2. Introduction
Filariasis is a parasitic disease caused by an infection with roundworms of the Filarioidea type. This
disease belongs to the group of diseases called helminthiases.
Eight known filarial nematodes use humans as their definitive hosts. These are divided into three groups
according to the niche they occupy in the body:
● Lymphatic filariasis is caused by the worms Wuchereria bancrofti, Brugia malayi, and Brugia
timori. These worms occupy the lymphatic system, including the lymph nodes; in chronic cases,
these worms lead to the syndrome of elephantiasis.
● Subcutaneous filariasis is caused by Loa loa (the eye worm), Mansonella streptocerca, and
Onchocerca volvulus. These worms occupy the subcutaneous layer of the skin, in the fat layer. L.
loa causes Loa loa filariasis, while O. volvulus causes river blindness.
● Serous cavity filariasis is caused by the worms Mansonella perstans and Mansonella ozzardi,
which occupy the serous cavity of the abdomen.
● The adult worms, which usually stay in one tissue, release early larval forms known as
microfilariae into the host's bloodstream. These circulating microfilariae can be taken up with a
blood meal by the arthropod vector; in the vector, they develop into infective larvae that can be
transmitted to a new host.
3. Taxonomy classification of filarial worms
Kingdom Animalia Animalia Animalia Animalia Animalia
Phylum Nematoda Nematoda Nematoda Nematoda Nematoda
Class Secementea Chromadorea Secementea Secementea Secememtea
Order Spirurida Spirurida Spirurida Spiruridae Spiruridae
Sub Order Spirurina Filarioidea Spirurina Spirurina Spirurina
Family Onchocercidae Onchocercidae Onchocercida
e
Onchocercidae Onchocercidae
Genus Wuchereria Loa Brugia Onchocerca Mansonella
Specie Bancrofti Loa Melayi, Timori Volvolus Ozzardi,Perstans,
Streptocerca
4. Distribution
● W. bancrofti Nocturnal periodic W. bancrofti is endemic in tropical America,
Caribbean, tropical Africa, Egypt, the Middle East, India and South East Asia,
southern and eastern China, the Far East and New Guinea.
● B. malayi and B. timori B. malayi is endemic in parts of South East Asia
including many of the islands of the Malay Archipelago. It also occurs in south
west India, the Philippines, Vietnam, China, and South Korea.
● LOIASIS: L. loa is restricted to the equatorial rain forest areas of West and
Central Africa particularly Congo, Gabon, Cameroon, southern Nigeria, and
equatorial Sudan
5. Transmission
● Infective larva of Microfilaria are transmitted through the bite of
mosquitoes(culex, aedes, anopheles) which participate in their life cycle as
vectors.
● Vector for LoaLoa: horseflies
of the genus Chrysops
● Onchocerca volvolus: female
biting blackflies of the genus
Simulium
11. Pathogenesis
● Wuchereria Bancrofti: They invade the lymphatic tissues and nodes.
They are transmitted by mosquitoes(culex, aedes, anopheles).
Signs and symptoms:
1. The asymptomatic phase: consists of high microfilariae infection, and
individuals show no symptoms of being infected
2. the inflammatory (acute) phase, the antigens from the female adult
worms elicit inflammatory responses. The worms in the lymph channels
disrupt the flow of the lymph, causing lymphedema. The individual
exhibits fever, chills, skin infections, painful lymph nodes, and tender skin
of the lymphedematous extremity. Other symptoms include
orchitis(inflammation of testes),epididymitis,
3. The obstructive (chronic) phase is marked by lymph varices, lymph
scrotum, hydrocele, chyluria (lymph in urine), and elephantiasis. include
thickening of the skin and elephantiasis, which develops gradually with
the attack of the lymphatic system. Elephantiasis affects men mainly in
the legs, arms, and scrotum. In women, the legs, arms, and breasts are
affected.
Elephantiasis
12. Pathogenesis
● Brugia Melayi: It similarly invades the lymphatic tissues and channel causing lymphatic filariasis.
● Lymphadenitis, the swelling of the lymph nodes, It is an early manifestation of filariasis, usually
occurs in the inguinal area during Brugia. malayi infection and can occur before the worms mature.
● Lymphangitis is the inflammation of the lymphatic vessels in response to infection. It occurs early in
the course of infection in response to worm development, molting, death, or bacterial and fungal
infection. The affected lymphatic vessels become distended and tender, and the overlying skin
becomes erythematous and hot. Abscess formation and ulceration of the affected lymph node
occasionally occurs during B. malayi infection,
● Lymphedema: The most obvious sign of infection, elephantiasis, is the enlargement of the limbs–
usually the legs. A late complication of infection, elephantiasis is a form of lymphedema and is
caused by repeated inflammation of the lymphatic vessels. Repeated inflammatory reactions causes
vessel dilation and thickening of the affected lymphatic vessels, which can compromise function..
Blockage of these vessels due to inflammatory induced fibrosis, dead worms, or granulomatous
reactions can interfere with normal fluid balance, thus leading to swelling in the extremities.[3]
Elephantiasis resulting from B. malayi infection typically affects the distal portions of the extremities.
Unlike Bancroftian filariasis, B. malayi rarely affects genitalia and does not cause funiculitis, orchitis,
epididymitis, hydrocele, or chyluria, conditions more often observed with Bancroftian infection.[2]
13. Pathogenesis
● Loa Loa: They invade the subcutaneous layer ( conjunctiva) of the eyes
causing localized allergic inflammations(Calabar swelling).L. loa adult worm
which travels under the skin can survive up to 10–15 years. The most visual
sign of adult worm infections is when the worm crosses the sclera of the eye,
● Onchocerca volvulus is a nematode that causes onchocerciasis (river
blindness), and is the second leading cause of blindness worldwide after
trachoma. it to be the causative agent of ‘craw-craw’ severe itching, a skin
disease found in West Africa. humans are the only known definitive host
Long-term infection can cause keratitis, an inflammation of the cornea in the
eye, and ultimately leads to blindness. Symptoms are caused by the
microfilariae and the immune response to infection, rather than the adults
themselves.
● Mansonella streptocerca: human parasitic roundworm causing the disease
streptocerciasis. It is a common parasite in the skin of humans in the rain
forests of Africa, filarial nematodes that cause subcutaneous filariasis in
humans
14. Periodicity of microfilarial and chyluria
● Nocturnal periodicity: Microfilariae are present in greatest numbers in
the peripheral blood during night hours, e.g. periodic Wuchereria
bancrofti, Brugia malayi and Brugia timori
● . Diurnal periodicity: Microfilariae are present in greatest numbers in the
peripheral blood during day hours, e.g. Loa loa.
Chyluria An uncommon complication of chronic bancroftian filariasis is
chyluria. It occurs when the urogenital lymphatic vessels which are linked to
those that transport chyle from the intestine become blocked and rupture.
Chyle and occasionally blood and microfilariae can be found in the urine
especially in early morning specimens. Microfilariae are usually present in
the fibrin clots which form.
15. Diagnosis
● Peripheral blood examination stained with giemsa: Concentration and
microhematocrit tube and membrane filtration technique.
● Examination of urine for chyluria suggestive for Wuchereria bancrofti
● Examination of skin nodes/ skin snips for onchocerca volvulus
Editor's Notes
Periodicity may be influenced by body temperature, oxygen and sleeping habits.
