Old World Hookworm | Parasitology

In this article we will discuss about:- 1. Histology of Hookworm 2. Habitat of Hookworm 3. Reproductive System 4. Different Species.

Histology of Hookworm:

A. duodenale is one of the hookworms of man in Europe, North Africa, Western Asia, China and Japan, has also been recorded from certain wild carnivora and the pig. The hookworm is common in countries with poor sanitation and poor per­sonal hygiene. A. duodenale was first discovered by Angelo Dubini in 1843.

Eggs of this parasite were identified by Grassi and Parana from human stool in 1878. Perroncito (1880) observed the develop­ment of the free living larva from the embryo con­taining eggs in soil and its metamorphosis into the filariform larva.

In 1897 Looss described the Struc­ture of the adult worm and life history was recor­ded by Chandler in 1929. A. duodenale is primarily a human parasite but on rare occasions has been found in pigs and experimentally can be reared occasionally in dogs, cats and monkeys.

Phylum – Aschelminthes

Class – Nematoda

Subclass – Phasmidia

Genus – Ancylostoma

Species – duodenale

Habitat of Hookworm:

The adult worm lives in the small intestine of man, particularly in the jejunum, less often in the duodenum and rarely in the ileum where they suck blood, lymph, bits of mucous membrane and tissue fluids from the lining of intestinal wall. The adult hookworms exist under primitive conditions where people go bare foot, modern sanitary conditions do not exist and human faeces are deposited on soil.

Reproductive System of Hookworm:

The male reproduc­tive system has a single tubular thread like testis starting as a fine tubule near the anterior end of the cement gland and coiling back and forth along the intestine in the middle of the body. It leads posteriorly into a vas deferens, followed by an elliptical seminal vesicle.

The posterior end of seminal vesicle tapers into a muscular ejaculatory duct. The ejaculatory duct along with the return receives the secretion of cement gland and opens into the cloaca. A pair of chitinoid copulatory spicules about one mm long lie in a sac lateral to the ejaculatory duct which can be protracted and retracted by muscles.

The female reproductive system has a pair of thread like ovaries, coiled back and forth over the intestine, one anterior and other posterior to the level of gonopore. Each ovary leads into a short oviduct that opens into a dilated seminal recep­tacle.

From each seminal receptacle arises a mus­cular uterus. The two uteri lead outward through short ovijectors. The two ovijectors unite with one another medially forming a short transverse vagina. The vagina finally opens outside through the com­mon gonopore or vulva (Fig. 12.3).

Different Species of Hookworms other than Ancylostoma Duodenale:

2. A. caninum Hall, 1913:

This is a common parasite of dog, fox and very rarely also in man. It occurs in the small intestine. It is cosmopolitan in distribution. The worms are rigid and grey or reddish in colour. The anterior end is bent dorsad and the oral aperture is directed antero-dorsally.

The buccal capsule has the largest orifice and the ventral margin of the buccal capsule bears three teeth on either side. There is a pair of tri­angular dorsal teeth and a pair of ventro-lateral teeth. The male is 10-12 mm long and its bursa is well developed and the spicules of male are 0.8-0.95 mm long. The female of A. caninum is about 14-16 mm long.

In female worm the vulva is located near the junction of the second and last thirds of the body. The uteri and ovaries produce numerous transverse coils in the body. The eggs contain an embryo of about eight cells when laid.

The life cycle of A. caninum is the same as that of other Ancylostomes. Infective filariform larvae are capable of producing creeping eruption in man. Thiabendazole has been found to be an effective remedy for creeping eruption. Stone and Mullins (1965) reported that about 99% of all the larvae stopped activity on the first day of therapy.

A. caninum is a common parasite of dogs but does not grow well in cats. The larvae of this can penetrate human skin, giving rise to cutaneous larva migrans.

Effect of temperature, carbon dioxide and humidity must greatly improve the chances of infecting hosts and these have been examined experimentally in the dog hook-worm. In A. caninum. snake-like move­ments were stimulated by warmth and vibrations of the substratum; waving behaviour was stimu­lated by carbon-dioxide content and heat and creeping directions by heat gradients (Fig. 12.6).

3. A. braziliense Gomez de Faria, 1910:

It occurs in the small intestine of dogs, cats, foxes and sometimes men and is found in most tropical and subtropical countries like Brazil, India and Malayasia. The adult worm is slightly smaller than A. caninum. The male measures about 6-7.75 mm long and the female measures about 7-10 mm long.

The buccal capsule has a small orifice and ventral dental plate comprises of one pair of large teeth. The life cycle is same as that of previous species. Man is the unsuitable host and filariform larvae pene­trating the human skin cannot localise in the bowels and are capable of producing creeping eruption.

4. A. ceylanicum, Biocca, 1951:

A less common species is A. ceylanicum, which is normally found in Sri Lanka, South East Asia, the Eastern India and the Philippines. It is an occa­sional human intestinal parasite in South East Asia and it however, does not produce cutaneous larva migrans in man.

Instances are on record where adult hookworms have been noticed in the intestine of man also and are regarded as biologi­cal variants. It is also common in cats and dogs. It has one large tooth and a rudimentary one on each side. Biocca (1951) showed clear differences between them (A braziliense and A. ceylanicum) both in mouth capsules and in bursas.

5. A. tubaeforme, Zeder, 1800:

It is the normal hookworm of cat. It has almost a cosmopolitan distribution. The full grown male hookworms measure 9.5-11.0 mm and the female worms measure about 12.0-15.0 mm. Mouth capsule is similar to A. caninum but teeth on the ventral margin are slightly larger. Spicules of the male worm are larger than 1 mm. A. tubaeforme and A. caninum are not distingui­shable between two hosts.

Distinguishable Features between the adult worms of A. duodenale and Necator americanus:

Necator americanus is the predominant species in the New World, but is also indigenous in India, Southeast Asia, China, Africa and some Pacific Islands. The life cycle, general morphology, pathogenicity, clinical features and treatment are same as for A. duodenale. But A. duodenale is much more injurious to its host and is harder to expel by means of anthelmintics.

Blood loss is higher in A. duodenale because it is a larger hookworm. It is armed with teeth and it is more migratory, leaving more bleeding points.