Introduction to Microbiology

1. Introduction to Microbiology Anas Abu-Humaidan M.D. Ph.D. Lecture 25

2. Helminths الديدان الطفيلية/Parasitic worms • Helminths are parasitic worms which share a similar form ,they are large multicellular organisms; adults can generally be seen with the naked eye. • Helminthiasis, is the disease caused by these organisms. • Anthelminthic medications (drugs that rid the body of parasitic worms), such as albendazole and mebendazole, are the drugs of choice for treatment. • Soil-transmitted helminths and tapeworms will be discussed in this course. Those are intestinal worms infecting humans that are transmitted through contaminated soil and undercooked meat and include: • Ascaris lumbricoides (sometimes called just “Ascaris“), • Whipworm (Trichuris trichiura), • Hookworm (Anclostoma duodenale and Necatoramericanus) • Tapeworms

3. Ascaris أَسْكارِس أو ثُعْبَانُ البَطْنِ • An estimated 807 million–1.2 billion people in the world are infected with Ascaris • Ascaris parasites live in the intestine and Ascaris eggs are passed in the feces of infected people • Infection occurs worldwide in warm and humid climates, where sanitation and hygiene are poor

4. Ascaris • Infection occurs by eating food or drink contaminated with Ascaris eggs from feces. The eggs hatch in the intestines, burrow through the gut wall, and migrate to the lungs via the blood. There they break into the alveoli and pass up the trachea, where they are coughed up and may be swallowed. • The larvae then pass through the stomach for a second time into the intestine, where they become adult worms.

5. Ascaris • 85% of people infected with Ascaris often show no symptoms. • If symptoms do occur they can be light and include abdominal discomfort. Heavy infections can cause intestinal blockage and impair growth in children. • Stool samples are used to look for the presence of eggs under the microscope. • Infection is prevented by Avoiding contact with soil that may be contaminated with human feces, and proper hand washing. The larva of Ascaris developing in egg

6. Whipworm الدودة السوطية • An estimated 604-795 million people in the world are infected with whipworm. • Whipworms live in the intestine and whipworm eggs are passed in the feces of infected persons.

7. Whipworm • Infection occurs by eating food or drink contaminated with eggs from feces. the eggs hatch in the small intestine, and release larvae that mature and establish themselves as adults in the colon • The adult worms (approximately 4 cm in length) live in the cecum and ascending colon. The adult worms are fixed in that location. • Female worms in the cecum shed between 3,000 and 20,000 eggs per day. The life span of the adults is about 1 year.

8. Whipworm • People with light infections usually have no symptoms. • People with heavy symptoms can experience frequent, painful passage of stool that contains a mixture of mucus, water, and blood. • Stool samples are used to look for the presence of eggs under the microscope.

9. Hookworms الديدان الخطافية • An estimated 576-740 million people in the world are infected with hookworm. • Hookworms live in the small intestine. Hookworm eggs are passed in the feces of an infected person, Infection of the host is by the larvae, not the eggs. Hookworms attached to intestinal mucosa

10. Hookworms • Eggs are passed in the stool, and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days. • On contact with the human host, the larvae penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. • They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed • The larvae reach the small intestine, where they reside and mature into adults.

11. Hookworms • Usually asymptomatic. But patients may experience Ground-itch, which is an allergic reaction at the site of parasitic penetration and entry • The most serious effects of hookworm infection are the development of anemia and protein deficiency caused by blood loss at the site of the intestinal attachment of the adult worms. • Stool samples are used to look for the presence of eggs under the microscope. • The disease can be prevented on an individual level by not walking barefoot in areas where the disease is common

12. Tapeworms الديدان الشريطية • Taeniasis in humans is a parasitic infection caused by the tapeworm species Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm) and occurs world wide. • Cestodes are exclusively hermaphrodites, with both male and female reproductive systems in each body • The tapeworm body is composed of a series of segments called proglottids • The scolex, attaches to the intestine of the definitive host (humans)

13. Tapeworms • Cattle (T. saginata) and pigs (T. solium) become infected by ingesting vegetation contaminated with eggs • Humans become infected by ingesting raw or undercooked infected meat • In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. • Adult worms produce segments and eggs that are passed in feces.

14. Tapeworms • There may be few or no symptoms, and the first indication of the infection may be the presence of one or more proglottids (appear as whitish objects the size of a grain of rice) in the stools. • Tapeworms can cause digestive problems including abdominal pain, loss of appetite, weight loss, and upset stomach. • Cysticercosis is a dangerous complication of pig worm Taenia solium. • Cysticercosis is caused by larval cysts of the tapeworm Taenia solium. These larval cysts infect brain, muscle, or other tissue Dog feces containing proglottids

15. Further reading: • Sherris Medical Microbiology, sixth edition • Chapter 54-57