2. • Filarial worms are nematodes that dwell in the
subcutaneous tissue and lymphatics.
• Eight filarial species infect humans of these,
four Wuchereria bancrofti,
• Brugia malayi,
• Onchocerca volvulus, and
• Loa loa are responsible for most serious
filarial infections.
• Filarial parasites infect an estimated 140
million persons worldwide,
• are transmitted by specific species of
mosquitoes or other arthropods and
• have a complex life cycle including infective
larval stages that are carried by insects and
adult worms that reside in either lymphatic or
subcutaneous tissues of humans.
3. The offspring of adults are
microfilariae, which, depending
on their species, are 200 to 250
um long and 5 to 7 um wide,
either circulate in the blood or
migrate through the skin
To complete the life cycle,
microfilariae are ingested by
the arthropod vector and
develop over 1 to 2 weeks into
new infective larvae.
Adult worms live for many years,
whereas microfilariae survive
from 3 to 36 months.
4. LYMPHATIC FILARIASIS
Lymphatic filariasis is caused by:
W. bancrofti, B. malayi, Brugia
timori
• The threadlike adult parasites
reside in lymphatic channels
or lymph nodes, where they
may remain viable for more
than two decades.
EPIDEMIOLOGY
• W. bancrofti, the most widely
distributed human filarial
parasite, affects an estimated
80 million people and is found
throughout the tropics and
subtropics, including Asia and
the Pacific Islands, Africa,
areas of South America, and
the Caribbean basin.
5. Humans are the only definitive host for the
parasite.
• Generally, the subperiodic form is found
only in the Pacific Islands; elsewhere, W.
bancrofti is nocturnally periodic.
• (Nocturnally periodic forms of
microfilariae are scarce in peripheral
blood by day and increase at
night, whereas subperiodic forms are
present in peripheral blood at all times and
reach maximal levels in the afternoon.)
• Natural vectors for W. bancrofti are Culex
fatigans mosquitoes in urban settings and
anopheline or aedean mosquitoes in rural
areas.
6. Brugian filariasis
• due to B. malayi occurs primarily
in
China, India, Indonesia, Korea, J
apan, Malaysia, and the
Philippines.
• B. malayi also has two forms
distinguished by the periodicity
of microfilaremia. The more
common nocturnal form is
transmitted in areas of coastal
rice fields, while the subperiodic
form is found in forests.
• B. malayi naturally infects cats as
well as humans.
• B. timori exists only on islands of
the Indonesian archipelago.
7. PATHOLOGY
• The principal pathologic changes result from inflammatory
damage to the lymphatics, which is caused by adult worms
and not by microfilariae.
• Adult worms live in afferent lymphatics or sinuses of
lymph nodes and cause lymphatic dilatation and thickening
of the vessel walls.
• The infiltration of plasma cells, eosinophils, and
macrophages in and around the infected vessels, along with
endothelial and connective tissue proliferation, leads to
tortuosity of the lymphatics and damaged or incompetent
lymph valves.
• Lymphedema and chronic-stasis changes with hard or
brawny edema develop
8. CLINICAL FEATURES
The common manifestations of lymphatic filariasis are:
• asymptomatic microfilaremia,
• hydrocele,
• lymphatic inflammation, and
• lymphatic obstruction.
• Asymptomatic microfilaremia is found in most infected
individuals who are clinically well.
• Infected males frequently develop disease in the scrotum
primarily because of the presence of adult worms in the
lymphatics of the spermatic cord.
• Hydrocele may develop and, in advanced stages, may evolve
into scrotal elephantiasis.
• Acute lymphangitis and lymphadenitis with high fever
("filarial fevers") are often accompanied by shaking chills
and transient local edema.
• Episodes can recur frequently and usually abate
spontaneously after 7 to 10 days.
9. • Lymphadenitis and lymphangitis
involve both the upper and the lower
extremities in bancroftian and
brugian filariasis, but genital
lymphatic involvement develops
almost exclusively in relation to W.
bancrofti infection.
• Eosinophilia and elevations of serum
concentrations of IgE and antifilarial
antibody support the diagnosis of
lymphatic filariasis.
• TREATMENT
• Treatment for lymphatic filariasis is
currently limited to
diethylcarbamazine (DEC) given at
6 mg/kg per day in either single or
divided doses for 2 to 3 weeks.
