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.
What drugs are used to treat mansonella spp.
Usually drugs not very effective but:
Perstans: DEC + mebendazole
Ozzari: ivermectin
What are the the lymphatic filariases?
Wuchereria bancrofti
Brugia malayi
Brugia timori
What are the lymphatic filariases spread by?
Biting mosquitos. Do not confuse with other filariases and vectors!
Which is the most common LF?
W bancrofti
Why does LF infection require long exposure?
Because of the inefficient transmission from mosq, therefore people exposed for short periods of time usually don’t get it.
Inefficient because lots of larvae fail to penetrate the skin.
Where does mating of LF occur?
Between males and females lodged in the lymphatics.
What are the vectors of LF?
Mansonia, Aedes, culex and anopheles.
Which mosquito genera spread wuchereria?
Aedes and culex (e.g quinquefasciatus).
Where do c quinquefasciatus breed?
An urban problem- pit latrines, and cesspits.
What are the LF vectors in Asia?
Anopheles and mansonia spp.
What mosq is the main LF vector in Africa?
Anopheles.
Which LF is zoonotic and what can it infect?
BRUGIA is zoonotic (NOT wuchereria) and can infect monkeys which act as reservoirs and cats.
Which LF species are nocturnally periodic?
Wuchereria bancrofti and Brugia malayi, in most areas.
Which LF species are diurnally sub periodic?
Wuchereria bancrofti in polynesia.
Which LF species are nocturnally sub periodic?
Zoonotic strains of Brugia malayi in Malaysia, Phillippines and Indonesia.
What does the periodicity in diff areas relate to?
The local vectors- increases transmission.
What are the early signs of LF infection? What follows this?
- Episodic fever
- Inflammation of lymph nodes
- Hydrocele
- Followed by a chronic obstructive stage.
What do repeated episodes of inflammation and lymphedema lead to?
- Lymphatic damage
- Fibrosis
- Chronic swelling (esp extremities)
- Elephantiasis (legs, arms, scrotum, breasts, vulva).
- Skin changes (warts, depigmentation, secondary bacterial and fungal infection).
What is chyluria (a symptom of LF)?
Lymph fluid in urine (turns it white and milky).
How are female filarial worms easy to identify?
Double uterus.
What is tropical pulmonary eosinophilia? Where is it common? How does it present? Why is diagnosis harder?
A rare form of presentation of filariasis occurring in <1% of filarial cases. Common in SE asia and coastal India and more so in younger men.
Causes a hypersensitivity reaction in lung (potentially serious lung disease) characterised by dry night coughing, fever and wheezing. ALso show high levels of eosinophils and IgE in serum.
Harer to diagnose because all sequestered to lungs so do not test positive for filariasis.
How is tropical pulmonary eosinophilia treated?
Responds well to DEC but if left untreated interstitial lung disease develops over time.