1.nematodes - eastern mediterranean university
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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