14. Tissue nematodes

Question 1

What are the 3 tissue nematodes that we saw?

Answer 1

• Onchocerca volvulus
• Dracunculus medinensis
• Wucheria bancrofti

Question 2

what is the common name for the disease caused by Onchocerca volvulus?

Answer 2

River blindness

Question 3

what is the common name for Dracunculus medinensis?

Answer 3

Guinea worm

Question 4

what is the common name for the disease caused by Wuchereria bancrofti?

Answer 4

Elephantiasis

Question 5

what is required for the Onchocerca volvulus life cycle?

Answer 5

• humans

- black flies

Question 6

what is required for the Dracunculus medinensis life cycle?

Answer 6

• humans

- Cyclops (an aquatic invertibrate)

Question 7

how do humans aquire Onchocerca volvulus?

Answer 7

via fly bite

Question 8

how do humans acquire Dracunculus volvulus?

Answer 8

ingestion of water containing Cyclops

Question 9

which are the tissue nematodes that are transmitted by arthropods?

Answer 9

• Wuchereria bancrofti (Elephantiasis)

- Onchocerca volvulus (River blindness)

Question 10

which are the tissue nematodes that are transmitted by copepods?

Answer 10

• Dracunculus medinensis (Guinea worm disease)

Question 11

what are the three parasites that can cause lymphatic filariasis?

Answer 11

the three filarial worms:

• Wuchereria bancrofti
• Brugia malayi
• Brugia timori

Question 12

what us caused by chronic infection by a filarial worm?

Answer 12

elephatiasis

Question 13

what is the vector for Wuchereria bancrofti?

Answer 13

mosquito, most of which feed at night

Question 14

what is the preference of mosquito vectors?

Answer 14

they prefer human blood

Question 15

what is special about the nocturnal microfilariae?

Answer 15

they appear in the peripheral circulation at night (so that they can be easily picked up by mosquitos)

Question 16

which are the “threadlike” nematodes

Answer 16

Wuchereria

Question 17

where are Wuchereria nematodes located?

Answer 17

in the lumen of lymphatic vessels

Question 18

what is the name of Wuchereria larvae?

Answer 18

microfilariae

Question 19

what is oviviparous and which parasite uses this reproductive strategy?

Answer 19

• mode of reproduction in which embryos develop inside eggs that are retained within the mother’s body until they are ready to hatch

Question 20

how many microfilariae can be release by the female in a day?

Answer 20

10,000

Question 21

where do the worms most commonly live in the body?

Answer 21

in the lymphatics of the lower and upper extremities and in male genitalia

Question 22

what are microfilariae encased in?

Answer 22

a sheath of chitin - which is possibly a remnant of an eggshell

Question 23

when and where do the microfilariae migrate in the body?

Answer 23

from the lymphatic circulation to the blood circulation and are typically present in large numbers between 10pm and 6am

Question 24

where can the microfilariae be found in the day?

Answer 24

in the capillaries of the lungs

Question 25

how long do microfilariae live?

Answer 25

1.5 years

Question 26

how are microfilariae transmitted?

Answer 26

- by mosquito bite, they penetrate the mosquitoes stomach wall and locate the thoracic flight muscles - when infectious, they locate to the mosquito biting mouth parts are are deposited on the skin NEXT to the wound

Question 27

how many molts do microfilariae have?

Answer 27

2 molts

Question 28

what is the infective stage of the microfilariae?

Answer 28

L3

Question 29

how long can the adults live in the host?

Answer 29

5-8 years, infections lasting 40y have been reported

Question 30

do all patients with chronic exposure to infective larvae develop over clinical disease?

Answer 30

no

Question 31

what are the three phases of wuchereria infection in the clinical disease?

Answer 31

- asymptomatic phase - inflammatory (acute) phase - obstructive (chronic) phase

Question 32

what is the asymptomatic phase

Answer 32

high microfilariae infection where individuals show no symptoms of being infected

Question 33

what is the inflammatory (acute) phase

Answer 33

- the antigens from the female adult worms elicit inflammatory responses - worms in the ;ymph channels disrupt the flow of the lymph - the individual will exhibit fever, chills, skin infections, painful lymph nodes and tender skin of the extremity - symptoms often lessen after 5-7 days

Question 34

what is the obstructive (chronic) phase

Answer 34

- marked by elephantiasis - lymphatic dysfunction causing lymphedema and elephantiasis and scrotal elephantiasis - scar formation on the affected areas - thickening of the skin

Question 35

how is Wuchereria infection diagnosed?

Answer 35

- blood smear, provided that the sample is taken at the time in the day where microfilariae can be found - PCR for filarial DNA

Question 36

what is the disease associated with Oncocerca volvolus?

Answer 36

Oncocerciasis (river blindness)

Question 37

what are the four parasites that cause subcutaneous filariasis?

Answer 37

- Oncocerca volvulus - Dracunculus medinensis (the Guinea worm) - Loa loa (the African eye worm) - Mansonella streptocerca

Question 38

which parasite does not have any reservoir hosts?

Answer 38

Oncocerca

Question 39

what is the vector for Oncocerca?

Answer 39

various species of blackfly

Question 40

what do blackflies AND mosquitos require to mature their eggs?

Answer 40

bloodmeal

Question 41

where do the larvae of the blackflies live?

Answer 41

in fast-flowing streams and rivers

Question 42

River blindness is the ______ leading cause of blindness in the developing world

Answer 42

fourth

Question 43

__________ has reduced onchocerciasis incidence and prevalence by more than 90% in certain regions

Answer 43

Ivermectin program

Question 44

which nematodes lie intertwined within each other in subcutaneous fibrous nodules

Answer 44

Oncocerca

Question 45

where are Oncocerca micrfilariae produced?

Answer 45

in the subcutaneous fibrous nodules

Question 46

what is a main consideration with treatment of Oncocerca microfilariae?

Answer 46

the dead microfilariae induce inflammatory reactions

Question 47

what are the clinical features of oncocerciasis?

Answer 47

- dermatitis - eye lesions - oncocercomas

Question 48

what causes the lesions seen in oncocerciasis?

Answer 48

as a consequence of cell mediated immunity

Question 49

what is keratitis?

Answer 49

results from the accumulation of punctate opacities in the cornea arising from immunopathologic damage to microfilariae in the eye

Question 50

how is Oncocerca diagnosed?

Answer 50

- examination of a piece of skin | - serological tests that measure IgG antibodies for onchocerciasis are sensitive but the specific is poor

Question 51

what is the drug of choice for Oncocerca

Answer 51

Ivermectin

Question 52

what disease do Drancunculus medinensis cause?

Answer 52

Guinea worm disease

Question 53

what is guinea worm disease

Answer 53

a disease unique to humans, can be eradicated by providing safe water supply (prevents D. medinensis from completing its life cycle)

Question 54

where can Dracunculus adult worms be found?

Answer 54

they dwell primarily in the subcutaneous tissues, usually in the lower extremeties

Question 55

what do both sexes of Dracuncula have in common?

Answer 55

they both have acutely curved tails, to anchor to tissues

Question 56

does the female drancunculus release larvae or eggs?

Answer 56

the female releases motile larvae

Question 57

what happens to Dracunculus larvae after they are released by the female?

Answer 57

they are ingested by copepods and develop into L3

Question 58

what is the infective stage of Dracunculus

Answer 58

L3

Question 59

what is the path of Dracunculus in the infected human?

Answer 59

they are ingested, and the larvae are released where they penetrate the wall of the intestine. larvae migrate in the connective tissue and molt twice before adult

Question 60

where do gravid females migrate?

Answer 60

through subcutaneous tissues into the extremities, causing ulcers that burst when coming in contact with water

Question 61

what is the pathology of Dracunculus infection?

Answer 61

- multiple cutaneous blisters and ulcers - allergic rxn in advance of rupture - substantial disability - secondary bacterial infections! (tetanus, gangrene, and death)

Question 62

how are the worms removed in a Drancunculus infection?

Answer 62

a person will wind the worm on a think stick until it is completely extracted - carefully in order to not break the worm

Question 63

give 4 reasons why Dracunculus infection has successful eradication efforts.

Answer 63

- no human carrier state beyond the 1-year incubation period - Transmission is seasonal - cases are easily detected - methods for controlling are relatively simple (water purification)