The intermediate host is the organism in which the parasite lives and multiplies

The life cycle of many parasites is surprisingly complex. To go through all the stages of development, they need to change their host several times. One of these hosts will be the main one. In his body, the parasite will be able to reproduce sexually or asexually. But we will talk about the intermediate host.

What is or who is an intermediate host?

The intermediate host is an insect, an animal or a person whose organism gives the parasite the possibility of living in the larval stage. Inside the intermediate host, asexual reproduction can occur . For example, the human body provides a temporary habitat for malarial plasmodium, echinococcus and other parasites.

However, not every organism in which the parasite has visited different stages of development is considered to be its intermediate host. This is the name of only an animal, the passage through the organism of which is an indispensable condition for the transition to the next cycle of parasite development.

How does the parasite behave in the body of the intermediate host?

The behavior of larvae in the intermediate environment is divided into 3 types:

1. The intermediate organism prepares the larva for transfer to the final host. In this case, there is no noticeable development of it. A vivid example is the trypanosomes that develop in the mammalian organism, with the bite of the hind legs get on their proboscis with blood, survive the form of the insect intestinal form and are transmitted at the next bite to another mammal.
2. The second type of behavior is observed in the body of intermediate hosts, where parasites vary significantly, but do not multiply. At the exit from the body, the number of parasites that have entered it does not increase. Such a cycle of development is present in several species of roundworms and chainworms.
3. The third type of behavior is observed if the intermediate host is an organism in which not only development but also asexual reproduction is carried out. In this case, one parasite will burn into the intermediate organism, and on the output there will be several thousand ready for infection of the final hosts.

Intermediate hosts of parasites

Consider a specific type of parasite, the main owner of which is a man, the intermediate owner - cattle (a cow, a bull). This is an unarmed bull chain.

In the human body, this largest tapeworm gets with poorly processed beef. Zesters are introduced into tissues and begin active development. The result of this development is a huge tapeworm living in the human intestine. The length of the worm can reach 12-14 meters!

In the body of the main host, the parasite can live up to twenty years, during which time it produces billions of eggs that leave the intestine with calves, some of which continue to develop in the body of the intermediate host. As it was said, in this case the intermediate owner is a cow or bull.

In the intestines of these representatives of cattle from eggs, larvae (oncospheres), equipped with special hooks, will appear. They will drill the intestinal tissues and spread throughout the body. In the muscles of cows, the larvae will move to the next stage, they form Finns, who will expect to enter the body of the main carrier.

Hepatic fluke

Let us consider another type of parasite with a complex maturation cycle in which several intermediate hosts are present. This is a group called the liver flukes. This includes hepatic and feline fluke, giant, lanceolate and Chinese trematode.

The first intermediate host of the hepatic trematode is the mollusk. In his body, larvae undergo several stages of degeneration: miracidia, sporocysts, redias. And only the third generation of larvae - cecaria, leave the body of the mollusc in search of the next intermediate host.

The second intermediate host of the hepatic trematode (fluke) is fish. Most often they belong to the family of cyprinids. In violation of the technology of salting or inadequate heat treatment from fish tissues, the cecaria enter the organism of the final host, settling in the liver or biliary tract. For a man, the Chinese trematode and the cat's fluke are dangerous.

Lancet-shaped fluke

Another species is the lanceolate trematode, from the body of the first intermediate mollusk enters the body of the next intermediate host, the ant, and then into the organism of the final host, the herbivore.

In order for the cycle of development to repeat, from the organism of the main host, the eggs must fall into the natural environment, namely into the body of water. Here they are "swallowed" by the intermediate owner. This happens from generation to generation, as a person does not sufficiently monitor the cleanliness of water bodies and allows himself to discharge sewage without adequate cleaning.

By and large, evolution, forcing parasites to change hosts, reduces the burden on one organism, reduces intraspecific competition and eliminates dependence on one condition. A complex evolutionary path is fixed at the genetic level of parasites and allows them to derive maximum benefits at each stage of development.