MICROFILARIA

Wuchereria Bancrofti• It is a human parasitic roundworm that is the

major cause of lymphatic filariasis.• Found in lymphatic nodes and vessels.

W. Bancrofti was named after physician Otto Wucherer and parasitologist Joseph Bancroft.

Otto Wucherer Joseph Bancroft

Taxonomy Domain : Eukaryota Kingdom : Metazoa Phylum : Nematoda Class : Secernentea Order : Spirurida Family : Filariidae Genus : Wuchereria Species : Bancrofti

Morphology A transparent worms with a smooth cuticle. Creamy-white in colour. In females the tail tapers gradually and is

rounded at the tip. While in males the tail curves ventrally. Males and females live coiled together

and is difficult to separate. Females are ovo-viviparous. Life span: 5-10 years Sizes:

Female: 80-100 mm x 0.2-0.3 mm Male : 25-40 mm x 0.1 mm

Microfilariae The embryonic form of Wuchereria Bancrofti

(adult worm) is known as Microfilariae. Present in the peripheral blood of human.

Morphology They are colourless and transparent with

blunt head and pointed tails. Covered by hyaline sheath. The sheath is much longer than the embryo

so that they can move within it. The somatic cells or nuclei appear as

granules in the central axis of the embryo and extend from the head to tail-end.

The granules do not extend up to the tip of the tail and is a distinguishing feature of Microfiaria bancrofti.

Life Cycle

W. bancrofti passes its life cycle in two hosts: Man - Definitive host. Mosquito - Intermediate host. Eg:

Culex Aedes Anopheles

Geographical DistibutionLymphatic Filariasis affects over 120 million people in 73 countries throughout the tropics and sub-tropics of Asia, Africa, the Western Pacific, and parts of the Caribbean and South America.

Pathogenesis The infection with this parasite is named

wuchereriasis or filariasis. The disease is of two types:

1. Classical filariasis:• Caused by adult worm.• Eg: lymphangitis, elephantiasis,

lymphedema.2. Occult filariasis:• Caused by embryo.• Eg: eosinophilia, hepato-splenomegaly.

Lymphedema

Abnormal accumulation of lymph in tissues causing swelling of arms, breasts, or genitals.

ElephantiasisThe swelling and the decreased function of the lymph system make it difficult for the body to fight germs and infections. These people will have more bacterial infections in the skin and lymph system. This causes hardening and thickening of the skin, which is called elephantiasis. Many of these bacterial infections can be prevented with appropriate skin hygiene and exercise.

LymphangitisIt is an inflammation or an infection of the lymphatic channels that occurs as a result of infection at a site distal to the channel. 

EosinophiliaIt is a condition in which the eosinophil count in the peripheral blood exceeds 4.5×108/L (450/µL). Eosinophils usually account for less than 7% of the circulating leukocytes. A marked increase in non-blood tissue eosinophil count noticed upon histopathologic examination is diagnostic for tissue eosinophilia. Several causes are known, with the most common being some form of allergic reaction or parasitic infection.

Hepato-splenomegaly

Hepatosplenomegaly (commonly abbreviated HSM) is the simultaneous enlargement of both the liver (hepatomegaly) and the spleen (splenomegaly).

Diagnosis Direct evidence:

Demonstration of microfilariae in peripheral blood film, chylous urine, hydrocele fluid & lymph varix.

Microfilariae appear in large numbers in peripheral blood at night. Hence, blood film should be made in night between 10PM-2AM.

Indirect evidence: Serological test like ELISA, IFA and IHA can be

used but these test have low sensitivity and specifity.

Treatment Antifilarial Drugs• Diethylcarbamazine (DEC)

Dosage: 6 mg/kg/day for 12 days• Ivermectin

Dosage: single oral dose of 150 ug/kg body weight

• Combination of 2 (better results)

Treatment General Measures:• Rest• Antibiotics• Antifungal• Physiotherapy• Bandaging

ElephantiasisElephantoid tissues can be corrected surgically.

Prevention And ControlAvoiding mosquito bites is the best form of prevention. The mosquitoes that carry the microscopic worms usually bite between the hours of dusk and dawn. If you live in or travel to an area with lymphatic filariasis: Sleep under a mosquito net. Wear long sleeves and trousers. Use mosquito repellent on exposed skin

between dusk and dawn