Brugia malayi - Pathogenesis, Pathology
Pathogenesis, Pathology of Brugia malayi
On the basis of the stage of infection
Pathogenicity of Brugia malayi is not achieved by infective third-stage larvae (L3) as they do not produce any pathological lesions while invading the host skin.
Similarly, circulating microfilariae larvae also are not pathogenic to the mammal host.
The pathogenesis, and pathology of Brugia malayi are achieved by the adult male, and adult female parasites as well as the fourth-stage larvae. They are the causative agent of filariasis.
Lymphatic filariasis occurs in the following stages:
Dilation of lymphatic vessels
Infection of the lymphatic vessels (lymphangitis)
Obstruction of lymph nodes
Dilation of lymphatic vessels
caused by an inflammatory reaction
inflammatory reaction provoked by the presence of adult Brugia malayi, developing larvae, metabolic products released during larval molt, and unsheathing of microfilariae during molting
during the early stage of infection, inflammatory changes lead to the dilation of lymphatic vessels
although the exact mechanism of dilation of lymphatic vessels is not known, the action of the host immune response or toxicity and toxic products from the parasite is suggested to be responsible
Infection of the lymphatic vessels (lymphangitis)
as the Brugia malayi infection progresses, lymphangitis gradually develop
characterized by the presence of dilated, inflamed, and thickened lymphatic vessels
this condition is associated with edema, tender painful areas, erythema
as lymphatics are dilated, secretion of proteinaceous material from lymphatics into the surrounding tissue is increased
the result of this stage of infection is the formation of conspicuous lymphoedema and thickening of the endothelium
Obstruction of lymph nodes
lymphangitis is followed by fibrotic degenerative changes in the lymphatic vessels proximal to the lymph nodes
sclerosis, obstruction of the proximal lymphatic channels, and fibrotic necrosis are observed in lymph nodes
valves close to the Brugia malayi parasite also undergo degeneration
The host lymph node obstruction is caused by the:
presence of adult parasites in the lumen
endothelial cell proliferation
thickening of lymphatic vessels
focal necrosis
fibrosis, cellular changes, giant cell formation of the lymphatic vessels close to the residing parasite
Pathological changes due to obstruction of lymph nodes are elephantiasis. This classical feature involves affected tissues becoming grossly oedematous with the overlaying skin becoming highly stretched and thickened.
On the basis of the infected time frame
Acute filariasis
Acute filariasis includes:
Lymphadenitis
Lymphangitis
Lymphatic abscess
Lymphadenitis
a typical feature of acute filariasis
Brugia malayi attacks lymphadenitis at regular intervals
precipitated by muscular exercise
episodes of attack vary from 1 to 2 attacks per year
typically occurs in the inguinal region and occasionally the axillary lymph nodes
in some cases, lymphadenitis can occur in atypical sites such as popliteal lymph nodes or breasts
rarely occurs simultaneously at more than one site
Lymphangitis
Lymphadenitis is followed by retrograde lymphangitis
Lymphatic abscess
lymphatic abscesses are usually superficial
infected lymph nodes may suppurate and form abscesses
an ulcer is formed after an infected lymph node explodes
In chronic filariasis
Chronic filariasis caused by Brugia malayi infection occurs mostly below the knee. In some cases, the arm below the elbow may also be involved.
Chyluria and genital involvement are absent.