Ascariasis

What is Ascariasis?

Ascaridosis (ascaridosis -lat., Ascariasis, lumbricosis – English, ascaridiose, lumbricose – French) is an invasion characterized by the presence of an early phase with manifestations of an allergic syndrome and a late one with a predominant gastrointestinal pathology.

Causes of Ascaridosis

The causative agent of human ascariasis Ascaris lumbricoides, belongs to the suborder Ascaridate (Skrjabin, 1915), the family Ascaridae (Baird, 1853), the genus Ascaris (Linnaeus, 1758).

In a living state, helminths are spindle-shaped, reddish, after the death of a yellowish-white color.

Males reach 15 – 25 cm in length and 2 – 4 mm in width. The tail end in a fixed state is hook-shaped. On the ventral side of the tail there are up to 70 pairs of preanal and 7 pairs of postanal papillae – organs of touch. Two equal spicules reach 1.5 – 2 mm in length.

Females are much larger – 20 – 40 cm in length and up to 6 mm in width. The rear end of their body is conically pointed. The vulva opens at the end of the anterior third of the body, where sexually mature females have a ring-shaped constriction. Near the posterior end, the anus opens on the ventral side.

The head end of the roundworm is provided with three lips that surround the mouth opening. On the lateral sides, longitudinal lateral lines are clearly visible, in which the tubules of the excretory system pass.

The digestive system is represented by the mouth, a long cylindrical esophagus, an intestinal tube ending in the anus.

The female reproductive system is represented by paired ovaries, oviducts and two uterus passing into the vagina, in the male – by the testes, vas deferens, the ejaculatory canal, which flows into the cloaca, and two spicules 1.5 – 2 mm long.

Ascaris fecundity is very high. At the same time, up to 27 million eggs at different stages of development are found in the body of females. An adult female lays about 240 thousand eggs per day; in the year of ascaris, it lays 64 million eggs. Both fertilized and unfertilized eggs are secreted into the external environment. Fertilized eggs are often oval, rarely spherical in size 50 – 70 x 40 – 50 microns. The eggs are covered with a thick multilayer membrane, the outer one is a tuberous protein, which, being in the genitals of the female, is colorless and transparent, when it enters the intestines, it is stained with feces pigment in dark yellow, brown color and becomes opaque. The inner shell – lipoid, multilayer, smooth, colorless, transparent protects the developing germ of chemicals. Inside the egg is a fine-grained spherical blastomere.

Sometimes eggs without a protein coat are found; they are smooth, colorless, transparent, and difficult to diagnose.

Unfertilized eggs can have the most diverse form – more often they are elongated, elongated, pear-shaped, trihedral. Their sizes vary widely – 50 – 100 x 40 – 45 microns. The protein shell of such eggs is rough, its teeth are uneven, long alternate with short ones. The entire contents of the egg is filled with large yolk cells. Rarely, there are unfertilized eggs without a protein outer shell. Such eggs are especially difficult to diagnose; they are often mistaken for plant cells.

Ascaris is a typical geohelminth. Its development takes place with the participation of one host and depends on the natural and climatic conditions of the area, determining the possibility of maturation of helminth eggs to an invasive stage in the external environment.

Mature helminths parasitize in the human small intestine. While parasitizing individuals of both sexes – females and males – females secrete fertilized eggs that can further develop, complete the biological cycle to the stage of an invasive larva. Eggs ripen in the soil at temperatures from + 13 to + 36 ° C and humidity not lower than 4 – 6 – 8%. In the process of development, the embryo in the egg goes through the stages of the blastomere, morula, gastrula, tadpole and, finally, the larva.

In the case of non-intensive invasion, when 1-2 females parasitize, they secrete unfertilized eggs, the detection of the second confirms the presence of invasion (this is important for the clinic), but such eggs do not develop further.

In the human intestines, the eggshell is destroyed, and the larvae are released. Then they make a difficult migration path by penetrating the mucous membrane, enter the blood capillaries of the intestinal wall, and then enter the liver through the portal vein system, from where they enter the right side of the heart through the lower genital vein and into the lungs through the pulmonary artery. Here, through torn capillaries, the larvae enter the lumen of the alveoli, with the help of the ciliated epithelium lining the bronchioles, bronchi, the trachea advance along the airways and enter the pharynx and oral cavity. When saliva is swallowed, they enter the stomach, then into the intestines, where they mature to adults.

The duration of the migration phase is 12-14 days. Only the last migration of the larva is able to mature in the intestine to the state when sexually mature individuals begin to secrete eggs. From the moment of infection to the appearance of eggs in the feces, 2.5 – months pass. The duration of parasitization in adults in the intestine does not exceed one year.