helminthic infection

Ascaris lumbricoides

Ascariasis or ascariosis; roundworm infection. It is a soil-transmitted infection, It is the most common human helminthic infection caused by Ascaris lumbricoides . Current estimates indicate that more than 1.4 billion people are infected worldwide.

Morphology
These are large, stout nematodes, tapering at both ends. The females are slightly larger than the males but may show great variation in size, depending on age and worm load. The mouth opens terminally and has three lips, each of which has a pair of sensory papillae on its lateral margin, and rows of small denticles or teeth.
The principal structural protein of the cuticle is collagen.
In the female the paired, tortuous, tubular ovaries, oviducts, seminal receptacles and uteri lead into a vagina, which opens by a small vulva on the ventral surface about a third of the body length from the anterior end. The average daily output of eggs is about 200,000 per female and each may lay a total of 25 million during her lifetime. The posterior end of the male is curved ventrally and there are two almost equal copulatory spicules (measuring 2.0–3.5 mm) and numerous preanal and postanal papillae.
The eggs are broadly ovoid and measure 45–70 µm - 35–50 µm. The shell is thick and transparent and usually has a coarsely mammilated outer albuminous coat, stained light brown with bile pigments .

















Life cycle
The unsegmented, fertilized, ova, passed in the faeces, take 10–15 days to develop to the infective stage at 20–30°C in moist soil or water. The ?rst-stage larva inside the egg moult after about a week and it is the egg containing the second-stage larva that is infective. In moist loose soil with moderate shade, infective eggs may survive for up to 7 years .
When the infective eggs are ingested, the larvae hatch in the duodenum. The
eggshell is dissolved when there is a temperature of 37°C. The second-stage larvae have a rhabditiform esophagus.
They penetrate the mucosa and are carried in the lymphatics or veins through the liver and heart to reach the lungs in 3 days. The larvae moult twice in the lungs (at 5–6 days and 10 days) and then penetrate the alveolae, ascend the trachea and pass down the esophagus to reach the ileum. They develop into adult males and females in about 65 days and live for 1–2 years.


Clinical features
About 85% of ascariasis cases are symptomless; however, the most frequent symptom is upper abdominal discomfort of varying intensity. Symptoms such as asthma, insomnia, eye pain, and rashes represent allergic responses of the host to metabolic excretions and secretions of adult worms, as well as to dead and dying worms. Little damage results from larval penetration of the host’s intestinal mucosa. However The larvae cause lesions in the liver, spleen and lymph nodes. Sometimes necrotic foci are also found, encapsulated larvae causing a granulomatous reaction. In the lungs they cause petechiae and ulceration of the bronchial mucosa also High IgE production.
Surgical complications are more common in areas where patients have greater worm loads, which in turn are found where the intensity of transmission and prevalence are high.
Treatment
Clinical: Intestinal obstruction in children can usually be treated conservatively with intravenous ?uids, but acute infections Nematodes may require surgical removal. Biliary obstruction, which is more common in
adults than in children, can sometimes be treated by using retrograde endoscopy.
Chemotherapy
? Albendazole
This is 100% effective at a single oral standard dosage of 400 mg for all individuals except pregnant women and the under-5s and will have action against all the geohelminths.
? Mebendazole
This can similarly be used at a standard single oral dose of 400 mg for all geohelminths although best against Ascaris (100%).
? Levamisole
When given at 150–250 mg (2.5–5 mg kg -1) it is completely effective (paralysing Ascaris) but less so against other intestinal nematodes.

Prevention
Where there is a marked rise in standards of sanitation over a large area, Ascaris infection falls quickly, usually within a year. At the personal level, thorough washing and preferably cooking of vegetables and supervision of children’s play areas are important. However, it is dif?cult to prevent infection and reinfection in young children.
















Fasciola hepatica

Fascioliasis or fasciolosis, distomiasis; liver-?uke infection, liver-rot (in sheep).
Adult worms inhabit the bile-ducts. Fasciola is primarily an animal parasite of great veterinary importance and is found in sheep and cattle kept on damp and muddy pastures in all the sheep- and cattle-raising areas of the world.

MORPHOLOGY
The hermaphroditic adult ?ukes measure 20–30 mm _ 13 mm wide (specimens are usually smaller in heavy infections) and are ?at and lea?ike, with a spiny tegument . The oral sucker measures 1.0 mm in diameter and the ventral sucker, which lies close behind it, about 1.6 mm. The male and female reproductive systems are very dendritic, the two gut caeca are also highly branched.
The dendritic testes lie one behind the other in the middle portion of the body. The small, highly branched, ovary is in front of the anterior testis. The dendritic vitellaria lie in the lateral ?elds and have vitelline ducts leading to the ootype. The uterus, ?lled with eggs, is con?ned to the anterior third of the body.

LIFE CYCLE
In sheep the eggs are laid in the biliary tracts, reach the intestine and are passed out in the faeces. The undifferentiated ovum develops into a miracidium under moist conditions in 9–15 days at 22–25°C. The miracidium that hatches out of the egg lives for only about 8 h and can move in a ?lm of moisture on damp pastures. For further development the free-living miracidium must penetrate an amphibious snail, usually a species of Lymnaea . Once inside the snail, there is a sporocyst, followed by two redia stages; the cercariae, which emerge 30–40 days after penetration at 24°C, encyst as metacercariae on vegetation . This is usually wet grass, but watercress, water mint (in Iran) or other salad vegetables are of most importance in human infections (or perhaps sometimes in drinking water). When cysts are ingested, the larvae excyst in the duodenum, migrate through the intestinal wall and reach the bile-ducts by eating their way through the hepatic parenchyma from the surface of the liver. The adult worms mature
in 3–4 months and live for 5–12 years.