Lec.1 Prof.Dr.Abdulsalam Al-Mukhtar Medically important Cestodes (Tapeworms) of human beings

Scientific nameCommon name Echinococcus granulosusDog tapeworm, Hydatid tapeworm Taenia saginataBeef tapeworm Taenia solium Pork tapeworm Diphyllobothrium latum Broad fish tapeworm Hymenolepis nana Dwarf tapeworm

Morphology of adult worm :( 2-7 mm long). The body consist the head (scolex with 4 suckers and hooks ) and three segments (proglottids). Immature, mature and gravid segments.

The mature segment contain fully developed male and female sexual organs. The gravid segment contain only uterus full with eggs.

Hydatid disease (hydatidosis) Is caused by the larval stages (hydatid cyst) of dogs tapeworm called Echinococcus granulosus.

Morphology of the eggs 1- Spherical,35-45um in diameter. 2- Hexacanth Embryo centrally located. 3- Radially staited shell. 4- Infective to human, sheep & cattle. 5- Diagnostic stage to infected dogs 6- Thousands of worms may present in small intestine of dogs and can produce thousands of eggs.

Life cycle The adult Echinococcus granulosus inhabit the upper part of small intestine of the definitive hosts, dogs or other canids( cats, foxes and wolves). Gravid proglottids release eggs that are passed in the feces as a diognostic stage for infected dogs. These eggs are infective stage to a suitable intermediate host (sheep, goat, cattle and man).

After ingestion, the eggs hatches in small intestine and releases an oncospher (emberyo) that penetrates the intestinal wall and migrates through the circulatory system into various organs, especially the liver and lungs. In these organs, the oncosphere develops into a hydatid cyst that enlarges gradually, producing protoscolicis incide the cyst.

The dogs ( definitive host )and other canids becomes infected by ingesting the H. cyst- containing organs of the infected intermediate host. After ingestion, the scolex evaginate, attach to the intestinal mucosa, and develop into adult stages in 30 to 80 days.

Hydatid cyst (larval stage) 1. Diagnostic larval stage developed in tissues of humans, sheep or cattle's. 2. The size of H.cyst depend on the tissues infected. 3. H.cyst either sterile contain only fluid (non- infective), without scolecis or fertile contain large number of scolecis (infective).

Types of hydatid cysts (Unilocular & Osseous) Unilocular type: The majority of human H. cysts are unilocular type.It may reach 15 cm or more in diameter after 10 to 20 Years of age. Morphologically consist of three layers with central fluid contain protoscolices (invaginated scolecis called Hydatid sand).

Unilocular H cyst of the liver in human being

The layers are: 1- Inner thin germinal layer. 2- Cyst wall (non-nucleated). 3- Outer host- tissue capsule.

The osseous H. cyst : developed in bone when hexacanth embryo filtered out of the blood vessels in bony tissues in this case laminated layers will developed & the cyst grow as a protoplasmic material erodes the structure of bones.

Hydatid cyst

Hydatid Sand

Osseous H. cyst : It developed in bone when hexacanth embryo filtered out of the blood vessels in bony tissues in this case laminated layers will developed & the cyst grow as a protoplasmic material erodes the structure of bones.

Epidemiology Distrebution 1.Worldwide in its distribution. 2.Rural infection more than urban aeas because sheep raising areas.

3.Transmission of infection frequently occurs when dogs living in close to human and fed the infected viscera of home- slaughtered animals. 4.Contaminated water or vegetables with infec feces.

5.Direct infection through fecal-oral contact ( especially in children ). 6.Transmission occur also mechanically via arthropods.

Pathogenesis and Symptomatology 1. Disease called H. Cyst, Hydatid disease,Hydatosis. 2. The severity of the disease vary according to location of the cyst in tissues affected. 3. No symptoms until the cyst gets large or ruptures during biopsy procedures..

4. Hepatic H.cyst Liver affected in about two third of patients and approximately 70% right lobe is affected. Usually no symptoms until the cyst reach 10 cm in diameter, hepatomegaly, nausea, vomiting.

5. Pulmonary H.cyst Lung affected in about 25%. Rupture of pulmonary H.cyst into bronchules results in coughing, shortness of breath, secondary bacterial infection, plural effusion may developed. 6. H. cyst of brain Brain occasionally infected, produce increasing symptomatic evidence of an intracranial tumors.

7.Osseous H.cyst Bones occasionally infected and the cyst is gradually erroding the bone to a stage where fracture or crumbling suddenly occurs. 8. Other organs, muscle, Kidney, heart and pancrease in small proportion or occasionally infected. 9.Rupture of abdominal H.C will cause anaphylactic shock, Scolecis will produce multiple secondary H.cyst.

Diagnosis 1. History of patients in endemic areas. 2. X-ray picture, detection of the cyst mass in organ. 3. Ultrasound scan. 4. MRI & CT scan. 5. Biopsy not recommended before operation, but is essential to confirm the diagnosis after surgical operation.

6. Serology tests E.g.: Indect hemagglutination (IHA). Indirect immunofluescence. Casoni skin test. Latex agglutination test. Enzyme-linked immunosrbent assay (ELISA). Polymerase chain reaction (PCR).

Treatment 1. Surgical operation to remove the cyst is the only option for the treatment. 2. Mebendazol or albendazol given to reduce the risk of secondary hydatidosis, it also given for 60 days on 200mg dose duration to reduce the size of the cyst. Before the surgical interference.

. Prevention &control 1. Avoiding close contact with dogs. 2. Careful washing of the vegetable with runing water. 3. Preventing home-slaughter of sheep will prevent dogs from consuming infected viscera.