Parasitology/Helminths

1.Nematodes

Helminths

• all helminths are relatively large (> 1 mm long);

• some are very large (> 1 m long).

• all have well-developed organ systems and most are active feeders.

• the body is either flattened and covered with plasma membrane (flatworms)

• or cylindrical and covered with cuticle (roundworms).

• some helminths are hermaphrodites;

• others have separate sexes.

Helminths

• Helminths are worldwide in distribution; infection is most common and most serious in poor countries.

• The distribution of these diseases is determined by climate, hygiene, diet, and exposure to vectors.

• The mode of transmission varies with the type of worm; – ingestion of eggs or larvae,

– penetration by larvae,

– bite of vectors,

– ingestion of stages in the meat of intermediate hosts.

Worms are often long-lived.

Helminths

• Helminth is a general term for a parasitic worm.

• The helminths include

– the Platyhelminthes or flatworms (flukes and tapeworms)

– the Nematoda or roundworms

Nemathodes (roundworms)

• nematodes are cylindrical rather than flattened

• the body wall is composed of – an outer cuticle that has a noncellular, chemically complex structure,

– a thin hypodermis,

– musculature.

• The cuticle in some species has longitudinal ridges called alae.

• The bursa, a flaplike extension of the cuticle on the posterior end of some species of male nematodes, is used to grasp the female during copulation.

Nematodes

• Ascaris lumbricoides

• Dracunculus medinensis

• Enterobius vermicularis

• Wuchereria bacrofti

• Ancylostoma duodenale

• Necator americanus

• Toxocara spp.

• Loa loa

• Strongyloides stercoralis

• Trichinella spiralis

• Trichuris trichiura

• Nematodes are usually bisexual.

• Males are usually smaller than females,

• a curved posterior end, and possess (in some species) copulatory structures, such as spicules (usually two), a bursa, or both.

• The males have one or (in a few cases) two testes, which lie at the free end of a convoluted or recurved tube leading into a seminal vesicle and eventually into the cloaca.

Ascariasis

• Ascaris lumbricoides

• largest nematode (roundworm) parasitizing the human intestine

• adult females: 20 to 35 cm

• adult male: 15 to 30 cm

• Size is expressed in cm!!!!

Symptoms

• High worm burdens may cause abdominal pain and intestinal obstruction.

• Migrating adult worms may cause symptomatic occlusion of the biliary tract or oral expulsion.

• During the lung phase of larval migration, pulmonary symptoms can occur

– cough

– dyspnea,

– hemoptysis,

– eosinophilic pneumonitis - Loeffler’s syndrome

Treatment

• albendazole,

• mebendazole,

• pyrantel pamoate

• The most effective method to control ascariasis, as well as other soil-transmitted helminthiasis, is sanitary disposal of feces.

• Care must be taken in treating mixed helminthic infections involving

A lumbricoides, because an ineffective ascaricide may stimulate the parasite to

migrate to another location. Persons in whom asymptomatic ascariasis is

detected incidentally should be treated to prevent the possibility of a future

abnormal migration of these large worms into extraintestinal sites.

Drancunculus medinensis

• Dracunculiasis (guinea worm disease)

• isolated areas in a narrow belt of African countries

• Humans become infected:– by drinking unfiltered water containing copepods (small

crustaceans) which are infected with larvae of D. medinensis

• Following ingestion, the copepods die and release the larvae, which penetrate the host stomach and intestinal wall and enter the abdominal cavity and retroperitoneal space.

• After maturation into adults and copulation, the male worms die and the females (length: 70 to 120 cm) migrate in the subcutaneous tissues towards the skin surface.

• approximately one year after infection, the female worm induces a blister on the skin, generally on the distal lower extremity, which ruptures.

• when this lesion comes into contact with water, a contact that the patient seeks to relieve the local discomfort, the female worm emerges and releases larvae.

• The larvae are ingested by a copepod and after two weeks (and two molts) have developed into infective larvae.

Treatment

• local cleansing of the lesion

• local application of antibiotics because of bacterial superinfection.

• mechanical, progressive extraction of the worm over a period of several days.

• no curative antihelminthic treatment available

• winding the protruding worm on a stick

• because the worm protrudes only a few centimeters per exposure to water, this procedure takes, on average, three months to completely remove the worm.

Enterobius vermicularis

• Enterobius vermicularis (previously Oxyuris vermicularis)

• pinworm infection

• adult females: 8 to 13 mm,

• adult male: 2 to 5 mm

• more frequent in school- or preschool- children and

in crowded conditions

• Eggs are deposited on perianal folds.

• Self-infection occurs by transferring infective eggs tothe mouth with hands that have scratched the perianalarea.

• Person-to-person transmission can also occur throughhandling of contaminated clothes or bed linens.

• Enterobiasis may also be acquired through surfaces inthe environment that are contaminated with pinwormeggs (e.g., curtains, carpeting).

• Some small number of eggs may become airborne andinhaled. These would be swallowed and follow thesame development as ingested eggs.

Symptoms• perianal pruritus (itching), especially at night,

• invasion of the female genital tract with vulvovaginitis , pelvic or peritoneal granulomas

• anorexia, irritability, and abdominal pain.

• The most common symptom is pruritus, which disturbs sleep and which, in children, may be responsible for loss of appetite. abdominal pain, irritability, and pallor (paleness)

• a cause of appendicitis,

• female worms migrate up the vagina and fallopian tubes and into the peritoneal cavity, where they become encapsulated with granulomatous tissue.

• Recurrent urinary tract infections have been attributed to ectopic pinworm infections.

Diagnosis• "Scotch test", cellulose-tape slide test

• Eggs can also be found in the stool,

• encountered in the urine or vaginal smears.

• found in the perianal area, or during ano-rectal or vaginal examinations.

Treatment

• pyrantel pamoate

• advisable to re-treat the patient one month later.

Medical Microbiology

• Patrick R Murray

• Ken S Rosenthal

• Michael A Pfaller

• 2002-2005-…2009-2013