Filarial nematodes Flashcards
What is the type of lifecycle that filarial nematodes have?
Indirect lifecycle (transmitted by a vector or intermediate host).
Where do eggs hatch?
Within the female to release anL1 larvae from the female. This is a microfilariae (mf).
Where do L2 and L3 larvae develop? Where do they go after?
In the mosquito after mf have been taken up in the blood meal. They migrate from the thoracic flight muscles to the head and through the proboscis.
Describe the lifecle of filarial worms.
Humans are infected by mosquitos when they take a blood meal and inoculate L3 larvae –> adults are in the lymphatics –> adults produce mf (eggs hatch in females and mf are released) –> the sheathed mf migrate to the lymph and blood channels –> mf taken up by mosquito in blood meal –> mfs lose their sheath and peentrate mosquito midgut and thoracic flight muscles –> develop into L1 to L3 –> L3 migrate to head and penetrate through proboscis.
What is the infective agent that causes river blindness?
Onchocerca volvulus.
What is loa loa transmitted by?
Deerflies/ mangoflies. (Chrysops)
What is onchocerca transmitted by?
Blackflies and biting midges.
What is dracunculus medinensis?
Guinea worm. Not a filarial nematode but is grouped together. Spread by ingestion of infected copepods.
How do we treat LF?
- Loa loa: repeated treatment with DEC (diethylcarbamazine) to target adults as the drug usually only affects the mf.
- Onchocerca: ivermectin (ivermectin NOT used for loa loa)
Albendazole is sometimes used in combination with DEC or ivermectin respectively.
How does DEC work?
Mode of action unclear but appears to involve immune system components- requires a good immune system. Results in the paralysis of worms.
Why is DEC not used for oncho?
Life-threatening immune reaction produced, this is called the mazzotti reaction.
How does ivermectin work for onchocerca?
Binds to GABA with high affinity and causes an increase in chloride ions and paralysis of worms.
Other than filarial worms (onchocerca) what else is ivermectin effective against?
Ascaris, strongyloides, scabies and headlice.
What is body cavity filariasis caused by?
Mansonella perstans and m ozzardi
What are mansonella spp of filarial nematodes spread by?
Culicoides biting midge and simulium blackflies.
Where do we find mansonella:
- Ozzardi
- Sterptocerca
- Perstans
Ozzardi: central and south america and the carribbean
Streptocerca: West africa
Perstans: Sub saharan africa, central and south america and caribbean
Why are mansonella infctions seen as non-pathogenic?B
Because they usually produce very mild infections. sometimes general inflammatory symptoms and occasional dermatitis for streptocerca (as it resides in skin)
Where is the location of mansonella spp?
Sterptocerca- in the skin/dermis
Perstans and ozzardi- in subcutaneous tissues or body cavities.
Microfilariae in blood.
Where does the sheath come from?
A gelatinous bag from the females uterus.
What is the sheathing situation with mansonella species? lol
All mf are UNsheathed. They also are much smaller than other filarial worms which helps in their identification.
Where is the most common location of m perstans?
Pleural or peritoneal cavities.
Mf in blood
Where is the most common location for m ozzardi?
Subcutaneous or body cavities.
Mf in skin or blood
Where is the most common location for m streptocerca?
Dermis.
Mf in skin or blood.
How do we diagnose mansonella spp?
Skin snip or look in blood for mf.