotic diseases are common invasive infectious diseases in humans and animals.

Medical parasitology consists of 3 main sections:

1. Protozoan parasites - Protozoology.
2. Parasites, helminths - Helminthology.
3. Arthropods - Arachnology.

life cycle stage

In most cases, protozoa have specialized stages adapted to carry out the transitional stages from one host to another. These stages are called propagation stages.in intestinal parasitesbreeding stageUsually adapted to the experience of the external environment. Most intestinal protozoa form cysts covered with a dense membrane. When the cysts of many species (Enamoeba histolytica, Escherichia coli, Enterobacteriaceae, etc. ) mature, the nucleus undergoes multiple successive divisions.beat until maturemultinucleated cystIn the new host, the cytoplasm divides to form several individuals. Cysts typically provide nutrients that are consumed during maturation and while the cyst remains in the external environment. The reproductive stage of coccidia is the encapsulated fertilized female germ cells (oocysts).Most parasitic protozoaVertebrate tissue and blood are transmitted from one host to another by vectors. In this case, the reproductive stage is located in the blood or in the outer integument of the vertebrate. Trypanosoma cruzi, the causative agent of Chagas disease, multiplies in the cells of visceral organs during the leishmaniasis stage. The Leishmania form of the parasite turns into a trypanosome, which penetrates the bloodstream but does not multiply in it.spread of infectionOccurs through vectors - blood-sucking worms. Leishmania dunovani, the causative agent of Indian visceral leishmaniasis (kala-azar), colonizes tissue phagocytes in tissues that are inaccessible to the vector. However, during later stages of the process, advanced leishmaniasis (lesions containing large numbers of Leishmania parasites) may develop on the patient's skin. In some cases, Leishmania is also found in the blood with this disease. The reproductive stage of the malaria parasite is the gametes circulating in the host's blood.along withbreeding stageIn the life cycle of a tissue parasite, there is the so-calledinvasion stage, suitable for penetration into vertebrate hosts. Thus, the development of representatives of the genus Trypanosoma in the vector ends with the formation of metacyclic trypanosomes, which no longer reproduce in the vector and adapt to development in the vertebrate host.

The invasive stage of the malaria parasite is the sporozoite.

Worm group

Each type of worm only grows under specific conditions. Parasites are divided into two main categories based on developmental conditions:biological wormandsoil worm.

biological worm

arrivebiological wormThese include parasites that develop with the participation of two or more organisms. In one organism live the adult worm and in the other organism live the larval stage.Organisms that parasitize adults and reproduce sexually are calledfinal(or ultimate) owner.The organism that develops in larval form isMiddleOwner. For example, the adult bovine tapeworm is a parasite in the human intestine, and its larval development occurs in cattle.Therefore, for this tapeworm, humans are the final host and cattle are the intermediate host.

Biological worms include most representatives of flatworm types.

soil worm

soil wormare those parasites that do not need to change hosts during development. The eggs are excreted with the feces and develop into larvae in the body under a certain temperature and humidity.The eggs containing larvae are contagious. Once inside the body (in the intestines), the larvae are released from the egg shell, penetrate certain organs and grow into sexually mature forms. In some worms, larvae are released from the eggs into the external environment. The larvae live in water or soil, go through certain stages of development and then actively penetrate the body through the skin.