TM: Tissue Nematodes (Filaria) (i)

Intro

roundworms

in lymphatics + subcut tissue

visible to naked eye

Lymphatic filariasis

aka elephantiasis

complication of longstanding lower lomb lymphoeerma

caused by 3 worms

Wuchereria bancrofti

90% of cases

travel to lungs

Dx = thick blood smear

Tx = DEC (diethylcarbamazine)

Brugia malayi

B timori

vector (intermediate host) = mosquito (anopheles, aedes, culex, mansonia spp

risk factors: tropics/subtropics, repeated bites

Onchocerca volvulus

causes onchocerciasis (river blindness)

vector = black flies (simulium app)

Loa Loa

causes loaisis (African eye worm)

vector = deer flies (chrysops spp)

Mansonella

causes mansonelliasis

peritoneal/pleural/pericardial disease

vector = midges (culicoides spp)

humans are the definitive host for all filarial spp (supports the adult or sexually reproductive form of the parasite)

No known reservoirs

also in macaques, leaf monkeys, cats + civet cats

2nd most common cause of infectious blindness

43 countries, 50 million people @ risk

loss of visual acuity + blindness related to duration + severity of infection

99.9% of cases in Africa

also in the Americas

abnormal host immune response to microfilariae

punctate keratitis (death of cells on cornea surface - red, watery, photosensitive, vision may decrease)

pannus formation (abnormal layer of fibrovasc/granulation tissue over cornea)

corneal fibrosis

iridocyclitis (iris inflamm)

glaucoma (pressure buildup damages optic N)

choroiditis

optic atrophy

clinical triad...

dermatitis

skin nodules (onchocercomas)

ocular lesions

skin manifestations

onchodermatitis

leopard skin (depigmentation)

hanging groin (lost elasticity)

Dx

skin snips to visualise microfilariae

microscopy (insensitive)

PCR = gold-standard

Mazotti test

dose of DEC, +ve if itching exacerbated (due to dying larvae)

only do if skin snips, eye exam + filtration are -ve

biopsy of possible nodule

Tx

Ivermectin

150 micrograms/kg for 6-12 months

microfilaricidal only

eventually sterilises females

contraindicated in highly microfilaraemic loaisis

Suramin (last resort if intractable symptoms)

NB: DEC = TOXIC IN ONCHOCERCIASIS - NEVER USE (makes it worse)

good hygiene NB

worms reside in subcut tissues + can actively migrate across subconjunctiva (visible) + other tissues

symptoms usually confined to subcut swellings on extremities, localised pain, pruritus + urticaria

microfilaraemia tends to be assymptomatic

Calabar swelling

diagnostic feature

large transient area of localised nonerythematous subcut angioedema most common around joints

rarer manifestations

arthritis

breast calcification

meningoencephalopathy

endomyocardial fibrosis

peripheral neuropathy

pleural effusions

retinopathy

Dx

clinical

blood smear

blood filtration @ 4pm

expats usually amicrofilaraemic

adult worm isolation

serology

filaria specific IgG (doesn't speciate

Tx

best = DEC

micro + macrofilaricidal

risk of encephalopathy with high microfilaraemias

aphaeresis

separating the cellular + soluble components of blood using a machine

pre-tx to reduce the load 1st - if not available don't tx

albendazole (macro + maybe microfilaricidal)

ivermectin

microfilaricidal only in multiple doses

risk of encephalopathy with high microfilaraemias

NB rule out onchocerciasis

extraction of adult loa (light infections only)

Control

most effective = avoiding bites

bednet

long sleeves + trousers

insect repellent esp @ night

reduce amount of standing water (where eggs are laid)

cover water storage containers

improve waste-water + solid waste tx systems

kill eggs (oviciding)

killing larva (larviciding)

adults unsheathed + reside in subcut tissues

adults are sheathed + reside in lymphatic vessels + nodes, blocking them + causing non- pitting (unlike HF) oedema