Wuchereria BancroftiAby Elijah L. Bernardino

CLASSIFICATION Domain: Eukaryota: Multicellular, heterotrophic,

nucleus Kingdom: Metazoa: Animals, lack rigid cell wallsPhylum: Nematoda: Psuedoceolom, lack cilia

Class: Secernentea: Almost exclusively terrestrial, no caudal glandsOrder: Spirurida: collapsed stoma, use vertebrate as host, invertebrate as intermediateFamily: Filariidae: living in blood of vertebrate, transferred by insect biteGenus: Wuchereria: enclosed in a characteristic sheath, males smaller than females

General Characteristics• COMMON NAME: Bancroftian filariasis, Elephantiasis• Wuchereria Bancrofti is

a parasitic filarial nematode (roundworm) spread by a mosquito vector. The most common vectors are the mosquito species: Culex, Anopheles, Mansonia, and Aedes.

• It is one of the parasites that cause lymphatic filariasis or elephantiasis, an infection of the lymphatic system by filarial worms. This disease causes enlargement of body organs, such as the scrotum and legs.

• These worms lodge in the lymphatic system, the network of nodes and vessels that maintain the delicate fluid balance between the tissues and blood and are an essential component for the body's immune defense system.

• Wuchereria bancrofti in the blood of a human

Morphology• The adult worm is long, slender, and smooth with rounded

ends. It has a short cephalic region, dispersed nuclei throughout its body cavity, with no nuclei at the tail tip.

• Creamy, white , long filariform in shape.• The male worm is 40 mm long and 100 μm wide, and features a

curved tail. • The female is 6 cm to 10 cm long and 300 μm wide, nearly three

times larger in diameter than the male.• Females are ovoviviparous and can produce thousands of

juveniles known as microfilariae. Microfilariae of W. bancrofti retain the egg membrane as a sheath and are often considered advanced embryos.

Life Cycle• Mosquitoes carry the Wuchereria bancrofti larvae. When the mosquito

lands on a person, larvae in the infectious stage get on the skin and enter through the mosquito's bite.

• The larvae then travel to and lodge in the lymphatic vessels, where they develop into adult worms, which live for about five to seven years. They damage the lymphatic vessels, which in some people causes fluid build-up and swelling of the lymphatic system. This makes it difficult for the body to fight infection.

• The adult worms mate and produce millions of microfilariae, which resemble tiny larvae and are encased in a protective sheath. These microfilariae migrate into the lymph and blood channels.

• When another mosquito bites the host, it also picks up the microfilariae. Inside the mosquito, the microfilariae lose their sheaths and work their way through the mosquito's body until they can lodge in its thoracic muscles.In the thoracic muscles of the mosquito, the microfilariae develop into larvae and pass through two more larval stages until they reach the infective third stage.

• In the thoracic muscles of the mosquito, the microfilariae develop into larvae and pass through two more larval stages until they reach the infective third stage.

• The larvae in this infective stage travel to the mosquito's proboscis. When the mosquito bites another human, the Wuchereria bancrofti larvae enter through the wound and begin the cycle in the new host. It takes repeated bites from infected mosquitoes over several months or even years before lymphatic filariasis will develop.

• The microfilariae of W. bancrofti can be identified in blood smears by their sheath, size (280 x 7 micrometers), and the anterior V spot near the head and posterior V spot near the tail

Epidemiology• W. bancrofti is responsible for 90% of lymphatic

filariasis. Recently, it was estimated that there were 120 million worldwide cases of lymphatic filariasis. W. bancrofti largely affects areas across the broad equatorial belt (Africa, the Nile Delta, Turkey, India, the East Indies, Southeast Asia, Philippines, Oceanic Islands, Australia, and parts of South America.)

• The mosquito vectors of W. bancrofti have a preference for human blood and it appears that humans are the only animals naturally infected with W. bancrofti.

Pathology• The pathogenesis of W. bancrofti infection is

dependent on the immune system and inflammatory responses of the host.

There are 3 clinical phases. Asymptomatic Phase Acute Inflammatory Phase Chronic Obstructive Phase

Asymptomatic Phase• Usually consists of high microfilaremia

infection and individuals show no symptoms of being infected. This occurs due to the cytokine IL-4 suppressing the activity of TH1 cells in our immune system. This can occur for years until the inflammatory reaction rises again.

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 will exhibit fever, chills, skin infections, painful lymph nodes, and tender skin of the lymphedematous extremity.

• These symptoms often lessen after 5–7 days.• Other symptoms that may occur

include: orchitis-inflammation of the testes, which is accompanied by painful immediate enlargement and epididymitis-which is the inflammation of the spermatic cord.

Chronic Obstructive Phase• Marked by lymph varices, lymph

scrotum, hydrocele, chyluria (lymph in urine), and elephantiasis. Microfilariae are not normally present in this phase. A key feature of this phase is scar formation from affected tissue areas. Other features 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 and arms are affected.

ELEPHANTIASIS

HYDROCELE

Diagnosis• Blood Smear• Polymerase chain reaction test• Knott’s Technique • *Ultrasonography• *X-ray examinations

Treatment• The drug of choice has been Diethylcarbamazine (DEC)

which is capable of killing both microfilariae and adult worms with a dosage of 6 mg/kg semiannually or annually.

• Ivermectin• Albendazole• Polytherapy treatment that includes ivermectin with DEC

or albendazole is more effective than each drug alone.• Surgery

Prevention and Control• Insect repellents and mosquito nets are

useful manners in which to protect against mosquito bites.

• Mass chemotherapy for the endemic regions. This will decrease the overall micro-filarial titer in blood significantly in mass, hence decreasing the transmission through mosquitoes during their subsequent bites.