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.
Infected mosquito bite introduces the third stage larva onto the skin and then enters to the blood through the wound.
The larvae develop to adult which reside in the lymphatic vessels.
Adult worm produce sheathed microfiliae that migrate to lymph and blood. They have nocturnal periodicity.
Another mosquito ingests the microfiliae.
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
Microfiliae grow up inside the mosquito till third stage larvae.
In another bite to a host skin the mosquito introduces the larvae onto the skin.
The difference between the nematodes causing lymphatic filariasis is in the shape and size of the worm.
The Brugia worms are similar to the W. bancrofti but smaller.
Infected fly bite introduces the third stage larva onto the skin and then enters to the blood through the wound.
The larvae develop to adult which reside in the subcutaneous tissue.
Loa Loa adult worm produce sheathed microfilariae that are found in the blood during day and in the lungs during the non circulating phase. They have diurnal periodicity.
Another fly ingests the microfiliae.
After ingestion, the microfilariae lose their sheaths and migrate from the fly's midgut through the hemocoel to the thoracic muscles of the arthropod.
Microfiliae grow up inside the fly till third stage larvae.
The third-stage infective larvae migrate to the fly's proboscis and in another bite the cycle restarts.
Unlike Loa Loa filaria, Mansonella streptocerca , Mansonella ozzardi and Onchocerca volvolus produce unsheathed non-periodic microfilariae.
Mansonela streptocerca adults residue in the dermis.
Onchocerca volvulus adults residue mainly in the subcutaneous nodules. Their microfilariae can be found in the peripheral blood, urine, and sputum but are typically found in the skin and in the lymphatics of connective tissue.