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 • 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 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. 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. 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 .