The Parasites of Medical Importance

1. The Parasites of Medical Importance Protozoa, Helminths, and Arthropod Vectors Chapter 23

2. Parasitology • the study of eucaryotic parasites, protozoa and helminths • cause 20% of all infectious diseases • less prevalent in industrialized countries

3. Protozoans

4. Protozoa • single-celled, animal-like microbes, usually having some form of motility • life cycles vary • most reproduce by simple asexual cell division of the active feeding cell (trophozoite) • many undergo formation of a cyst • others have a complex life cycle that includes asexual & sexual phases

5. amoebas ciliates flagellates Apicomplexans/sporozoans

6. Entamoeba histolytica • alternates between a large trophozoite, motile by means of pseudopods & a smaller nonmotile cyst • trophozoite has a large nucleus and lacks most other organelles • humans are the primary hosts • Ingested (fecal-oral transmission) • carried by 10% of world population

7. Entamoeba histolytica

8. Entamoeba histolytica cyst • cysts are swallowed & arrive at the small intestine; alkaline pH & digestive juices stimulate cyst to release 4 trophozoites • trophozoites attach, multiply, actively move about & feed • asymptomatic in 90% of patients • ameba may secrete enzymes that dissolve tissues & penetrate deeper layers of the mucosa • causing dysentery, abdominal pain, fever, diarrhea & weight loss

9. Entamoeba histolytica

10. Entamoeba histolytica • life-threatening manifestations are hemorrhage, perforation, appendicitis, & tumorlike growths (amebomas) • may invade liver & lung • severe forms of disease result in 10% fatality rate • effective drugs are iodoquinol, metronidazole, & chloroquine

11. Amebic brain infections • caused by Naegleria fowleri & Acanthamoeba • ordinarily inhabit standing water • primary acute meningoencephalitis is acquired though nasal contact with water or traumatic eye damage. • infiltration of brain is usually fatal

12. Naegleria fowleri Phase-contrast of Naegleria feeding on bacteria. Organism is free-living in fresh water

13. Balantidium coli • an occupant of the intestines of domestic animals such as pigs & cattle • acquired by ingesting cyst-containing food or water • trophozoite erodes intestine & elicits intestinal symptoms • healthy humans are resistant • rarely penetrates intestine or enters blood • treatment – tetracycline, iodoquinol, nitrimidazine or metronidazole

14. Trichomonas • Small, pear-shaped • 4 anterior flagella & an undulating membrane • Exist only in trophozoite form • 3 species infect humans • T. vaginalis • T. tenax • T. hominis

16. Trichomonas vaginalis • causes an STD called trichomoniasis • reservoir is human urogenital tract • 50% of infected are asymptomatic • strict parasite, cannot survive long outside of host • 3 Million new cases a year in U.S., a top STD • female symptoms – foul-smelling, green-to-yellow discharge; vulvitis; cervicitis; urinary frequency & pain • male symptoms – urethritis, thin, milky discharge, occasionally prostate infection • metronidazole

17. Trichomonas tenax • small • resides in oral cavity of 5-10% • only flagellate in oral cavity • not a true pathogen, but an opportunist in lesions of gingivitis & peridontal pockets

18. Trichomonas hominis • a resident of the cecum of a small percentage of humans & great apes • not associated with disease

19. Giardialamblia • pathogenic flagellate • unique symmetrical heart shape • cysts can survive for 2 months in environment • cysts enter duodenum, germinate, & travel to jejunum to feed & multiply • causes giardiasis – diarrhea, abdominal pain • diagnosis is difficult because organism is shed in feces intermittently • Treatment: quinacrine or metronidazole • agent is killed by boiling, ozone, & iodine

20. hemoflagellates • live in blood & tissues of human host • obligate parasites • cause life-threatening and debilitating zoonoses • spread by blood-sucking insects that serve as intermediate hosts • acquired in specific tropical regions • have complicated life cycles & undergo morphological changes • Trypanosoma • Leishmania

21. Trypanosoma • distinguished by their infective stage, trypomastigote is an elongate, spindle-shaped cell with tapered ends, eel-like motility • 2 types of trypanosomiasis • T. brucei – African sleeping sickness • T. cruzi – Chagas disease – endemic to Central and South America

22. Trypanosoma brucei • causes African Sleeping Sickness • spread by tsetse flies • harbored by reservoir mammals • biting of fly inoculates skin with trypanosome, which multiplies in blood & damages spleen, lymph nodes & brain • chronic disease symptoms are sleep disturbances, tremors, paralysis & coma • treatment before neurological involvement melarsoprol, difluormethylornithine

23. Trypanosoma brucei

24. Trypanosoma cruzi • causes Chagas disease • reduviid bug (kissing) bug is the vector • infection occurs when bug feces are inoculated into a cutaneous portal • local lesion, fever, & swelling of lymph nodes, spleen, & liver • heart muscle & large intestine harbor masses of amastigotes • chronic inflammation occurs in the organs (especially heart & brain)

25. Trypanosoma cruzi Heart pathology in Chagas disease

26. Leishmania • Leishmaniasis is a zoonosis transmitted among mammalian hosts by female sand flies that require a blood meal to produce eggs • infected macrophages carry the pathogen into the skin (cutaneousleishmaniasis) & bloodstream (systemic or visceral leishmaniasis), giving rise to fever, enlarged organs & anemia (Kala azar is the most severe & fatal form)

27. Life cycle of Leishmania Disseminated leishmaniasis

28. Apicomplexan parasites • sporozoans • lack locomotor organelles in the mature state • alternate between sexual & asexual phases & between different animal hosts • most form specialized infective bodies that are transmitted by arthropod vectors, food, water, or other means • Plasmodium • Toxoplasma • Cryptosporidium

29. Plasmodium • causes malaria • female Anopheles mosquito is the vector • obligate intracellular sporozoan • 4 species: P. malariae, P. vivax, P. falciparum & P. ovale • 300-500 Million new cases each year • 2 Million deaths each year

30. Plasmodium • infective forms for humans (sporozoites) enter blood with mosquito saliva, penetrate liver cells, multiply, and form hundreds of merozoites, which multiply in & lyse RBCs. • symptoms include episodes of chills-fever-sweating, anemia, and organ enlargement. • therapy is chloroquine, quinine, or primaquine

31. Sexual phase with sporozoite formation in the mosquito) Asexual phase in humans as sporozoite enters Gametocytes produced and ingested by mosquito Liver phase (sporozoites invade & merozoites produced) RBCs infected by merozoites from the liver

32. Plasmodium falciparum infection of RBCs showing ring form

33. Toxoplasma gondii • obligate apicomplexan parasite with extensive distribution • lives naturally in cats that harbor oocysts in the GI tract • acquired by ingesting raw meats or substances contaminated by cat feces • most cases of toxoplasmosis go unnoticed except in fetus & AIDS patients which can suffer brain & heart damage • treatment: pyrimethamine & sulfadiazine

34. Life cycle of Toxoplasma gondii

35. Biopsy showing clusters of intracelluar T. gondii CAT scan of brain showing lesion Toxoplasmosis in an AIDS patient

36. Cryptosporidium Oocysts shed in feces • an intestinal pathogen • infects a variety of animals • exists in tissue & oocyst (passed in feces) phases • 1990s – 370,000 cases in Milwaukee, WI due to contaminated water • causes enteric symptoms • AIDS patients may suffer chronic persistent diarrhea • no real effective drugs

37. Babesia • causes babesiosis • first protozoan found to cause a disease • first protozoan found to be associated with a tick • infection resembles malaria

38. Helminths • adults are large, multicellular animals with specialized tissues & organs • adult worms mate & produce fertilized eggs that hatch into larvae that mature in several stages to adults (the sexes may separate or hermaphroditic) • Hosts • adults live in the definitive host • eggs & larvae may develop in the same host, external environment, or intermediate host • a transport host experiences no parasitic development • pathology arises from worms feeding on & migrating through tissues and accumulation of worms & worm products

39. Nematodes - roundworms • Filamentous with protective cuticles, a complete digestive tract, & separate sexes • Ascaris lumbricoides • Trichuris trichiura (whipworm) • Enterobius vermicularis (pinworm) • Hookworms • Strongyloides stercoralis • Trichinella spiralis • Filarial worms

40. Ascaris lumbricoides • a large (up to a foot long) intestinal roundworm • 1 Billion cases worldwide • Most cases in the US occur in the southeastern states • indigenous to humans • Ascaris spends its larval & adult stages in humans & releases embryonic eggs in feces, which are spread to other humans • ingested eggs hatch into larvae & burrow through the intestine into circulation & travel to the lungs & pharynx & are swallowed. Adult worms complete cycle in intestines.

41. Ascaris lumbricoides

42. Ascaris lumbricoides • worms retain motility, do not attach • severe inflammatory reactions mark the migratory route, • allergic reactions can occur • heavy worm loads can retard physical & mental development

43. Roundworm Zoonoses-1 • Don’t play with the animal feces ! • Don’t eat dirt ! • Dog and Cat Roundworms (toxocariasis) • estimated 10,000 new cases of roundworm infection occur in children every year, most often as a result of eating dirt contaminated with animal feces. • Most human infections are mild enough to go unnoticed and apparently produce no permanent damage……But…. • Visceral Larval Migrans (VLM) • Ocular Larval Migrans (OLM).

44. Roundworm Zoonoses-2 • Raccoon roundworm (Baylisascarisprocyonis) • Raccoons are very common in the urban/suburban environment, and perhaps 80%+ carry the roundworm. • Worm eggs are very hardy, surviving years outdoors. • When ingested by humans the larvae migrate throughout the body. Some enter the brain and death my ensue.

45. Trichuris trichiura • whipworm • humans sole host • trichuriasis has its highest incidence in tropics • remains in intestine Egg in fecal sample

46. Enterobius vermicularis • pinworm • enterobiasis most common worm disease of children in temperate zones • eggs are picked up from surroundings & swallowed. • after hatching in the small intestine, they develop into adults • anal itching occurs when mature females emerge from intestine to release eggs • self-inoculation is common • tape test

47. Tape test for pinworms Flashlight Test: At night, the female adult worms deposit their eggs outside the rectum or anal area.

48. Enterobiusvermicularispinworm

49. Hookworms • characteristic curved ends & hooked mouths • Endemic to tropics and subtropics • Necator americanus & Ancylostoma duodenale • humans shed eggs in feces, which hatch into filariform (threadlike) larvae & burrow into the skin of lower legs (may cause a local irritation…”ground itch”) • larvae travel from blood to lungs, proceed up bronchi & throat & are swallowed. • worms mature & reproduce in small intestine & complete cycle • may cause pneumonia, nausea, vomiting, cramps & bloody diarrhea…blood loss can be significant - anemia

50. Hookworms