Development Diagram Of The Life Cycle Of Roundworm

2024 Author: Josephine Shorter | [email protected]. Last modified: 2023-12-16 21:43

Development diagram of the life cycle of roundworm

Ascaris is a round parasitic worm that lives in the small intestine of a person and provokes the development of a disease such as ascariasis. The life cycle of the parasite is complex, although it does not require multiple hosts to do so. The worm can live only in the human body.

Despite the complex process of development of a worm from a laid egg, ascariasis is common throughout the world. According to the WHO, the average number of infected people is close to 1 billion. Ascaris eggs cannot be found only in permafrost zones and in dry deserts

The development scheme of the roundworm life cycle is as follows:

• After fertilization, ascaris eggs are released together with feces into the external environment. After a certain time, they enter the soil, where they begin to ripen. In order for the eggs to be able to invade humans, three conditions will be required: high soil moisture (roundworms prefer silty, clayey and chernozem soils), its good aeration and high ambient temperature. In soil, eggs retain their potential for a long time. There is evidence that they can remain viable for 7 years. So, if all the conditions are met, then after 14 days of being in the soil, the roundworm eggs will be ready for human invasion.
• The next stage is called the larval stage. The fact is that immediately after maturation, the larva cannot infect a person, it must go through the molting process. Before molting, the egg contains the first instar larva, and after molting, the second instar larva. In general, in the process of migration, ascaris larvae make 4 molts.

• When an invasive larva, surrounded by protective membranes, enters the human gastrointestinal tract, it needs to get rid of them. The destruction of the egg shell occurs in the duodenum. In order for the protective layer to dissolve, a high concentration of carbon dioxide, an acidity of the environment equal to pH 7 and a temperature of +37 degrees Celsius are required. If all three of these conditions are met, then a microscopic larva will hatch from the egg. Its size is so small that it seeps through the intestinal mucosa without any difficulty and enters the bloodstream.
• The larvae penetrate the venous vessels, then, with the blood flow, they are sent to the portal vein, to the right atrium, to the ventricle of the heart, and then to the capillary network of the lungs. Until the moment when the ascaris larvae penetrate from the intestine into the pulmonary capillaries, on average, it takes three days. Sometimes part of the larvae can linger in the heart, in the liver and in other organs.
• From the capillaries of the lungs, the larvae enter the alveoli, which make up the lung tissue. It is there that there are the most favorable conditions for their further development. In the alveoli, the larvae can stay for 8-10 days. During this period, they undergo two more molts, the first on the 5th or 6th day, and the second on the 10th day.

• Through the wall of the alveoli, the larva penetrates the bronchioles, bronchi and trachea. The cilia, which densely line the trachea, lift the larvae upward into the larynx with their flickering movements. In parallel, the patient develops a cough reflex, which contributes to their throwing into the oral cavity. There, the larvae are swallowed again along with saliva and again enter the stomach and then into the intestines.
• From this moment in the life cycle, the formation of a full-fledged adult begins. Doctors call this phase intestinal. The larvae reintroduced into the intestine are too large to pass through its pores. In addition, they already have sufficient mobility to be able to stay in it, opposing the feces. It will turn into an adult ascaris after 2-3 months. It has been established that the first clutch of eggs will appear in 75-100 days from the entry of the egg into the human body.
• In order for fertilization to take place, both the male and the female must be in the intestines. After the female lays the finished eggs, they, together with the feces, will go outside, fall into the soil and will wait for the optimal moment for the subsequent invasion. When this happens, the worm's life cycle will repeat itself.

As a rule, it is according to this scheme that the life cycle of ascaris occurs. However, atypical life cycles are described. This means that the intestinal phase does not always replace the migration phase. Sometimes the larvae can settle in the liver and die there. In addition, during an intense cough, a large number of larvae come out with mucus into the external environment. And before reaching sexual maturity, they die.

It should be noted that some of the ascaris larvae can exist in other organs for a long time, causing characteristic symptoms. Ascariasis of the heart, lungs, brain and liver is very dangerous not only for health, but also for human life. Indeed, in the process of migration, even without settling in the organs, the larvae provoke the appearance of inflammatory infiltrates and zones of micronecrosis in the liver and lungs. It is easy to imagine what will happen to the life-supporting organs of a person if a worm settles in them.

The parasitization of ascaris in the intestine causes immunosuppression, which negatively affects the course of other infectious diseases. As a result, a person gets sick longer and more often.

An adult ascaris lives in the intestines for about a year, after which it dies from old age. Therefore, if no re-infection has occurred in a year, then ascariasis will be self-destructed.

Article author: Mochalov Pavel Alexandrovich | d. m. n. therapist

Education: Moscow Medical Institute. IM Sechenov, specialty - "General Medicine" in 1991, in 1993 "Occupational Diseases", in 1996 "Therapy".