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Geohelminths.pdf

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Geohelminths.pdf

  1. 1. Geohelminthes Lecture 10 Dr. Harriet Angwech Gulu University
  2. 2. Introduction  Soil-transmitted helminths refer to the intestinal worms infecting humans that are transmitted through contaminated soil.  Soil-transmitted helminthic infections are of two types: Ø The hookworms, which undergo a cycle of development in the soil; the larvae being infective and; Ø A group of nematodes which survive in the soil merely as eggs.
  3. 3. Introduction  More than one billion people are infected with at least one species.  Recent estimates suggest that:  A. lumbricoides infects 1.221 million,  T. trichiura 795 million, and  hookworms 740 million people.  85% of infected people in the world are estimated to be in sub-Saharan Africa. Continued
  4. 4. Transmission Ø Soil-transmitted helminths are transmitted by eggs that are passed in the faeces of infected people. Ø Adult worms live in the intestine where they produce thousands of eggs each day.
  5. 5. Transmission cont’d Ø In areas that lack adequate sanitation, eggs contaminate the soil. Ø Transmission can happen in several ways: Ø eggs that are attached to vegetables are ingested when the vegetables are not carefully cooked, washed or peeled; Ø eggs are ingested from contaminated water sources; Ø eggs are ingested by children who play in soil and then put their hands in their mouths without washing them.
  6. 6. Transmission Ø Hookworm eggs hatch in the soil, releasing larvae that mature into a form that can actively penetrate the skin. Ø Infection with hookworms occur primarily by walking barefoot on the contaminated soil. Continued
  7. 7. Transmission Ø There is no direct person-to-person transmission, or infection from fresh faeces, Ø because eggs passed in faeces need about 3 weeks to mature in the soil before they become infective. Ø Since these worms do not multiply in the human host, re-infection occurs only as a result of contact with infective stages in the environment. Continued
  8. 8. Transmission cycle  Adult Necator and Ancylostoma : the upper part of small intestine.  Ascaris (roundworms): parasites of the entire small intestine.  Adult Trichuris (whipworms): large intestine, especially the caecum.
  9. 9. Transmission cycle cont’d  Man - only major definitive host for these parasites, although Ascaris infections can also be acquired from pigs.  After mating, each adult female produces thousands of eggs per day, which leave the body in the faeces.
  10. 10. Transmission cycle cont’d  People become infected with T. trichiura and A. lumbricoides by ingesting the fully developed (embryonated)eggs.  The released larvae of T. trichiura moult and travel to the colon where;  they burrow into the epithelia and develop into adult whipworms within 12 weeks.
  11. 11. Transmission cycle cont’d  Ascaris larvae penetrate the intestinal mucosa and enter the liver, the lungs, before passing over the epiglottis to re-enter the gastrointestinal tract and develop into egg-laying adult worms.  This takes about 9-11 weeks after egg ingestion.
  12. 12. Transmission cycle cont’d  N. americanus and A. duodenale (hookworm) eggs hatch in soil.  The larvae moult twice to become infective third-stage larvae, which are non-feeding but motile organisms.  After skin penetration, they enter the blood stream and ultimately the larvae become trapped in pulmonary capillaries, enter the lungs, pass over the epiglottis, and migrate into the gastrointestinal tract.  About 5-9 weeks -from skin penetration to development of egg-laying adults.
  13. 13. Transmission cycle cont’d  A. duodenale larvae are also orally infective.  Eggs are thus released together with faecal material in to the soil hence completing the cycle.
  14. 14. Epidemiology of geohelminth infections  The geographical distribution of the hookworms is limited by the requirements of the developing larvae for:  warmth and  humidity.  Generally speaking, they can occur not only in the tropics and subtropics, but also in temperate regions.
  15. 15. Epidemiology of geohelminth infections  In tropical and subtropical areas, wet soil (such as that found at the edges of rice fields, rubber plantations and the surroundings of villages in areas of high rainfall)  supports the maturation of hookworm larvae from eggs, deposited by indiscriminate defaecation.  In contrast, the well-protected eggs of Ascaris lumbricoides and Trichuris trichiura) can survive in drier conditions. Continued
  16. 16. Ø Equally important risk factors are: Ø poverty, Ø inadequate water supplies and Ø sanitation. Ø All these helminthiases provide an index of the level of personal hygiene and sanitation in a community, Epidemiology of geohelminthes infections Continued
  17. 17. Epidemiology of geohelminthes infections Ø Since they depend for their dispersal on: Ø the indiscriminate deposition of faecal material, Ø the use of untreated night soil as an agricultural fertilizer and similar unsophisticated human habits, Ø The provision of adequate sewage disposal facilities virtually excludes these diseases. Continued
  18. 18. Ø Faecal contaminated soil in the neighbourhood of human habitations or on farmland is the source of hookworm infection for the barefoot inhabitants. Ø Conversely, the use of footwear greatly reduces the prevalence of Necator americanus infection, but not necessarily that of Ancylostoma duodenale infection. Epidemiology of geohelminthes infections Continued
  19. 19. Prevention Ø Improved water supply and sanitation Ø Deworming Ø Mebendazole and albendazole are used for large- scale prevention of morbidity in children living in endemic areas Ø Diagnosis : Ø Stool examination Ø Serology.
  20. 20. Fertilized Ascaris Egg A fertilized Ascaris egg, still at the unicellular stage, as they are when passed in stool.
  21. 21. Unfertilized egg The chitinous layer and albuminous coat a r e thinner than those of the fertilized eggs without ascaroside and fertilizing membrane. The content is made of many refractable granules of variable sizes.
  22. 22. Some pictures
  23. 23. Some pictures n Trichuris trichuria - These have opercular plugs at either end of the egg shell. Hookworm Egg Typical nematode egg
  24. 24. Pathogenesis Symptoms associated with larval migration Ø Migration of larvae in lungs may cause hemorrhagic/ eosinophilic pneumonia, cough (Loeffler's Syndrome) Ø Breathing difficulties and fever Ø Complications caused by parasite proteins that are highly allergenic - asthmatic attacks, pulmonary infiltration and urticaria
  25. 25. Pathogenesis Cont. Symptoms associated with adult parasites in the intestine Ø Usually asymptomatic Ø Abdominal discomfort, nausea in mild cases Ø Malnutrition in host especially children in severe cases Ø Sometimes fatality may occur when mass of worm blocks the intestine

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