Lymphatic filariasis is a disease caused by the parasites of Filaria bancrofti, Brugia malayi, or Brugia timori in the lymphatic tissues. The main manifestations are lymphangitis and lymphadenitis in the early stage and various symptoms and signs caused by lymphatic obstruction in the late stage. Filaria bancrofti invade the lymphatic vessels and lymph nodes of the genitourinary system, while Brugia malayi and Brugia timori never invade the genitourinary organs.


Causes

The pathogen is Filaria bancrofti, Brugia malayi, and Brugia timori.

The adults are linear, milky white, with smooth surface.

Microfilariae can stay in the lymph fluid after escaping from their mothers, but most of them immediately enter the blood circulation.

Filaria bancrofti can be nocturnally periodic, diurnally subperiodic, and nocturnally subperiodic. Nocturnally periodic microfilariae cluster in the capillaries of the lungs during the daytime, appear in the peripheral blood at dusk, reaching a peak from 10pm to 2am in count, and then gradually decrease until absent after dawn. Diurnally subperiodic microfilariae can be found in the peripheral blood at any time, but the peak of count is present in the afternoon. Nocturnally subperiodic microfilariae mostly appear in the peripheral blood at night and can also be found during the day, but the count during the day is only 20% of that at night.

Brugia malayi are nocturnally periodic, and the peak of microfilariae in the peripheral blood is present from 8pm to 4am.

Brugia timori are nocturnally periodic, and the peak of microfilariae in the peripheral blood is present from 9pm to 3am.

Source of infection

Patients with microfilariae in the blood and asymptomatic carriers are the main sources of infection. Filaria bancrofti mainly infect humans. In addition to infecting humans, Brugia malayi can also infect mammals such as monkeys and cats. Therefore, the infected animals may also be sources of infection.

Route of transmission

The disease is transmitted by mosquito bites.


Signs and Symptoms

Filaria bancrofti parasitize the deep or superficial lymph nodes and lymph vessels, mostly in the abdominal cavity, pelvic cavity, retroperitoneal tissue, renal pelvis, epididymis, and spermatic cord. The clinical manifestations are diversified due to the different sites of lymphatic obstruction. Obstructions in the lymphatic vessels of spermatic cord or testicles can cause hydrocele and lymphangiovarix. Obstructions in the superficial inguinal lymph nodes or lymph vessels may result in inguinal lymphangiovarix, scrotal lymphedema, or scrotal elephantiasis. When the obstructions are in the inguinal lymph nodes or lymphatic vessels, the lymphatic circulation of the lower limbs is blocked, and the lymphatic fluid is retained in the subcutaneous tissue of the lower limbs, stimulating the proliferation of the subcutaneous connective tissue, leading to lower limb lymphedema or elephantiasis. If retroperitoneal lymph nodes and lymph vessels, preaortic lymph nodes, intestinal lymph vessels, and thoracic ducts are obstructed, chylous fluids flow to the renal lymph vessels, the latter ruptures, and the chylous fluids leak to the renal pelvis, renal calyces, ureters, and bladder and is excreted in urine, which is termed chyluria. When the obstruction is in the lateral aortic lymph nodes or the lymphatic vessels of the lumbar stem, the circulation of lymphatic fluid from the kidney and the upper ureter is blocked, and the discharged urine contains large amounts of lymphatic fluid, which is termed lymphuria. Elephantiasis is the advanced lymphedema. The retention of lymph fluid in the subcutaneous tissue results in lymphedema. The high protein content in the lymph fluids stimulates the proliferation of fibrous tissue, thickening significantly the skin and subcutaneous tissue, resulting in rough and folded skin, termed elephantiasis. Due to circulatory embarrassment of the skin and impaired function of the sweat glands, sebaceous glands, and hair follicles, secondary bacterial infection may occur and promote the proliferation of fibrous tissue, aggravating elephantiasis.

Figure 1 elephantiasis

Figure 2 lymphedema

Brugia malayi adults mainly parasitize the superficial lymphatic system of human extremities, particularly the lower limbs. There are not chyluria, hydrocele, and scrotal lymphedema. Lymphangitis and lymphadenitis relapse frequently, persisting for a long time, and the symptoms are severe. Lymphagitis and elephantiasis of the lower limbs are mainly in the calves and dorsal feet, and the thighs are rarely involved. There is not giant elephantiasis.

Lymphatic filariasisis caused by Brugia timori is mainly manifested by lymphangitis and lymphadenitis in the groin, femoral vein, and great saphenous vein, and elephantiasis below the knees.


Diagnosis

If there are typical clinical manifestations such as lymphedema and elephantiasis, the disease should be suspected.

If there are microfilariae found in microscopy or live adults seen in ultrasound examinations, the disease can be diagnosed.


Treatment

The treatment regimen is diethylcarbamazine 0.5g orally once weekly for 7 weeks, repeating with withdrawal intervals of 1 - 2 months, until microfilariae are absent, furapyrimidone 20mg/(kg.d) orally in 3 divided doses for 7 days, or ivermectin 100 - 200µg/kg orally once a day for 2 days.

Elephantiasis and lymphedema can be treated with heating and compression bandage treatment. After being heated with radiant heat for 60 minutes or microwave diathermy for 30 minutes, the affected sites are dressed with elastic bandage. In radiant heat therapy, the regimen is once daily for 20 days, repeating with withdrawal intervals of 15 days, while in microwave diathermy treatment, the regimen is once daily for 15 days, repeating with withdrawal intervals of 2 months.

Surgery may be required if there is giant elephantiasis.