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