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

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Presentation on theme: "The Parasites of Medical Importance Protozoa, Helminths, and Arthropod Vectors 1 Chapter 23."— Presentation transcript:

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

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

3 3 Protozoans

4 4 Protozoa single-celled, animal-like microbes, usually having some form of motility single-celled, animal-like microbes, usually having some form of motility life cycles vary 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 5 amoebas ciliates flagellates Apicomplexans/sporozoans

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

7 7 Entamoeba histolytica

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

9 9 Entamoeba histolytica

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

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

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

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

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

15 15

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

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

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

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

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

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

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

23 23 Trypanosoma brucei

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

25 25 Trypanosoma cruzi Heart pathology in Chagas disease

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

27 27 Life cycle of Leishmania Disseminated leishmaniasis

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

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

30 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. 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. symptoms include episodes of chills-fever- sweating, anemia, and organ enlargement. therapy is chloroquine, quinine, or primaquine therapy is chloroquine, quinine, or primaquine

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

32 32 Plasmodium falciparum infection of RBCs showing ring form

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

34 34 Life cycle of Toxoplasma gondii

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

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

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

38 38 Helminths adults are large, multicellular animals with specialized tissues & organs 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) adult worms mate & produce fertilized eggs that hatch into larvae that mature in several stages to adults (the sexes may separate or hermaphroditic) Hosts 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 pathology arises from worms feeding on & migrating through tissues and accumulation of worms & worm products

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

40 40 Ascaris lumbricoides a large (up to a foot long) intestinal roundworm a large (up to a foot long) intestinal roundworm 1 Billion cases worldwide 1 Billion cases worldwide Most cases in the US occur in the southeastern states Most cases in the US occur in the southeastern states indigenous to humans indigenous to humans Ascaris spends its larval & adult stages in humans & releases embryonic eggs in feces, which are spread to other 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. 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 42 Ascaris lumbricoides worms retain motility, do not attach worms retain motility, do not attach severe inflammatory reactions mark the migratory route, severe inflammatory reactions mark the migratory route, allergic reactions can occur allergic reactions can occur heavy worm loads can retard physical & mental development heavy worm loads can retard physical & mental development

43 Roundworm Zoonoses-1 Don’t play with the animal feces ! Don’t play with the animal feces ! Don’t eat dirt ! Don’t eat dirt ! Dog and Cat Roundworms (toxocariasis) 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). 43

44 Roundworm Zoonoses-2 Raccoon roundworm (Baylisascaris procyonis) Raccoon roundworm (Baylisascaris procyonis) –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. 44

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

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

49 49 Hookworms characteristic curved ends & hooked mouths characteristic curved ends & hooked mouths Endemic to tropics and subtropics Endemic to tropics and subtropics Necator americanus & Ancylostoma duodenale 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”) 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. larvae travel from blood to lungs, proceed up bronchi & throat & are swallowed. worms mature & reproduce in small intestine & complete cycle worms mature & reproduce in small intestine & complete cycle may cause pneumonia, nausea, vomiting, cramps & bloody diarrhea…blood loss can be significant - anemia may cause pneumonia, nausea, vomiting, cramps & bloody diarrhea…blood loss can be significant - anemia

50 Hookworms

51 51 Strongyloides stercoralis threadworm threadworm tiny roundworm tiny roundworm completes life cycle in humans or moist soil completes life cycle in humans or moist soil larvae penetrate skin & migrate to lungs, are swallowed & complete development in intestine larvae penetrate skin & migrate to lungs, are swallowed & complete development in intestine can reinfect the same host without leaving the body can reinfect the same host without leaving the body heavy worm loads can cause pneumonitis & eosinophilia, bloody diarrhea, liver enlargement, bowel obstruction & malabsorption heavy worm loads can cause pneumonitis & eosinophilia, bloody diarrhea, liver enlargement, bowel obstruction & malabsorption

52 52 Strongyloides stercoralis Worm migration tracks under the skin

53 53 Trichinella spiralis causes trichinosis causes trichinosis life cycle entirely within mammalian host life cycle entirely within mammalian host acquired from eating undercooked pork (also bear) acquired from eating undercooked pork (also bear) larvae migrate from intestine to blood vessels, muscle, heart, & brain, where it forms cysts larvae migrate from intestine to blood vessels, muscle, heart, & brain, where it forms cysts first symptoms –flulike, diarrhea first symptoms –flulike, diarrhea second symptoms – muscle & joint pain, shortness of breath, pronounced eosinophilia second symptoms – muscle & joint pain, shortness of breath, pronounced eosinophilia no cure after larva have encysted no cure after larva have encysted

54 54

55 55 Filarial worms long threadlike worms with tiny larvae that circulate in blood & reside in various organs long threadlike worms with tiny larvae that circulate in blood & reside in various organs spread by biting insects spread by biting insects Wuchereia bancrofti – elephantitis Wuchereia bancrofti – elephantitis Onchocerca volvulus – river blindness Onchocerca volvulus – river blindness Loa loa – eye worm Loa loa – eye worm Edema from blockage of lymphatics

56 Heartworm in dogs 56

57 57 Trematodes (flukes) flatworms with ovoid leaflike bodies flatworms with ovoid leaflike bodies have digestive, excretory, neuromuscular, & reproductive systems have digestive, excretory, neuromuscular, & reproductive systems lack circulatory & respiratory systems lack circulatory & respiratory systems animals such as snails or fish are usually the intermediate hosts & humans are the definitive hosts animals such as snails or fish are usually the intermediate hosts & humans are the definitive hosts

58 58 Blood flukes: Schistosomes schistomiasis is the 2 nd most prominent parasitic disease (after malaria) schistomiasis is the 2 nd most prominent parasitic disease (after malaria) adult flukes live in humans & release eggs into water. The early larva develops in freshwater snail into a 2nd larva adult flukes live in humans & release eggs into water. The early larva develops in freshwater snail into a 2nd larva this larva penetrates human skin & moves into the liver to mature; adults migrate to intestine or bladder & shed eggs, giving rise to chronic organ enlargement this larva penetrates human skin & moves into the liver to mature; adults migrate to intestine or bladder & shed eggs, giving rise to chronic organ enlargement

59 59 Tapeworms flatworms flatworms long, very thin, ribbonlike bodies composed of sacs (proglottids) & a scolex that grips the intestine long, very thin, ribbonlike bodies composed of sacs (proglottids) & a scolex that grips the intestine each proglottid is an independent unit adapted to absorbing food & making & releasing eggs each proglottid is an independent unit adapted to absorbing food & making & releasing eggs Taenia saginata Taenia saginata Taenia solium Taenia solium

60 60 Taenia saginata beef tapeworm beef tapeworm very large, up to 2,000 proglottids very large, up to 2,000 proglottids humans are the definitive host humans are the definitive host animals are infected by grazing on land contaminated with human feces animals are infected by grazing on land contaminated with human feces infection occurs from eating raw beef in which the larval form has encysted infection occurs from eating raw beef in which the larval form has encysted larva attaches to the small intestine & becomes an adult larva attaches to the small intestine & becomes an adult causes few symptoms causes few symptoms

61 61 Beef Tapeworm Tanenia saginata

62 62 Taenia solium pork tapeworm pork tapeworm infects humans through ingesting cysts or eggs infects humans through ingesting cysts or eggs eggs hatch in intestine, releasing tapeworm larva that migrate to all tissues & encyst eggs hatch in intestine, releasing tapeworm larva that migrate to all tissues & encyst most damaging if they lodge in heart muscle, eye, or brain most damaging if they lodge in heart muscle, eye, or brain may cause seizures, psychiatric disturbances may cause seizures, psychiatric disturbances

63 Arthropod Vectors Vectors are animals that carry microbial pathogens Vectors are animals that carry microbial pathogens Arthropods are a common vector Arthropods are a common vector Some arthropods also serve as hosts for the pathogens they transmit Some arthropods also serve as hosts for the pathogens they transmit Disease vectors belong to two classes of arthropods Disease vectors belong to two classes of arthropods –Arachnida –Insecta

64 64 TickMite FleaLice Fly Mosquito Kissing Bug

65 Arachnids Adult arachnids have four pairs of legs Adult arachnids have four pairs of legs Ticks and mites resemble each other morphologically Ticks and mites resemble each other morphologically Ticks are the most important arachnid vectors Ticks are the most important arachnid vectors –Serve as vectors for bacterial, viral, and protozoan diseases –Second only to mosquitoes in the number of diseases they transmit –Hard ticks are the most prominent disease vector –Transmit Lyme disease, Rocky Mountain spotted fever, tularemia, relapsing fever, and tick-borne encephalitis

66 Arachnids Parasitic mites are found wherever humans and animals coexist Parasitic mites are found wherever humans and animals coexist –Transmit rickettsial diseases among animals and humans

67 Insects Adults have three pairs of legs as well as a head, thorax, and abdomen Adults have three pairs of legs as well as a head, thorax, and abdomen Fleas Fleas –Most fleas are not associated with humans but a few do feed on humans –Plague is the most significant disease transmitted by fleas Body lice Body lice –Parasites that can also transmit disease –Most common among poor or overcrowded communities

68 Insects Flies Flies –Among the most common insects –Those that transmit disease are generally bloodsuckers Mosquitoes Mosquitoes –Most important arthropod vector of disease –Carry some of the world’s most devastating diseases Kissing bugs Kissing bugs –Often take blood meals near the mouth of their human hosts –Feed on blood nocturnally while the host sleeps


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