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TM: Tissue Nematodes (Filaria) (ii) (Lifecycle (Infected larva transmitted…
TM: Tissue Nematodes (Filaria) (ii)
Lifecycle
Infected larva transmitted by infected biting arthropods during blood meal
larva migrate to appropriate site in host's body + develop into microfilariae producing macrofilaria (adults)
adults dwell in human tissues + can live for yrs
microfilariae migrate to lymph + blood channels to infect insects taking a blood meal
microfilariae penetrate insect's midgut + migrate to thoracic muscles to produce larvae
Larvae develop from L1-L3 then migrate to proboscis
Clinical features
Acute
inflamm phase
lymphangitis
filarial fever
tropical pul eosinophilia
nocturnal wheezing
caused by an immune hyper responsiveness to microfilariae trapped in lungs
typically seen in young males shortly after exposure
Chronic
lymphoedema
hydrocele
renal involvement
elephantiasis (enlargement of limbs, scrotum + breasts)
chyluria (milky white urine)
Can be assymptomatic
Often late
may take yrs (4-6 after infection)
takes 9 months for L3 larvae to develop to adults
Dx
traditional method = detection of microfilariae in peripheral blood or skin (skin more likely to detect them that blood)
in blood: all spp causing lymphatic filariasis, loa loa, M ozzardi, M perstans
microfilariae may periodically appear in peripheral circulation
hence blood should be examined @ different intervals over a 24hr period
W Brancrofti + B malayi + B timori tend to show nocturnal periodicity (samples between 10pm-2am)
skin snips: O volvulus + M stertocerca
O volvulus can be detected in cornea or ant chamber of eye using slit-lamp examination
filarial antigen blood test
also used to monitor response to tx
remains +ve for 3 yrs post tx
Tx
community approach
aim = break transmission
single dose DEC (as effective as multi dose)
mass drug admin in endemic countries - depends on prevalence
single dose ivermectin
combination tx
DEC-albendazole
ivermectin-albendazole
DEC salt
possible new target = wolbachia
gram -ve bacterium that has symbiotic relationship with human filaria except Loa Loa
can be eradicated with doxycycline for 6-8 wks
filarial infertility + occasional macrofilaricial effect