Test one Onchocerca volvulus and Loa loa Flashcards
River blindness is caused by what parasite?
Onchocerca volvulus
What super family is onchorcerca a part of? Describe them.
Filarioidea. Threadlike worms, transmitted by arthropods.
Which arthropod transmits Onchorcerca?
Blackfly
Describe the lifecycle of Onchocerca.
Blackfly carrying the infective form of the worm bites a human injecting the worm. The adults produce unsheathed microfilariae that migrate into the surrounding tissue. The microfilariae usually stay in the surrounding tissue but sometimes they migrate further into the blood, sputum, lymph, and even urine. A blackfly bites the affected person ingesting the microfilariae which migrate to the fly’s thoracic muscles where they mature into the infective form.
Where do adult onchocerca hang out?
Nodules on the surface of the skin
How does onchocerca ensure its survival in a human?
It releases chemicals that manipulate the immune system into doing a Th2 response, which allows the parasite to live.
What is the pathology of the worm in reference to?
Dead larval worms and the bacteria they carry, wolbachia. Live worms stop the immune system from mounting a response. when they die they stop suppressing the immune system which leads to inflammation.
Differentiate onchocerca infection from an african blackfly to a brazilian blackfly.
African blackflies tend to bite below the waist while american blackflies bite above the waist. So youll see nodules either on the legs in africa, or on the torso or head for americans.
What accounts for the blindness seen in river blindness? how long does it take?
Dead microfilariae in the eyes results in chronic inflammations which leads to fibroblast proliferation and scarring. takes 20-30 years to set in
What is the etiology of onchocerca volvulus?
Larva mature in one year
adults lie coiled in subcutaneous nodules
females release microfilariae for 15 years
Unsheathed microfilariae under skin, in eye
Vector: black fly
Epidimiology?
Tropical africa, mexico, guatamala, NE S. america
20 million people affected
5% are blind
What are the clinical manifestations of onchocerciasis?
Sub cutaneous nodules
- 2-3 cm in diameter
- Firm, non tender, moveable
- 1-100
How does one diagnose an Onchocerca infection?
Microfilaria will crawl out of a skin snip over night.
Find adults in nodules
Eosinophilia
Rash and allergic manifestations after DEC challenge
Describe the treatment for Onchocerciasis.
Ivermectin is administered. Ivermectin causes paralysis in the microfiaria, which causes the itching to stop. While ivermectin doesnt kill the adult worms it does prevent them from reproducing.
What are the main differences between Onchocerca and Loa Loa?
Similar life cycle except the Loa Loa dont form nodule in the skin. The microfilaria also live in the blood rather than the skin. Loa loa are carried by the mango fly rather than the black fly.
