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6. Parasitic diseases
Filariasis
F ilariases are h elm inth iases d ue to tissue-d w elling nem atod e w orm s (filariae).
H um an
to h um an transm ission takes place th roug h th e bite of an insect v ector.
T h e m ost im portant path og ens are outlined in th e table below . M ixed infections are
com m on in co-end em ic reg ions.
E ach filarial species is found in 2 principal d ev elopm ental stag es: m acrofilariae (ad ult
w orm s) and m icrofilariae (larv al offspring ). T h e treatm ent d epend s on th e path og enic
stag e of th e species consid ered and targ ets m icrofilariae for O. volvulus and
m acrofilariae for th e oth er species.
Species /Infections Location of Location of Pathogenic Presence of
macrofilariae microfilariae stage Wolbachia
Onchocerca volvulus Subcutaneous Skin and eye M icrofilariae Y es 6
(onch ocerciasis) nod ules B lood M acrofilariae No
Loa loa Subcutaneous
(loiasis) tissue
Wuchereria bancrofti, L ym ph v essels B lood M acrofilariae Y es
Brugia malayi and
Brugia timori
(lym ph atic filariasis)
C lassical antifilarial ag ents includ e d ieth ylcarbam azine ( D E C ) , iv erm ectin and
albend azole. D oxycycline is used solely in th e treatm ent of O. volvulus and lym ph atic
filarial w orm s, w h ich h arbour an end osym biotic bacterium ( Wolbachia) sensitiv e to
d oxycycline.
Onchocerciasis (river blindness)
T h e d istribution of onch ocerciasis is linked to th at of its v ector ( Simulium) , w h ich
reprod uces near rapid ly flow ing riv ers in intertropical A frica ( 9 9 % of cases) , L atin
A m erica (G uatem ala, M exico, E cuad or, C olom bia, V enezuela, B razil) and Y em en.
Clinical features
I n end em ic areas, th e follow ing sig ns, alone or in com bination, are sug g estiv e of
onch ocerciasis:
– O nch ocercom as: painless subcutaneous nod ules containing ad ult w orm s, usually
found ov er a bony prom inence (iliac crest, troch anters, sacrum , rib cag e, skull, etc.),
m easuring sev eral m m or cm in size, firm , sm ooth , round or ov al, m obile or
ad h erent
to und erlying tissue; sing le, or m ultiple and clustered .
– A cute papular onch od erm atitis: papular rash , som etim es d iffuse but often confined
to th e buttocks or low er extrem ities, intensely itch y, associated w ith scratch m arks,
157
Filariasis
F ilariases are h elm inth iases d ue to tissue-d w elling nem atod e w orm s (filariae).
H um an
to h um an transm ission takes place th roug h th e bite of an insect v ector.
T h e m ost im portant path og ens are outlined in th e table below . M ixed infections are
com m on in co-end em ic reg ions.
E ach filarial species is found in 2 principal d ev elopm ental stag es: m acrofilariae (ad ult
w orm s) and m icrofilariae (larv al offspring ). T h e treatm ent d epend s on th e path og enic
stag e of th e species consid ered and targ ets m icrofilariae for O. volvulus and
m acrofilariae for th e oth er species.
Species /Infections Location of Location of Pathogenic Presence of
macrofilariae microfilariae stage Wolbachia
Onchocerca volvulus Subcutaneous Skin and eye M icrofilariae Y es 6
(onch ocerciasis) nod ules B lood M acrofilariae No
Loa loa Subcutaneous
(loiasis) tissue
Wuchereria bancrofti, L ym ph v essels B lood M acrofilariae Y es
Brugia malayi and
Brugia timori
(lym ph atic filariasis)
C lassical antifilarial ag ents includ e d ieth ylcarbam azine ( D E C ) , iv erm ectin and
albend azole. D oxycycline is used solely in th e treatm ent of O. volvulus and lym ph atic
filarial w orm s, w h ich h arbour an end osym biotic bacterium ( Wolbachia) sensitiv e to
d oxycycline.
Onchocerciasis (river blindness)
T h e d istribution of onch ocerciasis is linked to th at of its v ector ( Simulium) , w h ich
reprod uces near rapid ly flow ing riv ers in intertropical A frica ( 9 9 % of cases) , L atin
A m erica (G uatem ala, M exico, E cuad or, C olom bia, V enezuela, B razil) and Y em en.
Clinical features
I n end em ic areas, th e follow ing sig ns, alone or in com bination, are sug g estiv e of
onch ocerciasis:
– O nch ocercom as: painless subcutaneous nod ules containing ad ult w orm s, usually
found ov er a bony prom inence (iliac crest, troch anters, sacrum , rib cag e, skull, etc.),
m easuring sev eral m m or cm in size, firm , sm ooth , round or ov al, m obile or
ad h erent
to und erlying tissue; sing le, or m ultiple and clustered .
– A cute papular onch od erm atitis: papular rash , som etim es d iffuse but often confined
to th e buttocks or low er extrem ities, intensely itch y, associated w ith scratch m arks,
157
