Lymphatic filariasis is caused by filarial worms (filariae) – specialised nematodes (roundworms).
90 % caused by Wuchereria bancrofti, otherwise Brugia species (B. malayi or B. timori)
Endemic areas are parts of Latin America, sub-saharan Africa and southeast Asia.
Life cycle
- Mosquito -> human -> mosquito
- Infective larvae transmitted to humans via mosquito bites
- Larvae migrate to central vessels and mature into adult males and females
- Adults then live in primarily in afferent lymphatics (inguinal, iliac, para-aortic)
- bancrofti specifically live in the male genitalia
- Adult worms live for 5 – 7 years
- Males and females can mate, releasing microfilariae, peaking at midnight – mosquitos bite humans and the microfilariae mature in the mosquito into infective larvae
Pathophysiology
- Initial lymphatic obstruction and dilation due to adult worms living in lymphatics
- Secondary bacterial infections (Wolbachia) cause inflammatory responses to dying and dead worms
- Granulomas and suppuration around the worms seen on histology
- Vicious cycle as acute inflammatory attacks worsen the lymphoedema, leading to inflammation, healing and fibrosis
- Eventually the lymphatics are obliterated and replaced by scar
Clinical features
- Variable – ranging from subclinical to massively disfiguring
- Low level symptoms include dilated lymphatics, scrotal lymphangectasia and microhaematuria (most infected people have minimal symptoms)
- Acute adenolymphangitis
- Fever with lymphadenopathy and oedema
- Lymphoedema
- Epididymo-orchitis and funiculitis
- Hydrocele
- Scrotal elephantiasis
- Chyluria
- Tropical pulmonary eosinophilia
Differential diagnoses
- Think other causes of lymphatic obstruction – post surgical disruption, malignancy
- TB
- Schistosomiasis
- Gonorrhoea
- Non filarial hydrocele
Diagnosis and work-up
- Occasionally the worms can be seen in blood or other fluids – aim to draw at midnight when most active
- PCR/ELISA testing for antigens is sensitive but not widely available
- Ultrasound can be up to 80 % sensitive
- Filarial dance sign (in lymphatics or epididymis) (DDx dancing megasperm post vasectomy or obstruction)
- Xray may show calcification of lymphatics
- Radionuclide lymphoscintigraphy can demonstrate lymphatic disease, but not the underlying cause
Management
Albendazole 400 mg BD for 3 weeks – treats both microfilariae and macrofilariae
Ivermectin 150 – 400 ug STAT – useful for microfilariae only
Diethylcarbamazine (DEC) – 2 mg/kg TDS orally for one day
Not registered in Aust. but can be made available.
Doxycycline 200 mg daily augments the above drugs and prolonged 1-2 month courses renders adult worms sterile with improvements in lymphoedema with prolonged courses.
Non medical measures:
- Prevention of secondary infections
- Good hygiene / as best able
- Elastic stockings
- Elevation
- Physiotherapy and occupation therapy
Surgery:
- Excision of diseased tissue / scrotectomy with flap/graft reconstruction – consider in conjunction with plastic surgery in experienced centres – high morbidity and risks of recurrence, wound issues, infection, bleeding.
- Hydrocelectomy in small cases may be useful, but high risk of recurrence if concurrent disease