1.Nematodes. Parasitology/Helminths

Transcription

1 1.Nematodes Parasitology/Helminths

2 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.

3 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.

4 Helminths Helminth is a general term for a parasitic worm. The helminths include the Platyhelminthes or flatworms (flukes and tapeworms) the Nematoda or roundworms

5 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.

6 Nematodes Ascaris lumbricoides Dracunculus medinensis Enterobius vermicularis Wuchereria bacrofti Ancylostoma duodenale Toxocara spp. Loa loa Strongyloides stercoralis Trichinella spiralis Trichuris trichiura

7 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.

8 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!!!!

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10 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

11 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.

12 Drancunculus medinensis Dracunculiasis (guinea worm disease) isolated areas in a narrow belt of African countries

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14 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.

15 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.

16 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.

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18 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

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20 Eggs are deposited on perianal folds. Self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perianal area. Person-to-person transmission can also occur through handling of contaminated clothes or bed linens. Enterobiasis may also be acquired through surfaces in the environment that are contaminated with pinworm eggs (e.g., curtains, carpeting). Some small number of eggs may become airborne and inhaled. These would be swallowed and follow the same development as ingested eggs.

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22 Symptoms perianal pruritus, 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 ani, which disturbs sleep and which, in children, may be responsible for loss of appetite. abdominal pain, irritability, and pallor 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.

23 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.

24 Treatment pyrantel pamoate advisable to re-treat the patient one month later.

25 Medical Microbiology Patrick R Murray Ken S Rosenthal Michael A Pfaller