Reproductive system in Ascaris lumbricoides
Sexes are separate and there is a well distinct sexual dimorphism.
I. Male Reproductive System
The male reproductive organs are :
1. Testis. The testis is a long thin, coiled and thread-like structure in the anterior part of pseudococl. It represents monorchic condition (presence of single testis) and telogonic mode of origin of germ cells (i.e. germ cells developing only from the proximal part of gonad). The testis can be distinguished into three parts:-
(a) anterior solid part consisting of sex cell, (b) middle part and (c) posterior part. The central axis of the tube is in the form of a solid cytoplasmic rachis, around which the clusters of amoeboid sperms in various stages of development.
Testis is continued posteriorly into the vas deferens.
2. Vas deferens. The vas deferens is as wide as the testis and the two cannot be marked externally. It is very short and leads into the seminal vesicle.
3. Vesicula seminal. The vesicular seminalis is a wide tube present in the posterior l/3rd part of the body. It joins the ejaculatory duct.
4. Ejaculatory duct. It is a short, narrow but muscular tube opening into the cloaca, which leads outside by cloacal opening.
5. Penial sacs with penial setae. On the dorsal side of the cloaca there is a pair of sac-like structures called penial sacs. These are formed by evaginations of the cloaca. Each pouch secretes and lodges a club- shaped spicule or penial seta. The spicula is enclosed in a sheath and consists of a cytoplasmic core surrounded by thick cuticle. Each spicule measures 2-3.5 mm. in length, the penial sac nave special protractor and retractor muscles from their walls, the musclcs push the spicule out and withdraw them back into the pocket.
II. Female Reproductive Organs
The female reproductive organs include:
1. Ovaries. The ovaries represent didelphic condition i.e. there are two ovaries. Each ovary is a long, thread-like, much twisted and blind tubule occupying posterior l/3rd of the body. Its walls consist of a single layer of cuboidal epithelial cells lined externally by basement membrane. There is no lumen, the central part is occupied by the cytoplasmic rachis, around which young eggs are clustered.
2. Oviducts. The oviducts are two thin ducts very similar to the ovaries. These open into the uteri.
3. Uteri. Each oviduct continues into a much wider, thicker and almost untwisted tube, the uterus. The wall of the uterus is composed of tufted cells, surrounded by a muscle layer with inner circular and outer oblique fibres.
4. Vagina. Two uteri join to form one vagina which opens to the outside by female genital pore or vulva, lying on mid-ventral side about 1 /3 of the length of the body posterior to anterior end.
Ascaris is monogenetic i.e., it requires only one host to complete its life-cycle.
1. Copulation and Fertilization
Ascaris copulate in the intestine of man. During the process sperms are ejected by male into vagina of the female. These move in the uterus where fertilization occurs. While moving further the eggs become covered by a chitinous shell and an outer inegular albuminous coat.
The eggs are round or oval (60 µm x 45µm), light brown in colour and float in saturated solution of common salt. The unfertilized eggs laid by the mother, may mix up with the fertilized eggs are larger (90 µm x 45 µm) and sink in saturated salt solution.
The uteri of a single female may contain as many as 2,70.000 eggs (Cram, 1927), with an average daily production of about 2,00,000 eggs. The fertilized eggs are released in the intestine of host through the vulva. From the intestine of host they are eliminated along with faecal matters.
Development takes place at 85 ºF, i.e. outside the body of man. It is stopped at 60 ºF and eggs gradually degenerated at 10085 ºF. They can remain alive for years in moist soil. After repeated division, 16-celled embryo is formed in the form of a hollow ball. It is termed as blastula, and the cavity, the blastocoel. Blastula undergoes a process of invagination and becomes gastrula. It grows in length to become an active juvenile in 10-14 days from the start of cleavage. For its close resemblance with the nematode genus Rhabditis, found in soil and human faeces, the juvenile is also termed rhabditoid or rhabdifiform larva of first stage. It is not infective. In another week’s time, it moults within the egg, shell and becomes the second stage rhabditoid, which is capable of infecting the host. Under suitable conditions of moisture, oxygen and temperature, infective eggs of Ascaris lumbroicoides are known to remain viable for about six years.
4. Infection and Emergence of Larva
The eggs containing rhabditiform larvae contaminate food and water. If someone takes this contaminated food or drink contaminated water the eggs reach the healthy man. This type of transference is called contaminative transference or infection. The shell of the egg is weakened in oesophagus and is disssolved in the intestine of the new host. The larva is about 200-300 µm in length and 14µm in width. It has fully formed alimentary canal, excretory and nervous systems.
5. Primary Migration of Larva
The larva burrows the mucous membrane of the intestine of the host and through hepatic portal vein reaches the liver. From here through portal vein and post-caval reaches the right auricle of the heart. From here through pulomonary arteries reaches lungs. In lungs it moults twice. The first moulting takes place after 5-6 days (third stage larva) and second moulting after 10 days forming fourth stage larva. This larva now increases in size and is about 2 mm. in length.
6. Secondary Migration
From lung the larva reaches bronchii, trachea, larynx and finally to pharynx where it irritates causing coughing by which it re-enters the alimentary canal when the cough is swallowed. After reaching the intestine through stomach it moults fourth or last time. The young Ascaris becomes adult sexually mature within 6-10 weeks and begins its life-cycle again, the whole migration is completed within 10 days.
Ascaris is pathogenetic to man. When larvae migrate through the lungs, they cause lung-inflammation and fatal pneumonia. Sometimes,fever. anaemia, leucocytosis (presence of excess of white corpuscles in the blood) and eosinophilia result. In mature form, Ascaris may or may not disturb life-activities. Some abdominal discomfort and acute colic pains with vomiting, diarrhoea and slight temperature occur. Often masses of Asians block the intestine, in which condition they can only be removed by surgical operations. Several hundred thousands of worms are responsible for blockage and they are fatal. Appendicitis is also caused by the blocking of appendix by Ascaris. Toxic substances produced by Ascaris cause convulsions, (an involuntary contraction of the involuntary muscles of the body), delirium, (insanity or disorder in mind), coma and general nervousness.
Sang (1922) found that toxins produced by Ascaris cause interference with the digestion of proteins.
Therapy against Ascariasis
Several drugs like Santonin. Antepar. Chenopodium and Hexylresorcinol are used effectively under physician’s directions. A mixture of oil of chenopdium, tetrachloroethyene is usually successfully used Lamson discovered that hyxylresorcinol is also very effective particularly when given as crystoids (in gelatin capsules) with fasting for 12 hours before treatment and 4 hours afterwards followed by sodium sulphate for removal of dead worms.
Prevention against Ascariasis
Adequate sanitation plus education should prevent ascariasis. Lack of adequate fertilizer in many parts of the undeveloped world means that night soil must be used to fertilize crops. Due to the resistance of Ascaris eggs to standard disinfectants, the situation would appear to be hopeless. There is a realistic solution. Thitasut (1961) reported that aqueous solution containing 120 ppm free iodine killed Ascaris lumhricoides eggs within 5 min or less and did not effect the flavour of leafy vegetables.
One of the problems in control is preventing children from ingesting eggs with contaminated soil. Given the habits of children throughout the world, including dirt eating, playing in contaminated soil and then placing their fingers in their mouths, ascariasis will unfortunately be with us until adequate sanitation is accomplished