Wuchereria bancrofti (Filariasis, Elephantiasis)

Notes
  • It is the major cause of lymphatic filariasis (90% of all cases). The rest is caused by malayi and B.timori.
  • Mostly found in Central Africa, Nile delta, South America, Central America and South China.
  • The common vectors of bancrofti are mosquitoes of the genus Culex, Anopheles and Aedes.
  • The peak amounts of microfilariae in the peripheral blood is normally from 10 p.m. to 4 a.m
  • Statistics: Size (thread-like): female - 10cm x 2mm, male - about 4 cm x 2mm. Global disease burden: 120 million people; prevalence of Bancrofti in Kwale Kenya - 6.3 to 24%. Time taken for a worm to mature - 6 to 8 months.
  1. Transmission

Life-cycle;

_Adults W. bancrofti in the lymphatics of human host.

_Adult W. bancrofti releases sheathed microfilariae (early larval forms) into the blood stream

_Mosquito feeds on microfilariae infested blood.

_In the mosquito microfilariae shed the sheath, migrate into midgut and then to thoracic muscles.

_ Microfilariae develop into L1 larvae then L3 larvae.

_L3 larvae migrate into mosquito proboscis and are innoculated into human host during the feeding of mosquito.

Symptoms

There are 3 phases of  W. Bancrofti infection each with specific symptoms and signs:

  • The asymptomatic phase:

_Characterized by high microfilaremia infection

_Barely any symptom of disease.

_It can occur for years.

  • Inflammatory (acute) phase (for 5-7 days):

_W. Bancrofti in the lymph channels block the flow of the lymph leading to lymphedema.

_Inflammatory responses are elicited by antigens from the female adult worms causing fever and chills

_Skin infections

_Painful lymph nodes

_Tender skin of the lymphedematous extremity.

_Orchitis

_Epididymitis

  • The obstructive (chronic) phase:

_Lymph varices

_Lymph scrotum

_Hydrocele

_Chyluria

_Elephantiasis

Diagnosis
  • Physical examination
  • Microscopic examination of blood smear
  • Molecular diagnostics (DNA PCR)
Management
  • Currently, there is no effective treatment against adult worms as the drug ivermectin and diethylcarbamazine are only effective on clearing microfilaria.

Either;

_Tabs Ivermectin 150-200mcg/kg Stat. repeated at 6 and 12 months  

Or:

_Tabs Diethycarbamazine: 6 mg/kg repeated at 6 and 12 months.

_Massive hydroceles and scrotal elephantiasis are managed surgically. Surgery of limb elephantiasis is often is often less successful requiring multiple procedures and skin grafting.

_W. bancrofti requires the bacteria Wolbachia for survival and embryogenesis hence justifying the use of doxycycline or any other effective antibiotic as adjuvant in the treatment regime for the infestation.

_Some studies have shown that a polytherapy treatment that includes ivermectin with Diethycarbamazine or albendazole can be more effective.

_Prevention is by vector control and mass chemotherapy.

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