This document summarizes various unicellular and multicellular parasites that can infect humans. It discusses the life cycles, transmission, clinical presentations, and treatments of intestinal protozoa like Entamoeba histolytica, Giardia lamblia, and Cryptosporidium parvum. It also covers trematodes, cestodes, and nematodes including Ascaris lumbricoides, Strongyloides stercoralis, and hookworms. Major topics include the clinical effects of these parasites, methods of diagnosis, and recommended drug treatments.

1. Unicellular organisms

2. Intestinal Protozoa
 Amoeba: Entamoeba histolytica
 Flagellates: Giardia lamblia & Trichomonas
parvum/hominis
 Ciliates: Balantidum coli
 Sporozoa:
 Isospora belli
 Cyclospora cayetanensis
 Cryptosporidium parvum/hominis
 Sarcocystis hominis

3. Entamoeba histolytica Amoebiasis
 World wide distribution – 3rd after malaria and




schistosomiasis
Hand-mouth; fecal-oral; sexual transmission
Increasing in homosexuals
Resistant to chlorine
Major complications: amoebic abscesses in
liver, brain, lung
 Amoebic pericarditis (rare) is most dangerous
complication of amoebic liver abscess

4. Clinical Classification of Amoebiasis
 Asymptomatic infection
 Colonization without invasion
 Symptomatic infection
 Invasion with mild symptoms
 Intestinal disease
 Dysentery, colitis, amoeba
 Extraintestinal amoebiasis
 Liver, skin, lung, pleura, brain

5. Pathogenesis of Amoebiasis
 Ingested cysts  trophozoites in large intestine 75%
remain in lumen 15% invasive disease;
adherence/digestion of epithelium; formation of
flask-shaped ulcers  bacterial superinfection may
occur  dissemination  liver abscess  rupture 
pericardial disease

6. Clinical Presentation of Amoebiasis
 Asymptomatic
 Mild GI discomfort
 Diarrhea, pain, blood, mucus
 Weight loss
 Organ specific symptoms
 Dx: history, cysts/trophozoites, ELISA/PCR

7. Intestinal Flagellates
 Giardia lamblia
 Giardia intestinalis
 Giardia duodenalis
 Trichomonas hominis
 Epidemiology: worldwide
 Traveler’s/backpacker’s diarrhea: hikers/campers
 Day care centers
 Zoonotic; water, food (fecal-oral)

8. Life Cycle of Giardia
 Ingestion of cysts  trophozoites attach to duodenal
brush border causing irritation and obstruction of
absorption  cysts in colon; passed in feces
 See them moving in stool

9. Clinical Presentation of Giardia
 Watery diarrhea, abdominal cramps
 Weight loss
 No blood, no pus, no fever
 Steatorrhea – fatty and foul-smelling
 Lactose intolerance
 Antibody deficiency
 Dx: fecal cysts/trophozoites; enterotest; ELISA;
duodenal aspiration

10. Comparison of Clinical
Presentations
Amoebiasis
Giardiasis
 Asymptomatic
 Non-inflammatory watery
 Mild GI discomfort

 Inflammatory




Diarrhea, pain, blood, mucu
s
Weight loss, fever
Organ specific symptoms
Dx:
history, cysts/trophozoites, E
LISA/PCR
History: international travel






diarrhea, abdominal cramps
Steatorrhea – fatty and foulsmelling
No blood, no pus, no fever
Weight loss
Lactose intolerance
Antibody deficiency
Dx: fecal cysts/trophozoites;
enterotest; ELISA; duodenal
aspiration
History: Camping in Northern US
wilderness; drink mountain water

11. Oral Flagellate
 Trichomonas tenax

12. Intestinal Ciliate
 Balantidum coli – Balantidiasis
 The only ciliated protozoa!
 Common parasite of animals
 No extraintestinal spread
 Easily treated, not very common
 Seen in ppl who are around animals all the time

Farmers, zoo workers
 Tx: tetracycline

13. Intestinal Sporozoa





Isospora belli
Cyclospora cayetanesis water or produce
Cryptosporidium parvum/hominis water and food
Non-inflammatory diarrhea
Infection by ingestion of oocyst  infection of
intestinal epithelium
 Sexual & asexual stages – sporogony/schizogony
 Self-limiting in immunocompetent; Severe in AIDS or
other immunocompromised individuals
 Dx: acid-fast oocysts in stool & history

14. Urogenital Flagellate
 Trichomonas vaginalis
 Sexual transmission

15. Amoeboflagellates
 Primary CNS pathogens
 Naegleria fowleri
 Enter thru olfactory neuroepithelium causing primary
amoebic meningoencephalitis (PAM) in healthy ppl
 Trophozoites in CSF and tissue
 Acanthamoeba culbertsoni
 Balamuthia mandrillaris
 Acanthamoeba and Balamuthia enter thru lower respiratory
tract or thru broken skin causing granulomatous amoebic
encephalitis (GAE) in immunocompromised individuals
 Trophozoites and cysts in tissue

16. Haemoflagellates
 Trypanosoma & Leishmania
 Insect borne
 Found in blood, tissue, lymph and CSF
 Amastigote and trypomastigote most imp forms

17. Trypanosomiasis
 T. Gambiense
 Tsetse fly; West Africa
 T. Rhodesiense
 Tsetse fly; East Africa
 T. Cruzi
 Reduviid bug, Americas

18. T. Cruzi – American
trypanosomiasis
 Chagas disease
 Vector: reduviid bug (triatomine bug)
 Zoonotic
 South/Central America
 Infection thru eyes or open cuts, transplacental, at parturition
or breastfeeding, blood, uncooked or contaminated food
 Patho: bug feces  infection of local tissue  ulceration &
inflammation  spread  localization in mesenchymal
tissues of heart, GI, esophagus, etc  markedly enlarged
heart, esophagus, and megacolon  tachycardia, chest
pain, ECG changes, constipation

19. Chagas’ Disease
 Chagoma, Romana’s sign
 Hepatosplenomegaly, lymphadenopathy
 Myocarditis w/ CHF; Meningoencephalitis
 Tx: nifurtimox, benznidazole

20. Leishmaniasis sand fly
 Vector – Phlebotomine
 3 forms
 Leishmania tropica: dermal/cutaneous form
 Leishmania brasiliensis: mucocutaneous form
 Leishmania donovanii: visceral form




Most severe form (KALA AZAR) – 100% fatality if untreated
Hypoalbuminemia; hypergammaglobulinemia
Irregular fever, marked weight
loss, anemia, hepatosplenomegaly
Amastigotes in deep tissue – liver, spleen, bone marrow
 Drug: Sodium stibogluconate

21. Visceral leishmaniasis
 Patho: Parasite localization in macro of RES 
PANCYTOPENIA  high output heart failure 
myocarditis/pericarditis
 Leishmania – HIV coinfection on the rise

22. Tissue Sporozoa
 Plasmodium (blood & tissue)
 Malaria; Vector: female anopheles mosquito
 Babesia (blood)
 Babesiosis; Vector: Ixodes scapularis

Ixodes also carries lyme disease and human granulocytic
anaplasmosis
 Toxoplasma gondii (tissue)
 Toxoplasmosis; Vector: cat
 Most commonly reported parasitic disease following heart
transplantation
 Two life cycles, two hosts: sexual (sporogony) – definitive
host; Asexual (schizogony) – intermediate host

23. Malaria

24. Plasmodium
 P. falciparum, ovale, vivax, malariae

25. Parasite detection: HRP2
detection, parasite LDH ...
Dipstick tests

26. Complications of Malaria
 Parasitized RBCs adhere  fibrin thrombi 
microinfarcts in brain, heart  CHF, encephalopathy
 death
 Phagocytosis by macro  macro hyperplasia 
hepatosplenomegaly  nephrosis  death

27. Pathology of Malaria
 Fever, anemia, jaundice
 Hepatosplenomegaly, hepatorenal syndrome
 Pulmonary edema, CHF
 Blackwater fever – dark urine
 Encephalopathy – cerebral malaria

28. Protection against Malaria
 Absence of receptor (“duffy antigen” FyaFyb)
 G6PD deficiency
 HbS
 Thal

29. Malaria hypnozoites
 P. vivax & P. Ovale
 Use primaquin against hypnozoites
 Chloroquine against severe malaria
 Quinine in severe parasitemia and resistant malaria
 Metronidazole for amoebic liver abscesses
 Also for giardiasis, trichomoniasis, dracunculis
medinensis

30. Babesiosis
 Similar to malaria; co-infection w/ Lyme disease;
Ixodes scapularis
 Fever, chills, sweating, myalgias, fatigue, hepatospleno
megaly, hemolytic anemia

31. Toxoplasmosis
 Infection  flu-like  latency  reactivation if pt
becomes immunocompromised 
myocarditis, pericarditis, CHF

33. Helminthology
 Platyhelminthes
 Cestodes – tapeworms Tx: Praziquantel, Niclosamide
 Trematodes – flukes Tx: Praziquantel
 Nemathelminthes (Nematodes)
 Intestinal worms Tx: Mebendazole
 Tissue worms - filaria

34. Trematodes
 Hermaphroditic flukes
 Mammals – definitive hosts
 Snails – 1st intermediate hosts
 Fish, crustacea, vegetable – 2nd intermediate hosts
 Schistosomes
 Mammals – definitive hosts
 Snails intermediate hosts

35. Clinical Classification
 Lung fluke
 Paragonimus westermanii CRAB
 Liver fluke
 Clonorchis sinensis FISH
 Fasciola hepatica PLANT/VEGETABLE
 Intestinal fluke
 Heterophyes heterophyes FISH
 Fasciolopsis buski PLANT/VEGETBALE
 Tx: Praziquantel for all trematodes

36. Schistosomiasis (blood fluke)
 Direct skin penetration by cecariae
 S. Mansoni – intestinal (side spine)
 S. Japonicum – intestinal (no spine)
 S. Hematobium – urinary (terminal spine)
 Tx: Praziquantel
 Picture:
 Left, S. mansoni
 Middle, S. Haematobium
 Right, S. japonicum

37. Diphylobothrium Latum
 Broad or fish tapeworm
 Very big
 From ingestion of larvae in RAW fish
 Clinical:
 Low serum B12, eosinophilia
 Atrophic gastritis
 Megaloblastic anemia
 Dx: history, presentation, eggs in stool
 Tx: Praziquantel, Niclosamide

38. Taeniasis
 Beef tapeworm – T. Saginata
 Ingestion of larvae in undercooked/raw beef
 Pork tapeworm – T. Solium
 Ingestion of eggs in undercooked/raw pork
 Associated w/ heart problems
 Dx – eggs/proglottids in human feces; adult in
intestines
 Tx: Praziquantel, Niclosamide

39. Nemathelminthes
 Intestinal nematodes
 Ascaris lumbricoides – Roundworm
 Strongyloides stercoralis – Threadworm
 Ancylostoma duodenale – Hookworm
 Necator americanus – Hookworm
 Enterobius vermicularis – Pinworm
 Trichuris trichiura – Whipworm
 Trichinella spiralis – Porkworm
 Infections characterized by eosinophilia and high IgE
levels; hygiene and lifestyle is important

40. Ascaris lumbricoides - Roundworm
 One of the most common human infections worldwide
 Patho:
 Stage 1: “infective” eggs ingested  larval migration 
cough, hemoptysis (bloody sputum), dyspnea, hemorrhagic
pneumonia, asthma attacks, pulmonary infiltration, urticaria
 Stage 2: adult in intestine  dependent on worm load 
pain, distension, nausea, anorexia, malnutrition (growth
stunting in children), intestinal obstruction
 Stage 3: adult migration  acute pancreatitis or obstruction,
biliary obstruction, jaundice, appendicitis, peritonitis
 Dx: larvae in sputum; ova & parasites in stool
 Tx: Mebendazole

41. Strongyloides stercoralis Threadworm
 Direct skin penetration
 2 distinct adult forms
 Filariform (infective form): larvae penetrate intact skin
initiating infection  enter circulatory system  lungs
 penetrate alveolar spaces  reach small intestine 
mature to adult female (not male)  produce
uninfective larvae  autoinfection


Uninfective  infective in intestine and stool
Uninfective  adults in soil or become infective
 Rhabditiform (uninfective form)

42. Strongyloides Clinical Features
 Acute disease:
 Ground itch, cough, dyspnea, wheezing, fever, epigastric pain
 Chronic disease:
 Abdominal cramping, diarrhea, pain
 Severe disease
 Hyperinfection syndrome
 Extraintestinal spread (CNS, etc)
 **dissemination in AIDS pts**
 Dx: larvae in stool, urine, duodenum, enterotest
 Tx: Ivermectin

43. Enterobius Vermicularis - Pinworm
 Common in US; children
 Eggs on perianal folds  perianal itching
 Pricking anal pain, restlessness, sleeplessness
 Dx: see them around anus, eggs on scotch tape
 Tx: pyrantel pamoate or mebendazole
Enterobius vermicularis

44. Necator Americanus &
Ancylostoma Duodenale –
Hookworms
 Worldwide distribution; Enter thru FEET
 Clinical stages:
 Cutaneous Stage: ground itch
 Pulmonary Stage: pulmonary hemorrhage

Cough, wheezing, pneumonitis
 Intestinal Stage: GI discomfort, blood loss

45. Hookworm Infection Complications
 Protein losing enteropathy
 Fe deficiency anemia
 Tachycardia
 Stillbirth
 Poor physical development
 Dx: history and eggs in stool
 Tx: mebendazole + dietary supplements
 Wear shoes!!

46. Trichuris Trichura - Whipworm
 Fecal-oral transmission; rare
 Clinical:
 Light infection: asymptomatic
 Moderate infection:

Discomfort, gas, diarrhea/constipation
 Heavy infection


Distension, vomiting, diarrhea, weight loss
**RECTAL PROLAPSE**
 Dx: history & eggs in stool
 Tx: mebendazole

47. Trichinella Spiralis - Porkworm
 No eggs
 No external phase
 Dead end transmission! – ingestion of undercooked
meat  larvae turn to adults in intestinal cells 
migrate to muscle  encyst

48. Clinical Presentation of Trichinella
Spiralis




Diarrhea, constipation
Fever, myalgia, fatigue
Macular or petechial rash
Periorbital edema, conjunctivitis/retinal
hemmorrhage
 Splinter hemmorhage; heart problems
 Dx: muscle biopsy, positive serology, presentation
symptoms
 Tx: Thiabendazole – before tissue invasion
 Rest + analgesics for after invasion

49. Tissue Nematodes = Filaria
 Adults in tissue
 Eggs not produced; microfilaria produced
 Wuchereria bancrofti – mosquito
 Brugia malayi/timori – mosquito
 Loa loa – deer fly
 Onchocerca volvulus – simulium black fly
 Dracunculus medinensis – Cyclops (water flea)

50. Elephantiasis/Lymphatic filariasis
 Wuchereria bancrofti
 Brugia malayi & Brugia timori
 Patho: microfilaria  adult worms in lymphatics 
more microfilariae  lymphoedema  inflammatory
reaction  elephantiasis
 Early: acute inflammation, hypereosinophilia, massive
lymphatic dilatation, bacterial and fungal infections,
infection by wolbachia bacteria (tx: tetracycline)
 Late: lymphoedema/elephantiasis; chyluria (lymph in
urine)
 Tx: DEC + Albendazole or Albendazole + Ivermectin

51. Elephantiasis
 Dx: presentation, very high increase in eosinophils, IgE, IgG4, and
specific antifilarial Ab; microfilariae in blood (nocturnal periodicity)
 Sheath = pathogenic; no sheath = nonpathogenic

52. Onchocerca Volvulus
 River blindness/onchocerciasis
 Vector: Simulium Black Fly
 Larvae in subcutaneous tissue
 Patho: adult in onchocercoma  millions of migrating
microfilariae  death due to immune response 
onchodermatitis/keratitis
 Dx: Skin biopsy nodules  tons of little worms
 Tx: DEC or Ivermection (single dose)

54. Dracunculiasis
 Dog, horse, cow, monkey
 Vector: Cyclops (Water Flea)
 Debilitatin skin eruptions  worms come out of
them!!
 Tx: metronidazole/thiabendazole
Dracunculus medinensis

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