Parasitology Flashcards
/ˌpɛrəsəˈtɑlədʒi/ – n. a synonym for death
1
Q
What is a parasite?
A
An organism that lives in (endoparasitic) or on (ectoparasitic) another organism (host) for survival
2
Q
What is a host?
A
A living organism that harbors a parasite
3
Q
What are the phyla of the parasitic kingdom?
A
- Protozoa
- Helminths
- Arthropods
4
Q
How many classes are there in the phylum Protozoa?
A
4 classes
- Sarcodina/Rhizopada
- Mastigophora (flagellates)
- Ciliates
- Sporozoa
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)
6
Q
What are the characteristics of the class Sarcodina/Rhizopada?
A
- Asexual reproduction
- Move by pseudopodia
7
Q
What are the characteristics of the class Mastigophora?
A
- Asexual reproduction
- Move by flagella (hence their alternative name, flagellates)
8
Q
What are the characteristics of the class Ciliates?
A
- Asexual reproduction
- Move by cilia
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
10
Q
To what phylum does the class Sporozoa belong?
A
Protozoa
11
Q
To what phylum does the class Mastigophora belong?
A
Protozoa
12
Q
To what phylum does the class Ciliates belong?
A
Protozoa
13
Q
To what phylum does the class Sarcodina/Rhizopada belong?
A
Protozoa
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)
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
16
Q
What are the divisions of the class Nematoda?
A
- Intestinal nematodes
- Tissue nematodes
17
Q
What are the characteristics of the class Cestoda?
A
- Tapeworms
- Flattened and segmented
- Hermaphroditic
18
Q
What are the characteristics of the class Trematoda?
A
- Flukes
- Flattened, leaf-shaped worms
- Hermaphroditic except Schistoma spp.
19
Q
Are cestodes dioecious (showing sexual dimorphism)?
A
No, they are hermaphroditic
20
Q
Are trematodes dioecious (showing sexual dimorphism)?
A
No, except Schistosoma spp.
21
Q
Are nematodes dioecious (showing sexual dimorphism)?
A
Yes
22
Q
What are the characteristics of arthropods?
A
- Have an exoskeleton
- Have jointed legs
23
Q
How many classes are there in the phylum Arthropoda?
A
Two classes
- Insecta
- Arachnida
24
Q
What are examples of Insecta parasites?
A
- Mosquitoes
- Lice
- Fleas
25
What are examples of Arachnida parasites?
* Ticks
* Mites
26
To what phylum does the class Insecta belong?
Arthropoda
27
To what phylum does the class Arachnida belong?
Arthropoda
28
To what phylum does the class Nematoda belong?
Metazoa
29
To what phylum does the class Cestoda belong?
Metazoa
30
To what phylum does the class Trematoda belong?
Metazoa
31
What taxon encompasses both Trematoda and Cestoda?
Platyhelminthes
32
How are arthropods classified by their role as vectors?
* 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
33
Which kind of arthropod only transmitts parasites from host to susceptible individual?
Mechanical arthropods
34
What kind of arthropod actively participate in the life cycle of parasites?
Biological arthropods
35
What are the types of parasites (by pathogenesis)?
* Ectoparasites
* Endoparasites
* Obligatory parasites
* Facultative parasites
* Permanent parasites
* Temporary/intermittent parasites
* Opportunistic parasites
* Coprozoic/spurious parasites
36
# Define
Endoparasite
A parasites that lives inside the bodies of its host and causes infection
37
# Define
Ectoparasite
A parasite that lives on the surface of its host and causes infection
38
# Define
Obligatory parasite
A parasite that is completely dependent on its host for survival
39
# Define
Facultative parasite
A parasite capable of surviving on its own or in association with a host
40
# Define
Permanent parasite
A parasite that spends its entire life cycle in or on the body of its host
41
# Define
Temporary (intermittent) parasite
A parasite that occupies its host transiently for resources and can complete its life cycle with or without the host
42
# Define
Opportunistic parasite
A parasite that causes disease only in immunodeficient patients (e.g. AIDS patients, patients undergoing chemotherapy)
43
# Define
Coprozoic (spurious) parasite
An organism that passes through its host's GI tract without causing any symptom or disease. It is detected in the stool
44
What is the result of infection with an opportunistic parasite in **immunocompetent** individuals?
Latent form, producing mild or no symptoms
45
What are the types of hosts?
* Definitive host
* Reservoir host
* Intermediate host
* Accidental host
46
# Define
Definitive host
A host that harbors the mature, adult stage of the parasite, **or** in which sexual reproduction of the parasite takes place
47
# Define
Reservoir host
A host that harbors the parasite and is considered a source of human infection
48
# Define
Intermediate host
A host that harbors the larval (immature, non-sexually reproducing) form of the parasite
49
# Define
Accidental host
A host that harbors a parasite that normally doesn't infect its species
50
What is an example of a parasite with a human definitive host?
*Taenia* spp.
51
What is an example of a reservoir host and its parasite?
Dogs with *Leishmania donovani* (the causative agent of visceral leishmaniasis, aka *kala azar* – black fever)
52
What is an example of an intermediate host and its parasite?
Snails with *Schistosoma* spp. (the causative agents of schistosomiasis, aka bilharzia)
53
What is an example of a parasite for which humans can be an accidental host?
*Toxocara canis* (dog roundworm), which normally infects dogs
54
# Define
Symbiosis
The relationship between two living organisms and the nature of their interactions
55
What are the types of symbiotic relationships?
* Mutualistic
* Commensal
* Parasitic
56
# Define
Mutualism
A symbiotic relationship where both organisms benefit and can successfully live apart
57
# Define
Commensalism
A symbiotic relationship where one organism benefits and the other is not harmed
58
# Define
Parasitism
A symbiotic relationship where one organism benefits and the other is harmed
59
What are the modes of transmission of parasitic infections?
* 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
60
What is the most common mode of transmission of parasitic infections involving contaminated food/drink
Fecal–oral route
61
What are the types of congenital/vertical infection with parasitic diseases?
* Transplacental to the fetus
* Transmammary through lactation
62
# Define
Autoinfection
When the complete life cycle of a parasite happens in a single host organism without the involvement of another host
63
What are the types of autoinfection?
* 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
64
# Define
Infective stage
The stage during which a parasite can enter the body and cause infection
65
# Define
Diagnostic stage
The stage during which a parasite leaves the body and can be detected diagnostically
66
# Define
Zoonosis
| (In parasitology)
A disease that is transmitted from animals to humans, either directly or via a vector (e.g. arthropods)
67
What are the methods of parasite pathogenesis?
* Mechanical
* Traumatic implantation
* Toxin production
* Tissue damage and necrosis
* Cellular destruction
* Immune stimulation
* Allergic reaction to insect bites or parasite toxins
68
What is mechanical pathogenesis of parasites?
The parasite may obstruct normal passages like the small intestine, bile tract, or colon
69
What are the types of traumatic pathogenesis of parasites?
* External: via invasion of the skin
* Internal: via attachment to the intestinal mucosa by the buccal capsule, producing ulcers
70
How do tissue damage and necrosis occur in parasitic infections?
By the enzymes secreted by parasites
71
How does cellular destruction occur in parasitic infections?
By feeding on cells or ROS damage
72
How is the immune system stimulated by parasites?
Parasitic antigens lead to adaptive immune responses and the formation of a fibrous capsule around the parasite
73
What factors affect the pathogenesis of a parasite?
* Number, size, and morphology of the parasite
* Movement and migration capabilities
* Site of infection
* Toxin production
* Host reaction
74
What are the broad types of diagnosis for parasitic infections?
* Clinical diagnosis: by characteristic signs and symptoms
* Laboratory diagnosis of samples (stool, urine, blood, tissue biopsy, sputum, or aspirates)
75
What are the types of samples used for diagnosis of parasitic infections?
* Urine sample
* Stool sample
* Blood sample
* Tissue biopsy
* Sputum sample
* Aspirated fluid
76
What types of parasitic infections are stool samples suitable for?
Intestinal infections
77
What are stool samples assessed for macroscopically?
* Consistency
* Color
* Composition
* Presence of adult parasites
78
How are stool samples microscopically examined?
* 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
79
What are the types of blood sample examinations?
* 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
80
For which parasites are tissue biopsies recommended?
* *Trichinella spiralis* (muscle biopsy)
* *Schistosoma* ova (rectal biopsy)
81
What types of parasitic infections require sputum examination?
* Parasites that live in the lung
* Parasites that are migrating through the lung
* Parasites that result from the rupture of cysts in the lung
82
Where may aspirates be taken from?
* The CNS (cerebrospinal fluid)
* Duodenum
83
What species may be detected through CSF aspirates?
* *Trypanosoma* spp.
* *Naeglaria* spp.
84
What species may be detected through duodenal aspirates?
* *Giardia lamblia*
* *Strongyloides* larva
* *Cryptosporidium parvum*
85
Which protozoa colonize the GI tract?
* *Entamoeba histolytica* (amoeba)
* *Blantidium coli* (ciliate)
* *Giardia lamblia* (flagellate)
* *Cryptosporidium* (sporozoate—coccidium)
86
Which protozoa colonize the blood?
* *Trypanosoma* (flagellate)
* *Leishmania* (flagellate)
* Malaria (sporozoate)
* *Babesia* (sporozoate)
87
Which protozoa colonize tissue?
* *Trypanosoma* (flagellate)
* *Leishmania* (flagellate)
* *Toxoplasma* (sporozoate)
* *Sarcocystis* (sporozoate)
88
Which protozoa colonize the genitourinary tract?
*Trochomonas vaginalis* (flagellate)
89
Which amoebae live in the large intestine?
* *Entamoeba histolytica* (pathogenic)
* *Entamoeba coli*
90
Which amoebae live in the buccal cavity?
* *Entamoeba gingivalis* (commensal)
91
Why are the commensal amoebae of the GI tract clinically important?
They often contaminate specimens and can be confused for *E. histolytica*, which is pathogenic
92
How can commensal amoebae be differentiated from pathogenic amoebae?
* PCR
* Commensal amoebae cannot phagocytose RBCs, while pathogenic ones can
93
Which amoebae live freely in the GI tract?
* *Naegleria fowleri* (pathogenic)
* *Acanthomoeba* (pathogenic)
* Coprozoic amoebae (commensal)
94
What is the geographical distribution of *Entamoeba histolytica*?
Worldwide, especially in temperate areas and places with poor sanitation
95
What is the habitat of *Entamoeba histolytica*?
Large intestine:
* Cecum
* Colonic flexures
* Sigmoidorectal region
96
What is the definitive host of *Entamoeba histolytica*?
Humans
97
What are the reservoir hosts of *Entamoeba histolytica*?
* Humans
* Dogs
* Pigs
* Rats
* Monkeys
98
What diseases does *Entamoeba histolytica* cause?
Amebiasis (amoebic dysentery)
99
What is the trophozoite stage of *Entamoeba histolytica*?
The vegitative, active, motile form found in tissues
100
What are the features of the trophozoite stage of *Entamoeba histolytica*?
* Protoplasm
* Central nucleus
* Karyosome
* Granular endoplasm with food vacuoles and RBCs
* Ectoplasm
101
Where is the trophozoite stage of *Entamoeba histolytica* found?
In tissue
102
Where is the cyst stage of *Entamoeba histolytica* found?
In the lumen or outside the body
103
What is the cyst stage of *Entamoeba histolytica*?
A quiescent form used to protect the amoeba from stresses
104
What types of cysts does *Entamoeba histolytica* form?
* Immature (non-infectious): uninucleate or binucleate
* Mature (infectious): quadrinucleate
105
How is *Entamoeba histolytica* transmitted?
* 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
106
What is the infective stage of *Entamoeba histolytica*?
The mature, quadrinucleate cyst
107
What is the diagnostic stage of *Entamoeba histolytica*?
* The mature, quadrinucleate cyst
* Trophozoite stage
108
How can *Entamoeba histolytica* infection be diagnosed?
Identification of cysts of trophozoite stage in feces
109
What are the clinical features of intestinal amebiasis?
* 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
110
When does chronic infection of intestinal amebiasis occur?
When the acute dysentery phase is not properly treated
111
What are the complications of intestinal amebiasis?
* 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
What is the pathogenesis of symptomatic intestinal amebiasis?
* 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
What is the pathogenesis of asymptomatic intestinal amebiasis?
No infection of the mucosa and submucosa
114
How does extra-intestinal amebiasis occur?
The trophozoites reach the blood through the intestinal ulcer and spread to different organs
115
What are the common sites of extra-intestinal amebiasis?
* Liver
* Lung
* Brain
* Skin
116
What are the features of liver amebiasis?
* 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
Why is the right lobe of the liver more commonly affected by amebiasis?
* Spread via the hepatic portal vein
* Extension from a perforating ulcer in the **right** colonic flexure
118
What are the features of lung amebiasis?
Lung abscess, leading to pneumonitis with chest pain, cough, and fever, typically in the lower part of the right lung
119
Why is the lower part of the right lung more commonly affected by amebiasis?
* Direct spread from liver lesions through the diaphragm
* Reached through the blood (very rare)
120
What are the features of brain amebiasis?
Brain abscess leading to encephalitis (potentially fatal)
121
What is the most fatal form of *Entamoeba histolytica* infection?
Extra-intestinal brain abscess; encephalitis
122
What are the features of cutaneous (skin) amebiasis?
Typically occurs in the perianal region
123
How does *Entamoeba histolytica* reach the skin to cause cutaneous amebiasis?
Rupture of the abdominal wall from the hepatic, colonic, or appendicular lesions
124
What type of parasite is *Entamoeba histolytica*?
Protozoal amoeba
125
What type of parasite is *Giardia lamblia*?
Protozoal flagellate
126
What diseases does *Entamoeba histolytica* cause?
Giardiasis
127
What is the habitat of *Giardia lamblia*?
* Duodenum
* Jejunum
128
What is the causative organism of beaver fever?
*Giardia lamblia*
129
What stages does *Giardia lamblia* have?
* Trophozoite
* Cyst
130
What is the morphology of the trophozoite form of *Giardia lamblia*?
* Heart shaped
* Two nuclei separated by a ventral disk used for attachment to the intestinal villi
* Four pairs of flagella
131
What is the morphology of the cyst form of *Giardia lamblia*?
* Ellipsoid
* Thick walled
* Highly resistant
* Immature: binucleate
* Mature: quadrinucleate
132
What is the infective stage of *Giardia lamblia*?
The mature, quadrinucleate cyst
133
What is the diagnostic stage of *Giardia lamblia*?
* Trophozoite (more commonly)
* Mature, quadrinucleate cyst
134
How is *Giardia lamblia* transmitted?
* 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
What are the clinical features of *Giardia lamblia*?
* Mostly asymptomatic
* Giardiasis when large numbers of the parasite attach to the bowel wall and cause irritation
136
What are the features of giardiasis?
* 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
How is giardiasis diagnosed?
* 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
What are the common pathogenic species of the genus *Cryptosporidium*?
* *C. hominis*
* *C. parvum*
139
What type of parasite are *Cryptosporidium* spp.?
Protozoal sporozoate
140
In which groups of people does *Cryptosporidium* infection typically occur?
Immunocompromised persons
141
What is the animal reservoir of *Cryptosporidium* spp.?
* Rodents
* Fowl
* Rhesus monkeys
* Cattle
* Other herbivores
142
What is the habitat of *Cryptosporidium* spp.?
Brush border of mucosal epithelial cells of the GI tract, especially the surface of villi of the lower small intestine
143
What are the features of *Cryptosporidium* infection?
* 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
How is *Cryptosporidium* infection diagnosed?
* 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
How is *Cryptosporidium* infection treated?
Nitozoxanide
146
How are *Cryptosporidium* spp. transmitted?
* Direct contact
* Autoinfection
147
What type of parasite are *Cyclospora* spp.?
Protozoal sporozoate
148
What is the habitat of *Cyclospora* spp.?
Brush border of mucosal epithelial cells of the GI tract, especially the surface of villi of the lower small intestine
149
What is the pathogenesis of *Cyclospora* infections?
Altered intestinal mucosa architecture with shortening of the villi due to diffuse edema and infiltration of inflammatory cells
150
What are the features of *Cyclospora* infection?
* Diarrhea
* Anorexia
* Fatigue
* Weight loss
151
How are *Cyclospora* infections diagnosed?
Examining stools for oocysts using acid fast stain
152
How are *Cyclospora* infections treated?
Trimethoprim-sulfamethoxazole (TMP-SMZ)
153
What type of parasite is *Balantidium coli*?
Protozoal ciliate
154
What diseases does *Balantidium coli* cause?
Balantidiasis (balantidial dysentery)
155
Which clinically significant protozoa of humans is the largest?
*Balantidium coli*
156
What are the features of *Balantidium coli* infection?
* Usually harmless
* Rarely, trophozoites invade the large intestine and terminal ileum causing erosions and ulceration
157
How is *Balantidium coli* infection treated?
Oxytetracycline, followed by iodoquinol or metronidazole
158
What are the morphologic features of the forms of *Balantidium coli*?
* Trophozoite: two nuclei, one sausage-shaped macronucleus, one micronucleus
* Cyst form
159
What type of parasite is *Trichomonas vaginalis*?
Protozoal flagellate
160
What are the forms of *Trichomonas vaginalis*?
Trophozoite only
161
What is the disease caused by *Trichomonas vaginalis*?
Trichomoniasis
162
What is the morphology of *Trichomonas vaginalis*?
* Pear shaped
* Central undulating membrane
* 5 flagella: 4 anterior and one along the undulating membrane
* Moves via a wobbling or rotating motion (corkscrew)
163
What is the habitat of *Trichomonas vaginalis*?
* In females: vulva, vagina, cervix
* In males: prostate, seminal vesciles, urethra
164
What is the pathogenesis of *Trichomonas vaginalis*?
* Destruction of the squamous epithelium of the genitourinary tract
* Development of a neutrophilic inflammatory reaction and petechial hemorrhages
165
How is *Trichomonas vaginalis* infection diagnosed?
Wet mount examination for motile trophozoites
166
How is trichomoniasis treated?
Topical and systemic metronidazole (or tinidazole, ornidazole, which have fewer side effects)
167
What are the clinical features of trichomoniasis in females?
* Low-grade inflammation
* Frothy yellow or creamy discharge
168
What are the clinical features of trichomoniasis in males?
* Dysuria
* Dyspareunia
169
What type of parasite are *Trypanosoma* spp.?
Protozoal flagellate
170
What diseases does *Trypanosoma* cause?
* African trypanosomiasis (African sleeping sickness)
* American trypanosomiasis (Chagas' disease)
171
How are the hemoflagellates transmitted?
Promastigotes and epimastigotes carried by vectors
172
What are the hemoflagellates?
* *Trypanosoma* spp.
* *Leishmania* spp.
173
What is the intracellular form of the hemoflagellates?
Amastigote
174
What are the diagnostic stages of the hemoflagellates?
* Amastigote
* Trypomastigote
175
What is the morphology of *Trypanosoma* spp.?
* Spindly, uniflagellate stages (trypomastigote, epimastigote, promastigote)
* Rounded, amastigote form
176
Which of the hemoflagellates does not have an intracellular form?
African *Trypanosoma*
177
How is African *Trypanosoma* transmitted?
The tsetse fly (*Glossina* spp.) as a vector, which is only found in rural Africa
178
How is American *Trypanosoma* transmitted?
Reduviid bugs as vectors, which defecate while taking a blood meal
179
What are the definitive hosts of American *Trypanosoma*?
* Humans
* Dogs
* Cats
* Rats
180
What is the habitat of American *Trypanosoma*?
* Blood (trypomastigote)
* Tissue (amastigote)
181
How is *Trypanosoma* diagnosed?
* Tissue biopsy
* Blood test for identification
182
What type of parasite are *Leishmania* spp.?
Protozoal flagellate
183
How is *Leishmania* transmitted?
* Female sand fly as a biological vector
* Blood transfusion
* Transplantation
* Vertical transmission
* Direct contact through nasal secretions
184
What is the pathogenesis of *Leishmania*?
* Obligate intracellular
* Infects phagocytic cells and macrophages
* Incubation period ranges from 10 days to 2 years
185
What diseases does *Leishmania* cause?
* Cutaneous leishmaniasis (confined to epidermis or dermis)
* Mucocutaneous leishmaniasis (nasopharyngeal)
* Visceral leishmaniasis (in secondary lymphoid organs, causes abdominal distension; *kala azar*)
186
What type of parasite are *Plasmodium* spp.?
Protozoal sporozoate
187
What is the causative organism of malaria?
*Plasmodium*
188
Which species of *Plasmodium* is the major species associated with deadly infection?
*Plasmodium falciparum*
189
What is the pathogenesis of malaria?
* 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
What is the morphology of the sporozoites of *Plasmodium*?
Round or oval
191
How do sporozoites of *Plasmodium* replicate?
Schizogony—multiple asexual fission producing merozoites
192
What is the alternative route of replication of *Plasmodium* sporozoites?
Dormant schizogony, remaining quiescent in the liver as hypnozoites, which may cause a relapse within 1–5 years
193
What are the steps of *Plasmodium* development in the erythrocytic cycle?
* 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
What type of parasite is *Toxoplasma gondii*?
Protozoal sporozoate
195
What are the definitive hosts of *Toxoplasma gondii*?
Cats
196
How are humans infected with *Toxoplasma gondii*?
Consumption of food/drink contaminated with cat feces
197
What are the features of *Toxoplasma gondii* infection?
* Immunocompetent persons: asymptomatic or flu-like illness
* Pregnant women in first pregnancy: developmental delays in the fetus
* Immuncompromised persons: disseminated toxoplasmosis
198
What are the forms of *Toxoplasma gondii*?
* Tachyzoites (like trophozoites)
* Bradyzoites (like hypnozoites of malaria or cyst forms)
199
What type of parasite is *Ascaris lumbricoides*?
Metazoal nematode
200
How is *Ascaris lumbricoides* transmitted?
By eggs. Freshly passed eggs are not infective, they require 2–3 weeks to be embryonated
* Foodborne
* Waterborne
* Soilborne
201
Which clinically significant nematode of humans is the largest?
*Ascaris lumbricoides*
202
What is the morphology of *Ascaris lumbricoides* eggs?
* Have a thick mammillated (covered with lumps) brownish shell
* Highly resistant to desiccation and environmental stresses
203
What are the general phases of the metazoal life cycle?
egg → larva → adult
204
What is the habitat of *Ascaris lumbricoides*?
Intestine
205
What is the infective stage of *Ascaris lumbricoides*?
Eggs
206
What is the diagnostic stage of *Ascaris lumbricoides*?
Eggs in the stool
207
What diseases does *Ascaris lumbricoides* cause?
Ascariasis
208
What is the pathogenesis of *Ascaris lumbricoides* infections?
* 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
What are the clinical features of *Ascaris lumbricoides* larvae passage in the lungs?
Induction of an inflammatory response (pneumonitis), leading to:
* bronchial spasm,
* mucus production, and
* Löffler syndrome (cough and hemoptysis, eosinophilia, and pulmonary infiltrates)
210
How are *Ascaris lumbricoides* infections diagnosed?
* Larvae from a sputum sample
* Eggs in the stool
* Endoscopy
* Cholangiograms (X-ray examination of the bile ducts)
211
How can male and female worms of *Ascaris lumbricoides* be differentiated?
* Females are longer
* Males have a copulatory spicule (their reproductive organ)
212
What type of parasite is *Enterobius vermicularis*?
Metazoal nematode
213
What is the common name of *Enterobius vermicularis*?
Pinworm
214
How can male and female pinworms be differentiated?
* Females are longer
* Females have a slender, pointed posterior end
* Males have a curved posterior end
215
Where, geographically, are pinworms found?
Found worldwide but more common in temperate climates
216
Infection with which helminth is the most common?
*Enterobius vermicularis* (pinworm)
217
What is the morphology of *Enterobius vermicularis* eggs?
* Rugby ball shaped
* Have a thin outer shell
* Infectious larvae may be visible inside the egg
* Immediately infectious
218
Where are *Enterobius vermicularis* eggs found?
The perianal region. Females lay them there at night
219
What is the main symptom of pinworm infection?
Perianal pruritus (itching) due to hypersensitivity from the eggs
220
How is *Enterobius vermicularis* transmitted?
* Autoinfection by itching the perianal region and transmitting the eggs found there to the mouth for re-ingestion
* Exposure to eggs on fomites
221
How is *Enterobius vermicularis* infection diagnosed?
The "Scotch tape" technique: sampling the perianal region in the morning for eggs laid the previous night, **before** bathing or defecation
222
What is the infective stage of *Enterobius vermicularis*?
Eggs ingested by human
223
What is the diagnostic stage of *Enterobius vermicularis*?
Eggs on the perianal folds
224
What type of parasite is *Trichuris trichiura*?
Metazoal nematode
225
What is the common name of *Trichuris trichiura*?
Whipworm
226
How can male and female whipworms be differentiated?
Females are longer
227
What is the morphology of adult *Trichuris trichiura* worms?
The anterior end of the worms is slender and the posterior end is thicker, like a buggy whip
228
What is the morphology of *Trichuris trichiura* eggs?
Barrel shaped with polar plugs
229
What is the life cycle of *Trichuris trichiura*?
* 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
Which species are referred to as hookworms?
* *Ancylostoma duodenale*
* *Necator americanus*
231
How can male and female hookworms be differentiated?
* Females are longer
* Males have a copulatory bursa (a broadened posterior end)
232
What is the infective stage of hookworms?
Filariform larvae
233
What is the pathogenesis of *Ancylostoma duodenale*?
* 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
What are the features of hookworm infection?
* Severe anemia and iron deficiency
* Abdominal pain and diarrhea
* Ground itch: erythema and pruritus at the site of skin invasion
235
What is the diagnostic stage of hookworms?
Eggs in the stool
236
Where do hookworm eggs hatch?
Outside the body, after 1–2 days
237
What type of parasite is *Strongyloides stercoralis*
Metazoal nematode
238
What is the common name of *Strongyloides stercoralis*?
Threadworm
239
What in their reproduction distinguishes *Strongyloides stercoralis* from other nematodes
Females are parthenogenic—they do not need to mate with males to reproduce
240
What is the pathogenesis of *Strongyloides stercoralis* (from exogenous sources)?
* 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
What are the fates of *Strongyloides stercoralis* eggs laid in the intestine?
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
What type of parasite is *Trichinella spiralis*?
Metazoal nematode
243
Which metazoal species causes intracellular infection?
*Trichinella spiralis*
244
How is *Trichinella spiralis* transmitted?
Eating raw or undercooked pork infected with the larval stage
245
What is the diagnostic stage of *Strongyloides stercolaris*?
Rhabditiform larvae in the stool
246
What is the infective stage of *Strongyloides stercolaris*?
Filariform larvae
247
What is the pathogenesis of *Trichinella spiralis*?
* 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
What are the clinical features of *Trichinella spiralis* infection?
* Diarrhea
* Abdominal pain
* Nausea
249
What are the features of tissue nematodes?
* Females lay larvae, not eggs
* Larvae require an intermediate host to complete their development into the infective stage
250
What are the Filariidae nematodes and their vectors??
* *Wucherieria bancrofti* (mosquito)
* *Brugia malayi* (mosquito)
* *Loa loa* (day-biting flies)
* *Onchocerca volvulus* (black flies)
251
What is the features of filariae?
* 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
What disease is caused by filariae?
Elephantiasis
253
What are the features of elephantiasis?
* 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
What disease is caused by *Onchocerca volvolus* and *Loa loa*?
Eye worm
255
What are the features of trematodes? (flukes)
* 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
Which flukes belong to the family Fascilodae?
* *Clonorchis sinensis* (Chinese liver fluke)
* *Fasciola hepatica* (Sheep liver fluke)
* *Paragonimus westermani* (lung fluke)
257
What type of parasite are *Schistosoma* spp.?
Metazoal trematodes
258
What are the species of *Schistosoma*?
* *S. mansoni*
* *S. japonicum*
* *S. haematobium*
259
What is the pathogenesis of schistosomiasis?
* 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
What are the clinical features of liver schistosomiasis?
* Liver fibrosis
* Impeded blood flow to the liver
* Portal hypertension
* Accummulation of ascites in the abdominal cavity
* Hepatosplenomegaly
* Esophageal varices
261
What are the clinical features of urinary tract schistosomiasis?
* Urethral pain
* Increased urinary frequency
* Dysuria
* Hematuria
* Bladder obstruction leading to secondary bacterial infection
262
How are cestodes transmitted?
Eating infected flesh
263
What type of parasite is *Taenia saginata*?
Metazoal cestode
264
What is the morphology of *Taenia saginata*?
* Grows to 4–8 m
* Consists of about 1000 segments called proglottids
265
What is the common name of *Taenia saginata*?
Beef tapeworm
266
What type of parasite is *Taenia solium*?
Metazoal cestode
267
What is the common name of *Taenia solium*?
Pork tapeworm
268
What are the features of *Taenia solium* infection?
* Cysticercosis is the presence of larval stage in human tissue
* Cysticerci encyst in muscles or in the brain, where they lead to epilepsy
269
What type of parasite is *Echinococcus granulosus*?
Metazoal cestode
270
What are the features of *Echinococcus granulosus* infection?
* Cysts containing the larvae develop after ingestion of eggs
* These cysts form primarily in the liver and the lung (hydatid cyst)
271
What type of parasite is *Diphyllobothrium latum*?
Metazoal cestode
272
What is the common name of *Diphyllobothrium latum*?
Broad fish tapeworm
273
Which clinically significant cestode of humans is the largest?
*Diphyllobothrium latum*
274
How is *Diphyllobothrium latum* transmitted?
Eating improperly cooked or raw fish infected with the larvae (plerocercoids)
