Filariasis is a disease caused by worms.

Filariasis, also known as lymphatic filariasis, is a parasitic disease caused by infection with thread-like filarial worms. These worms belong to the family Filarioidea and mainly include three species: Wuchereria bancrofti, Brugia malayi, and Brugia timori.

Mode of transmission:
- Filariasis is transmitted through the bite of infected mosquitoes. Mosquitoes become infected after biting a person who has microfilariae (immature larvae) in their blood.
- When an infected mosquito bites a healthy person, it deposits the infective larvae onto the person's skin. The larvae then enter the body through the mosquito bite wound.

Life cycle of filarial worms:
1. Adult worms: The adult worms reside in the lymphatic vessels and lymph nodes of the infected person.
2. Microfilariae: The adult worms produce microscopic larvae called microfilariae, which circulate in the bloodstream and lymphatic system of the infected person.
3. Mosquito transmission: When an infected mosquito bites a person, it ingests the microfilariae along with the blood.
4. Development in mosquito: Inside the mosquito, the microfilariae develop into infective larvae over a period of 10 to 14 days.
5. Transmission to another person: When the infected mosquito bites another person, it injects the infective larvae into their skin, completing the transmission cycle.

Symptoms:
- The symptoms of filariasis vary depending on the stage of the infection.
- In the early stage, individuals may not experience any symptoms.
- In the later stages, symptoms may include lymphedema (swelling), elephantiasis (severe swelling and thickening of the skin and underlying tissues), hydrocele (swelling of the scrotum), and recurrent episodes of fever and inflammation.
- Long-term infection can lead to permanent disability and disfigurement.

Treatment and prevention:
- The treatment of filariasis typically involves the use of antiparasitic medications, such as diethylcarbamazine (DEC) or ivermectin, to kill the adult worms and interrupt the transmission cycle.
- Preventive measures include vector control (mosquito control), avoiding mosquito bites by using bed nets and insect repellents, and treating infected individuals to reduce the number of microfilariae in the community.

In conclusion, filariasis is a disease caused by the infection of humans with filarial worms. These worms are transmitted through the bite of infected mosquitoes. Understanding the life cycle of these worms is crucial for developing effective treatment and prevention strategies to control the spread of filariasis.