Helminthiasis

COMMON HELMINTHIASIS

GENERAL FEATURES The helminths are worm-like

parasites Outer protective

covering-cuticle/integument Locomotion-muscular contraction &

relaxation. Donot possess true coelomic cavity. Eggs or larvae produced in enormous

numbers. Inability to multiply in the body of

the host.

CLASSIFICATIONBased on external and internal

morphology of egg, larval, and adult stages & the host organ they inhabit

1)Nemathelminthes -Cylindrical worms- a)NEMATODES .. Eg: ascaris, ancylostoma, trichuris,

strongyloides, enterobius, filariasis, dracunculus.2) Platyhelminthes-Flat worms. a)Leaf-like TREMATODES or Flukes. Eg.Blood flukes(schistosomiasis),

fasciola, clonorchis, paragonimus,. b)Tape-like CESTODES or Tape worms.

Eg.Taenia,echinococcus,diphyllobothrium…

NEMATODES

Most worm-like of all helminths, mostly free living forms found in soil.

Elongated,cylindrical ,unsegmented worms with tapering ends.

Sexes separate. Produce eggs(oviparous),

larvae(viviparous) or lay eggs containing larvae(ovoviviparous).

Life cycle has 4 larval stages & the adult form.

Site of inhabitationINTESTINAL NEMATODES: Small intestine: Ascaris , strongyloides,

necator , ancylostoma Cecum: Enterobius Large intestine: Trichuris

NON TISSUE NEMATODES:Brugia malayi, B.timori, Wuchereria

bancroftiLoa Loa, Onchocerca volvulusToxocara canis, Trichinella spiralis,

Dracunculus

Pathogenesis :

Roundworms deprive host of nutrients

Hookworms suck 0.03-0.15ml of blood per worm

Roundworms cause intestinal obstruction

Hydatid cyst may form large masses in liver,lung or other viscera

Cysticerci may lodge in various parts including brain

Hypersensitivity reaction

Ascaris lumbricoides

Largest nematode parasite in the human intestine.

The adults are cylindrical in shape, creamy-white or pinkish in color. The female averages 20-35cm in length.The male is smaller, averaging 15-31cm .

The typical curled tail with a pair sickle like copulatory spines. On the tip of the head there are three lips, arranged as a Chinese word “ 品 ” .

The lips of Ascaris lumbricoides

The mouth at the anterior end has three finely denticulated lips one dorsal & two ventrolateral.

Fertilized Ascaris Egg• Embryonated infective eggs enclosed in a stout translucent shell with 3 layers.

(thick mamillated covering)

• In the middle is a large unsegmented ovum, containing a mass of lecithin granules.

Unfertilized egg

Non embryonated ,non infective eggs.Longer & elliptical with thinner shell.

Decorticated eggs: Both fertilized and unfertilized eggs sometimes may lack their outer albuminous coats and are colorless

LIFE CYCLE

Adult worms live in the lumen of the small intestine.  A female may produce approximately 200,000 eggs per day, which are passed with the feces . 

 Fertile eggs embryonate and become infective , depending on the environmental conditions (optimum: moist, warm, shaded soil).  After infective eggs are swallowed , the larvae hatch , invade the intestinal mucosa portal, systemic circulation lungs penetrate the alveolar walls ascend the bronchial tree to the throat, and are swallowed .  

Upon reaching the small intestine, they develop into adult worms .  Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female.  Adult worms can live 1 to 2 years.

Pathogenesis & clinical features.

The blood-lung migration phase of the larvae:

Allergic reaction-infiltration with eosinophils, macrophages & epithelioid cells Ascaris pneumonialow grade fever,dry cough,asthmatic wheezing, urticaria, eosinophilia, mottled lung infiltration in CXR-Loeffler ‘ s syndrome.

The intestinal phase of the adults

Usually produces no symptoms, but may give rise to vague abdominal pains or intermittent colic.

A heavy worm burden can result in malnutrition.

Wandering adults may block the appendical lumen or the common bile duct and perforate the intestinal wall. Thus complications of ascariasis, such as intestinal obstruction, appendicitis, biliary ascariasis, perforation of the intestine, cholecystitis, pancreatitis and peritonitis, etc., may occur.

DIAGNOSIS

Ascaris pneumonitisdemonstarting larvae in gastric washings /sputum, eosinophilia.charcoat leyden crystals in sputum.

Most imp. Methoddemonstration of eggs in faeces.

TREATMENT:Albendazole 400mg /200mg(below 2yrs) stat.Mebendazole :100mg BD x 3 days /500mg stat.Pyrantel palmoate:11mg/kg.Piperazine citrate (intestinal

obstruction),paralyses myoneural jn of worms,antagonist of pyrantel palmoate.

HOOK WORM

One of the most important of the infections in the developing world.

At least two species of hookworms infect man, Necator americanus and Ancylostoma duodenale.

Adult worms live in small intestine.

1. Adults: They look like an odd piece thread and are about 1cm. They are white or light pinkish when living. ♀is slightly larger than ♂.

2. Ancylostoma – buccal teeth

Necator – cutting plates

3. Eggs: 60×40 µm in size, oval in shape, shell is thin and colorless. Content is 2-8cells.

I.   Morphology

Eggs are passed in the stool , and under favorable conditions , larvae hatch in 1 to 2 days.  The released rhabditiform larvae grow in the feces and/or the soil , and after 5 to 10 days (and two molts) they become filariform (third-stage) larvae that are infective .  These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. 

On contact with the human host, the larvae penetrate the skin blood vessels to the heartlungs(penetrate into the pulmonary alveoli)bronchial tree pharynxreach the small intestine, where they reside and mature into adults. They attach to the intestinal wall with resultant blood loss by the host . 

Pathogenesis and Clinical Manifestations Larval migration (1) Dermatitis, known as "ground

itch" .The larvae penetrating the skin cause allergic reaction, petechiae 0r papule with itching and burning sensation. Scratching leads to secondary infection.

(2) pneumonitis (allergic reaction), Loeffier's syndrome: cough, asthma, low fever, blood-tinged sputum or hemoptysis, chest-pain, inflammation shadows in lungs under X-ray. These manifestations go on about 2 weeks.

Adults in small intestine (1)Acute intestinal phase has

abdominal pain, diarrhoea, nausea & anorexia. Major source of injury to host is loss of blood.

(2)A large worm burden results in microcytic hypochromatic anemia.

(3)Pica is due to the lack of trace element iron .

(4)Deficits in physical & intellectual growth.

(5) Children may develop yellow green pallor known as chlorosis.

Diagnosis & treatment

Identification of characteristic eggs . Rx: albendazole/mebendaole/pyrantel

pamoate. Iron supplementation & transfusion. Prevention: Proper disposal of excreta. Wearing shoes?? As N .americanus

enters through upper extremities,torso & A.duodenale is orally infective too..

Enterobius vermicularis-pin worm

The pinworms are one of the most common intestinal nematodes.

The adult worms inhabit the cecum and colon. Right after mating, the male dies.

Therefore, the male worms are rarely seen. The female worms migrate out the anus depositing eggs on the perianal skin. Humans get this infection by ingesion of infective eggs picked up on perianal skin, in the air ,bedclothes, undergarments.

EggEgg: 50 to 60 by 25

µm, colorless and transparent, thick and asymmetric shell, content is a larva.

Anal smear showing large numbers of Enterobius eggs under the lower power. In the background are also two Ascaris eggs.

Life Cycle

1. site of inhabitation: cecum and colon

2. infective stage: embryonated egg

3.  infective route: by mouth

4. without intermediate host and reservoir host

5. life span of female adults: 1-2 months

SymptomsAbout one-third of pinworm-infected

persons are asymptomatic, The adult worms may cause slight irritation of the intestinal mucosa.

Major symptom is anal pruritus, which associates with the nocturnal migration of the gravid females from the anus and deposition of eggs in the perianal folds of the skin.

Restlessness, nervousness, and irritability, probably resulting from poor sleep .

In young girls, migration of the worms may produce vaginitis and salpingitis or granuloma of the peritoneal cavity.

Adult Pinworms on the perianal skin

Diagnosis

Diagnosis depends on recovery of the

characteristic eggs.

The eggs and the female adults can be

removed from the folds of the skin in

the perianal regions by the use of the

cellophane tape method. The

examination should be made in the

morning, before the patient has

washed or defecated

Treatment and prevention

The major problem is reinfection. Single dose therapy with

mebendazole(100mg),albendazole(400mg) or pyrantelpamoate

is effective. Repeated retreatment may be

necessary for a radical cure. Prevention: 1. treat the patients and

carriers 2. individual health 3. public health 4. health education and

hygienic habits

LYMPHATIC FILARIASISLargest no: of cases occur in India Estimated 100 million infections world

wide. W.Bancrofti -vector(culex

quinquefasciatus) B.malayi-Vector(mansonia spp) B.timori-vector(anopheles barbirostris) In India, 99.4% of the cases are caused by the

species - Wuchereria bancrofti whereas Brugia malayi is responsible for 0.6% of the problem.

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Adults of Wuchereria bancrofti are long and threadlike.  The males measure up to 40 mm long and females are 80-100 mm long.  Adults are found primarily in lymphatic vessels, less commonly in blood vessels.

The microfilaria of Wuchereria bancrofti are sheathed and measure 240-250 µm in stained blood smears .  They have a gently curved body, and a tail that is tapered to a point.  The nuclear column (the cells that constitute the body of the microfilaria) is loosely packed; the cells can be visualized individually and do not extend to the tip of the tail. 

Microfilariae of Brugia malayi are sheathed and in stained blood smears measure 175-230 µm.  The tail is tapered, with a significant gap between the terminal and subterminal nuclei.

Pathophysiology

By the adult parasite, host response & bacterial superinfection of tissues with compromised lymphatic function.

Adult worms induce lymphatic dilation that results in lymphatic dysfunction, lymphedema & susceptibility to bacterial infection.

Microfilaremia often asymptomatic but may be associated with immmune complex nephritis ,tropical pulmonary eosinophilia syn.

Clinical features 1/3rd of children living in endemic areas

infected before 5 years of age. Repeated exposure acute adenolymphangitis

with fever (filarial fever) .They reflect either inflammatory response to dying parasites with retrograde lymphangitis or bacterial superinfection.

Progression to lymphedema is uncommon until puberty.

Recurrent eosinophilic pneumonitis associated with wheezing ,cough,pulmonary infiltrations & hypeosinophilia( tropical pulmonary eosinophilia) is an IgE mediated hypersensitivity reaction to microfilaria trapped in lungs,if untreatedinterstitial pneumonitis

Diagnosis

By detecting adult parasites in lymphatics through USG or by recovering microfilaria from blood.

Circadian periodicity of appearance of microfilaria, specimen collected between 10pm & 2 am.

Immunochromatographic card test that measures specific filarial antigen.

Treatment

Antimicrofilarial drug DEC 6mg/kg/day, 12 day course.

Side efffects due to inflammatory response to dying microfilariae symptomatic Rx.

DEC also used in tropical pulmonary eosinophilia.

Other drugs, Ivermectin ,albendazole

TAPEWORM-cestodes.Segmented tape like worms

with size varying from few mm to several metres.Adult worm consists of 3 parts: 1)Head(scolex) carrying

grooved or cup like suckers,2)Neck,immediately behind the

head is the region of growthsegments of body continuuously generated.

3)Trunk,composed of chain of proglottides or segmentsimmature,mature & gravid.

Classification

Giant tapeworms: Taenia saginata, T. Solium and Diphyllobothrium latum

Dwarf tapeworms: Hymenolopsis nana

Zoonotic cestodes: Echinococcus granulosus,

E. multilocularis

Taeniasis/cysticercosis Two distinct life forms in human host,

taeniasis(infection of gut lumen) & cysticercosis( infection of tissues with larval cysticercus form).

It accounts for 10% of acute neurological admissions in endemic areas NEUROCYSTICERCOSIS.

Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata or Taenia solium.  Humans are the only definitive hosts

Length of adult worms is usually 5 m or less for T. saginata (however it may reach up to 25 m) and 2 to 7 m for T. solium.

Eggs or gravid proglottids are passed with feces survive for days to months  Cattle (T. saginata) and pigs (T. solium) become infected by ingesting vegetation contaminated with eggs or gravid proglottids . 

In the animal's intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci.

  Humans become infected by ingesting raw or undercooked infected meat .  In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. 

The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine .   The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day).  The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces

Human infection - taeniasis The scolex attaches to the mucosa and

begins forming segments (proglotids) After two months of infection, gravid

proglotids begin to detach from the distal end - excreted in the feces

Each segment contains 60,000 eggs Worm causes only minor inflammation

to the intestine (mild symptoms - abdominal pain, distension, diarrhea and nausea - or none at all)

Human cysticercosis Larvae of T.solium (cysticercus cellulosae) .

T solium has a complex two-host life cycle. Human beings are the only definitive host and harbour the adult tapeworm (taeniasis), whereas both humans and pigs can act as intermediate hosts and harbour the larvae or Cysticerci(cysticercosis).

Humans infected following 1) ingesion of T. solium eggs in water or

vegetables. 2)autoinfection & infection of close contacts by

finger contamination with eggs from perianal skin or faeces of persons harbouring the adult worms.

Muscle - small, palpable, movable nodules - chests and arms - mild or no symptoms

Ophthalmic cysticercosis - intraocular cysts floating freely in the vitreous humor - decreased visual acuity

Neurocysticercosis - most symptoms are because of the inflammatory reaction associated with cyst degeneration (that may take years to happen) - epilepsy, hydrocephalus, encephalitis, meningitis.

(A): ocular cyst floating in the vitreous humour. (B): calcified cysts on CT(three-dimensional filtered reconstruction). (C) and (D): massive infectioncausing muscular pseudohypertrophia; thousands of cysts following the muscle planes can be seen.

MRI of viable (A) and degenerating (B) cysts, and CT of calcified cysticerci (C).

Diagnosis-Taeniasis By demonstration of eggs, proglottides in stool.

Mature proglottid of T. saginata, stained with carmine. Note the number of primary uterine branches (>12).

Mature proglottid of T. solium, stained with carmine.  Note the number of primary uterine branches (<13).

Egg containing oncosphere-(six hooked hexacanth embryo)

Diagnosis - cysticercosis Depends on the targeted organ:

CNS - CSF immunology, neuroimaging (CT/MRI)

Viable cystecerci appear as rounded fluid collections,1-2cm in diameter.

Inflammed cysticerci has perilesional edema,contrast enhancement.

DD:Tuberculoma,brain abscess,tumours.Muscle - imaging, bx->microscopic

examination(invaginated scolex with suckers & hooks)

Eye - imaging (ultrasound)(serological exam - ELISA)

Treatment - taeniasis Niclosamide Adult(total 2g),children 2-6yrs,1 g. Niclosamide acts by inhibiting oxidative

phosphorylation in mitochondriaATP depletioninjured tape worms partly digested.

Praziquantel(10mg/kg)kills tape worm larvae.

Acts by leakage of intracellular calcium from membranes.

Treatment - cysticercosis

The problem of the cyst is the inflammatory reaction

Use of antiparasitic agent(albendazole 15mg/kg/day BD x 28 days)

plus simultaneous course of corticosteroids & antiepileptics.

ANTI-HELMINTHIC DRUGS

Either kill(vermicide) or expel (vermifuge) infesting helminths.

MEBENDAZOLE: Benzimidazole. Acts by blocking glucose uptake in the

parasite & depletion of glycogen stores. Site of action is microtubular

protein( beta tubulin ) of parasiteinhibits polymerisation.

Minimal absorption from intestine.

Adverse effects: Diarrhoea,nausea,vomiting when

used in heavy infestation. With higher doses; allergic

reactions,loss of hair,granulocytopenia.

Dose: Round worm,hook

worm,trichuris:100mg BD x 3 days. Enterobius:100mg single

dose,repeated after 2-3 weeks.

Albendazole Congener of mebendazole with

advantage of single dose administration in many cases

Ascaris,hookworm,enterobius,trichuris.

Also in trichinosis,neurocysticercosis,hydatid disease,filariasis.

Absorption after oral administration is moderate but inconsistent.

Sulfoxide metabolite activeagainst tissue helminths.

Adverse effects: Usualy well tolerated,only GI side

effects. Few had dizziness. Prolonged use headache,

fever,alopecia, jaundice,neutropenia.

Pyrantel palmoate

Introduced in 1969 for thread worm infestation.

Efficacy against ascaris, enterobius, ancylostoma is high, comparable to mebendazole.

Causes activation of nicotinic cholinergic receptors in wormspersistent depolarisationspastic paralysis.

Remarkably free of side effects,taste less,non irritant, abnormal migration of worms is not provoked.

DEC(Diethyl carbamazine citrate) Highly selective effect on microfilariae. Alteration of Mf membrane so that they are

readily phagocytosed by tissue monocytes. Also has effect on muscular activity of Mf &

adult worms causing hyperpolerisation, hence they are dislodged.

Uses: Filariasis:2mg/kg TDS ,Mf disappear from

blood in 7 days,radical cure by 12 days-3 weeks

Tropical eosinophilia: 2-4mg/kg TDS for 2-3 weeks.

Adverse effects: Nausea,loss oof appetite,dizziness. Febrile reaction with

rash,pruritis,enlargement of lymphnodes & fall in BP may occur due to mass destruction of Mf & adult worms.