Parasites Flashcards
Focus on the parasites mentioned in Flaherty's SAS
1
Q
What is the difference between an intermediate host and a definitive host of a parasite?
A
Intermediate = harbors the larval (asexual) stage of the parasite
Definitive = harbors the adult (sexual) stage of the parasite
2
Q
Based on this image, which organism is the definitive host of malaria?
Which is the intermediate?
Why?
A
Mosquitos are the definitive hosts
Humans are the intermediate hosts
Adult sexual stage occurs in mosquitos
3
Q
What is a paratenic host of a parasite?
A
A host that harbors a form of the parasite that does not undergo further development
4
Q
Cestodes are _____worms
A
Tapeworms
(a type of flat worm)
5
Q
Trematodes are _____worms
A
Flatworms/flukes
6
Q
Nematodes are _______worms
A
Roundworms
7
Q
A parasitic infection that causes eosinophilia is most likely a..
A) Protozoa
B) Helminth
A
Helminth
(Helminth infetions are associated with eosinophilia, protozoa infections are not)
8
Q
What are the three main groups of protozoa?
A
Amoebae
Flagellates
Sporozoans
9
Q
In which protozoal group is trypanosoma in?
What disease is it associated with?
A
Flagellates (Hemoflagellates)
Chaga’s disease (cruzi) and African Sleeping Sickness (brucei)
10
Q
Leishmania is in which protozoal group?
Which disease is it associated with?
A
Flagellates (hemoflagellate)
Leishmaniasis
11
Q
Which insect carries the parasite that causes Chagas’ disease?
Which parasite?
A
Reduviid (Triatomine, “kissing bug”)
Trypanosoma cruzi, a hemoflagellate
12
Q
What are the clinical manifestations of Trypanosoma cruzi infection?
A
Chagas’ Disease
- Acute phase (high parasitemia)
- Periorbital edema (Romana’s sign)
- Fever
- Anorexia
- Hepatomegaly
- Lymphadenopathy
- Death (occasionally, mostly in infants)
- Chronic phase (undetectable parasitemia)
- Cardiomyopathy
- Megaesophagus
- Megacolon
- (everything is swollen)
13
Q
Which of the following is a human pathogen?
A. Iodamoeba butschlii
B. Entamoeba coli
C .Entamoeba dispar
D. Entamoeba histolytica
E. Dientamoeba fragilis
A
D. Entamoeba histolytica
14
Q
List the intestinal protozoa relevant to FDN3
A
- Amoebae = Entamoeba histolytica
- Flagellates = Giardia lamblia
- Sporozoans = Cryptosporidium spp.
15
Q
List the blood and tissue protozoa relevant to FDN3
A
- Amoebae
- Naegleria spp
- Flagellates
- Trypanosoma spp (cruzi and bruci)
- Leishmania spp
- Trichomonas vaginalis
- Sporozoans
- Plsamodium spp
- Toxoplasma gondii
16
Q
Which insect carries the parasite that causes African Sleeping Sickness?
Which parasite?
A
Tsetse fly
Trypanosoma brucei
17
Q
Think about the two relevant Trypanosoma species:
What are they?
Which insect carries each one?
Which diseases do they cause?
A
-
Trypanosoma cruzi
- Reduviid bug (Triatomine, “Kissing bug”)
- Causes Chagas’ disease
-
Trypanosoma brucei
- Tsetse fly
- Causes African Sleeping Sickness
18
Q
What is the clinical presentation of Trypanosoma brucei infection?
A
African Sleeping Sickness
Bite: non-pustular, painful, itchy chancre 1-3 weeks after bite
- East African = Acute
- T. brucei rhodensiense
- Abrupt onset of fever
- Headache
- Occipital lymphadenopathy (Winterbottom’s sign)
- West African
- T. brucei gambiense
- Subacute, chronic meningoencephalitis
- Subtle personality changes
- Somnolence
- Coma
- Death
19
Q
How is African Sleeping Sickness diagnosed?
A
See trypomastigotes of Trypanosoma in blood smear or CSF
20
Q
This sample from the patient’s blood shows a parasite, identified as a flagellated protozoa
Could this be Leishmania? Why or why not?
A
This could not be leishmania
Leishmania spp. in humans do not swim around in the blood, as this protozoa is doing; they only infect macrophages in their amastigote form
(amastigote = a-mobile = immobile)
The species shown above is Trypanosoma, in its trypomastigote form
21
Q
How is Chagas’ disease diagnosed?
A
Serology
22
Q
How does Trypanosoma brucei evade the host immune system?
A
Trypanosoma brucei = African Sleeping Sickness
Variant surface glycoproteins (VSGs) sheild the parasite and prevent the host immune system from accessing the plasma membrane or any other stable epitopes
If an antibody binds a VSG, the VSG is absorbed and recycled
23
Q
Which insect carries the parasite that causes Leishmaniasis?
Which parasite?
A
The sandfly (phlebotamine)
Carries Leishmania spp
Note: Different species are associated with different regions and flavors of disease
24
Q
Which protozoa can be sexually transmitted?
A
Trichomonas vaginalis
25
Which stage of the protozoal flagellate life cycle is most likely to be found in the tissues and macrophages of humans?
Amastigote
This is the form that is NOT mobile, found in tissues and macrophages
(*Leishmania, T. cruzi)*
Trypomastigotes are also found in humans, but ARE mobile; They are found in blood/serum
26
Which stage of the protozoal flagellate life cycle is most likely to be found in the blood/serum of humans?
Trypomastigote
This is the form that is mobile in human blood
(*T. cruzi, T, brucei)*
Amastigotes are also found in humans, but are not mobile; They are found in tissues and macrophages
27
A patient's blood sample is positive for *Trypanosoma bruci.*
Which form/stage of its lifecycle is the protozoa in?
Trypanosoma; this is the stage that is found in the blood
28
Which form of *Trypanosoma* spp. exist in the guts of their insect hosts?
Epimastigotes
(In general: epimastigotes and promastigotes are in flies, while amastigotes and trypomastigotes are in humans; not all protozoa take every form)
29
If a test question asks you about the life cycle stage of a hemoflagellate protozoa, what is a good rule of thumb to use?
* In flies:
* Epimastigote (replicative)
* Promastigote (infective)
* In humans:
* Amastigote (immobile, in macrophages or tissues)
* Trypomastigote (mobile, in bloodstream)
30
Which component of our immune system is most important in fighting helminths?
Eosinophils: Antibody-dependent cellular cytotoxicity
31
This picture shows a sample of heart tissue infected with *Trypanosoma**.*
Which *Trypanosoma* is this most likely to be?
Which life cycle stage are we looking at?
*Trypanosoma cruzi* - Chagas' disease - infects heart tissue to cause cardiomyopathy
This is the amastigote stage that is intracellular or in tisuses.
(Trypomastigotes are found in blood)
32
What are the 3 major types of Leishmaniasis and their causative parasites?
Which organisms carry the parasite?
Leishmaniasis is caused by *Leishmania* spp, and the vector is the **sandfly (phlebotamine)**
* Visceral leishmaniasis
* *L. donovani*
* *L. donovani chagasi*
* Cutaneous leishmaniasis
* Old World
* *L. major*
* *L. tropica*
* *L. ethiopia*
* New World
* *L. mexicana*
* *L. braziliensis*
* Mucocutaneous leishmaniasis
* *L. braziliensis*
33
How is Leishmaniasis diagnosed?
Skin or bone marrow biopsy or culture
Note: Blood culture will be negative. In humans, *Leishmania* only has an amastigote form, found in cells and tissues
(does not have a trypomastigote form, which is found in blood)
34
What is the clinical presentation of visceral leishmaniasis?
Parasites in macrophages of reticuloendothelial system
* Hepatosplenomegaly
* Pancytopenia (may look like lymphoma)
35
What is the clinical presentation of cutaneous leishmaniasis?
Chronic, non-healing ulcer
* Usually resolves within several months; leaves a scar
* Can relapse
* Therapy helps prevent relapse
36
A patient presents with the following ulcer.
They travelled to Brazil last month, and reported that the ulcer apeared while they were there.
What is your leading diagnosis?
How would you confirm?
Cutaneous leishmaniasis
Confirm with tissue biopsy; look for *L. braziliensis* amastigotes
37
How does mucocutaneousl leighmaniasis develop?
New World Cutaneous Leishmania can disseminate from the skin to the naso/oropharyngeal mucosal to cause mucosal leishmaniasis
This can occur months to years after initial cutanous infection with *L. braziliensisb*
38
A 28-year-old male returns from a safari in Tanzania with fever, headache, muscle and joint pains. On exam he has a large sore on his right arm and enlarged lymph nodes. His blood smear is shown.
Untreated, he is at risk of developing which of the following complications:
A. Severe anemia
B. Meningoencephalitis
C. Cardiomyopathy
D. Megaesophagus
E. Hypersplenism
B. Meningoencephalitis
The patient has African Sleeping Sickness, cause
(Note: Chagas disease can result in cardiomyopathy, megaesophagus, and hypersplenism, effectively ruling all three of those out; additionally, **Chagas is endemic to South America, not Africa**)
39
How can you use travel history to differentiate between a disease caused by *T. brucei* vs *T. cruzi?*
The Americas
* Trypanosoma cruzi* is endemic to the Americas -\> Chagas disease
* Trypanosoma brucei* is endemic to Africa -\> African Sleeping Sickness
40
Which of the following protozoal infections may be transmitted via blood transfusion?
A. Entamoeba histolytica
B. Cryptosporidium parvum
C. Trichomonas vaginalis
D. Trypanosoma cruzi
E. Giardia lamblia
D. Trypanosoma cruzi; the only one that can be found in the blood
*Entamoeba hystolitica, cryptosporidium parvum*, and *giardia lamblia* are transmitted fecal-orally; reservoir in soil
Trichomonas vaginalis is in the genital tract
41
Which of the following is a zoonotic infection?
A. Chagas disease
B. Cutaneous leishmaniasis
C. Amoebiasis
D. Trichomoniasis
A. Chagas disese
Other animals are hosts; humans are an incidental host
42
Describe the lifecycle of malaria
For each step: Location (life cycle stage)
Transmission to human host = mosquito bite
* Human blood stream (sporozoite)
* Liver: kupffer cells (schiznot -\> merozoite)
* Merozoites multiply
* Merozoites leave
* *P. vivax* and *P. ovale* may turn into hypnozoites and lay dormant (latent liver phase)
* Bloodstream: RBCs (merozoite -\> trophozoite)
* -\> Schiznot -\> merozoites burst through RBC
OR
* -\> Gametocyte gets sucked up by mosquito
In mosquito body
* Enters gut as gametocytes
* Undegoes sexual reproduction
* Gets into mosquito saliva (sporozoite)
* Transferred to human host via bite (sporozoite)
43
Where would you find *plasmodium* schiznots?
Red blood cells of human hosts
44
What organisms cause malaria?
*Plasmodium* spp
* *Plasmodium falciparum*
* *Plasmodium vivax*
* *Plasmodium ovale*
* *Plasmodium malariae*
* *Plasmodium knowlesi*
45
Which group of protozoa does the causative agent of malaria fall in?
Sporozoans
46
What is the clinical presentation of *Plasmodium vivax* or *Plasmodium ovale* infection?
Malaria (mild)
* Low-level parasitemia
* \<0.5%; only infects immature RBCs
* 48h fever cycle; fever on day 1, 3, 5
* Latent liver phase = potential for relapse
47
What is the clinical presentation of *Plasmodium malariae* infection?
Malaria (mild)
* Low level parasitemia
* \<1%; only infects older RBCs
* 72 hour fever cycle
* Fever on days 1, 4, 7 etc
* No latent liver infection
* Potential for chronic, persistent bloodstream infection (10-30 years)
48
What is the clinical presentation of *Plasmodium knowlesi* infection?
Malaria (Moderate to severe)
* Infects primates
* Infects young and old RBCs
* 24 h cycle
49
What is the clinical presentation of *Plasmodium falciparum* infection?
Malaria (most severe)
* High level parasitemia
* \>2%; infects all RBCs
* Fever cycle is often erratic
* CNS disease possible (cerebral malaria)
50
Which malaria-causing parasite poses the greates threat of relapse?
*Plasmodium malariae*
51
Which malaria-causing parasite might have a "banana-shaped appearance?"
*Plasmodium falciparum*
52
Describe the pathogenesis that causes the major symptoms of malaria
Anemia
* *Plasmodium* digests hemoglobin -\> RBC lysis
Capillary leak syndrome
* Cytokine release (TNF, IFN-gamma, IL-1) causes diffuse endothelial activation and inflammation
* This may cause diffuse intravascular coagulation and capillary leak syndrome
End-organ dysfunction
* Sequestration and endothelial cyto-adherence -\> capillary bed occlusion
Jaundice
* Hepatocyte injury
CNS injury
* *P. falciparum, P. knowlesi*
53
How is malaria diagnosed?
History of fever spikes
* *P. vivax and P. ovale* = tertian (every 2 days)
* *P. malariae* = quartan (evern 3 days)
* *P. falciparum* = erratic
* *P. knowlesi* = every 24 hours
Malaise, headache lethergy
Antigen tests (common *Plasmodium*, *P. falciparum* specific)
PCR
54
Why is *Plasmodium falciparum* so virulent?
*Plasmodium falciparum* Erythrocyte Membrane Protein-1 (PfEMP1) is a protein encoded by a multi-copy gene called **var.**
This protein mediates **cytoadherence** of RBCs to vascular endothelium as well as **antigenic variation.**
The parasite's ability to modify red blood cells results in capillary bed occlusion (and downstream injury), as well as **evasion of the host immune system**
55
Does exposure confer immunity to malaria? Why or why not?
A little; there is little cross-reactivity, so memory is region-specific and short-lived
Sub-species (region)-specific immunity develops slowly durign initial infection and provides protection from future identical infections.
However, it is lost within months-years of leaving the region
56
How is malaria treated?
Target the asexual stage of intravascular infection
Use druges that end in -quine (as well as some others)
Ex: quinine, chloroquine, mefloquine, primaquine...
57
Why would you prescribe mefloquine to a patinet who is going on a 6-month research project in the DRC?
Malaria prophylaxis
58
What exposures are associated with *Toxoplasma gondii*?
Cat poop
Consumption of undercooked meat
59
Which genetic polymorphisms may provide protection against malaria?
* Thalassemia
* G6PD deficiency
* Sickle Cell Trait
* Hemoglobin C disease
* Ovalcytosis (100% protective against cerebral malaria)
* RBC Duffy negativity
60
List the 3 major groups of helminths
* Platyhelminths (flatworms)
* Trematodes (flukes)
* Cestodes (tapeworms)
* Nematodes (roundworms)
* Annelids (segmented roundworms)
* Ex: Leeches
61
Name 3 species of blood fluke relevant to FDN3
* Schistosoma mansoni*
* Schistosoma japonicum*
* Schistosoma haematobium*
62
Failure to eradiate which tissue reservoir of hypnozoites following infection with P. vivax may result in resurgence of infection
Liver
63
Which *Plasmodium* spp. have a "latent liver phase?"
What does this mean?
*Plasmodium ovale* and *Plasmodium vivax*
Latent liver phase = they can turn into hypnozoites and lay dormant in the liver, causing relapse years after the initial infection
64
Failure to eradiate which tissue reservoir of hypnozoites following infection with *P. vivax* may result in resurgence of infection?
A. Lung
B. Brain
C. Spleen
D. Liver
E. Bone marrow
D. Liver
*P. ovale* can also form hypnozoites and lay dormant in the liver.
This is known as the "latent liver phase"
65
Which *plasmodium* species is causing this infection?
*Plasmodium falciparum*
Many cells are infected; *P. faclciparum* has the highest parasite load and will infect \>2% of RBCs
66
What is the correct sequence for malaria parasite development?
## Footnote
A. Merozoite→Trophozoite→Schizont→Sporozoite→Merozoite
B. Sporozoite→Merozoite→Trophozoite→Schizont→Merozoite
C. Trophozoite→Merozoite→Schizont→Sporozoite→Merozoite
B. Sporozoite→Merozoite→Trophozoite→Schizont→Merozoite
67
A young woman has just learned she is pregnant and wishes to minimize the risk of congenital disease in her baby. Which of the following will NOT reduce that risk?
## Footnote
A. Avoid travel to Lyme endemic regions
B. Have her spouse clean the cat litter box
C. Consume meat only when cooked “well done”
D. Wash her hands after changing diapers at the day care center where she works
A. Avoid travel to Lyme endemic regions
Lyme disease is not a TORCH agent
* Spouse cleaning litter box, consuming meat when well done = **prevents toxoplasmosis**
* Washing hands after diaper change = **prevents CMV** (High levels in urine)
68
77-year-old man presents with fever and chills 2 weeks after returning from Brazil. What is the cause of his illness?
His blood smear is shown below:
A. Trypanosoma cruzi
B. Trypanosoma brucei gambiense
C. Plasmodium falciparum
D. Plasmodium vivax
D. Plasmodium vivax
Not *Trypanosoma;* Trypanosoma are not intracellular (and *T. brucei* is only found in Africa)
Not *P. falciparum;* *P. falciparum* causes RBCs to get sticky and clump when it turns into trophozoites (due to action of PfEMP1), and these cells are not clumped
69
Describe the *Schistosoma* life cycle
Location (life cycle stage)
* Water (egg)
* Water (egg hatches to release miracidium)
* Snail (Miracidium -\> Sporocyst -\> Cercariae)
* Water (Cercariae)
* Human (Cercariae -\> Schistosomulae during penetration)
* Circulation (Schistosomulae)
* Liver (Schistosomulae -\> Paired adult worm)
* Migrate
* *S**. japonium, S. mansoni -\>* Bowel
* *S. haematobium -\>* Bladder
* Eggs excreted in feces in urine in fresh water
* Hatch, infect snail
70
Which parasites are most likely to cause portal vein hypertension?
* Schistosoma japonicum*
* Schistoma mansoni*
71
Describe the immune response to a schistosome infection
No response to adults; the worms absorb human antigens
Inflammatory response to eggs (100s-1000s produced daily)
* Delayed-type hypersensitivity reaction
* Granuloma formation
72
This egg belongs to which helminth?
*Schistosoma mansoni*
Lateral spine
73
This egg belongs to which helminth?
*Schistosoma japonicum*
No spine
74
This egg belongs to which helminth?
*Schistosoma haematobium*
Terminal spine
75
What are the three disease presentations of *Schistosoma* spp. in general?
Describe each one briefly
* Cercarial dermatitis
* Cercariae that die part-way through penetrating the skin
* Acute schistosomiasis = Katayama fever
* Onset 4-6 weeks after heavy primary infection
* Immune complex deposition, tissue damage due to complement + neutrophils
* Lasts for weeks
* Significnat mortality
* Chronic schistosomiasis
* Due to granulomatous reaction to eggs deposited in various tissues
* Gastrointestinal *(S. mansoni, S. japonicum)* or urinary tract *(S. haematobium)*
76
Which form of *Schistosoma* is likely to be found floating in fresh water?
Cercariae - can infect humans
Miracida - newly hatched, can infect snails
77
Which form of *Schistosoma* infects humans
Cercariae
78
Where do *Schistosoma* mature?
From which form to which form?
Liver
Schistomulae -\> paired adult worms
79
Where in the body do *Schistosoma* lay eggs?
* Schistosoma japonicum, Schistosoma mansoni* = bowl/colon
* Schistosoma haematobium* = bladder
80
Which *Schistosoma* form infects snails?
Miracida enter snails -\> sporocysts replicate in snails -\> cercariae are released from snails
81
How is Schistosomiasis diagnosed?
Look for **eggs**
* In the feces
* *S. japonicum, S. mansoni,* maybe some *S. haematobium*
* In the urine
* *S. haematobium*, maybe some *S. japonicum*
82
What are the 4 relevant cestodes?
Cestode = tapeworm (A type of flatworm)
* *Diphyllobothrium lactum* = **fish** tapeworm
* *Taeniasis saginata* = **beef** tapeworm
* *Taeniasis solium* = **pork** tapeworm
* *Echinococcus* spp = **dog** tapeworm
83
Where is each *Schistosoma* species endemic?
* *S. mansoni* = Africa, Middle East, South America, Carribean
* *S. japonicum* = Far East
* *S. haematobium* = Africa (esp. Nile River Valley)
84
A patient with no significant travel history is diagnosed with a helminth.
Which kind of helminth is this most likely to be? (general)
A cestode (tapeworm)
* *Diphyllobothrium lactum* from eating fish
* *Taenia saginata* from eating beef
* *Taenia solium* from eating pork
* *Echinococcus* spp. from exposure to dog poop
85
What are the risk factors for *Echinococcosis* infection?
Contact with dog feces
86
What is the definative host of *Echinococcus*?
Wild or domestic dogs
| (Humans are incidental/intermediate)
87
What are the possible clinical presentations of infection by an *Echinococcus* spp?
Tissue infection
* Cystic hydatid disease/cystic echinococcosis
* *Echinococcus granulosis*
* Most common
* Cyst in liver (most common), lung, other organs
* Slow growing
* Usually asymptomatic (unless very large)
* Rupture may cause anaphylactic reaction
* Alveolar hydatid disease (rare)
* *Echinococcus mutilocularis*
88
Which parasite is most likely to cause bladder calcifications?
*Schistosoma hematobium*
89
How do humans acquire infection with *Schistosoma mansoni*?
Contact with contaminated fresh water
90
Which agent causes hydatid disease?
*Echinococcus granulosus* (Dog tapeworm)
Hydatid disease = cycstic echinococcosis
91
How can Echinococcosis be prevented?
* Wash hands after handling dogs and before handling food
* Avoid ingestion of food, water, or soil contaminated with dog feces
* Don't allow dogs to eat raw meat
* Sheep, cattle, pigs, goats (intermediate hosts)
92
What are the features of a chronic infection with *Schistosoma mansoni?*
Portal hypertension
93
Which helminths are associated with anemia?
Hookworm
94
Which organism is associated with neurocysticercosis?
What are the symptoms?
*Taenia solium =* pork tapeworm
Ingestion of **eggs** causes neurocysticerosis
Brain lesions, brain injury, calcifications, **seizures**
95
What is the diagnostic test of choice when humans with *taenia solium* are the **definitive** host?
Definitive host = the host that has the adult male/female parasites
Diagnose with **stool exam**
(Brain imaging would diagnose neurocysticercosis; infection of eggs only)
96
What is cysticercosis?
Which organism causes it?
Cysticercosis is a centran nervous system disease caused by ingestion of*Taeniasis solium* **eggs.** Characterized by...
* Seizures
* Focal defects
* Hydrocephalus
* Ocular disease
(If *Taeniasis solium* proglottids are ingested, a tapeworm infection will result)
97
What is the presentation of Taeniasis solium?
If *Taeniasis solium* proglottids are ingested = tapeworm infection
If *Taeniasis solium* eggs are ingested = cysticercosis (CNS disease)
98
Which life cycle form of *Echinococcus* infects humans?
Which one infects dogs?
Humans: consume embyonated **egg** (found in dog feces)
Dogs: Ingest **cysts** from meat/organs of infected sheep
99
*Enterobius vermicularis* is a...
Pinworm (intestinal nematode)
100
*Trichuris trichiura* is a...
Whipworm (intestinal nematode)
101
*Ancylostoma duodenale* is a...
Old world hookworm (intestinal nematode)
102
*Necator americanus* is a...
New world hookworm (intestinal nematode)
103
*Ascaris lumbricoides* is a...
Intestinal nematode
104
*Strongyloides stercoralis* is a...
Intestinal nematode
105
*Trichinella spiralis* is a...
Intestinal nematode
106
Which two parasites cause elephantiasis?
* Wulchereria bancrofti*
* Brugia malayi*
107
Which parasite causes river blindness?
*Onchocerca volvulus*
108
What does *Toxocara* cause?
Visceral larva migranes
109
What does *Ancylostoma braziliense* cause?
Cutaneous larva migrans
110
How is Bancroftian filariasis transmitted to humans?
Which life cycle stages are present? Where?
**Mosquitos** transmit *Wuchereria bancrofti* larvae to humans
The adult worm lives in the lymphatic vessels and nodes
Sheathed microfilariae live in the bloodstream
(Causes elephantiasis)
111
List 4 filarial parasites
* Wuchereria bancrofti*
* Brugia malayi*
* Loa loa*
* Onchocerca volvulus*
112
What is the principal complication of infection with *Ancylostoma duodenale?*
Anemia
113
Describe the life cycle of the filarial parasites
Filarial parasites = *W**uchereria bancrofti, Brugia malayi, Loa loa, Onchocerca volvulus*
* **Microfilariae** exist in human blood (*W**. bancrofti, B. malayi, L. loa)* or skin *(O. volvulus)*
* Mosquito ingests **microfilariae** during blood meal
* **Microfilariae** -\> **L3 larvae** in mosquito
* Shed sheath
* **L3 larvae** are transmitted from mosquito to human during blood meal
* **L3 larvae** -\> **adults** in human lymphatics
* **Adults** produce **sheathed\* microfilariae** that migrate into blood or skin
* *\*Ochocerca volvulvus* is unsheathed
* Mosquito ingests **microfilariae** and the process repeats
114
What is *Wolbachia?*
Why is it significant to parasitic infection?
*Wolbachia* is a gram-negative, intracellular bacteria
**The bacteria are endosymbionts of arthropods and some filarial nematodes; without the bacteria, the nematodes cannot reproduce.** Contribute significantly to virulence
* Found in...
* *Wuchereria bancrofti*
* *Brugia malayi*
* *Onchocerca volvulus*
* Not found in...
* *Loa loa*
| (like Rickettsiae)
115
How is Loiasis transmitted to humans?
Which life cycle stages are present? Where?
**Horseflies** transmit *Loa loa* larvae to humans
The adult worm lives in the lymphatic vessels and nodes
Sheathed microfilariae live in the bloodstream
(Causes **calabar swelling)**
116
How is river blindness transmitted to humans?
Which life cycle stages are present? Where?
**Blackflies** transmit *Onchocerca volvulus* (Savanna strain) larvae to humans
The adult worm lives in the lymphatic vessels and nodes
Microfilariae live in the **skin**
(Causes **river blindness**)
117
How is Malayan filariasis transmitted to humans?
Which life cycle stages are present? Where?
**Mosquitos** transmit *Brugia malayi* larvae to humans
The adult worm lives in the lymphatic vessels and nodes
Sheathed microfilariae live in the bloodstream
(Causes elephantiasis)
118
Describe the pathogenesis of *O**nchocera volvulus* infection.
* Adults reside in nodules in subcutaneous tissue
* Adults are infected with endosymbiotic **wolbachia bacteria**
* Without wolbachia, the adult worms cannot reproduce
* If the adult worm dies, wolbachia are released; this causes a severe inflammatory response
* **Increased wolbachia population = increased blindness**
* Microfilariae live in skin
119
Which filarial nematode cannot be infected by wolbachia?
*Loa loa*
(*Wuchereria bancrofti, Brugia malayi, Onchocerca volvulus* cannot replicate without wolbachia endosymbiont)
120
Describe the pathogenesis of *Loa loa*
Adult worms migrate through subcutaneous tissue, conjunctivae
Calabar swelling (Subcutaneal swelling as the worm migrates; may reach several centimeters, appear suddenly in different locations, and last for several days)
Subconjunctival migration = "eye worm"
121
What is the causative agent of "eye worm"?
What is the causative agent of river blindness?
Eye worm = Loa loa
River blindness = *Onchocerca volvulus*
122
Which filarial parasite is most likely to cause blindness?
Why?
***Onchocerca volvulus*** is most likely to cause blindness becasue it caries high levels of *Wolbachia* bacteria
(*Wuchererica bancrofti* and *Brugia malayi* can also cause blindness, but typically do not carry as many *wolbachia* as *O. volvulus)*
123
Why isn't *Onchocerca volvulus* treated wtih diethylcarbamazine, an agent that would kill adult worms and microfilaria?
Killing the adult worms would release the endosymbiont *W**olbachia* living inside of the worms;
Instead, ivermectin is used to kill only the microfilariae
124
Why might doxycycline be used to treat *Wuchererica bancrofti, Brugia malayi,* and *Onchocerca volvulus*, but not *Loa loa*?
*Wuchererica bancrofti, Brugia malayi,* and *Onchocerca volvulus* harbor *Wolbachia* bacteria
Doxycycline can kill *Wolbachia* to reduce the severe, damaging immune response that the bacteria has when it is released from its dying worm host
*Loa loa* do not harbor *Wolbachia*
125
What parasite causes Dracunculiasis?
The guinea worm
126
Which organism is thought to have inspired the "symbol of medicine?"
How?
The guinea worm
It is extracted from humans by slowly winding it around a wooden peg
128
What approach has helped to achieve significant control of lymphatic filariasis?
Mass drug administration
129
What is the role of *Wolbachia* in lymphatic filariasis?
*Wolbachia* enhance the inflammatory responses when microfilaria die following treatment
(Wolbachia are endosymbionts of the filarial nematodes that cause lymphatic filariasis... not *Loa loa*)
