Ascaris: Ascariasis and Parasitic adaptations
Posted on : 29-11-2017 Posted by : Admin

Ascaris Parasitic Adaptations

Ascaris is an endoparasitic roundworm residing in the internal organs like intestine, heart, liver, lungs etc.… of humans. To suit its parasitic mode of life it has to overcome to several adverse conditions. And accordingly this roundworm shows several parasitic adaptations. The following are the important parasitic adaptations of Ascaris.

1. The presence of though, thick and resistant cuticle. This cuticle covers entire body and gibes protection against the action of the digestive enzymes and antitoxins of the host. On the other hand Ascaris itself also secreted several anti-enzymes to protect itself from digestive enzymes of host.
2. Though these worms do not have adhesive suckers and spines, their ability of locomotion helps them counteract the peristaltic movement of the host’s intestine. Its power of locomotion helps it from getting displaced and it remains in the intestine of the host.
3. The muscular pharynx helps in ingestion of food particles through its sucking action
4. They are located in the regions where there is continuous supply of food material and so their alimentary tract is simple without any special storage organs.
5. The food they ingest is pre-digested and so there is no need for digestive glands
6. The function of absorption, transport and distribution of food, oxygen and waster products is served by pseudocoleomic fluid. As a result there is no need of circulatory system.
7. Anaerobic mode of respiration and extremely low metabolic rate helps the worms live inside the intestine of the host where there is no availability of free oxygen.
8. As these worms are endoparasites living well protected inside the human intestine, there is no need of special and complicated sensory organs.
9. The transfer to a new host is an extremely hazardous and passive process depending entirely on accidental ingestion of embryonated eggs by specific host. For example each egg laid by pig Ascaris must be consumed by another pig for its growth and development similarly the eggs laid by human Ascaris must be ingested by humans only. Also the temperature and environment must suit the development of the eggs. Thus to overcome all these conditions, these worms reproduce enormously to produce numerous eggs to increase chances of survival. So a single mature female lays as many as 27 million eggs per day.
10. The resistant shell on the zygotes protects them from unfavorable environmental factors. This shell also increases the viability of the zygote for years.
11. Also the minute size and resistant nature of eggs helps wide dispersal of the parasites.

Ascariais disease

Infection: The disease caused by the roundworm, Ascaris is known as ascariasis. Humans catch the infection by consuming food and water contaminated by the infective stages of this parasite. Ascariasis is more pronounced in children than in adults and this could be due to the sanitary habits.

Pathogenesis: Larvae cause hemorrhages and are considered more dangerous than the adult roundworms. The larvae also bore through the intestinal epithelium and enter general circulation to finally land in the organs like kidneys, spinal cord, brain or muscles and cause serious destruction. Infection of larvae of Ascaris is followed by fever, anemia, leukocytosis and eosinophilia.

On the other hand the adult roundworms cause enteritis. They migrate into vermiform appendix, gall bladder and bile duct to cause serious inflammation. The adults get their nourishment from the contents of the intestine. They also suck the blood from the intestinal walls. The adult worms produce toxins which irritate the mucous membrane which manifests in the form of convulsions, delirium, coma and nervousness.

The toxin produced by these worms combines with trypsin and interferes with the protein digestion finally leading to protein deficiency in the human body. This may also cause stunted growth among children. The presence of a few parasites may also show up symptoms like colic pains, abdominal discomforts, diarrhea, vomiting and mild temperature.

Treatment and therapy: Generally stool examination is done to diagnose the presence of Ascaris eggs. Ascariasis can be treated with a dose of hexylresorcinol crystals in a gelatinous capsule after about 12 hour fasting. This dose followed by another 4 hours of fasting kills the worms. The killed worms can be expelled out by a purgative like sodium sulphate.

Also anti-helminthic drugs like Chenopodium oil (Medicinally important fast-growing weedy annual plant). This oil is highly toxic to the worms. Some drugs like tetrachloroethane are used to irritate the worms which thus entangle themselves blocking the lumen. The mixture of Chenopodium oil and tetrachloroethane is considered very effective. Other anti-helminthic drugs like heterazan, piperazine hydrate, tetramisole and dithiazanine are also used in the treatment of this disease.

Prophylaxis

• Soil pollution is the chief source of infection and it should be prevented,
• Children must learn and  observe sanitary habits to prevent infection,
• Vegetables must be thoroughly washed and cooked before consuming,
• Regular trimming of finger nails is very important to avoid accumulation of eggs under them. Also hands should be thoroughly soap-washed before using them to eating.

1. Write about infection and treatment of Ascariasis.
2. Explain pathogenesis of Ascariasis.
3. Write parasitic adaptations of Ascaris.
4. Explain the transfer of Ascaris to a new host and how has this parasite adapted to this process.