ASCARIS LUMBRICOIDES (COMMON ROUNDWORM)

· Intestinal endoparasite of man in the small intestine (especially in the jejunum) and some other vertebrates like pigs, cattle, etc, more prevalent in children than in adults as they are more susceptible to infection.

· Body is cylindrical, unsegmented, elongated with tapering ends, anterior end is more slender than the posterior end.
· Distinct sexual dimorphism i.e. sexes are separate.
· Sanguivorous (Bloodsucking)
· The worm is ammonotelic and ureotelic.

Male size- up to 20 cm (length), 2-4 mm (diameter), smaller, curved tail, a pair of penial setae
Female size - 20-40 cm (length), 4-6 mm (diameter), longer, straight tail, anus and gonopore
· In males, Fifty pairs of pre-anal papillae are present in front of the cloaca and Five pairs of post-anal papillae behind the cloaca
· Mouth is bounded by three broad lips (triradiate). One dorsal and two ventral-laterals. The dorsal lip bears two double papillae, one on each side. Each latero-ventral lip bears one double papilla and a single papilla along with amphid.
· The excretory pore is situated mid-ventrally, a little behind the mouth.
· The body is covered externally by the cuticle. The cuticle has minute transverse striations that give the pseudo-segmented appearance to the worm.

· Colour- light yellow to light pink
· There are four longitudinal lines- one mid-dorsal, one mid-ventral, and two laterals. These lines are formed by the thickening of the epidermis.
· Body wall consists of three layers, an outer cuticle, a middle epidermis, and an inner layer of longitudinal muscles lining the body cavity.
· Cuticle is thick, four-layered, secreted by the underlying epidermis. It is permeable to water, salts, and products of digestion. It protects the body from the digestive enzymes of the host.
· Presence of the resistant cuticle is a special character with reference to parasitism.
· The epidermis is syncytial (coenocytic) with scattered nuclei and without partition walls.
· Fats and glycogen reserves are abundantly present in the epidermis.
· Longitudinal muscle layer is the innermost one and the circular muscle layer is absent.
· Body cavity is pseudocoel as it develops from blastocoel and does not contain the mesodermal lining. The body cavity contains pseudo-coelomic fluid for the transportation of metabolites.

Digestive system

· It is a complete tube extending from mouth to cloaca or anus. It consists of the tri-radiate mouth, a short pharynx (foregut), a long intestine (midgut), and a short rectum (hindgut).
· Salivary glands are absent.

· Mouth is the terminal and tri-radiate aperture guarded by three denticulate lips. The dorsal lip bears two sensory double papillae (tango receptors). Both sensory papillae and amphids (chemoreceptors) are present on ventrolateral lips.

· Digestion is extracellular and is aided by the enzymes- proteases, amylase, and lipase. Intestinal cells absorb digested food and it is distributed by pseudo-coelomic fluid.
· Excess food is stored in the form of glycogen and fat in the syncytial epithelium (epidermis).

Respiratory system

· Anaerobic and same as that of Fasciola and Taenia

Excretory system

· It consists of a single H-shaped excretory cell or Renette cell.

Excretory products are ammonia and urea.

Nervous system

· It is well-defined with nerve ring, ganglia, and nerves.
· The circumenteric nerve ring is located around the pharynx. Nine ganglia are attached to the nerve ring.
· Sense organs are simple like labial papillae, amphids, and phasmids.

Reproductive system

. Ascaris is dioecious or unisexual i.e., sexes are separate.
· The male reproductive organs are unpaired testis, vas deferens, seminal vesicle, ejaculatory duct, cloaca, and penial setae.
· Testis is monarchic (presence of single testis), long, thread-like coiled tube. Only the anterior part is functional so the testis is telogenic.
· Ascaris sperm is peculiar without a flagellum, tailless, asymmetrical, and amoeboid.
· Female Ascaris has paired ovaries, oviducts, uteri, and a median vagina. It has two parallel tracts, each consisting of an ovary, an oviduct, and a uterus (didelphic condition). The ovary is also telogenic.
· Eggs are fertilized in the lower part of the uteri.
· A median central rachis is present in both testis and ovaries from where sperms and ova are formed.

Life cycle of Ascaris

· Ascaris is monogenetic i.e. no intermediate host is required.

. The fertilized and cleaved eggs pass out from the body of the host through the faecal matter. A single mature female may contain as many as 27 million eggs with a daily production of 234,000 eggs or about 162 eggs per minute.

· The egg is mammilated, oval, with 3 protective coverings, i.e. outer protein layer, middle chitinous shell, and an inner membrane made up of esterified glycosides.
· Embryonic development takes place only outside the body of the human host in the soil as it requires low temperature, more oxygen, and suitable moisture. The optimum temperature for the development of Ascaris is 85 degrees F.

· Eggs containing infective larvae may remain viable in the soil for 2 years or longer.
· Zygote changes into a juvenile (first stage) in 10-14 days. It is not infective. In another week’s time, it moults and becomes the second stage Rhabditoid, which is infective. Under suitable conditions of temperature, moisture, and oxygen, it remains viable for about 6 years.
· The transmission of the infective stage through the embryonated eggs takes place by contaminated food and water. Eggshell dissolves by the pancreatic juice. Rhabditiform larva liberates.

· Three types of migrations by Ascaris larvae are:

Primary migration

· Intestinal wall- hepatic portal circulation- liver- hepatic vein- heart- pulmonary artery- lungs
· Secondary migration is from the lungs back to the intestine of the host, lungs-bronchi-trachea-pharynx-gullet- oesophagus-stomach-intestine. In the lungs, the larva completes second and third moultings. In the small intestine, it completes fourth or final moulting.
· Sometimes larva of Ascaris may not follow the normal primary and secondary migration.

Aberrant migration

· Sometimes, the larva of Ascaris reaches the brain or spinal cord, lymph nodes or eyes, or any such organs. It is unable to survive there and a calcareous cyst is formed around it.
· Duration of Rhabditiform larva to return back to the intestine is 20 days (About three weeks)
· The route through which the developmental stages of Ascaris serially pass in man is outside intestine-liver-lungs-trachea-oesophagus-intestine.

Moulting in Ascaris occurs four times.
1 time (1st moulting in soil)
2 times (2nd and 3rd moulting in lungs)
1 time (4th moulting) in the intestine

· 2nd stage larva enters the lung and fourth stage larva comes out of the lungs.

· Disease caused by Ascaris is Ascariasis

Symptoms are colic pain, indigestion, diarrhoea, weakness, insomnia, retarded physical or mental efficiency, abdominal discomfort, vomiting, fever, patient’s grit at night. Large numbers of adult worms sometimes cause mechanical blockage of the intestinal tract causing colic pain. The toxin produced by Ascaris may interfere with protein digestion.

· Can be treated by antihelminthic drugs like Oil of Chenopodium, Antipar, Tetrachloroethylene, Alcopar, Diethylcarbamazine, etc.
· One-time treatment of Pyrantel pamoate, mebendazole, or albendazole is highly effective.