Intestinal Helminths (With Diagram) | Microbiology

The below mentioned article provides a study-note on the intestinal helminths.

Cestoda. Diphyllobothrium latum, Taenia saginata, T. solium, Echinococcus granulosus, Hymenolepis nana, Dipylidium caninum.

Trematoda. Fasciolopsis buski, Fasciola hepatica, Gastrodiscoides hominis.

Nematoda. Trichinella spiralis, Trichuris trichiura, Strongyloides stercoralis, Ankylostoma duodenale, Necator americanus, Enterobius vermicularis, Ascaris lumbricoides.

Diphyllobothrium Latum (Fish Tapeworm):

The adult worm is ivory or yellowish grey in col­our, measuring 3-10 meters in length. The head (Fig. 47.1) (Scolex) is small, spatulated or spoon shaped, has a pair of slit grooves (bothria) ventrally and dorsally and has no rostellum (a beak-like projection on the head) and no hook lets. Scolex is followed by “neck” and 3,000 segments (proglottids) (Fig. 47.2). A single worm may discharge as many as one million eggs per day from ootype.

Life cycle:

When the egg (Fig. 47.3) of D. latum passed out along with the feces of the infected host (man) comes in contact with water, the ciliated em­bryo (coracidium) (Fig. 47.4), escapes from the egg and swims in the water. It is ingested by a Cyclops and transforms into procercoid larva.

When the infected Cyclops (Fig. 47.5, 6) is ingested by a fish, procercoid (Fig. 47.7) develops into plerocercoid or sparganum larva (Fig. 47.8) in the fish which is infective to man. On consuming insufficiently cooked fish, man be­comes infected. The plerocercoid larva develops into an adult worm, ultimately the eggs are excreted in the feces.

Clinical features:

The presence of adult worm in the intestinal tract causes no symptom, but some­times, non-specific abdominal symptoms have been ascribed. If the worms attach themselves to the jeju­num, clinical vitamin B₁₂ deficiency develops. In the laboratory, microscopical examination of the faeces will reveal the eggs; sometimes proglottids can be observed in the stool.

Treatment:

Quinacrine hydrochloride, niclosamide and paromomycin are found effective. Pernicious anaemia can be treated with folic acid.

Prophylaxis:

(1) Thorough cooking of suspected freshwater fish is important;

(2) Pollution of water can be prevented by efficient disposal of sewage;

(3) In endemic areas of infection, dogs and cats should not be given fish.

Taenia Saginata (Beef Tape Worm) AND T.SOLIUM (Pork-Tape Worm) have a cosmopolitan dis­tribution. 

Life Cycle of T. saginata:

While grazing on the polluted ground, the ma­ture eggs (Fig. 47.15) are ingested by cattle. The onchospheres are hatched out from the eggs in the duodenum.These embryos penetrate the intestinal wall of the cattle, are carried through blood stream and reach the liver, the right side of the heart, lungs, the left side of the heart and the systemic circulation. These oncospheres are filtered out in the striped muscles and transform into bladder worm (Cysticereus bovis). On ingesting infected raw beef, man becomes infected with this bladder worm.

The larva is digested out of the beef, the scolex evaginates, attaches itself to the intestinal wall of man and develops into adult worm, which liberates eggs. The life cycle of T.solium is similar to that of T.saginata but C. cellulose produce Cysticercosis cellulosae in man or neurocysticercosis in the brain of man, resulting into epilepti form seizures with a rapidly fatal outcome.

Recent dot-ELISA is very sensitive and quite spe­cific in the diagnosis of neurocysticercosis. Magnetic

Resonance Imaging (MRI) Ultrasonography and Com­puted Tomography (CT) scan detect C.cellulosae in the brain.

Clinical features. Because of its large size, T.saginata is responsible for considerable disturbance in the normal function of the intestine; whereas T. solium may cause irritation and less intestinal obstruction, vague abdominal discomfort, hunger pains, chronic indigestion and persistent diarrhoea alternating with constipation are the common symp­toms. Laboratory diagnosis can be done by demon­stration of Taenia egg (eggs of both Taenia sp. are identical), by recovery of gravid segments. A dot – ELISA test can be used to diagnose neurocysticercosis.

Treatment:

Quinacrine, niclosamide, bithionol, mebendazole, are effective. Albendazole is very ef­fective for neurocysticercosis, (T.solium).

Prophylaxis:

Consist of

(1) Personal hygiene;

(2) General sanitary measures;

(3) Avoidance of in­gestion of raw pork or beef and vegetables irrigated by sewage water;

(4) Rigid quality inspection of pork and beef in all slaughter-houses;

(5) Avoidance of fecal contamination.

Echinococcus Granulosus:

(Dog Tapeworm):

The adult worm (Fig. 47.16) is a minute tape worm, has a scolex, neck and strobila comprising three segments and measures 3-6 mm. in length. It has a pyriform scolex provided with four suckers and a protrusible rostellum armed with two circular rows of hook lets. The neck is short and thick. Its egg cannot be distinguished from that of Taenia and is infective to man, cattle, sheep (Fig. 47.17, 18).

Life Cycle:

The infected definite host (dog) passes the stool with the eggs onto the ground. While grazing on the polluted ground, the intermediate hosts (sheep, goats and cattle) swallow these eggs, whereas children get infected while playing with dogs.

The eggs hatch in the duodenum, the oncospheres migrate through the intestinal wail, en­ter the mesenteric venules and become lodged in the capillary filter beds in various organs and tissues (liver, lungs, various organs) and develop into a cystic cavity (hydatid cyst)(Fig. 47.19,20). When the organs or tissues containing fertile hydatid cysts are ingested by dog, the cysts develop into adult worms. The eggs are passed out in the dog’s faeces.

Clinical features. The damage produced by hy­datid cyst off. granulosus is both mechanical and toxic. The young cysts which develop into embryos lodged in the vital centers may interfere with the function of the organs, damage the organ (brain, or­bital capillary, heart valve) and even cause death.

Laboratory diagnosis:

Casoni’s test or intrader­mal test; precipitin test, complement fixation test; haemagglutination; bentonite flocculation test; latex agglutination test; fluorescent test; ELISA; exploratory cyst puncture; roentgenogram and recent Computed Tomography (CT) scan and Magnetic Resonance Imaging (MRI) are techniques used for the diagnosis of hydatid disease.

Immunoblot test is under trial. Hydatid disease can be diagnosed by ultrasonogra­phy and is confirmed by Dot-blot ELISA which can detect within 30 minutes the antibodies to antigen B of hydatid fluid.

Treatment:

Albendazole is most effective than thiobendazole and mebendazole. Surgical technique is also helpful.

Prophylaxis:

This consists of:

(1) avoidance of handling infected dogs;

(2) avoidance of ingestion of raw vegetable polluted with eggs;

(3) personal hy­giene (cleaning hands before eating);

(4) preventing dogs from eating the carcasses of sheep, cattle and dogs in infected areas;

(5) discarding all infected vis­cera in slaughter houses by dumping them into pits inaccessible to dogs, and

(6) educational propaganda in schools.

Polycystic Hydatid Disease (PHD):

It is caused by Echinococcus vogeli; the inter­mediate host is the wild rodent. PHD is mainly dis­tributed throughout America.

Surgical treatment of PHD is not feasible be­cause the multiple cysts involve extensive portion of the liver and other organs and disseminate through­out the peritoneum which are detected by ultrasonog­raphy.

Albendazole 10 mg / kg orally is effective in the treatment of patients with PHD.

Hymenolepis Nana:

H. nana is a cosmopolitan parasite. It is small and measures up to 25-40 mm in length by one mm in diameter. Its scolex (Fig.47.21) is minute, rhomboidal

and has four suckers and a short retractile (Fig. 47.22) rostellum armed with 20 – 30 hooklets in one single row. The rostellar hooklets are shaped like tuning forks

M.N.—14 and its neck is long and its segments (Fig. 47.23) are about 200. Its egg (Fig. 47.24) is spherical, contains an oncosphere enclosed in an inner envelope with two polar thickenings from which polar filaments.

Life cycle:

When fully embryonated eggs in human feces are ingested by man, only one host, they hatch in the intestine, then the free oncospheres penetrate into the villi of the small intestine and metamorphose into young cercocysts (larvae) (Fig. 47.25) which migrate into the lumen, become attached by their scolices to the small intestine and develop into mature worms which lay eggs.

Clinical features:

There is generalized toxaemia due to absorption of the metabolic wastes of the parasite. The general symptoms are headache, dizziness, anorexia, pruritus of nose and anus, periodic diarrhoea and abdominal pain. In the laboratory, the characteristic eggs can be demonstrated microscopically in the patient’s stool.

Treatment:

Niclosamide, Hexylresorcinol crys­talloid, Quinacrine and mebendazole are very effec­tive.

Prophylaxis:

This comprises

(1) avoidance of ingestion of eggs through contaminated food or drink (contamination may occur from toilet seats, soiled linen or directly from anus to mouth;

(2) Personal hygiene and

(3) a well-balanced diet which reduces susceptibility to infection.

Dipyllidium Caninum:

It is a common tapeworm of dog and cat. Its eggs deposited on the ground are ingested by dog flea. These eggs hatch in the intestine of the flea, develop into procercoid and, later, cysticercoid lar­vae. Man or dog gets infected by the ingestion of infected fleas. Clinical manifestations are intestinal disturbances, indigestion, lose of appetite and toxic nervous systems. Diagnosis by the demonstration of characteristic eggs in the mother capsules.

Treatment:

Quinacrine, mebendazole and niclosamide are effective. Prophylaxis by avoiding handling of infected dogs and by dusting of dogs with gammaxene or DDT.

Fasciolopsis Buski (Giant Intestinal Fluke):

It is an elongated and ovoidal trematode (Fig. 47.26, 27). The eggs of F. buski and F. hepatica are large like a hen’s egg and are identical.

Lifecycle:

When immature eggs are discharged in the feces, they mature in water and hatch out the micacidium (Fig. 47.28) which swims in the water, penetrates into the snail (Fig. 47.29) and develops into sporocysts, first, and second generation radiae and cercariae.

These cercariae encyst on the seed pods of water caltrop into metacercariae. Man gets infected by swallowing the metacercariae which excyst in the duodenum and ultimately develop into adult worm, which lays eggs in human faeces.

Clinical features. Toxic diarrhoea and hunger pains are the first signs. Heavy infections have symp­toms similar to gastric ulcer. Generalized toxic and allergic symptoms appear as edema of the face, ab­dominal wall and lower limbs. Specific diagnosis depends upon the recovery of the egg of F. buski which is similar to that of Fasciola hepatica.

Treatment:

Hexylresorcinol crystalloids and tetrachlorethylene are very effective.

Prophylaxis:

Destruction of snails by 1,50,000 copper sulphate solution, sterilisation of night soil, before it is used as fertiliser and cooking of raw veg­etables properly or immersing them in boiling water for few seconds before eating are all effective meas­ures.

Fasciola Hepatica (Sheep Liver Fluke):

It is a fleshy brown fluke (Fig. 47.30). Its eggs (Fig. 47.31) are large, ovoidal, operculated, light yel­lowish brown in colour. Life cycle is similar to that of F. buski. Cercaria (Fig. 47.32) is also developed but the excysted metacercariae (Fig. 47.33) of F. hepatica migrate through the intestinal wall into the peritoneal cavity. From here, they traverse the liver parenchyma to the biliary passages, where they settle down and grow to maturity. Adult worms liberate eggs in the feces.

Clinical features. The clinical manifestations are hepatic and obstructive jaundice with coughing and vomiting, generalized abdominal rigidity, abdominal pain on pressure, urticaria, irregular fever, persistent diarrhoea, later marked anaemia, cholelithiasis is a frequent complication.

Laboratory diagnosis is based on the recovery of typical egg of F. hepatica in the stool.

Treatment:

Emetine hydrochloride, bithionol, hexachloroparaxylene are effective.

Prophylaxis:

(1) Eradication of adult worms in reservoir hosts by adequate chemotherapy;

(2) De­struction of snails by the use of 1: 50,000 copper sulphate;

(3) Education of the local population about the danger in eating raw vegetables.

Gastrodiscus Hominis:

The living worm is bright pink in colour and pyriform in outline (Fig. 47.34). Its eggs are ovoidal operculate. Its life cycle is unknown. In man, it produces clinically mucous diarrhoea, In the laboratory it can be diagnosed by the demonstration of the typical eggs in the feces.

Othertrematodes:

Clonorchissinensis (Chinese liver fluke) is flat, transparent, flabby and spatulate. Its eggs are ovoidal, light yellowish and operculated.

Life cycle:

When fully embryonated eggs con­taining miracidium are ingested by snails (Bulimus), the miracidium hatches out from the egg and trans­forms ultimately into cercariae which escape from the snails and swim in the water. On contact with fresh water fish, these cercariae attach to the fishes and encyst in the skin or in the flesh. Man gets in­fected by ingestion of infected fish, the metacercariae excyst in the duodenum and enter the common bile duct where they mature and discharge eggs.

Clinical features:

There are three stages in the manifestation of symptoms:

(1) The mild, symptomless;

(2) The progressive stage with irregular appetite, fullness in the abdomen, diarrhoea and hepatomegaly and

(3) The severe stage with portal cirrhosis syndrome. Catarrhal cholangitis occurs due to occlusion of bile passages by sticky masses of eggs and by tissue proliferation. Symptoms of systemic toxaemia are palpitation of the heart, tachychardia, vertigo, tremor, cramps and mental depression.

Opisthorchis felineus (Cat liver fluke) is mor­phologically similar to C. sinensis and also its eggs. Its life cycle is too similar, but the cercariae attack fish. Clinical features, diagnosis, prophylaxis are similar to those of C. sinensis, but there is no specific treat­ment. Paragonimus westermani (Oriental lung fluke) is a reddish brown, plump, ovoidal fluke with rounded anterior end. The eggs are ovoidal and have a flat­tened operculum.

Life cycle:

Eggs escaping through the bronchioles are coughed up, are swallowed and passed out of faeces. They hatch out miracidia in the water which swim in the water and attack the snails in which redia, cercariae produced liberated swim in the water and invade the viscera of cray fish or crab where the metacercariae encyst.

Man becomes in­fected by ingestion of infected crabs. The metacercariae excyst in the duodenum and migrate through the intestinal wall, reach the abdominal cav­ity and travel through the diaphragm to the pleural cavity and settle in the lungs.

Clinical features. Chest pain, night sweats are common symptoms. Paroxysmal coughing is fol­lowed by haemoptysis after physical exertion. The manifestations are severe. Bronchopneumonia, or bronchiectasis with pleural effusion are the physical signs.

Diagnosis by the finding of the characteristic egg in the sputum or feces. The complement fixation test may be positive. Recent Dot-immuno binding (DIB) assay can also be used.

Treatment:

Emetine hydrochloride, bithional and hexachloro-paraxylol are found effective.

Prophylaxis:

(1) Avoid eating raw crabs;

(2) De­stroy the snails;

(3) Disinfect the sputum or feces.

Trichinella Spiralis (Trichina Worm):

It is one of the smallest nematode 1.4-1.6 mm in length by 40 -60 mm in diameter (Fig. 47.35, 36).

Life cycle:

When man consumes raw meat in­fected with the cysts of T.spiralis (Fig.47.37 ) the cysts are digested out of the meat in the stomach. After excystation, the larvae (Fig. 47.38) invade the intesti­nal mucosa and develop into adults. The males die after fertilizing the females which, in turn, discharge larvae.

Some of them escape into the lumen of the intestine and the majority enter into the circulation through the mesenteric lymphatics, and settle at last in the striated muscles. Pigs cannot perpetuate the infection.

Clinical features:

Symptoms of nausea, vomit­ing, toxic diarrhoea or dysentery, colic, profuse sweat­ing, muscular pain, edema around eyes, nose and limbs, encephalitis, meningitis, deafness may occur.

Laboratory diagnosis is by the demonstration of Trichina larvae in the muscles, adult worms in the feces, blood or spinal fluid.

Bechman intradermal test; precipitin test; Bentonite flocculation test and fluorescent antibody tests are useful to diagnose Trichnielliasis.

Treatment:

Thiobendazole is effective. Supportive treatment by analgesics to reduce muscular pain.

Prophylaxis:

(1) Destruction of all carcasses of pigs dying on farm;

(2) Elimination of raw garbage’s;

(3) Extermination of rats and mice;

(4) Thorough cook­ing of all pork to be consumed by man.

Trichuris Trichiura: (Whip Worm):

The male adult worm is brown in colour and resembles a whip with a handle. Its posterior end of the male is coiled with protruding spicule (Fig. 47.39, 40), whereas that of female is rounded (Fig. 47.41). The egg (Fig. 47.42) of T. trichiura is barrel shaped with mucoid plugs at either pole.

Life cycle:

Man gets infected by swallowing the fully embryonated egg containing the rabidity form larva which is infective to man. The egg shell is di­gested in the small intestine of man. The liberated larva gets attached for nourishment, to the small in­testine and passes down to the caecum to become adult worm which lays eggs, found late in the faeces.

Clinical features:

The common symptoms are abdominal pain, vomiting, constipation, abdominal distension and systemic intoxication. The skin is dry and the patient is emaciated. The clinical picture is similar to that of hookworm disease, appendicitis or dysentery. In the laboratory, the characteristic egg of T. Trichuris can be demonstrated in the patient’s stool.

Treatment:

Dithiazamine iodide, thiabendazole and mebendazole are effective. Very recent an­thelmintic Aldendazole (Chewable single dose) is most effective.

Prophylaxis:

Proper disposal of feces, thorough cleaning of hands, before meals, children not allowed to defecate on the ground, avoiding putting dirty fin­gers into mouth and consumption of properly cooked vegetables are the effective measures.

Strongyloides Stercoralis (Thread Worm):

The cylindrical muscular esophagus (Fig. 47.43) of the parasitic female (Fig. 47.44, 45) occupies the anterior third of the body, whereas the intestine fills up the posterior two-third. The anus opens mid- ventrally. The parasitic males are similar to the free living males and have two spicules (sp.) and a gubernaculum (Fig. 47.46, 47).

Rhabditiform larva (Fig. 47.49) develops directly from the gravid female and found in the intestine and has short mouth with double bulb of esophagus.

Life cycle:

When man walks barefoot on soil contaminated with ovoviviparous eggs (Fig. 47.48) of 5. Stercoralis containing filari form larvae, these filar­iform larvae (Fig. 47.50, 51, 52) penetrate directly through the skin enter into the circulation and break out of pulmonary capillaries into the alveoli, then migrate to the bronchi, trachea, larynx and epiglottis.

They are swallowed and re-enter the intestine. They develop into parasite females and males. The females penetrate the intestinal mucosa and begin to deposit eggs.

Clinical features:

There will be petechial hemorrhage at the site of entry of larvae followed by intense congestion, edema, and urticarial rash. There will be bronchopneumonia with consolidation of the lobules. Frequent coughing, pleural effusion and pyothorax are the symptoms.

Three types of enteritis may occur:

(a) Catarrhal enteritis;

(b) edematous enteritis; and

(c) ulcerative enteritis. There is accompanying diarrhoea with mu­cus and blood, which may be very painful.

Laboratory diagnosis is by the recovery of ac­tive rhabditi form larva from the stool, sputum, duo­denal washing. Serology is not quite satisfactory.

Treatment:

Thiabendazole, mebendazole and the current albendazole are drugs of choice.

Prophylaxis:

(1) The human body must be pro­tected from infective soil and from contaminated feces;

(2) Constipation should be avoided by use of cathartics;

(3) Careful cleaning of hands.

Ankylostoma Duodenale (Old World hook-worm):

Necatoramericanus (New world hookworm):

Differential Features:

Life cycle:

Eggs with four blastomeres (Fig. 47.63) faeces hatch out rhabditiform larva (Fig. 47.57) in soil which develops later into filariform larva (Fig. 47.58), infective to man, enters into the skin causing creeping eruption or cutaneous larva migrants. Blood circulation, breaks out from the pulmonary capillar­ies, migrate to epiglottis, esophagus, intestine where they grow into adult worm which lays eggs.

Clinical features:

In the moderate type, the symptoms are heart burn, flatulence, fullness in the abdomen, and epigastric pain. These are relieved by eating clay, mud or earth (which is known as pica or geophagy).There may be low grade, intermittent fe­ver, lassitude, dyspnea and palpitation of the heart. In the severe type, there is constipation or diarrhoea. The skin is dry, harsh and pale yellow. Pot belly is a typical physical sign in children. Finally, there is physical exhaustion, cardiac failure and anasarca.

Laboratory diagnosis:

Direct demonstration of characteristic egg in the stool; indirectly, blood ex­amination will reveal the nature of anaemia.

Treatment:

Supportive treatment for anaemia. Specific treatment by thiobendazole, mebendazole and current albendazole is very effective. N. americanus is cultivated in undefined media based on Chick Embryo Extract (CEE), serum, tissue extract.

Prophylaxis:

Personal protection by wearing gloves and boots; disinfection of faeces or soil and prevention of soil pollution; treatment of carrier and whole community is effective prophylaxis.

Enterobius Vermicularis (Pin Worm or Seat Worm):

The adult worm (Fig. 47.64, 65) is small, white, and similar to a small piece of threat. Posterior (Fig. 47, 67, 68) and anterior end (Fig. 47, 69) of this worm.

Life cycle:

When the fully embryonated eggs (Fig. 47.66), infective to man, are ingested by man, they hatch out the larvae in the intestine, which grow into adult worms which crawl out of the anus during the night and deposit eggs on the perianal skin. The mode of transmission is by anus to mouth (auto-in­fection).

 

Clinical features:

Absorbed metabolites may cause a characteristic helminthic toxaemia. Gravid females, migrating out of the anus, may oviposit on the perianal and perineal skin of the anus and cause severe pruritus with severe scratching which is charac­teristic of this infection. Sometimes, it may enter the female genital tract causing sapling it is and at last encyst in the peritoneal cavities. There may be ure­thritis, nocturnal enuresis (frequency of micturition) and masturbation. Loss of appetite, loss of weight, nervousness, insomnia, nightmare, nail biting, nose picking and grinding of teeth at night.

Laboratory diagnosis can be performed by:

(1) The identification of the recovered adult worm, and

(2) The microscopic demonstration of the char­acteristic egg.

Treatment: Piperazine adipate, thiabendazole, mebendazole and albendazole are effective an­thelmintic drugs.

Prophylaxis:

(1) Personal hygiene should be strictly observed;

(2) the boiling;

(3) finger nails should be cut short and thoroughly cleaned several times each day;

(4) toilet seats should be regularly scrubbed and sterilised;

(5) if cleanliness is inadequate, chemo- therapeutics should be provided.

Ascaris Lumbricoides (Round Worm):

The adult worm is the largest (20-35 cm) of the common intestinal nematodes of man. It is bright pink in colour (Fig. 47.70, 71).

The posterior end (Fig. 47.75, 76) of male is curved ventrally with a pair of copulatory spicules without gubernaculum. The female has a vulvar waist (w) situated mid ventrally (Fig. 47.70). Its anterior end (47.72, 73, 74) and posterior end (Fig. 47.77).

Life cycle:

When fully embryonated or ferti­lised eggs are ingested by man, their shells are di­gested by the digestive juice, the rhabditiform larvae (embryos) are liberated, penetrate into the intestinal wall, carried in the blood stream and break through the pulmonary capillaries into the alveoli. These lar­vae crawl up the bronchioles, epiglottis and are swal­lowed. In the intestine, they develop into adult worms, the female is fertilised and lays both fertilised (Fig. 47.78) and unfertilized (Fig. 47.79) eggs.

Clinical features:

The most common symptoms are vague abdominal discomfort, acute colicky pain in the epigastric region, poor digestion, diarrhoea and fever. The wandering worms may cause symptoms like acute appendicitis, gastric or duodenal trauma, esophageal perforation, severe involvement of the genitourinary tract of males and females; and inva­sion of the heart. Moreover, the larvae which migrate through the capillaries of the brain and eyeball may produce symptoms of meningitis, epilepsy, retinitis and palpebral edema visceral larva migrants.

Laboratory diagnosis:

(a) Detection of adult worm in stool or vomit,

(b) Demonstration of charac­teristic egg in the stool,

(c) The ‘Scratch’ test or skin test may be found positive and the results are vari­able. Ultrasonography can detect biliary ascariasis.

Treatment:

Piperazine (citrate, phosphate), thia­bendazole, albendazole and mebendazole are very effective.

Prophylaxis:

Proper disposal of human excreta, treatment of infected individuals, educating children about sanitation and hygiene and avoidance of raw vegetables, food or drink contaminated with the fae­ces of infected persons.