Lecture 6: Echinococcus granulosus (Hydatid Worm) PDF

Echinococcus granulosus (Hydatid worm) by Dr. Mona Mohamed Fahem Saleh Lecturer of medical parasitology Faculty of medicine Menoufia university  Echinococcus granulosus (Hydatid worm)  Geographical distribution: World...

Echinococcus granulosus (Hydatid worm) by Dr. Mona Mohamed Fahem Saleh Lecturer of medical parasitology Faculty of medicine Menoufia university  Echinococcus granulosus (Hydatid worm)  Geographical distribution: Worldwide  Definitive hosts: Dogs, foxes and wolves  Intermediate host; Man & cattle, pigs, sheep  Morphology:  Adult worms:  Adult size: 3:6mm.  Scolex: golobular with 2 rows of hooks  Strobila formed of 3 segments (immature, mature and gravid).  Egg: similar to taenia egg  Size: 28-40 μm.  Shape: spherical.  Shell: thick on which distinct radial striations reside.  Colour: yellowish brown.  Content: mature i.e., hexacanth embryo with three pairs of hooklets  Life cycle:  Adults live in the small intestine of definitive host (dogs and other canines).  Eggs pass in faeces and swallowed by man, sheep, cattles (I.H)  The onchosphere hatches in the intestine blood and spreads to different organs developing into hydatid cysts.  Hydatid disease (Echinococcosis or Hydatidosis)  Definition: it is a pathological condition where human tissues carry the hydatid cyst (the larval stage of Echinococcus granulosus) where man acts as the intermediate host of the parasite.  Mode of infection:  Ingestion of contaminated food and drinks by Echinococcus granulossus eggs by the following ways:  Ingestion of water or vegetables contaminated by infected dog feces.  Handling infected dogs where the hairs are usually contaminated with eggs  Hydatid cyst:  Size: 1-10 cm.  Shape: Spherical enclosed in a fibrous capsule produced by the host. The wall of the cyst has 2 layers: ,  Outer laminated non-cellular layer.  Inner cellular germinal layer which secretes the laminated layer and produces scolices, brood capsules and daughter cysts  Contents:  (a) Individual scolices (microscopic).  (b) Brood capsules: cysts formed by invagination of the germinal layer from which scolices develop.  (c) Daughter cysts: cysts formed of the 2 layers of the mother cyst, giving rise to scolices, brood capsules and even grand¬daughter cysts.  (d) Hydatid fluid.  (e) Hydatid sand: detached scolices, brood capsules and daughter cysts that fall in the hydatid fluid are called hydatid sand.  Clinical picture:  It depends on the site; size and the number of cysts present in the tissue.  Large sized cysts cause pressure atrophy of the affected organs.  The most common affected organs are Liver (70%) and lung (20%).  Other organs such as brain, bone, spleen, kidney, muscles, heart and eye (10%)  Spontaneous rupture of cysts leads to severe allergic reactions (anaphylactic shock)  Bacterial infection can occur leading to abscess formation.  Diagnosis:  X ray.  Ultrasound.  Scolicices in sputum or urine.  Puncture or aspiration of hydatid fluid.  Eosinophilia.  Serological tests.  PCR.  Intradermal test (Casoni test).  Treatment:  Surgical removal of the cyst.  Albendazole in inoperable cases and after surgery.  Prevention and control:  Health education  Avoid contamination of food with dog faeces  Fly control  Periodic examination and treatment of pet dogs  Infected organs in slatter houses should be destroyed.  Class Nematoda  General characters:  Nematodes are elongated, cylindrical in shape with both the ends pointed. They are unsegmented.  Variable in size, ranging from less than 5 mm (Trichinella and Strongyloides) to as long as one meter (Dracunculus).  Nematodes have separate sexes (male and female), female worms are longer than male worms.  Body wall: Made up of outer layer of tough a cellular cuticle and inner layer of longitudinal muscle.  They have a body cavity.  Nematodes move by contraction of the longitudinal muscles.  Alimentary canal: It is well developed and consists of mouth at the anterior end followed by a muscular and glandular esophagus, intestine and rectum that leads to sub terminal anus at the posterior end. In some species (e.g hookworm) mouth bears the teeth.  Nervous system: It is rudimentary and consists of circular nerve ring (brain).  Excretory system: It is also rudimentary.