TM: Tissue Nematodes (Filaria) (ii)

Lifecycle

  1. Infected larva transmitted by infected biting arthropods during blood meal
  1. larva migrate to appropriate site in host's body + develop into microfilariae producing macrofilaria (adults)
  1. adults dwell in human tissues + can live for yrs
  1. microfilariae migrate to lymph + blood channels to infect insects taking a blood meal
  1. microfilariae penetrate insect's midgut + migrate to thoracic muscles to produce larvae
  1. 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