The Loos cycle is the term used to designate the life cycle of nematodes within their host. The cycle consists of the stages that lead to maturity of the parasite in its host.
In mammals - including humans - the cycle involves a series of organs that nematode larvae often traverse to become mature entities. These generally reside in organs of the circulatory, digestive and respiratory systems.
One of the most common nematodes that parasitize humans is Ascaris lumbricoides, popularly known as intestinal worm, since its morphology is reminiscent of the common earthworm.
In man, this nematode is located in the small intestine. The parasite copulates in said cavity and the female releases the eggs. These go out into the environment, where they pollute the soils.
If a person ingests the eggs in the infectious stage, they will hatch inside them and the parasites will reach their intestines, completing the cycle..
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The Loos cycle describes the passage of nematodes through their host. Therefore, it is necessary to know a little more about nematodes.
Members of the phylum Nematoda are ubiquitous, vermiform pseudocoelomated animals commonly known as round or cylindrical worms..
There are more than 25,000 described species, although it is estimated that there are up to three times as many nematodes. They are considered the four richest animal group in species, surpassed only by arthropods, protozoa and mollusks..
Within nematodes, there are free-living species that have colonized a wide diversity of habitats, from fresh and salt water bodies to the polar regions. Many of these are capable of withstanding extreme environmental conditions.
Nematodes are characterized by their abundance. Fruits have been found to harbor extraordinary numbers of nematodes, more than 50,000 individuals in a decomposed fig!!
Another abundant group of nematodes includes parasitic forms of medical and veterinary interest..
The Loos cycle is a term that encompasses the life cycle of nematodes. Within helminths, the species Ascaris lumbricoides is, without a doubt, the best known.
In addition, it is the nematode that reaches the largest size. Females with lengths reaching almost 50 cm have been reported (females are usually larger than males).
A single female can harbor more than 27 million eggs, producing up to 200,000 eggs daily. These are expelled in the stool.
When the eggs are outdoors and in favorable environmental conditions (temperatures not higher than 30 ° C and not lower than 15 ° C, partially humid soil and controlled solar radiation), the egg embryo undergoes two molts - even indoors de la cascara - becoming an infectious biological entity.
The eggs remain in the ground for about two to four weeks. The passage to humans occurs through elements contaminated by eggs, generally by food or other utensils that have had contact with infected soils.
If the person ingests the egg in the non-larvated state, the infection does not take place. The egg must be ingested in the infecting stage.
The man acquires the parasite by the consumption (oral route) of the eggs. These develop in the small intestine, thanks to the enzymes that degrade the shell, a fact that favors hatching.
Later, the larvae cross the wall of the intestine and take the lymphatic or venous route to reach the heart. From this organ they pass to the capillaries of the lungs where they molt again. In this stage, the capillaries of the pulmonary alveoli break and undergo a molt..
The parasite ascends through the bronchi, trachea and pharynx, where they are swallowed and reach the intestine again, where they transform into an immature youth..
Already in the small intestine, the parasites copulate and the female releases the eggs. The intestinal contents of the host carry the eggs, which are expelled into the environment. For the cycle to be completed, the eggs must reach the soils with the environmental characteristics previously described..
The parasite lodged in the intestine does not pose major complications and they are not very aggressive. The damage includes mild intestinal dysfunction. When the volume of the parasite is massive, the complication can increase significantly causing subocclusion and intestinal occlusion..
It is common mainly in infants. In the most extreme cases, infection by A. lumbricoides it results in perforation, volvulus and torsion of the small intestine. On some occasions, so-called erratic migrations can occur, where adults stay outside the digestive tract.
The parasite can migrate to the upper parts of the digestive system, arising through various body orifices, including the mouth or nose. This migratory process can be complicated and the parasite is capable of obstructing the airways.
An ascariasis (medical term used to designate the infection by this nematode) can be demonstrated by the expulsion of the parasite in the patient's stool, where they will be clearly visualized or by performing a stool examination. In infected patients, the parasite eggs will be visible and quantifiable.
The diagnosis of the parasite does not involve major complications, since the expulsion of the eggs in the patient's stool occurs constantly and very abundantly..
For patients with A. lumbricoides the use of the drug piperazine is recommended. It has been observed that with the administration of 100 mg / kg / day for two days more than 90% of the cases are resolved.
Another suggested drug is pyrantel pamoate, mebendazole, kainic acid, and albendazole. In the most complicated cases, doctors resort to surgical removal.
As the active form of the parasite resides in soils, it is important to avoid soil contamination in order to effectively break the nematode's life cycle..
The most useful preventive measure is the proper handling of feces, properly sanitizing hands and utensils when consuming food.
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