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Parasitology Flashcards

/ˌpɛrəsəˈtɑlədʒi/ – n. a synonym for death

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Biology 101 flashcards
1
Q

What is a parasite?

A

An organism that lives in (endoparasitic) or on (ectoparasitic) another organism (host) for survival

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2
Q

What is a host?

A

A living organism that harbors a parasite

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3
Q

What are the phyla of the parasitic kingdom?

A
  • Protozoa
  • Helminths
  • Arthropods
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4
Q

How many classes are there in the phylum Protozoa?

A

4 classes

  • Sarcodina/Rhizopada
  • Mastigophora (flagellates)
  • Ciliates
  • Sporozoa
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5
Q

How are protozoa classified?

A
  • Their mode of reproduction (sexual/asexual)
  • Their mode of locomotion (psuedopodia, cilia, flagella, gliding)
  • Their location of habitation (habitat)
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6
Q

What are the characteristics of the class Sarcodina/Rhizopada?

A
  • Asexual reproduction
  • Move by pseudopodia
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7
Q

What are the characteristics of the class Mastigophora?

A
  • Asexual reproduction
  • Move by flagella (hence their alternative name, flagellates)
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8
Q

What are the characteristics of the class Ciliates?

A
  • Asexual reproduction
  • Move by cilia
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9
Q

What are the characteristics of the class Sporozoa?

A
  • Reproduce sexually and asexually
  • Obligate intracellular parasites
  • Have no organs of locomotion, so they move by gliding
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10
Q

To what phylum does the class Sporozoa belong?

A

Protozoa

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11
Q

To what phylum does the class Mastigophora belong?

A

Protozoa

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12
Q

To what phylum does the class Ciliates belong?

A

Protozoa

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13
Q

To what phylum does the class Sarcodina/Rhizopada belong?

A

Protozoa

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14
Q

How many classes are there in the phylum Metazoa?

A

Two/three classes

  • Nematoda (roundworms)

Platyhelminthes (flatworms), sometimes divided to

  • Cestoda (tapeworms)
  • Trematoda (flukes)
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15
Q

What are the characteristics of the class Nematoda?

A
  • Roundworms
  • Separate male and female sexes
  • Can be divided to intestinal nematodes and tissue nematodes
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16
Q

What are the divisions of the class Nematoda?

A
  • Intestinal nematodes
  • Tissue nematodes
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17
Q

What are the characteristics of the class Cestoda?

A
  • Tapeworms
  • Flattened and segmented
  • Hermaphroditic
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18
Q

What are the characteristics of the class Trematoda?

A
  • Flukes
  • Flattened, leaf-shaped worms
  • Hermaphroditic except Schistoma spp.
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19
Q

Are cestodes dioecious (showing sexual dimorphism)?

A

No, they are hermaphroditic

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20
Q

Are trematodes dioecious (showing sexual dimorphism)?

A

No, except Schistosoma spp.

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21
Q

Are nematodes dioecious (showing sexual dimorphism)?

A

Yes

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22
Q

What are the characteristics of arthropods?

A
  • Have an exoskeleton
  • Have jointed legs
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23
Q

How many classes are there in the phylum Arthropoda?

A

Two classes

  • Insecta
  • Arachnida
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24
Q

What are examples of Insecta parasites?

A
  • Mosquitoes
  • Lice
  • Fleas
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25
Q

What are examples of Arachnida parasites?

A
  • Ticks
  • Mites
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26
Q

To what phylum does the class Insecta belong?

A

Arthropoda

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27
Q

To what phylum does the class Arachnida belong?

A

Arthropoda

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28
Q

To what phylum does the class Nematoda belong?

A

Metazoa

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29
Q

To what phylum does the class Cestoda belong?

A

Metazoa

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30
Q

To what phylum does the class Trematoda belong?

A

Metazoa

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31
Q

What taxon encompasses both Trematoda and Cestoda?

A

Platyhelminthes

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32
Q

How are arthropods classified by their role as vectors?

A
  • Mechanical arthropods: only transfer the parasite from infected individuals to non-infected individuals
  • Biological arthropods: participate in the life cycle of the parasite they transmit
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33
Q

Which kind of arthropod only transmitts parasites from host to susceptible individual?

A

Mechanical arthropods

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34
Q

What kind of arthropod actively participate in the life cycle of parasites?

A

Biological arthropods

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35
Q

What are the types of parasites (by pathogenesis)?

A
  • Ectoparasites
  • Endoparasites
  • Obligatory parasites
  • Facultative parasites
  • Permanent parasites
  • Temporary/intermittent parasites
  • Opportunistic parasites
  • Coprozoic/spurious parasites
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36
Q

Define

Endoparasite

A

A parasites that lives inside the bodies of its host and causes infection

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37
Q

Define

Ectoparasite

A

A parasite that lives on the surface of its host and causes infection

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38
Q

Define

Obligatory parasite

A

A parasite that is completely dependent on its host for survival

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39
Q

Define

Facultative parasite

A

A parasite capable of surviving on its own or in association with a host

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40
Q

Define

Permanent parasite

A

A parasite that spends its entire life cycle in or on the body of its host

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41
Q

Define

Temporary (intermittent) parasite

A

A parasite that occupies its host transiently for resources and can complete its life cycle with or without the host

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42
Q

Define

Opportunistic parasite

A

A parasite that causes disease only in immunodeficient patients (e.g. AIDS patients, patients undergoing chemotherapy)

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43
Q

Define

Coprozoic (spurious) parasite

A

An organism that passes through its host’s GI tract without causing any symptom or disease. It is detected in the stool

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44
Q

What is the result of infection with an opportunistic parasite in immunocompetent individuals?

A

Latent form, producing mild or no symptoms

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45
Q

What are the types of hosts?

A
  • Definitive host
  • Reservoir host
  • Intermediate host
  • Accidental host
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46
Q

Define

Definitive host

A

A host that harbors the mature, adult stage of the parasite, or in which sexual reproduction of the parasite takes place

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47
Q

Define

Reservoir host

A

A host that harbors the parasite and is considered a source of human infection

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48
Q

Define

Intermediate host

A

A host that harbors the larval (immature, non-sexually reproducing) form of the parasite

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49
Q

Define

Accidental host

A

A host that harbors a parasite that normally doesn’t infect its species

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50
Q

What is an example of a parasite with a human definitive host?

A

Taenia spp.

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51
Q

What is an example of a reservoir host and its parasite?

A

Dogs with Leishmania donovani (the causative agent of visceral leishmaniasis, aka kala azar – black fever)

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52
Q

What is an example of an intermediate host and its parasite?

A

Snails with Schistosoma spp. (the causative agents of schistosomiasis, aka bilharzia)

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53
Q

What is an example of a parasite for which humans can be an accidental host?

A

Toxocara canis (dog roundworm), which normally infects dogs

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54
Q

Define

Symbiosis

A

The relationship between two living organisms and the nature of their interactions

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55
Q

What are the types of symbiotic relationships?

A
  • Mutualistic
  • Commensal
  • Parasitic
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56
Q

Define

Mutualism

A

A symbiotic relationship where both organisms benefit and can successfully live apart

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57
Q

Define

Commensalism

A

A symbiotic relationship where one organism benefits and the other is not harmed

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58
Q

Define

Parasitism

A

A symbiotic relationship where one organism benefits and the other is harmed

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59
Q

What are the modes of transmission of parasitic infections?

A
  • Direct contact through the skin
  • Skin penetration
  • Ingestion of contaminated food/water containing the infective stage
  • Sexual contact
  • Autoinfection: either internal or external
  • Congenital (vertical): either transplacental or transmammary
  • Vectors
  • Blood transfusion/contaminated syringes
  • Organ transplantation
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60
Q

What is the most common mode of transmission of parasitic infections involving contaminated food/drink

A

Fecal–oral route

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61
Q

What are the types of congenital/vertical infection with parasitic diseases?

A
  • Transplacental to the fetus
  • Transmammary through lactation
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62
Q

Define

Autoinfection

A

When the complete life cycle of a parasite happens in a single host organism without the involvement of another host

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63
Q

What are the types of autoinfection?

A
  • Internal: infection is reinitiated without the parasite leaving the host
  • External: the parasite exits the body and is reintroduced, e.g. with pinworm infection, females exit through the anus and lay eggs in the perineum, causing an itchy sensation. Children may scratch the region and reingest the parasite by then touching their mouths
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64
Q

Define

Infective stage

A

The stage during which a parasite can enter the body and cause infection

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65
Q

Define

Diagnostic stage

A

The stage during which a parasite leaves the body and can be detected diagnostically

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66
Q

Define

Zoonosis

(In parasitology)

A

A disease that is transmitted from animals to humans, either directly or via a vector (e.g. arthropods)

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67
Q

What are the methods of parasite pathogenesis?

A
  • Mechanical
  • Traumatic implantation
  • Toxin production
  • Tissue damage and necrosis
  • Cellular destruction
  • Immune stimulation
  • Allergic reaction to insect bites or parasite toxins
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68
Q

What is mechanical pathogenesis of parasites?

A

The parasite may obstruct normal passages like the small intestine, bile tract, or colon

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69
Q

What are the types of traumatic pathogenesis of parasites?

A
  • External: via invasion of the skin
  • Internal: via attachment to the intestinal mucosa by the buccal capsule, producing ulcers
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70
Q

How do tissue damage and necrosis occur in parasitic infections?

A

By the enzymes secreted by parasites

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71
Q

How does cellular destruction occur in parasitic infections?

A

By feeding on cells or ROS damage

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72
Q

How is the immune system stimulated by parasites?

A

Parasitic antigens lead to adaptive immune responses and the formation of a fibrous capsule around the parasite

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73
Q

What factors affect the pathogenesis of a parasite?

A
  • Number, size, and morphology of the parasite
  • Movement and migration capabilities
  • Site of infection
  • Toxin production
  • Host reaction
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74
Q

What are the broad types of diagnosis for parasitic infections?

A
  • Clinical diagnosis: by characteristic signs and symptoms
  • Laboratory diagnosis of samples (stool, urine, blood, tissue biopsy, sputum, or aspirates)
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75
Q

What are the types of samples used for diagnosis of parasitic infections?

A
  • Urine sample
  • Stool sample
  • Blood sample
  • Tissue biopsy
  • Sputum sample
  • Aspirated fluid
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76
Q

What types of parasitic infections are stool samples suitable for?

A

Intestinal infections

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77
Q

What are stool samples assessed for macroscopically?

A
  • Consistency
  • Color
  • Composition
  • Presence of adult parasites
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78
Q

How are stool samples microscopically examined?

A
  • Saline smears or iodine smears (when helminthic eggs or protozoal cysts are present)
  • Concentration techniques (when there are few parasites)
  • Permanent stained smear: fixation with formalin
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79
Q

What are the types of blood sample examinations?

A
  • Thin blood film: used to determine the morpholigcal features of the parasite
  • Thick blood film: used if the infection seems light, to increase the chance of detecting a parasite
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80
Q

For which parasites are tissue biopsies recommended?

A
  • Trichinella spiralis (muscle biopsy)
  • Schistosoma ova (rectal biopsy)
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81
Q

What types of parasitic infections require sputum examination?

A
  • Parasites that live in the lung
  • Parasites that are migrating through the lung
  • Parasites that result from the rupture of cysts in the lung
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82
Q

Where may aspirates be taken from?

A
  • The CNS (cerebrospinal fluid)
  • Duodenum
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83
Q

What species may be detected through CSF aspirates?

A
  • Trypanosoma spp.
  • Naeglaria spp.
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84
Q

What species may be detected through duodenal aspirates?

A
  • Giardia lamblia
  • Strongyloides larva
  • Cryptosporidium parvum
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85
Q

Which protozoa colonize the GI tract?

A
  • Entamoeba histolytica (amoeba)
  • Blantidium coli (ciliate)
  • Giardia lamblia (flagellate)
  • Cryptosporidium (sporozoate—coccidium)
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86
Q

Which protozoa colonize the blood?

A
  • Trypanosoma (flagellate)
  • Leishmania (flagellate)
  • Malaria (sporozoate)
  • Babesia (sporozoate)
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87
Q

Which protozoa colonize tissue?

A
  • Trypanosoma (flagellate)
  • Leishmania (flagellate)
  • Toxoplasma (sporozoate)
  • Sarcocystis (sporozoate)
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88
Q

Which protozoa colonize the genitourinary tract?

A

Trochomonas vaginalis (flagellate)

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89
Q

Which amoebae live in the large intestine?

A
  • Entamoeba histolytica (pathogenic)
  • Entamoeba coli
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90
Q

Which amoebae live in the buccal cavity?

A
  • Entamoeba gingivalis (commensal)
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91
Q

Why are the commensal amoebae of the GI tract clinically important?

A

They often contaminate specimens and can be confused for E. histolytica, which is pathogenic

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92
Q

How can commensal amoebae be differentiated from pathogenic amoebae?

A
  • PCR
  • Commensal amoebae cannot phagocytose RBCs, while pathogenic ones can
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93
Q

Which amoebae live freely in the GI tract?

A
  • Naegleria fowleri (pathogenic)
  • Acanthomoeba (pathogenic)
  • Coprozoic amoebae (commensal)
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94
Q

What is the geographical distribution of Entamoeba histolytica?

A

Worldwide, especially in temperate areas and places with poor sanitation

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95
Q

What is the habitat of Entamoeba histolytica?

A

Large intestine:

  • Cecum
  • Colonic flexures
  • Sigmoidorectal region
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96
Q

What is the definitive host of Entamoeba histolytica?

A

Humans

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97
Q

What are the reservoir hosts of Entamoeba histolytica?

A
  • Humans
  • Dogs
  • Pigs
  • Rats
  • Monkeys
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98
Q

What diseases does Entamoeba histolytica cause?

A

Amebiasis (amoebic dysentery)

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99
Q

What is the trophozoite stage of Entamoeba histolytica?

A

The vegitative, active, motile form found in tissues

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100
Q

What are the features of the trophozoite stage of Entamoeba histolytica?

A
  • Protoplasm
  • Central nucleus
  • Karyosome
  • Granular endoplasm with food vacuoles and RBCs
  • Ectoplasm
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101
Q

Where is the trophozoite stage of Entamoeba histolytica found?

A

In tissue

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102
Q

Where is the cyst stage of Entamoeba histolytica found?

A

In the lumen or outside the body

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103
Q

What is the cyst stage of Entamoeba histolytica?

A

A quiescent form used to protect the amoeba from stresses

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104
Q

What types of cysts does Entamoeba histolytica form?

A
  • Immature (non-infectious): uninucleate or binucleate
  • Mature (infectious): quadrinucleate
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105
Q

How is Entamoeba histolytica transmitted?

A
  • Contaminated food (e.g. green vegetables) and drink
  • Fecal–oral route with mature cysts (e.g. by food handlers)
  • Flies and cockroaches that carry cysts from feces to exposed food
  • Autoinfection (fecal–oral/hand-to-mouth)
  • Sexual transmission by MSM
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106
Q

What is the infective stage of Entamoeba histolytica?

A

The mature, quadrinucleate cyst

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107
Q

What is the diagnostic stage of Entamoeba histolytica?

A
  • The mature, quadrinucleate cyst
  • Trophozoite stage
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108
Q

How can Entamoeba histolytica infection be diagnosed?

A

Identification of cysts of trophozoite stage in feces

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109
Q

What are the clinical features of intestinal amebiasis?

A
  • Asymptomatic infection (carrier/cyst passer): most common outcome
  • Acute amoebic dysentery: fever, abdominal pain, tenderness, tenesmus, frequent movements of loose stool containing blood, mucus, and trophozoites
  • Chronic infection: low grade fever, recurrent episodes of diarrhea alternating with constipation, only cysts passed in stool
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110
Q

When does chronic infection of intestinal amebiasis occur?

A

When the acute dysentery phase is not properly treated

111
Q

What are the complications of intestinal amebiasis?

A
  • Hemorrhage due to erosion of large blood vessels
  • Intestinal perforation and peritonitis
  • Appendicitis
  • Ameboma (amoebic granuloma) around the ulcer, leading to constriction of the affected area
112
Q

What is the pathogenesis of symptomatic intestinal amebiasis?

A
  • Trophozoites invade the mucosa and submucosa of the large intestine by secreting lytic enzymes, leading to ulceration
  • The ulcer is flask-shaped with deeply undermined edges containing cytolyzed cells, mucus, and trophozoites
  • Most commonly occurs in the cecum, colonic flexures, and sigmoidorectal regions due to decreased peristalsis and slow colonic flow at these sites
113
Q

What is the pathogenesis of asymptomatic intestinal amebiasis?

A

No infection of the mucosa and submucosa

114
Q

How does extra-intestinal amebiasis occur?

A

The trophozoites reach the blood through the intestinal ulcer and spread to different organs

115
Q

What are the common sites of extra-intestinal amebiasis?

A
  • Liver
  • Lung
  • Brain
  • Skin
116
Q

What are the features of liver amebiasis?

A
  • Liver abscess (with a characteristic “anchovy paste” appearance)
  • Diffuse amoebic hepatitis
  • Most commonly affects the right lobe
  • Fever, hepatomegaly, pain in the right hypochondrium
117
Q

Why is the right lobe of the liver more commonly affected by amebiasis?

A
  • Spread via the hepatic portal vein
  • Extension from a perforating ulcer in the right colonic flexure
118
Q

What are the features of lung amebiasis?

A

Lung abscess, leading to pneumonitis with chest pain, cough, and fever, typically in the lower part of the right lung

119
Q

Why is the lower part of the right lung more commonly affected by amebiasis?

A
  • Direct spread from liver lesions through the diaphragm
  • Reached through the blood (very rare)
120
Q

What are the features of brain amebiasis?

A

Brain abscess leading to encephalitis (potentially fatal)

121
Q

What is the most fatal form of Entamoeba histolytica infection?

A

Extra-intestinal brain abscess; encephalitis

122
Q

What are the features of cutaneous (skin) amebiasis?

A

Typically occurs in the perianal region

123
Q

How does Entamoeba histolytica reach the skin to cause cutaneous amebiasis?

A

Rupture of the abdominal wall from the hepatic, colonic, or appendicular lesions

124
Q

What type of parasite is Entamoeba histolytica?

A

Protozoal amoeba

125
Q

What type of parasite is Giardia lamblia?

A

Protozoal flagellate

126
Q

What diseases does Entamoeba histolytica cause?

A

Giardiasis

127
Q

What is the habitat of Giardia lamblia?

A
  • Duodenum
  • Jejunum
128
Q

What is the causative organism of beaver fever?

A

Giardia lamblia

129
Q

What stages does Giardia lamblia have?

A
  • Trophozoite
  • Cyst
130
Q

What is the morphology of the trophozoite form of Giardia lamblia?

A
  • Heart shaped
  • Two nuclei separated by a ventral disk used for attachment to the intestinal villi
  • Four pairs of flagella
131
Q

What is the morphology of the cyst form of Giardia lamblia?

A
  • Ellipsoid
  • Thick walled
  • Highly resistant
  • Immature: binucleate
  • Mature: quadrinucleate
132
Q

What is the infective stage of Giardia lamblia?

A

The mature, quadrinucleate cyst

133
Q

What is the diagnostic stage of Giardia lamblia?

A
  • Trophozoite (more commonly)
  • Mature, quadrinucleate cyst
134
Q

How is Giardia lamblia transmitted?

A
  • Ingestion of fecally contaminated water or food with cysts
  • Direct fecal contamination (e.g. in day care centers, refugee camps, prisons, or anal–oral sex)
  • Cysts can survive in water for up to 3 months
135
Q

What are the clinical features of Giardia lamblia?

A
  • Mostly asymptomatic
  • Giardiasis when large numbers of the parasite attach to the bowel wall and cause irritation
136
Q

What are the features of giardiasis?

A
  • Acute or chronic diarrhea associate with crypt hypertrophy, villous atrophy or flattening, and epithelial cell damage
  • Stool is watery, semisolid, greasy, bulky, and foul smelling
  • Sometimes, low-grade fever occurs
137
Q

How is giardiasis diagnosed?

A
  • Finding cysts in formed stools
  • Finding trophozoite in diarrheal stools, duodenal secretions, or jejunal biopsy specimens (string test)
  • Enzyme immunoassay detects Giardia antigen in stool
138
Q

What are the common pathogenic species of the genus Cryptosporidium?

A
  • C. hominis
  • C. parvum
139
Q

What type of parasite are Cryptosporidium spp.?

A

Protozoal sporozoate

140
Q

In which groups of people does Cryptosporidium infection typically occur?

A

Immunocompromised persons

141
Q

What is the animal reservoir of Cryptosporidium spp.?

A
  • Rodents
  • Fowl
  • Rhesus monkeys
  • Cattle
  • Other herbivores
142
Q

What is the habitat of Cryptosporidium spp.?

A

Brush border of mucosal epithelial cells of the GI tract, especially the surface of villi of the lower small intestine

143
Q

What are the features of Cryptosporidium infection?

A
  • Self-limited watery diarrhea in immunocompetent persons
  • Chronic, severe, non-bloody diarrhea with nausea, vomiting, abdominal pain, and anorexia leading to wasting and death in immunocompromised persons
144
Q

How is Cryptosporidium infection diagnosed?

A
  • Detection of oocysts in fresh stool samples
  • Stool concentration techniques using a modified acid fast stain
  • Enzyme immunoassay tests for antigen
  • Fluorescent antibody tests for antigen
145
Q

How is Cryptosporidium infection treated?

A

Nitozoxanide

146
Q

How are Cryptosporidium spp. transmitted?

A
  • Direct contact
  • Autoinfection
147
Q

What type of parasite are Cyclospora spp.?

A

Protozoal sporozoate

148
Q

What is the habitat of Cyclospora spp.?

A

Brush border of mucosal epithelial cells of the GI tract, especially the surface of villi of the lower small intestine

149
Q

What is the pathogenesis of Cyclospora infections?

A

Altered intestinal mucosa architecture with shortening of the villi due to diffuse edema and infiltration of inflammatory cells

150
Q

What are the features of Cyclospora infection?

A
  • Diarrhea
  • Anorexia
  • Fatigue
  • Weight loss
151
Q

How are Cyclospora infections diagnosed?

A

Examining stools for oocysts using acid fast stain

152
Q

How are Cyclospora infections treated?

A

Trimethoprim-sulfamethoxazole (TMP-SMZ)

153
Q

What type of parasite is Balantidium coli?

A

Protozoal ciliate

154
Q

What diseases does Balantidium coli cause?

A

Balantidiasis (balantidial dysentery)

155
Q

Which clinically significant protozoa of humans is the largest?

A

Balantidium coli

156
Q

What are the features of Balantidium coli infection?

A
  • Usually harmless
  • Rarely, trophozoites invade the large intestine and terminal ileum causing erosions and ulceration
157
Q

How is Balantidium coli infection treated?

A

Oxytetracycline, followed by iodoquinol or metronidazole

158
Q

What are the morphologic features of the forms of Balantidium coli?

A
  • Trophozoite: two nuclei, one sausage-shaped macronucleus, one micronucleus
  • Cyst form
159
Q

What type of parasite is Trichomonas vaginalis?

A

Protozoal flagellate

160
Q

What are the forms of Trichomonas vaginalis?

A

Trophozoite only

161
Q

What is the disease caused by Trichomonas vaginalis?

A

Trichomoniasis

162
Q

What is the morphology of Trichomonas vaginalis?

A
  • Pear shaped
  • Central undulating membrane
  • 5 flagella: 4 anterior and one along the undulating membrane
  • Moves via a wobbling or rotating motion (corkscrew)
163
Q

What is the habitat of Trichomonas vaginalis?

A
  • In females: vulva, vagina, cervix
  • In males: prostate, seminal vesciles, urethra
164
Q

What is the pathogenesis of Trichomonas vaginalis?

A
  • Destruction of the squamous epithelium of the genitourinary tract
  • Development of a neutrophilic inflammatory reaction and petechial hemorrhages
165
Q

How is Trichomonas vaginalis infection diagnosed?

A

Wet mount examination for motile trophozoites

166
Q

How is trichomoniasis treated?

A

Topical and systemic metronidazole (or tinidazole, ornidazole, which have fewer side effects)

167
Q

What are the clinical features of trichomoniasis in females?

A
  • Low-grade inflammation
  • Frothy yellow or creamy discharge
168
Q

What are the clinical features of trichomoniasis in males?

A
  • Dysuria
  • Dyspareunia
169
Q

What type of parasite are Trypanosoma spp.?

A

Protozoal flagellate

170
Q

What diseases does Trypanosoma cause?

A
  • African trypanosomiasis (African sleeping sickness)
  • American trypanosomiasis (Chagas’ disease)
171
Q

How are the hemoflagellates transmitted?

A

Promastigotes and epimastigotes carried by vectors

172
Q

What are the hemoflagellates?

A
  • Trypanosoma spp.
  • Leishmania spp.
173
Q

What is the intracellular form of the hemoflagellates?

A

Amastigote

174
Q

What are the diagnostic stages of the hemoflagellates?

A
  • Amastigote
  • Trypomastigote
175
Q

What is the morphology of Trypanosoma spp.?

A
  • Spindly, uniflagellate stages (trypomastigote, epimastigote, promastigote)
  • Rounded, amastigote form
176
Q

Which of the hemoflagellates does not have an intracellular form?

A

African Trypanosoma

177
Q

How is African Trypanosoma transmitted?

A

The tsetse fly (Glossina spp.) as a vector, which is only found in rural Africa

178
Q

How is American Trypanosoma transmitted?

A

Reduviid bugs as vectors, which defecate while taking a blood meal

179
Q

What are the definitive hosts of American Trypanosoma?

A
  • Humans
  • Dogs
  • Cats
  • Rats
180
Q

What is the habitat of American Trypanosoma?

A
  • Blood (trypomastigote)
  • Tissue (amastigote)
181
Q

How is Trypanosoma diagnosed?

A
  • Tissue biopsy
  • Blood test for identification
182
Q

What type of parasite are Leishmania spp.?

A

Protozoal flagellate

183
Q

How is Leishmania transmitted?

A
  • Female sand fly as a biological vector
  • Blood transfusion
  • Transplantation
  • Vertical transmission
  • Direct contact through nasal secretions
184
Q

What is the pathogenesis of Leishmania?

A
  • Obligate intracellular
  • Infects phagocytic cells and macrophages
  • Incubation period ranges from 10 days to 2 years
185
Q

What diseases does Leishmania cause?

A
  • Cutaneous leishmaniasis (confined to epidermis or dermis)
  • Mucocutaneous leishmaniasis (nasopharyngeal)
  • Visceral leishmaniasis (in secondary lymphoid organs, causes abdominal distension; kala azar)
186
Q

What type of parasite are Plasmodium spp.?

A

Protozoal sporozoate

187
Q

What is the causative organism of malaria?

A

Plasmodium

188
Q

Which species of Plasmodium is the major species associated with deadly infection?

A

Plasmodium falciparum

189
Q

What is the pathogenesis of malaria?

A
  • Female anopheine mosquito as a biological vector
  • When the mosquito takes a blood meal, sporozoites in the salivary glands of the mosquito are discharged into the wound
  • These infective sporozoites are carred to the liver, where they penetrate hepatocytes and begin to grow, initiating the pre-erythrocytic/primary exoerythrocytic cycle
  • The sporozoites reproduce by schizogony to produce exoerythrocytic mezoroites
  • The merozoites leave the liver and invade RBCs, initating the erythrocytic cycle
190
Q

What is the morphology of the sporozoites of Plasmodium?

A

Round or oval

191
Q

How do sporozoites of Plasmodium replicate?

A

Schizogony—multiple asexual fission producing merozoites

192
Q

What is the alternative route of replication of Plasmodium sporozoites?

A

Dormant schizogony, remaining quiescent in the liver as hypnozoites, which may cause a relapse within 1–5 years

193
Q

What are the steps of Plasmodium development in the erythrocytic cycle?

A
  • The parasites grow and feed on hemoglobin
  • At this stage, the merozoites (young trophozoites) are vacuolated, ring shaped, amoeboid, and uninucleate
  • The excess protein and hematin formed from digestion of hemoglobin combine to form malarial pigment
  • Once the nucleus begins to divide, the trophozoites are called developing schizont
  • Mature schizonts release merozoites into the blood
194
Q

What type of parasite is Toxoplasma gondii?

A

Protozoal sporozoate

195
Q

What are the definitive hosts of Toxoplasma gondii?

A

Cats

196
Q

How are humans infected with Toxoplasma gondii?

A

Consumption of food/drink contaminated with cat feces

197
Q

What are the features of Toxoplasma gondii infection?

A
  • Immunocompetent persons: asymptomatic or flu-like illness
  • Pregnant women in first pregnancy: developmental delays in the fetus
  • Immuncompromised persons: disseminated toxoplasmosis
198
Q

What are the forms of Toxoplasma gondii?

A
  • Tachyzoites (like trophozoites)
  • Bradyzoites (like hypnozoites of malaria or cyst forms)
199
Q

What type of parasite is Ascaris lumbricoides?

A

Metazoal nematode

200
Q

How is Ascaris lumbricoides transmitted?

A

By eggs. Freshly passed eggs are not infective, they require 2–3 weeks to be embryonated

  • Foodborne
  • Waterborne
  • Soilborne
201
Q

Which clinically significant nematode of humans is the largest?

A

Ascaris lumbricoides

202
Q

What is the morphology of Ascaris lumbricoides eggs?

A
  • Have a thick mammillated (covered with lumps) brownish shell
  • Highly resistant to desiccation and environmental stresses
203
Q

What are the general phases of the metazoal life cycle?

A

egg → larva → adult

204
Q

What is the habitat of Ascaris lumbricoides?

A

Intestine

205
Q

What is the infective stage of Ascaris lumbricoides?

A

Eggs

206
Q

What is the diagnostic stage of Ascaris lumbricoides?

A

Eggs in the stool

207
Q

What diseases does Ascaris lumbricoides cause?

A

Ascariasis

208
Q

What is the pathogenesis of Ascaris lumbricoides infections?

A
  • If present in high numbers, adult worms cause mechanical obstruction of the bowels and the bile and pancreatic ducts
  • The worms migrate if drugs like anesthetics or steroids are given, leading to bowel perforation and peritonitis, anal passage of worms, vomiting, and abdominal pain
209
Q

What are the clinical features of Ascaris lumbricoides larvae passage in the lungs?

A

Induction of an inflammatory response (pneumonitis), leading to:

  • bronchial spasm,
  • mucus production, and
  • Löffler syndrome (cough and hemoptysis, eosinophilia, and pulmonary infiltrates)
210
Q

How are Ascaris lumbricoides infections diagnosed?

A
  • Larvae from a sputum sample
  • Eggs in the stool
  • Endoscopy
  • Cholangiograms (X-ray examination of the bile ducts)
211
Q

How can male and female worms of Ascaris lumbricoides be differentiated?

A
  • Females are longer
  • Males have a copulatory spicule (their reproductive organ)
212
Q

What type of parasite is Enterobius vermicularis?

A

Metazoal nematode

213
Q

What is the common name of Enterobius vermicularis?

A

Pinworm

214
Q

How can male and female pinworms be differentiated?

A
  • Females are longer
  • Females have a slender, pointed posterior end
  • Males have a curved posterior end
215
Q

Where, geographically, are pinworms found?

A

Found worldwide but more common in temperate climates

216
Q

Infection with which helminth is the most common?

A

Enterobius vermicularis (pinworm)

217
Q

What is the morphology of Enterobius vermicularis eggs?

A
  • Rugby ball shaped
  • Have a thin outer shell
  • Infectious larvae may be visible inside the egg
  • Immediately infectious
218
Q

Where are Enterobius vermicularis eggs found?

A

The perianal region. Females lay them there at night

219
Q

What is the main symptom of pinworm infection?

A

Perianal pruritus (itching) due to hypersensitivity from the eggs

220
Q

How is Enterobius vermicularis transmitted?

A
  • Autoinfection by itching the perianal region and transmitting the eggs found there to the mouth for re-ingestion
  • Exposure to eggs on fomites
221
Q

How is Enterobius vermicularis infection diagnosed?

A

The “Scotch tape” technique: sampling the perianal region in the morning for eggs laid the previous night, before bathing or defecation

222
Q

What is the infective stage of Enterobius vermicularis?

A

Eggs ingested by human

223
Q

What is the diagnostic stage of Enterobius vermicularis?

A

Eggs on the perianal folds

224
Q

What type of parasite is Trichuris trichiura?

A

Metazoal nematode

225
Q

What is the common name of Trichuris trichiura?

A

Whipworm

226
Q

How can male and female whipworms be differentiated?

A

Females are longer

227
Q

What is the morphology of adult Trichuris trichiura worms?

A

The anterior end of the worms is slender and the posterior end is thicker, like a buggy whip

228
Q

What is the morphology of Trichuris trichiura eggs?

A

Barrel shaped with polar plugs

229
Q

What is the life cycle of Trichuris trichiura?

A
  • Adult whipworms inhabit the colon, where male and female worms mate
  • Females release eggs that are passed in the feces
  • Eggs become infective after 3 weeks of incubation in moist and shady soil
230
Q

Which species are referred to as hookworms?

A
  • Ancylostoma duodenale
  • Necator americanus
231
Q

How can male and female hookworms be differentiated?

A
  • Females are longer
  • Males have a copulatory bursa (a broadened posterior end)
232
Q

What is the infective stage of hookworms?

A

Filariform larvae

233
Q

What is the pathogenesis of Ancylostoma duodenale?

A
  • Larvae can survive in moist soil for several weeks
  • The larvae penetrate host skin (typically on the feet) and migrate throughout the body, similarly to Ascaris, eventually leading to the intestine where they mature
  • In the intestine, adult worms attach to intestinal villi with their buccal teeth and feed on blood and tissue with the aid of anticoagulants that they produce
234
Q

What are the features of hookworm infection?

A
  • Severe anemia and iron deficiency
  • Abdominal pain and diarrhea
  • Ground itch: erythema and pruritus at the site of skin invasion
235
Q

What is the diagnostic stage of hookworms?

A

Eggs in the stool

236
Q

Where do hookworm eggs hatch?

A

Outside the body, after 1–2 days

237
Q

What type of parasite is Strongyloides stercoralis

A

Metazoal nematode

238
Q

What is the common name of Strongyloides stercoralis?

A

Threadworm

239
Q

What in their reproduction distinguishes Strongyloides stercoralis from other nematodes

A

Females are parthenogenic—they do not need to mate with males to reproduce

240
Q

What is the pathogenesis of Strongyloides stercoralis (from exogenous sources)?

A
  • Rhabditiform larvae develop into the parasitic filariform
  • Filariform larvae penetrate intact skin
  • The larvae pass through the body, similarly to Ascaris, eventually leading to the intestine where they mature
  • The adult female worm deposits eggs in the intestinal mucosa
  • The eggs hatch and migrate to the lumen
  • Rhabditiform larvae in the large intestine become filariform, penetrate the intestinal mucosa or perianal skin, and migrate to other organs
241
Q

What are the fates of Strongyloides stercoralis eggs laid in the intestine?

A

The eggs hatch, forming rhabditiform larvae, which:

  • Reinfect the large intestine
  • Form free-living adult worms that reproduce for several generation until forming a parasitic form
  • Form filariform larvae that invade the skin
242
Q

What type of parasite is Trichinella spiralis?

A

Metazoal nematode

243
Q

Which metazoal species causes intracellular infection?

A

Trichinella spiralis

244
Q

How is Trichinella spiralis transmitted?

A

Eating raw or undercooked pork infected with the larval stage

245
Q

What is the diagnostic stage of Strongyloides stercolaris?

A

Rhabditiform larvae in the stool

246
Q

What is the infective stage of Strongyloides stercolaris?

A

Filariform larvae

247
Q

What is the pathogenesis of Trichinella spiralis?

A
  • Larvae reach the small intestine, where they molt (shed) into adult worms and mate
  • The female worms release live larvae (not eggs)
  • These larvae circulate in the blood and eventually encyst in muscle tissue
248
Q

What are the clinical features of Trichinella spiralis infection?

A
  • Diarrhea
  • Abdominal pain
  • Nausea
249
Q

What are the features of tissue nematodes?

A
  • Females lay larvae, not eggs
  • Larvae require an intermediate host to complete their development into the infective stage
250
Q

What are the Filariidae nematodes and their vectors??

A
  • Wucherieria bancrofti (mosquito)
  • Brugia malayi (mosquito)
  • Loa loa (day-biting flies)
  • Onchocerca volvulus (black flies)
251
Q

What is the features of filariae?

A
  • Found in lymphatics, body cavities, and subcutaneous tissues
  • Progenies are embryoes which are not fully developed (microfilariae), which are between eggs and larvae
  • Microfilariae require an intermediate host
252
Q

What disease is caused by filariae?

A

Elephantiasis

253
Q

What are the features of elephantiasis?

A
  • The worms block the lymphatic system, causing fluid to collect in tissues
  • Great swelling (lymphedema) occurs in the extremities, resembling an elephant’s leg
254
Q

What disease is caused by Onchocerca volvolus and Loa loa?

A

Eye worm

255
Q

What are the features of trematodes? (flukes)

A
  • Leaf shaped with two muscular suckers
  • Fertilization occurs as either a cross between 2 worms, or self-fertilization
  • Larval stage occurs in a snail (their first intermediate host)
  • Eggs are oval, operculate, and passed to fresh water where they hatch a ciliated miracidium larval stage
  • The miracidium swims to find its snail host and develops inside the snail into a second larval stage, the cercaria, an infective
  • The cercariae swarm out to penetrate a second intermediate host and may encyst as metacercariae, another infective stage
256
Q

Which flukes belong to the family Fascilodae?

A
  • Clonorchis sinensis (Chinese liver fluke)
  • Fasciola hepatica (Sheep liver fluke)
  • Paragonimus westermani (lung fluke)
257
Q

What type of parasite are Schistosoma spp.?

A

Metazoal trematodes

258
Q

What are the species of Schistosoma?

A
  • S. mansoni
  • S. japonicum
  • S. haematobium
259
Q

What is the pathogenesis of schistosomiasis?

A
  • Cercariae freely swimming penetrate the skin
  • Female schistosomes lay eggs in the venous system
  • When the eggs are released, many are swept back into the circulation and lodge in the liver (S. mansoni, S. japonicum) or the urinary bladder (S. haematobium)
260
Q

What are the clinical features of liver schistosomiasis?

A
  • Liver fibrosis
  • Impeded blood flow to the liver
  • Portal hypertension
  • Accummulation of ascites in the abdominal cavity
  • Hepatosplenomegaly
  • Esophageal varices
261
Q

What are the clinical features of urinary tract schistosomiasis?

A
  • Urethral pain
  • Increased urinary frequency
  • Dysuria
  • Hematuria
  • Bladder obstruction leading to secondary bacterial infection
262
Q

How are cestodes transmitted?

A

Eating infected flesh

263
Q

What type of parasite is Taenia saginata?

A

Metazoal cestode

264
Q

What is the morphology of Taenia saginata?

A
  • Grows to 4–8 m
  • Consists of about 1000 segments called proglottids
265
Q

What is the common name of Taenia saginata?

A

Beef tapeworm

266
Q

What type of parasite is Taenia solium?

A

Metazoal cestode

267
Q

What is the common name of Taenia solium?

A

Pork tapeworm

268
Q

What are the features of Taenia solium infection?

A
  • Cysticercosis is the presence of larval stage in human tissue
  • Cysticerci encyst in muscles or in the brain, where they lead to epilepsy
269
Q

What type of parasite is Echinococcus granulosus?

A

Metazoal cestode

270
Q

What are the features of Echinococcus granulosus infection?

A
  • Cysts containing the larvae develop after ingestion of eggs
  • These cysts form primarily in the liver and the lung (hydatid cyst)
271
Q

What type of parasite is Diphyllobothrium latum?

A

Metazoal cestode

272
Q

What is the common name of Diphyllobothrium latum?

A

Broad fish tapeworm

273
Q

Which clinically significant cestode of humans is the largest?

A

Diphyllobothrium latum

274
Q

How is Diphyllobothrium latum transmitted?

A

Eating improperly cooked or raw fish infected with the larvae (plerocercoids)

Microbiology and immunology (33 decks)

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