Filariasis
dr Amanuel A
Filariasis
Lymphatic filariasis
• Lymphatic filariasis is caused by
- Wuchereria bancrofti,
- Brugia malayi or
- Brugia timori.
While thelater two are found in Asia, the former is prevalent
in the tropics and subtropics. Therefore, W.bancrofti is
discussed below.
Definition: Filariasis (bancrofti) is due to the presence of
adult W.bancrofti in the lymphatic system or connective
tissues of man. Many species of Anopheles, Culex,
Mansonia and Aedes are vectors.
Epidemiology:
• It is widespread throughout much of the
tropics and subtropics. It is also found in
some Far East countries.
• Complete development of the larval forms has
been found to occur in many species of
mosquitoes.
• Generally, W. bancrofti larvae are in lesser
number (scarce) in the peripheral blood by
day and increase at night.
Epidemiology
• W. bancrofti
• found throughout the tropics and subtropics, including
Africa, Asia, Pacific Islands, South America, and the
Caribbean basin.
• most widely distributed filarial parasite
• 115 million people are estimated to be affected
• humans are the only definitive host
• nocturnally periodic, only few subperiodic form
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• Culex fatigans mosquitoes in urban settings
• Anopheline or aedean in rural areas
• B. malayi (Brugian filariasis)
• primarily in China, India, Indonesia, Korea, Japan,
Malaysia, and the Philippines.
• two forms distinguished by the periodicity (nocturnal &
subperiodic) of m.f.
• naturally infects cats as well as humans.
• B. timori exists only on islands of the Indonesian.
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Life Cycles:
Infective larval stages carried by insects.
Adult worms reside in either lymphatic or subcutaneous
tissues of humans.
200 -250 um long & 5 -7 um wide microfilariae (offspring
of adults)
They may or may not be enveloped in a loose sheath, &
either circulate in the blood or migrate through the skin
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Clinical features:
• The most common presentations of the lymphatic filariasis
are asymptomatic (or subclinical) microfilaremia, hydrocele,
acute adenolymphangitis and chronic lymphatic disease.
• Most of infected individuals have few symptoms despite
large numbers of circulating microfilaria in the peripheral
blood.
• But sub-clinical disease is common with microscopic
hematuria and/or proteinuria and in men scrotal
lymphangiectasia.
• Only few patients progress to the acute and chronic stages of
infection.
• Patients may present acutely with high-grade fever,
lymphangitis, and transient local edema.
• Later patients may have lymphedema (upper and lower
extremities) and scrotal swelling.
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Diagnosis:-
• Difficult because microfilaria may not easily be
identified.
• Definitive diagnosis is by demonstration of
microfilaria from blood, hydrocele fluid or other
body fluids at night.
Treatment:
• Diethyl carbamazepine (DEC, 6mg/kg daily for 12
days is) the treatment of choice.
• Albendazol 400mg twice daily for 21 days has been
shown to have microfilaricidal activity.
Onchocerciasis
Definition:
• Onchocerciasis ("river blindness") is caused by
the filarial nematode Onchocerca volvulus.
Etiology:
• The living parasites are white or cream colored
and transparent.
• The males are 19-42mm long and
• the females 33 – 50 cm.
Epidemiology:-
• Infection in humans begins with deposition infective
larvae on the skin by the bite of an infected black fly.
• The larvae develop into adult in subcutaneous tissue
and form nodules.
• About 7 months to 3 years after infection the gravid
female releases microfilariae that migrate out of the
nodule and through out the tissues.
• Infection is transmitted to other persons when a
female black fly ingests microfilariae from the host’s
skin and these microfilariae then develop into
infective larvae.
Clinical features:
• Following the bite of an infected fly, there is an
incubation period of several months before
nodules appear.
• The subcutaneous nodules, onchocercomata,
are the most characteristic lesions of
onchocerciasis. They usually appear on coccyx,
sacrum, thigh and bony prominences.
• But the most frequent manifestations of
onchocerciasis are pruritus and rash.
Onchocerciasis
• pruritus, dermatitis, onchocercomata (subcutaneous nodules),
& lymphadenopathies
• primarily affects skin, eyes, & lymph nodes
• damage is elicited by m.f & not by adult worms
• in skin, there are mild but chronic inflammatory changes that
can result in loss of elastic fibers & fibrosis
• Onchocercomata: subcutaneous nodules, which can be palpable
and/or visible, contain the adult worm
• in eye, neovascularization and corneal scarring lead to corneal
opacities & blindness
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Infective larvae inoculated by insects during blood meal
Larvae migrate to appropriate site of the host's body,
where they develop into microfilariae-producing adults
Adults dwell in various human tissues where they can
live for several years
W. b, B.m, B. t reside lymphatic vessels, lymph nodes
In case of O. volvulus resides in nodules in subcutaneous
• The skin lesions are characterized by wrinkling of
skin and epidermal atrophy that can more often
lead to hypopigmentation than hyperpigmentation.
Eczematous dermatitis and pigmentary changes are
more common in the lower extremities.
• Visual impairment is the most serious complication
of onchocerciasis. This is due to intense
inflammation that surrounds the dying microfilaria.
Early lesions are conjuctivitis with photophobia;
sclerosing keratitis occurs in minority of patients,
which leads to blindness. Inflammation in the
interior eye cause iridocyclitis.
• Patients could have enlarged inguinal lymph
nodes (hanging groin).
• Heavily infected patients could have severe
wasting.
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Onchocerciasis
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Diagnosis:-
• Diagnosis depends on demonstration of the
microfilariae in the skin snip or nodules.
• Microfilariae are rarely found in blood smear,
but may be seen in urine.
Treatment:
Chemotherapy is the main treatment.
• Ivermectin orally in a single dose of 150mg/kg, yearly or
semiannually is the treatment of choice. No agent so far
eradicates the adult worm. The drug is microfilaricidal and has
many advantages:
– No severe ocular reaction and
– prevents blindness due to optic nerve disease by 50%,
– the drug is taken orally only once every 6 – 12 months &
– Inhibits the production of microfilariae by adult female worms for
some months.
• Ivermectin is contraindicated if there is co-infection with loa
loa, in pregnant or lactating women and children under the age
of 5 years.
• Antihistamines should be given for the pruritus.
Prevention
• Personal exposure in endemic areas can be reduced by
avoiding black fly localities and by protective clothing.
Repellents are of value only for short periods as they
are washed off by sweat.
• Control programmes (2 in Africa and one in America)
have covered over 99% of all population living in
endemic areas.
The control of onchocerciasis today is based on 2
strategies:
• Vector control by spraying insecticides. Onchocerciasis
control Programme in WestAfrica used this strategy
• Large scale Ivermectin chemotherapy is the
main strategy being used by Onchocerciasis
Elimination Programme in the Americas
(OEPA) and African Programme for
Onchocerciasis control (APOC)
