Wuchereria bancrofti and Brugia malayi

Taxonomy, Common Name, Disease

Historical

Elephantiasis has been written about since the time of the early Greeks and Romans.

Hosts

humans.

Distribution

Tropical or subtropical (41N. latitude to 31S. latitude). South America, Cuba, Puerto Rico, West Indies, Africa, Spain, Turkey, Asia, Australia, many South Pacific Islands.

Life Cycle

The adult worms are located in lymph vessels near lymph nodes and in lymph nodes. Adult females produce microfilaria which reach the blood and in most areas the microfilaria exhibit nocturnal periodicity and are found in peripheral blood between 10 p.m. and 2 a.m. South Pacific strains do not exhibit periodicity, and it is known that infected persons moving from the South Pacific to other areas do not change the non-periodicity.

The intermediate hosts (mosquitoes belonging to the genera Aedes, Culex, Anopheles, and Mansonia--about 77 species) become infected when they take a blood meal from an infected definitive host (man). The microfilaria ingested by the mosquito pass to the stomach where they lose the sheath within the first 2 to 6 hours. They then penetrate the gut wall, enter the body cavity and enter thoracic muscle. The first cuticular molt occurs about 2 days later. The second-stage juvenile is a short, sausage shaped worm. Within 2 weeks the second molt takes place. The juvenile is then an elongate, slender filariform third stage and development ceases. The filariform juveniles are 1.4 to 2 mm long and are infective to the definitive host. These migrate to the head of the mosquito and position themselves in the mouth parts. Infection of the definitive host takes place when the mosquito takes a blood meal. The route of the infecting juveniles is not completely known, but they apparently migrate in lymph vessels where they mature and finally locate in the lymph glands of the groin and lower extremities.

Symptoms-Pathogenicity

Four stages of the disease are recognized.
  1. The incubation period of 3 to 12 months in which there are no symptoms.
  2. The acute symptomatic stage in which some swelling of the extremities may occur and this may be accompanied by pain, weakness of arms and legs, headache, insomnia. Fever is usually not present.
  3. There is a period of recovery which is permanent if reinfection does not occur.
  4. If there is continued reinfection the cycle repeats and elephantiasis may result.
The worms in the lymphatic system cause tissue changes which restrict normal flow of lymph and result in swelling, fibrosis and eventually secondary infections in the affected tissues. The lower extremities and groin are the parts most likely to be affected. The adult worms live for several years.

Management

  1. Antibiotics to prevent secondary infections.
  2. Pressure bandages to reduce swelling.
  3. Surgical removal of infected tissues to improve lymph flow.
  4. Chemotherapy to kill circulating microfilaria. Diethylcarbamazine (Hetrazan), Metronidazole
  5. Vector (intermediate host) control.

Characteristics

Adult worms are long and slender with a smooth cuticle and bluntly rounded ends. The head is slightly swollen and bears two circles of well-defined papillae. The mouth is small; a buccal cavity is lacking. The male is about 40 mm long and 100 um wide. Its tail is fingerlike. The female is 6 to 10 cm long and 300 um wide. The vulva is near the level of the middle of the esophagus.