Diphyllobothriasis

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LABORATORY DIAGNOSIS

Occurrence: Commoner in temperate zones

Organism: Diphyllobothrium latum Reservoir: Humans, fish-eating mammals Transmission: Eating raw fish Control: Thorough cooking

Sanitary disposal of faeces

Control of fishing and export of raw fish

Infection by the fish tapeworm Diphyllobothrium latum is characterized by a megaloblastic anaemia due to vitamin B12 deficiency.

If segments are passed in the faeces or vomitus, diagnosis can be made by seeing the typical rosette-shaped uterus when the segment is crushed between two glass slides. More commonly, however, 'direct smear' examination of the faeces will reveal the characteristic operculate ova.

CONTROL

Thorough cooking of fish affords personal protec tion, all infected persons should be treated with niclosamide (Yomesan) or praziquantel in the same dosage as for taeniasis. Control of export raw or smoked fish should be exercised. Sanitary disposal of the human faeces will reduce infection of fish, and fishing should be forbidden in infected waters.

Three dwarf tapeworm infections can occur in man due to Hymenolepis nana, H. diminuta and Drepanido taemia lanceolata respectively. They all occur in the tropics and subtropics.

EPIDEMIOLOGY

H. nana is a common tapeworm of man in the southeastern United States, parts of South America, and India. Humans become infected by ingesting the ova in food or water that has been contaminated by human or rat faeces. The infection can also be transmitted directly from hand to mouth. Although rats and mice are commonly infected, man is the chief source of human infections, infection being spread directly from patient to patient without utilizing an intermediate host. Owing to their unhygienic habits, H. nana is more prevalent in children, with the highest incidence occurring between 4 and 9 years.

H. diminuta is an infection of rats and mice, humans being an incidental host. The principal source of infection is food contaminated by rat and mice droppings on which the intermediate insect hosts also thrive. When persons eat food containing these insect vectors they get accidentally infected. Human infection is chiefly in children who ingest rat fleas.

LABORATORY DIAGNOSIS

A moderate eosinophilia (4-16%) occurs in both H. nana and H. diminuta infections. Diagnosis is made by finding the characteristic ova in the faeces.

CONTROL

Personal hygiene, sanitary disposal of faeces and food hygiene will control these infections with dwarf tapeworms. The treatment of the individual is as for taeniasis, but it is advisable to repeat the dose after an interval of 3 weeks to kill any further tapeworms which may have emerged from their larval state in the intestinal villi.

Hydatid disease

Occurrence:

Worldwide

Organism:

Echinococcus spp.

Reservoir:

Dogs

Transmission:

Ingestion of infective ova

Control:

Personal hygiene

Albendazole

Deworming of dogs (praziquantel)

Abattoir hygiene

This disease can be caused by any one of three species of the genus Echinococcus: E. granulosus, E. multilocularis and E. oligaettas. Since the epidemiological and pathological features of these three tapeworms are very similar, only a detailed description of E. granulosus is given here.

LIFE CYCLE

See Figure 4.8.

EPIDEMIOLOGY

Hydatid disease, caused by the larval form of E. granulosus, has a cosmopolitan distribution, being particularly prevalent in the sheep- and cattle-raising areas of the world.

Reservoir and transmission

Dogs are the main reservoir of human infection. Humans acquire hydatid disease when they swallow infected ova as a result of their close association with dogs, and the insanitary habit of not washing hands before ingesting food. The ova may live for weeks in shady environments but they are quickly destroyed by sunlight and high tempera,..^; Tfe dog faeces contaminating fleeces of s'leep can also be an indirect source of human infection

Hymenolepiasis

Occurrence:

SE United States, S.America, India

Organism:

Hymenoiepsis and Drepanido

taemia spp.

Reservoir:

Humans, rodents

Transmission:

Contaminated water, food

Control:

Personal hygiene

Sanitary disposal of faeces

Eggs swallowed by sheep, cattle, rodents etc. or man, embryo develops into hydatid cyst in liver and other organs

Eggs swallowed by sheep, cattle, rodents etc. or man, embryo develops into hydatid cyst in liver and other organs

Hydatid cyst contains daughter cysts, brood capsules and scolices

Figure 4.8: Life cycle of Echinococcus granulosus (hydatid disease).

Hydatid cyst contains daughter cysts, brood capsules and scolices

Figure 4.8: Life cycle of Echinococcus granulosus (hydatid disease).

The main cycle of transmission in Kenya is between dogs and domestic livestock (Plate 31). It has been shown that in Kenya hydatid cysts are present in more than 30% of cattle, sheep and goats, though the disease in huirans occurs infrequently. except in the areas of Turkana Canines |8§ heavily infected while light infections have been recorded in wild carnivores, for example jackals and hyenas. Turkana tribesmen are the most heavily infected people in Kenya because of the intimate contact between children and the large number of infected canines in the area - here dogs are used to clean the face and anal regions of babies.

Host factors

Although infection is usually acquired in childhood, clinical symptoms do not appear until adult life.

LABORATORY DIAGNOSIS

If the hydatid cyst ruptures, its contents (hooklets, scolices, etc.) may be found in the faeces, sputum or urine. Eosinophilia is present but is usually moderate in degree (300-2000/mm2) and there may be hypergammaglobulinemia. Ultrasound technology, MR and CT scanning are often used in diagnosis. ELISA and indirect haemaglutination are procedures of choice in initial screening of sera.

CONTROL

This depends on raising the standards of personal hygiene, deworming of infected dogs with praziquantel (Droncit) and adequate supervision of abattoirs. Infected offal and meat should be destroyed, dogs excluded from slaughterhouses, and infected carcasses deeply buried or incinerated.

The individual

People must be warned of the danger of handling dogs or sheep and the importance of washing their hands immediately afterwards. The results of treatment with albendazole have shown great promise.

The community

Deworming of all infected dogs, if possible, is the best means of getting rid of the main reservoir of infection. The most suitable drug for this purpose is praziquantel (Droncit). In addition, all meat or offal containing hydatid cysts should be disposed of and thus be made inaccessible to dogs. Abattoir supervision and hygiene will exclude dogs from the premises and infected carcasses should be incinerated. In sheep-rearing areas burial or incineration of dead sheep should be carried out. Stray dogs should be eliminated.

Trematode (fluke) infections

Throughout the world over 40 million people have food-borne trematode infections and 750 million are at risk. They are particularly prevalent in South East and East Asia. The factors determining the epidemiology of these infections are: (i) food related (e.g. consumption of raw fish or food plants); (ii) social or cultural determinants; (iii) aquaculture; and (iv) water resources development. All of these factors are indirectly influenced by poverty, pollution and population growth.

National strategies for control must include the following components: (i) a national co-ordinating body to set up a 'horizontal' programme; (ii) training; (iii) health education; (iv) food control; (v) improvement in sanitation; and (vi) intersec-tional collaboration with agriculture and fisheries departments.

Immunodiagnostic tests (e.g. ELISA, complement fixation and preciputin tests) are useful in the diagnosis of extraintestinal and tissue-dwelling trematode infections. DNA detection and the polymerase reaction are available but not in general use.

Paragonimiasis

Occurrence:

East and South East Asia and

West Africa

Organism:

Paragonimus westermani

Reservoir:

Humans

Transmission:

Eating uncooked crab and crayfish

Control:

Adequate cooking of crab and

crayfish

Sanitary disposal of faeces

The infection is characterized by cough, expectoration of bloody sputum and later signs of bronchiectasus or lung abscess.

LIFE CYCLE

See Figure 4.9.

EPIDEMIOLOGY

Paragonimiasis is due to the liiilg i-uke Paragoiiiinus westermani, which has a world vide geographical distribution. It occurs focally throughout the Far East, South East Asia, the Pacific Islands, xVest Africa

Life Cycle Paragonimus
Figure 4.9: Life cycle of Paragonimus westermani.

and parts of South America (Fig. 4.10). A new species, P. africanus, which is considered to be a local causative agent of paragonimiasis, has been described from the Cameroons. Other species responsible for human infections are P. heterotremus and P. szechuanensis.

Reser\>oir

Humans are the reservoir of infection Although a considerable domestic and wild inirr.a. r.-servoir of paragonimus infection exists, the tan it plays in hi epidemiology of human disease has yet lo be fully detennined.

Transmission

CONTROL

Transmission is maintained by faecal and sputum pollution of water in which the appropriate snails and vector crustaceans live, and by the custom of eating uncooked crabs and crayfish soaked in alcohol, vinegar, brine or wine. Infection can also occur during the preparation of such food, when encysted cercariae can be left on the knife or other utensils.

Host factors

Although in most areas infection is higher in males than in females, in the Cameroons women are infected three times as often as men. The peak age of incidence is between 11 and 35 years of age. It has been reported that during a measles epidemic in Korea, 80% of paragonimus infections were produced by the administration of the fluid extract of crushed crabs given medicinally to the patients.

The infection may persist for many years after leaving endemic areas.

LABORATORY DIAGNOSIS

The infected sputum is characteristically sticky and bloody, usually of a dark, brownish red colour. The characteristically shaped eggs are usually found in the sputum or in the faeces on 'direct smear' examination or by concentration techniques. In the first year of infection eggs are seldom found but there is usually an eosinophilia of about 20-30%. ELISA is a sensitive and practical immunological test. Radiography may show patchy foci of fibrotic change, with a characteristic 'ring shadow'.

Crabs and crayfish should be cooked before eating. Faecal pollution of water should be prevented. Elevation of standards of personal and public hygiene and the provision of latrines will reduce transmission. Praziquantel has been used both for individual treatment and community control.

Clonorchiasis

Occurrence:

East Asia

Organism:

Clonorchis sinensis

Reservoir.

Humans

Transmission:

Eating raw or undercooked fish

Control:

Adequate cooking of fish

Chemotherapy

Sanitary disposal of faeces

This infection is caused by the oriental liver fluke Clonorchis sinensis and may be symptomless or result in severe liver damage with the possibility of malignant change.

LIFE CYCLE

See Figure 4.11.

EPIDEMIOLOGY

Clonorchiasis is mainly found in dr. Fa1- East. Endemic foci occur in Japan, South Korea, South

East China, Taiwan and Vietnam (Fig. 4.12).

Adult worms in bile ducts of man and animals

Adult worms in bile ducts of man and animals

Cercariae penetrate and encyst in fish

Miracidium hatches when egg is eaten by snail

Develops in snail into sporocysts, rediae and cercariae

Cercariae penetrate and encyst in fish

Miracidium hatches when egg is eaten by snail

Develops in snail into sporocysts, rediae and cercariae

Figure 4.11: Life cycle of Chlonorchis sinensis.

Reservoir

Humans are the reservoir of infection. As with paragonimiasis many animals harbour C. sinensis, but their importance in the epidemiology of the human disease has yet to be fully assessed.

Fish ponds fertilized with fresh human faeces are a common source of infection (Plate 32). Infected fish exported to other countries can result in the spread of the disease to areas where the parasite is hot normally found.

Transmission

Humans and other mammals are infected by eating raw or undercooked fish containing metacercariae.

Host factors wm

Clonorchiasis is rare in infants under 1 yerj oi ag § It begins, however, at about 2 years, rising to 65% in

Figure 4.12: Distribution of Chlonorchis sinensis.

those aged 21-30 years and to a peak of 80% in those dying between the ages 51 and 60 years. Males are more frequently infected than females, but there are no social differences in the prevalence of the disease because of the universal custom of eating raw fish. The lifespan of the worm is 25-30 years.

LABORATORY DIAGNOSIS

A definitive diagnosis is made by finding the typical operculated ova by 'direct smear' examination of the faeces or duodenal aspirate.

There is usually a leucocytosis (23000-48200) with eosinophilia. In severe cases with secondary infection of the bile ducts there may be severe hypoglycaemia and a raised alkaline phosphatase.

CONTROL

Fish should not be eaten raw and the use of human faeces in fish ponds should be avoided. Sanitary disposal of faeces and raising the standards of personal and community hygiene will reduce transmission. Praziquantel has been successfully used both for individual treatment, and community control.

Transmission: Eating raw fish Adequate Control: cooking of fish Chemotherapy

This infection is very similar to clonorchiasis, resulting in enlargement of the liver and eventually malignant change.

APPLIED BIOLOGY

The life cycle and pathogenesis of the two human hepatic trematodes Opisthorchis felineus and O. viverrini are similar to that of C. sinensis. The adults inhabit the distal bile ducts and the ova are passed out in the faeces. After ingestion by the appropriate snails (e.g. Bithynia) the miracidia develop into cercariae, which in turn penetrate the flesh of suitable species of freshwater fishes (e.g. cyprinoid family) in which they encyst and develop into metacercariae. When the metacercariae are ingested by a suitable host (man, domestic, wild and fur-bearing animals) they encyst in the duodenum and migrate to the distal bile ducts particularly those of the left lobe of the liver. The entire life cycle takes about 4 months.

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