Wuchereria bancrofti - Clinical Manifestation

Clinical Manifestation of Wuchereria bancrofti

The clinical manifestation of Wuchereria bancrofti includes Malayan lymphatic filariasis with the pre-patent period being short (i.e. 3.5 months on average). The incubation period is also short and may vary from 8 months to 16 months.

In humans, Wuchereria bancrofti may manifest as:

1. Endemic normal

2. Asymptomatic stage

3. Acute stage

4. Chronic stage

5. Occult filariasis

6. Less frequent lesions

Endemic normal

In areas endemic to filariasis caused by Wuchereria bancrofti, a portion of the population does not show any overt clinical manifestation of the disease. Such a population may also lack microfilariae in the blood even if they are exposed to the infective third-stage larvae (L3).

However, it is difficult to demonstrate if the said population is uninfected by Wuchereria bancrofti or simply has undetected filarial nematode infection.

Asymptomatic stage

Individuals in the asymptomatic stage of Wuchereria bancrofti infection have microfilariae in their blood but lack any clinical manifestations of filariasis. Such individuals may remain asymptomatic for years and even for a lifetime. If such individuals settle in non-endemic filarial areas, they may spontaneously become amicrofilariaemic.

The asymptomatic stage in individuals has been suggested to have been caused by the downregulation of the TH1 inflammatory component of the immune response while the TH2 is stimulatory. It also involves depressed cytokine IFN-c but elevated IL-4 levels (IL4 suppresses activation of TH1).

After several years, hyporesponsiveness breaks down and the appearance of inflammatory reactions begins.

Acute filariasis

The inflammatory phase i.e. acute filariasis is caused by antigens released from the female Wuchereria bancrofti parasite while microfilariae are not responsible for inflammatory changes.

This condition manifests as:

1. Filarial fever

2. Lymphadenitis

3. Adenolymphangitis

4. Lymphoedema

Filarial fever

• filarial fever due to Wuchereria bancrofti infection is usually low grade

• sometimes filarial fever may be accompanied by chills and become severe

• symptoms include general malaise, pain, headache

• episodes of filarial fever may occur several times a year – which lasts upto a week each time

Lymphoedema

• lymphoedema is caused by the presence of adult worms in the lymphatic channels

• lymph flow is hindered by the Wuchereria bancrofti parasite

• individuals with lymphoedema suffer from periodic attacks of filarial fever, adenolymphangitis, and lymphadenitis

Lymphadenitis

• in lymphadenitis, the lymph nodes are inflamed

• commonly infected lymph nodes include epitrochlear, cervical, axillary, inguinal, abdominal, pelvic, supraclavicular

• unusual lymph nodes infected include wrist, iliac, pectoral, creat, mediastinal, intercostal, mid humoral

• infected lymph nodes are tender, enlarged, and matted but are not attached to the skin

• such lymph nodes may or may not contain Wuchereria bancrofti parasites

• lymph nodes capsules are thickened with fibrotic septa while the middle layer of the node may contain dead or living male and female adult Wuchereria bancrofti filarial nematode

• scar tissue is present in the outer layers

Adenolymphangitis (ADL)

• adenolymphangitis (ADL) is the inflammation of lymph channels

• commonly occurs during the attacks of the acute stage

• lymphatic vessels are thickened, dilated, and folded

• thickened walls of lymphatic vessels contain a large number of inflammatory cells surrounded by tissue

• inflammation of inguinal lymph nodes, lymphoedema, testis, spermatic cord

• symptoms include fever episodes with tender, thickened, firm, red lymphatics, and tender skin

• usually, male genitals are affected which results in orchitis, epididymitis, or funiculitis

• in some cases, the lymphatic system of the upper extremities and breasts are infected

• ADL completely subsides after the acute stage but after each attack, edema becomes less resolved, resulting in the development of characteristic chronic filariasis

Chronic filariasis (Obstructive phase)

Chronic filariasis, also known as the obstructive phase, takes 10 to 15 years to develop after an individual is infected with Wuchereria bancrofti. During this stage, acute inflammation subsides while fibrosis advances as the parasitic worms die, are absorbed, or are calcified.

Microfilariae are usually absent in chronic cases.

Clinical manifestations of chronic filariasis caused by Wuchereria bancrofti include:

1. Lymph varices

2. Hydrocele

3. Elephantiasis

4. Granuloma of the female breast

5. Chyluria

Lymph varices

• involves varicose lymph ducts

• caused by obstruction of lymph nodes and accumulation of lymph in the ducts

• resulting condition is dilation of the ducts

Hydrocele

• hydrocele is the most common clinical manifestation in chronic Wuchereria bancrofti infection

• caused by obstruction of lymph vessels of the spermatic cord and exudation from the inflamed testes and epididymis

• hydrocele fluid is amber in color and contains fibrin, cholesterol crystals, calcium particles, old blood clots, and mesothelial cells

• microfilariae of Wuchereria bancrofti can be found in the hydrocele fluid while adult worms are present in the cord and epididymal tissues

Elephantiasis

• elephantiasis is a characteristic feature of chronic Wuchereria bancrofti infection

• caused by complex immune reactions for a long duration as well as repeated infections over many years

• this manifestation is seen only in a small percentage of infected individuals in endemic areas

• in males, elephantiasis occurs in the scrotum, legs, and arms

• in females, elephantiasis is seen in arms and legs

• if legs and arms are infected, swelling is seen below the knee and below the elbow respectively

• at first, swelling is pitting which later becomes non-pitting

• the elephantoid mass consists of fibrous tissues containing fat

• overlaying skin of the leg, the scrotum becomes thick, warty, and fissured

• ulceration and secondary infection with fungi or bacteria also may occur

• peripheral blood usually lacks Wuchereria bancrofti microfilariae

Granuloma of the female breast

• granuloma of the female breast is caused by adult parasites present in the lymphatics of the breast or axilla

• characterized by a solitary mass in the breast

• microscopically, the presence of eosinophils, histiocytes, and giant cells in and around degenerated microfilariae

Chyluria

• chyluria is an unusual complication of Wuchereria bancrofti manifestation

• urine contains chyle mixed with blood and sometimes microfilaria

• caused by obstruction of lymphatic cells of the kidney, abdomen

• due to obstruction, lymph drains into the site for collection of urine at the level of the renal pelvis or urinary bladder

Occult filariasis

Occult filariasis is a condition of hypersensitivity reaction of the host to microfilariae antigens. Both microfilariae in the peripheral blood and classical features of lymphatic filariasis are absent.

Syndromes include arthritis, dermatoses, and tenosynovitis with tropical pulmonary eosinophilia (TPE) being the most important manifestation.

Tropical pulmonary eosinophilia (TPE)

• symptoms of tropical pulmonary eosinophilia (TPE) include low-grade fever, cough, chest pain, and asthmatic attacks – mostly during the night

• associated with elevated levels of serum filarial antibodies including IgE

• histopathologically, lung tissue shows chronic interstitial fibrosis without tissue eosinophilia

• presence of microfilaria in the lung tissue, liver, or lymph nodes is rare

• absence of microfilariae in the peripheral blood

• patients with TPE show abnormal immune response – tapping and destruction of microfilariae in pulmonary capillaries

Less frequent lesions

Less frequent lesions of Wuchereria bancrofti infection involve granuloma of the spleen and other infected organs. The parasite may also be present in the anterior chamber of the eye.