Nematode roundworm

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infections Ascariasis

Table 4.2: Classification of important helminthic diseases transmitted through the gastro-intestinal tract

Occurrence:

Hot humid climates of the world

Organism:

Ascaris lumbricoides

Reservoir.

Humans

Transmission:

Contaminated hands, food, drink

Control:

Personal hygiene

Sanitary disposal of faeces

Chemotherapy

Table 4.2: Classification of important helminthic diseases transmitted through the gastro-intestinal tract

Roundworms

Tapeworms

Flukes

(Nematodes) (Cestodes)

(Trematodes)

Ascariasis

Taeniasis

Paragonimiasis

Trichuriasis

D i phyl lobothr iasis

; (lung)

Enterobiasis

Hydatid disease

Clonorchiasis

Toxocariasis

Hymenolepsiasis

(liver)

Trichinosis

Opistorchiasis

Dracontiasis

(liver)

(filarial worm)

Fascioliasis

(liver)

Fasciolopsiasis

(intestine)

This disease, due to the large intestinal roundworm, Ascaris lumbricoides, is often symptomless and infection is discovered incidentally; occasionally it causes intestinal obstruction in children.

The adult worms of A. lumbricoides live in the small intestine. Their colour is yellowish-white and they may reach a length of 40 cm. The female is prolific, laying up to 200000 eggs a day. The typical egg has a yellowish-brown mamillated appearance. Ascaris eggs are resistant to cold and to disinfectants in the strengths in normal use. They are killed by direct sunlight and by temperatures of about 45°C. Under optimum conditions, eggs may remain viable for as long as 1 year (Fig. 4.3).

EPIDEMIOLOGY

A. lumbricoides has a worldwide distribution, the incidence of which is largely determined by local habits in the disposal of faeces. Its highest prevalence is in the hot humid climates of Asia, Africa and tropical America.

Reservoir and transmission

Humans are the reservoir of infection which is spread by faecal pollution of the soil. The eggs are swallowed as a result of ingestion of soil or contact between the mouth and various inanimate objects carrying the adherent eggs. Contamination oi food or drink by dust or handling is also a ^¡ps of infection. Eggs of ascaris pass unaltered tVough the intestine of coprophagous animals ■■xad ;an ¡tnw be transported to locations other than human

Unne «nape in irn«ïlnr. enter blooditrdim ïrid Jrt ilrnci

Unne «nape in irn«ïlnr. enter blooditrdim ïrid Jrt ilrnci

Figure 4.3: Life cycle of Ascaris lumbricoides.

defecation sites. The well-protected eggs withstand drying and can survive for lengthy periods. A. suis, which infects pigs, is morphologically identical and can mature in humans, but cross-infection has not been proved.

Host factors

Although all age groups show infection in endemic areas, the incidence and intensity are highest in the younger age groups. Infants may be parasitized soon after birth by ova on the mother's fingers. The observed variation in incidence and intensity with age is probably due to differences in behaviour and occupational activities between children and adults, as well as to the development of acquired resistance. It has been claimed that ascaris infection retards growth in children. Clinical signs of protein-energy malnutrition increase in ascaris-infected children and significantly decrease after deworming.

The prevalence of ascaris infection in children can be usefully used as an index of faeco-oral transmission in a community.

LABORATORY DIAGNOSIS

The microscopical diagnosis of ascariasis can be confirmed by examination of faeces samples. Because of their characteristic morphology and colour the ova can be found relatively easily in 'direct smears'. Concentration nd quantitative techniques are available. The Kai o-Katz cellophane quantitative technique is the W;IO recomii »coded method.

CONTROL

The main method of control is the sanitary disposal of human excreta, complemented by chemotherapy.

The individual

Health education should raise standards of personal hygiene and mothers should encourage young children not to defecate indiscriminately. Chemotherapy will reduce morbidity.

The community Sanitation

A method of sanitary disposal of faeces (i.e. some type of latrine acceptable to the people and best suited to the terrain - see Chapter 1) should be introduced and its use encouraged. The provision and use of such facilities is particularly important for groups that spend long hours working out of doors (e.g. farmers). Human faeces should not be used as a fertilizer (Plate 27) unless previously composted so that the resulting high temperature can kill the eggs. Mass treatment of preschool and school children has been undertaken using a single dose of one of the broad-spectrum antihelminthics (see pp. 140-141).

Mass chemotherapy has been utilized as the medium-term approach to control, fortified by improvements in personal hygiene and sanitation as the long-term solution for ascaris and the other faeco-orally transmitted helminth infections. Whether this popular intervention (chemotherapy) is cost-effective has recently been challenged.

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