Nematodes- tissue nematodes Flashcards
Which three species of nematodes cause lymphatic filariasis?
Wucheria bancrofti, Brugia mlayai, Brugia timori
What condition does lymphatic filariasis develop into?
when it is chronic, it becomes elephantiasis
What is the distribution of Wucheria bancrofti?
primarily in Africa, South America, and other tropical and sub-tropical countries
What is the vector for Wucheria bancrofti?
mosquitoes that feed at night
When do the Wucheria bancrofti microfilariae appear in the peripheral circulation?
at night. they are nocturnal
Where are adult Wucheria bancrofti found in the body?
in the lumen of the lymphatic vessels. have been found in all lymphatic tissue, including adjacent subcutaneous tissues
Which sex of Wucheria bancrofti is bigger?
the female
Define ovoviviparous
when embryos develop inside the egg and are retained in the mother’s body until they are ready to hatch
In which parts of the body are Wucheria bancrofti more common?
in the upper and lower extremities and the male genitalia
What are the Wucheria microfilariae ensheathed in?
a sheath of chitin that may be a remnant of the egg
Describe the path taken by the microfilariae
- migrate between the lymphatic system and the bloodstream. during the day the aggregate in the lung capillaries.
- when ingested by a mosquito, they penetrate the stomach and move to the flight muscles.
- undergo 3 molts into L3 larvae
- move to the mosquito mouth parts
Why is it hypothesized that not all patients have the same symptoms to elephantiasis?
they think it is because different people have a different chance of activating their Th1 or Th2 response
What is the asymptomatic phase of W. bancrofti infection?
marked by a high microfiliarae infection but is asymptomatic
What is the inflammatory/acute phase of W. bancrofti infection?
female worm Ags elicit an inflammatory response. Worms block lymph. symptoms include fever, chills, skin infections, painful lymph nodes, tender skin
What is the obstructive/chronic phase of W. bancrofti infection?
marked by elephantiasis.
lymphatic dysfunction causing lymphedema and elephantiasis
scarring of affected areas occurs, as well as thickening of the skin
How can Wucheria bancrofti infection be diagnosed?
a blood smear taken from when the jevenile worms are in the periphery of the blood circulation
PCR is also effective
How can Wucheria bancrofti infection be treated?
severe symptoms can be avoided by cleansing the skin, surgery, or drugs (diethylcarbamazine, ivermectin, or albendazole). diethylcarbamazine is the drug of choice
no vaccines developed
How can Wucheria bancrofti infection be controlled?
mosquito control.
mosquitoe vector has a preference for human blood, W. bancrofti has no known reservoir
Which parasite causes river blindness?
Onchocerca volvulus
Which parasite species cause subcutaneous filariasis?
Onchocerca volvulus
Drancunculus medinensis
Loa loa
Mansonella streptocerca
What are the hosts of Onchocerca volvulus?
only known to affect humans, no reservoir host.
How is Onchocerca volvulus spread and in which niches?
transmitted through black fly (Simulium species), which are predominantly found near rivers
What problems does Onchocerca volvulus infection lead to?
fourth leading cause of blindness, worst disfiguring dermatitis second to polio
What has greatly reduced the occurrence of Onchocerca volvulus infection in endemic areas?
ivermectin program. one dose given to everyone each year, donated by Merck
Which parasites are ovoviviparous?
Wucheria bancrofti, Onchocerca volvulus, and Dracunculus medinensis
Describe the male and female worm association in Onchocerca volvulus infection
the female is much longer, and the two are often found intertwined
Where are the microfiliarae found in the body?
produced in the nodules and migrate throughout subcutaneous tissue
Describe the pathology of Onchocerca volvulus infection
- dead microfiliarae cause inflammatory reactions. Live worms cause dermatitis, eye lesions, and onchocercomas.
- lesions are due to immune system attacking worm Ag
- the higher the infection, the worse the symptoms are
- lesions on the cornea= keratitis
How can Onchocerca volvulus infection be diagnosed?
take skin from affected region
serological tests measure IgG. it is sensitive but not very specific
How can Onchocerca volvulus infection be treated?
ivermectin blocks the release of microfiliarae from the females, but does not kill adults. need to keep giving ivermectin to stop infection (live 10-15 years)
How can Onchocerca volvulus infection be controlled?
giving ivermectin once a year for 10-15 years
controlling black fly population
Which worm species is the longest nematode and also causes Guinea worm disease?
Drancunculus medinensis
How is Drancunculus medinensis transmitted?
through the cyclops (crustacean) in infected waters
Where does Guinea worm disease (drancunculiasis) occur?
only in Africa, a few villages in the Rajastan desert of India, and Yemen
Where do the female and male Dracunculus medinensis worms reside in the body?
in subcutaneous tissue, usually in the lower extremities. both have curved tails to anchor them to tissues
Describe the Dracunculus medinensis life cycle
- female adult releases microfiliarae into water.
- the copepods ingest the microfiliarae, which develop into L3 larvae
- humans eat infected copepods
- larvae penetrate wall of small intestine and migrate through connective tissue.
- two more molts until adult stage
- gravid females migrate through subcutaneous tissue to extremeties, causing ulcers
- ulcers burst when in contact with water, releasing microfiliarae
What is the pathology of Dracunculus medinensis infection?
multiple cutaneous blisters and ulcers
allergic rxns occur before ulcer bursts or when trying to remove worm
secondary bacterial infections from ulcers if untreated (tetanus, gangrene, death)
How can Dracunculus medinensis infection be diagnosed?
locating the head of the adult worm in the skin
identify larvae that are released in the water
How can Dracunculus medinensis infection be treated?
need to wind the worm on a stick very slowly, over days, to remove it without breaking it
sometimes surgical removal is possible
How are most Dracunculus medinensis infections prevented?
transmission is seasonal, cases are easily detected, methods of control (water purification) are very simple
