14. Tissue nematodes Flashcards
What are the 3 tissue nematodes that we saw?
- Onchocerca volvulus
- Dracunculus medinensis
- Wucheria bancrofti
what is the common name for the disease caused by Onchocerca volvulus?
River blindness
what is the common name for Dracunculus medinensis?
Guinea worm
what is the common name for the disease caused by Wuchereria bancrofti?
Elephantiasis
what is required for the Onchocerca volvulus life cycle?
- humans
- black flies
what is required for the Dracunculus medinensis life cycle?
- humans
- Cyclops (an aquatic invertibrate)
how do humans aquire Onchocerca volvulus?
via fly bite
how do humans acquire Dracunculus volvulus?
ingestion of water containing Cyclops
which are the tissue nematodes that are transmitted by arthropods?
- Wuchereria bancrofti (Elephantiasis)
- Onchocerca volvulus (River blindness)
which are the tissue nematodes that are transmitted by copepods?
- Dracunculus medinensis (Guinea worm disease)
what are the three parasites that can cause lymphatic filariasis?
the three filarial worms:
- Wuchereria bancrofti
- Brugia malayi
- Brugia timori
what us caused by chronic infection by a filarial worm?
elephatiasis
what is the vector for Wuchereria bancrofti?
mosquito, most of which feed at night
what is the preference of mosquito vectors?
they prefer human blood
what is special about the nocturnal microfilariae?
they appear in the peripheral circulation at night (so that they can be easily picked up by mosquitos)
which are the “threadlike” nematodes
Wuchereria
where are Wuchereria nematodes located?
in the lumen of lymphatic vessels
what is the name of Wuchereria larvae?
microfilariae
what is oviviparous and which parasite uses this reproductive strategy?
- mode of reproduction in which embryos develop inside eggs that are retained within the mother’s body until they are ready to hatch
how many microfilariae can be release by the female in a day?
10,000
where do the worms most commonly live in the body?
in the lymphatics of the lower and upper extremities and in male genitalia
what are microfilariae encased in?
a sheath of chitin - which is possibly a remnant of an eggshell
when and where do the microfilariae migrate in the body?
from the lymphatic circulation to the blood circulation and are typically present in large numbers between 10pm and 6am
where can the microfilariae be found in the day?
in the capillaries of the lungs
how long do microfilariae live?
1.5 years
how are microfilariae transmitted?
- 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
how many molts do microfilariae have?
2 molts
what is the infective stage of the microfilariae?
L3
how long can the adults live in the host?
5-8 years, infections lasting 40y have been reported
do all patients with chronic exposure to infective larvae develop over clinical disease?
no
what are the three phases of wuchereria infection in the clinical disease?
- asymptomatic phase
- inflammatory (acute) phase
- obstructive (chronic) phase
what is the asymptomatic phase
high microfilariae infection where individuals show no symptoms of being infected
what is the inflammatory (acute) phase
- 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
what is the obstructive (chronic) phase
- marked by elephantiasis
- lymphatic dysfunction causing lymphedema and elephantiasis and scrotal elephantiasis
- scar formation on the affected areas
- thickening of the skin
how is Wuchereria infection diagnosed?
- blood smear, provided that the sample is taken at the time in the day where microfilariae can be found
- PCR for filarial DNA
what is the disease associated with Oncocerca volvolus?
Oncocerciasis (river blindness)
what are the four parasites that cause subcutaneous filariasis?
- Oncocerca volvulus
- Dracunculus medinensis (the Guinea worm)
- Loa loa (the African eye worm)
- Mansonella streptocerca
which parasite does not have any reservoir hosts?
Oncocerca
what is the vector for Oncocerca?
various species of blackfly
what do blackflies AND mosquitos require to mature their eggs?
bloodmeal
where do the larvae of the blackflies live?
in fast-flowing streams and rivers
River blindness is the ______ leading cause of blindness in the developing world
fourth
__________ has reduced onchocerciasis incidence and prevalence by more than 90% in certain regions
Ivermectin program
which nematodes lie intertwined within each other in subcutaneous fibrous nodules
Oncocerca
where are Oncocerca micrfilariae produced?
in the subcutaneous fibrous nodules
what is a main consideration with treatment of Oncocerca microfilariae?
the dead microfilariae induce inflammatory reactions
what are the clinical features of oncocerciasis?
- dermatitis
- eye lesions
- oncocercomas
what causes the lesions seen in oncocerciasis?
as a consequence of cell mediated immunity
what is keratitis?
results from the accumulation of punctate opacities in the cornea arising from immunopathologic damage to microfilariae in the eye
how is Oncocerca diagnosed?
- examination of a piece of skin
- serological tests that measure IgG antibodies for onchocerciasis are sensitive but the specific is poor
what is the drug of choice for Oncocerca
Ivermectin
what disease do Drancunculus medinensis cause?
Guinea worm disease
what is guinea worm disease
a disease unique to humans, can be eradicated by providing safe water supply (prevents D. medinensis from completing its life cycle)
where can Dracunculus adult worms be found?
they dwell primarily in the subcutaneous tissues, usually in the lower extremeties
what do both sexes of Dracuncula have in common?
they both have acutely curved tails, to anchor to tissues
does the female drancunculus release larvae or eggs?
the female releases motile larvae
what happens to Dracunculus larvae after they are released by the female?
they are ingested by copepods and develop into L3
what is the infective stage of Dracunculus
L3
what is the path of Dracunculus in the infected human?
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
where do gravid females migrate?
through subcutaneous tissues into the extremities, causing ulcers that burst when coming in contact with water
what is the pathology of Dracunculus infection?
- multiple cutaneous blisters and ulcers
- allergic rxn in advance of rupture
- substantial disability
- secondary bacterial infections! (tetanus, gangrene, and death)
how are the worms removed in a Drancunculus infection?
a person will wind the worm on a think stick until it is completely extracted - carefully in order to not break the worm
give 4 reasons why Dracunculus infection has successful eradication efforts.
- 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)
