Ascaris lumbricoides : Life Cycle |Disease |Pathogenesis |Prevention

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Ascaris lumbricoides : Life Cycle |Disease |Pathogenesis |Prevention

Classification :

  • Phylum- Nemathelminthes
  • Order- Ascaroidea
  • Genus- Ascaris
  • Species- lumbricoides

It is commonly known as ‘Roundworm’ and inhabits the small intestine of man and is more common in children. Roundworms are cosmopolitan in distribution. It completes its life cycle without intermediate host. Ascaris lumbricoides is light yellow to light pink in colour. The body is elongated, cylindrical and pointed at both the ends. The female is about 20 to 40 cm and the male is about 15 to 30 cm in length. Mouth is situated at the anterior end and is guarded by 3 lips. The alimentary canal comprises of foregut, midgut and hindgut. Ascaris lumbricoides respires anaerobically.

Life Cycle :

The copulation takes place inside the intestine of the host. After fertilization the ovum undergoes maturation division and is released in the intestine of the host from where they pass out with the faeces. Under suitable environmental conditions the eggs develop into the rhabditoid larvae, an infective stage, which again reaches the intestine of man by ingestion of contaminated food or water. In the host’s intestine the egg shells are dissolved and juveniles hatch out. These juveniles bore the intestine and enter in the hepatic portal system and are distributed to the liver, heart and finally the lungs where they attain the third larval stage which is followed by fourth larval stage. The fourth stage larvae reach the pharynx through trachea and finally reach the gut where it attains adult stage. The average life span of this worm is 9 to 12 months in man.

Disease :

Ascaris lumbricoides causes ascariasis which is more in children than in the adult persons. In the intestine of man these worms take the digested food materials. The larvae are more harmful and cause a number of complications in the kidney, muscles, brain, lungs and spinal cord. Ascaris lumbricoides causes fever, haemorrhage, appendicitis, tumour, colic pain, ulcer, diarrhoea, indigestion, eosinophilia or any other deceptive symptoms in severe infections.

Pathogenesis :

The pathogenesis of Ascaris infection has three important aspects i.e., larval migrations, toxemia due to reactions of the host to metabolic products of the worm and direct injury to tissues and organs caused by the robust, active adults.

    During the course of larval movement from intestine to the lungs, there is no remarkable pathological change but sometimes there may be a transient hepatitis while larvae are marching through hepatic capillaries. During this march each larva breaks out of pulmonary capillaries into air sacs, a minute hemorrhage is caused but if a number of larvae are marching simultaneously through the lungs, the damage of lung tissues is considerable. The local cellular reactions going on around the moving larvae in the air sacs of lung cause infiltration of eosinophils, epithelioid cells and macrophages, and produce a typical Ascaris pneumonitis.

     The maturating and adult worms inhabiting the small intestine, take nourishment from semi-digested food of human beings and sometimes suck the blood from the villi. In average infection in children, there is intermittent intestinal pain, loss of appetite and weight, disturbed sleep and sometimes nervousness.

    From time to time, adult or immature Ascaris makes movement from stomach to anus and sometimes enters into the bile duct-causing jaundice, the appendix-causing acute appendicitis or pancreas-causing pancreatic hemorrhage. On reaching the posterior pharynx, a worm may be sucked into the respiratory tract and obstruct the larynx. Ascaris has also been found in the female genital tract and once in the heart. The adult can perforate the intestine to bring about peritonitis. They sometimes leave the host by the nose or mouth or via the anus causing more alarm than injury. Rarely larvae, migrated through the lungs, may reach the anterior chamber of eyes and possibly the cerebral or renal blood vessels with hemorrhage into adjacent tissues. The changes in the blood in case of ascariasis consists of a prolonged moderate increase in eosinophils and possibly a low-grade anaemia.

     Toxemia, a general systemic poisoning, has been noted in many cases of ascariasis of long duration. The waste products of these large worms can be absorbed directly through the wall of the intestine. Some individuals become sensitized to these wastes, which act as poisons. Various symptoms observed due to toxemia are utricaria, bronchial asthma, photophobia, retinitis, meningitis and even hematuria but all these symptoms are not common in every case of Ascaris infection.

Prevention and control :

  1. Ascariasis, one of the most common and difficult problems in public health, therefore, it is directly concerned with the health education in the home and in the elementary school. Mothers must learn that ascariasis results from pollution of the soil with human excreta. So, there must be clean, convenient places for the children to defecate and the child must be taught to use these toilet facilities regularly. But it is not possible to transform such a community into a sanitary place. Unfortunately, even if, these very changes can be made in human behaviour, infective Ascaris eggs by the billion will remain in the soil and reinfection can be expected to occur. Perhaps the best prospect for the control of ascariasis lies in the general hope for improvement in living standards throughout the world.
  2. Before eating, the green vegetables should be thoroughly washed and cooked properly.
  3. The standard treatment of intestinal ascariasis is the oral administration of
  • Hexylresorcinol crystoids in hard gelatin capsule should be taken orally by the patient on an empty stomach in the morning hours. It may be repeated safely any time to remove the worms still present,
  • Piperazine citirate in syrup (antepar) has been found to be very much effective in eliminating Ascaris. It is highly acceptable to children, easily administered and requires no fasting period,
  • Thiabendazole is probably no better than antepar for use against Ascaris alone but because of its effectiveness against other worms especially Trichuris, it may supersede antepar in regions where both Ascaris and Trichuris are a problem,
  • Santonin, diphenan and egressin are all relatively safer but their rate of effect is very lower in comparison to others.

 It is believed that the above treatments do not affect the larval migratory phase of Ascaris lumbricoides.

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