Brugia malayi - Clinical Manifestation

Clinical Manifestation of Brugia malayi

The clinical manifestation of Brugia malayi 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, Brugia malayi may manifest as:

1. Endemic normal

2. Asymptomatic stage

3. Acute stage

4. Chronic stage

Endemic normal

In areas endemic to filariasis caused by Brugia malayi, 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 Brugia malayi or simply has undetected filarial nematode infection.

Asymptomatic stage

Individuals in the asymptomatic stage of Brugia malayi 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 microfilaraemia.

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 Brugia malayi parasite while microfilariae are not responsible for inflammatory changes.

This condition manifests as:

1. Filarial fever

2. Lymphadenitis

3. Adenolymphangitis (ADL)

4. Lymphoedema

Filarial fever

• filarial fever due to Brugia malayi 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 Brugia malayi 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 Brugia malayi 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 Brugia malayi 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 Brugia malayi. 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 Brugia malayi include:

1. Lymph varices

2. Hydrocele

3. Elephantiasis

Lymph varices

• involves varicose lymph ducts

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

• resulted condition is dilation of the ducts

Hydrocele

• hydrocele is the most common clinical manifestation in chronic Brugia malayi 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 Brugia malayi 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 Brugia malayi 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 Brugia malayi microfilariae