Filariasis is caused by filarial nematodes like Wuchereria bancrofti and Brugia malayi; its chronic manifestations include elephantiasis (lymphoedema) and hydrocele.
The Concept: Why These Worms Cause Such Damage
Filariasis is a parasitic disease caused by thread-like roundworms (nematodes) that live in the human lymphatic system. The lymphatic system is our body's drainage network — it collects excess fluid from tissues and returns it to the blood, and it also houses immune cells. When filarial worms block these lymphatic vessels, fluid cannot drain properly. Over years of repeated infection, the blockage becomes permanent, leading to massive swelling and tissue damage.
The two most important species responsible for human filariasis are Wuchereria bancrofti (causing about 90% of cases) and Brugia malayi (common in Southeast Asia). Both are transmitted by mosquito bites — the mosquito picks up microscopic larvae (called microfilariae) from an infected person's blood and injects them into a new host.
Step-by-Step Reasoning
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Identify the causative organisms.
The disease is caused by filarial nematodes. The two most common species are:
- Wuchereria bancrofti
- Brugia malayi
(A third species, Brugia timori, is less common but also causes filariasis in parts of Indonesia.)
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Understand the chronic manifestations.
Chronic filariasis develops after years of repeated infection. The adult worms lodge in lymphatic vessels, causing inflammation and scarring. Over time, the lymphatic system becomes blocked. This leads to two hallmark chronic conditions:
- Elephantiasis (lymphoedema): The affected limb (usually a leg, but sometimes an arm, breast, or scrotum) swells enormously because lymph fluid cannot drain. The skin becomes thick, rough, and warty — resembling an elephant's leg. This is not just swelling; it is permanent tissue damage. …