Filariasis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Kalsang Dolma, M.B.B.S.[2] Ahmed Elsaiey, MBBCH [3]
Overview
Pathophysiology
Generally, filariasis infection occurs when a larva carrying mosquito bites individual skin introducing these larvae onto the skin. The larvae then enter the patient blood through the skin wound and spread to the different sites of infection either lymphatic vessels, subcutaneous tissues or the serous cavities. At those different sites, The larvae tend to mature in a six to twelve months process to be adult filariae which can live up to fifteen years. Reproduction takes place between the male and female adult worms producing microfilariae which are premature organisms with sheath that circulate the blood in case they are settled in the lymphatic vessels. During another blood meal, the mosquito takes up the microfilariae then those microfilariae lose their sheath within two weeks to be larvae that enter the human body when the human is bitten by a mosquito and the cycle restarts again.[1]
Pathogenesis
- Factors affecting the pathogenesis of filariasis:
- Immune response of the patient
- Insect bite extent
- The number of filarial and bacterial infection
- The accumulation of the worm antigen in the lymphatic vessels.
Life Cycle of Wuchereria Bancrofti
Different species of the following genera of mosquitoes are vectors of W. bancrofti filariasis depending on geographical distribution. Among them are: Culex (C. annulirostris, C. bitaeniorhynchus, C. quinquefasciatus, and C. pipiens); Anopheles (A. arabinensis, A. bancroftii, A. farauti, A. funestus, A. gambiae, A. koliensis, A. melas, A. merus, A. punctulatus and A. wellcomei); Aedes (A. aegypti, A. aquasalis, A. bellator, A. cooki, A. darlingi, A. kochi, A. polynesiensis, A. pseudoscutellaris, A. rotumae, A. scapularis, and A. vigilax); Mansonia (M. pseudotitillans, M. uniformis); Coquillettidia (C. juxtamansonia). During a blood meal, an infected mosquito introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). They develop in adults that commonly reside in the lymphatics (2) . The female worms measure 80 to 100 mm in length and 0.24 to 0.30 mm in diameter, while the males measure about 40 mm by .1 mm. Adults produce microfilariae measuring 244 to 296 μm by 7.5 to 10 μm, which are sheathed and have nocturnal periodicity, except the South Pacific microfilariae which have the absence of marked periodicity. The microfilariae migrate intolymph and blood channels moving actively through lymph and blood (3) . A mosquito ingests the microfilariae during a blood meal (4). After ingestion, the microfilariae lose their sheaths and some of them work their way through the wall of the proventriculus and cardiac portion of the mosquito's midgut and reach the thoracic muscles (5). There the microfilariae develop into first-stage larvae (6) and subsequently into third-stage infective larvae (7). The third-stage infective larvae migrate through the hemocoel to the mosquito's prosbocis (8) and can infect another human when the mosquito takes a blood meal (1).
Life Cycle of Brugia Malayi
The typical vector for Brugia malayi filariasis are mosquito species from the genera Mansonia and Aedes. During a blood meal, an infectedmosquito introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). They develop into adults that commonly reside in the lymphatics (2). The adult worms resemble those of Wuchereria bancrofti but are smaller. Female worms measure 43 to 55 mm in length by 130 to 170 μm in width, and males measure 13 to 23 mm in length by 70 to 80 μm in width. Adults produce microfilariae, measuring 177 to 230 μm in length and 5 to 7 μm in width, which are sheathed and have nocturnal periodicity. The microfilariae migrate into lymph and enter theblood stream reaching the peripheral blood (3). A mosquito ingests the microfilariae during a blood meal (4). After ingestion, the microfilariae lose their sheaths and work their way through the wall of the proventriculus and cardiac portion of the midgut to reach the thoracic muscles(5). There the microfilariae develop into first-stage larvae (6) and subsequently into third-stage larvae (7). The third-stage larvae migrate through the hemocoel to the mosquito's prosbocis (8) and can infect another human when the mosquito takes a blood meal (1).
Life Cycle of Onchocerca volvulus
During a blood meal, an infected blackfly (genus Simulium) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). In subcutaneous tissues the larvae (2) develop into adult filariae, which commonly reside in nodules in subcutaneous connective tissues (3). Adults can live in the nodules for approximately 15 years. Some nodules may contain numerous male and female worms. Females measure 33 to 50 cm in length and 270 to 400 μm in diameter, while males measure 19 to 42 mm by 130 to 210 μm. In the subcutaneous nodules, the female worms are capable of producing microfilariae for approximately 9 years. The microfilariae, measuring 220 to 360 µm by 5 to 9 µm and unsheathed, have a life span that may reach 2 years. They are occasionally found in peripheral blood, urine, and sputum but are typically found in the skin and in the lymphatics of connective tissues (4). A blackfly ingests the microfilariae during a blood meal (5). After ingestion, the microfilariae migrate from the blackfly's midgut through the hemocoel to the thoracic muscles (6). There the microfilariae develop into first-stage larvae (7) and subsequently into third-stage infective larvae (8) . The third-stage infective larvae migrate to the blackfly's proboscis (9) and can infect another human when the fly takes a blood meal (1).
Life Cycle of Loa loa filaria
The vector for Loa loa filariasis are flies from two species of the genus Chrysops, C. silacea and C. dimidiata. During a blood meal, an infected fly (genus Chrysops, day-biting flies) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). The larvae develop into adults that commonly reside in subcutaneous tissue (2). The female worms measure 40 to 70 mm in length and 0.5 mm in diameter, while the males measure 30 to 34 mm in length and 0.35 to 0.43 mm in diameter. Adults produce microfilariae measuring 250 to 300 μm by 6 to 8 μm, which are sheathed and have diurnal periodicity. Microfilariae have been recovered from spinal fluids, urine, and sputum. During the day they are found in peripheral blood, but during the noncirculation phase, they are found in the lungs (3). The fly ingests microfilariae during a blood meal (4) . After ingestion, the microfilariae lose their sheaths and migrate from the fly's midgut through the hemocoel to the thoracic muscles of the arthropod(5). There the microfilariae develop into first-stage larvae (6) and subsequently into third-stage infective larvae (7). The third-stage infective larvae migrate to the fly's proboscis (8) and can infect another human when the fly takes a blood meal (1).
Life Cycle of Mansonella Perstans
During a blood meal, an infected midge (genus Culicoides) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1) . They develop into adults that reside in body cavities, most commonly the peritoneal cavity or pleural cavity, but less frequently in the pericardium (2) . The size range for female worms is 70 to 80 mm in length and 120 μm in diameter, and the males measure approximately 45 mm by 60 μm. Adults produce unsheathed and subperiodic microfilariae, measuring 200 by 4.5 μm that reach the blood stream (3) . A midge ingests microfilariae during a blood meal (4) . After ingestion, the microfilariae migrate from the midge's midgut through the hemocoel to the thoracic muscles of the arthropod (5) . There the microfilariae develop into first-stage larvae (6) and subsequently into third-stage infective larvae (7) . The third-stage infective larvae migrate to the midge's proboscis (8) and can infect another human when the midge takes a blood meal (1) .
Life Cycle of Mansonella Ozzardi
During a blood meal, an infected arthropod (midges, genus Culicoides, or blackflies, genus Simulium) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1) . They develop into adults that commonly reside in subcutaneous tissues (2) . Adult worms are rarely found in humans. The size range for females worms is 65 to 81 mm in length and 0.21 to 0.25 mm in diameter but unknown for males. Adults worms recovered from experimentally infected Patas monkeys measured 24 to 28 mm in length and 70 to 80 μm in diameter (males) and 32 to 62 mm in length and .130 to .160 mm in diameter (females). Adults produce unsheathed and non-periodic microfilariae that reach the blood stream (3) . The arthropod ingests microfilariae during a blood meal (4) . After ingestion, the microfilariae migrate from the arthropod's midgut through the hemocoel to the thoracic muscles (5) . There the microfilariae develop into first-stage larvae (6) and subsequently into third-stage infective larvae (7) . The third-stage infective larvae migrate to arthropod's proboscis (8) and can infect another human when the arthropod takes a blood meal (1)
Life Cycle of Mansonella Streptocerca
During a blood meal, an infected midge (genus Culicoides) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1) . They develop into adults that reside in the dermis, most commonly less than 1 mm from the skin surface (2) . The females measure approximately 27 mm in length. Their diameter is 50 μm at the level of the vulva (anteriorly) and ovaries (near the posterior end), and up to 85 μm at the mid-body. Males measure 50 μm in diameter. Adults produce unsheathed and non-periodic microfilariae, measuring 180 to 240 μm by 3 to 5 μm, which reside in the skin but can also reach the peripheral blood (3) . A midge ingests the microfilariae during a blood meal (4) . After ingestion, the microfilariae migrate from the midge's midgut through the hemocoel to the thoracic muscles (5) . There the microfilariae develop into first-stage larvae (6) and subsequently into third-stage larvae (7) . The third-stage larvae migrate to the midge's proboscis (8) and can infect another human when the midge takes another blood meal(1) .
References
- ↑ Chandy A, Thakur AS, Singh MP, Manigauha A (2011). "A review of neglected tropical diseases: filariasis". Asian Pac J Trop Med. 4 (7): 581–6. doi:10.1016/S1995-7645(11)60150-8. PMID 21803313.