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FDN3 By Nathan and Minnie > Parasites > Flashcards

Flashcards in Parasites Deck (128)
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1

What is the difference between an intermediate host and a definitive host of a parasite?

Intermediate = harbors the larval (asexual) stage of the parasite

Definitive = harbors the adult (sexual) stage of the parasite

 

2

Based on this image, which organism is the definitive host of malaria?

Which is the intermediate?

Why?

Mosquitos are the definitive hosts

Humans are the intermediate hosts

Adult sexual stage occurs in mosquitos

3

What is a paratenic host of a parasite?

A host that harbors a form of the parasite that does not undergo further development

4

Cestodes are _____worms

Tapeworms

(a type of flat worm)

5

Trematodes are _____worms

Flatworms/flukes

6

Nematodes are _______worms

Roundworms

7

A parasitic infection that causes eosinophilia is most likely a..

A) Protozoa

B) Helminth

Helminth

(Helminth infetions are associated with eosinophilia, protozoa infections are not)

8

What are the three main groups of protozoa?

Amoebae

Flagellates

Sporozoans

9

In which protozoal group is trypanosoma in?

What disease is it associated with?

Flagellates (Hemoflagellates)

Chaga's disease (cruzi) and African Sleeping Sickness (brucei)

10

Leishmania is in which protozoal group?

Which disease is it associated with?

Flagellates (hemoflagellate)

Leishmaniasis

11

Which insect carries the parasite that causes Chagas' disease?

Which parasite?

Reduviid (Triatomine, "kissing bug")

Trypanosoma cruzi, a hemoflagellate

12

What are the clinical manifestations of Trypanosoma cruzi infection?

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

Which of the following is a human pathogen?

A. Iodamoeba butschlii

B. Entamoeba coli

C .Entamoeba dispar

D. Entamoeba histolytica

E. Dientamoeba fragilis

D. Entamoeba histolytica

14

List the intestinal protozoa relevant to FDN3

  • Amoebae = Entamoeba histolytica
  • Flagellates = Giardia lamblia
  • Sporozoans = Cryptosporidium spp. 

 

 

15

List the blood and tissue protozoa relevant to FDN3

  • Amoebae
    • Naegleria spp
  • Flagellates
    • Trypanosoma spp (cruzi and bruci)
    • Leishmania spp
    • Trichomonas vaginalis
  • Sporozoans
    • Plsamodium spp
    • Toxoplasma gondii

 

16

Which insect carries the parasite that causes African Sleeping Sickness?

Which parasite?

Tsetse fly

Trypanosoma brucei

17

Think about the two relevant Trypanosoma species:

What are they?

Which insect carries each one?

Which diseases do they cause?

  • Trypanosoma cruzi
    • Reduviid bug (Triatomine, "Kissing bug")
    • Causes Chagas' disease
       
  • Trypanosoma brucei
    • Tsetse fly
    • Causes African Sleeping Sickness

18

What is the clinical presentation of Trypanosoma brucei infection?

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

How is African Sleeping Sickness diagnosed?

See trypomastigotes of Trypanosoma in blood smear or CSF

20

This sample from the patient's blood shows a parasite, identified as a flagellated protozoa 

Could this be Leishmania? Why or why not?

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

How is Chagas' disease diagnosed?

Serology

22

How does Trypanosoma brucei evade the host immune system?

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

Which insect carries the parasite that causes Leishmaniasis?

Which parasite?

The sandfly (phlebotamine)

Carries Leishmania spp

Note: Different species are associated with different regions and flavors of disease

24

Which protozoa can be sexually transmitted?

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 PlasmodiumP. 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?

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?

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 ofTaeniasis 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 = Wuchereria 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
(like Rickettsiae)

The bacteria are endosymbiont​s 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

 

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 Onchocera 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 Wolbachia 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)