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Filariasis is a parasitic disease caused by thread-like filarial nematodes (worms) that are transmitted to humans through the bites of infected mosquitoes. This neglected tropical disease primarily affects populations in tropical and subtropical regions, posing significant public health and socioeconomic burdens.
Filariasis represents a group of vector-borne diseases caused by filarial worms of the family Filariidae. The most well-known forms affecting humans include lymphatic filariasis, caused by Wuchereria bancrofti, Brugia malayi, and Brugia timori, and subcutaneous filariasis, caused by Loa loa and Onchocerca volvulus. These parasites are primarily transmitted by mosquito species such as Culex, Anopheles, and Aedes. The countries with the highest burden are bihar, Andhra Pradesh, Gujarat, Kerala and Tamilnadu etc states of India. Microfilariae appear in the blood at night between 10 pm and 2 am, display nocturnal periodicity.
According to the World Health Organization (WHO), over 120 million people are infected with lymphatic filariasis in more than 70 countries, with nearly 40 million disfigured or incapacitated. Sub-Saharan Africa, Southeast Asia, and parts of South America bear the heaviest burden. The transmission is closely associated with poverty, inadequate sanitation, and limited access to healthcare. The life cycle of filarial worm begins when infected mosquito bites a human onto the skin. After 1 to 2 hours of ingestion, exsheathing takes place. The stages includes first stage larva , in that larvae migrate to thoracic muscle develops into a thick form. In the second stage larvae, larva increases in length , but remains inactive in alimentary canal. In the third stage which is active stage and infectious stage of larva. Cycle restarts when mosquito bites another person. Once transmitted via a mosquito bite, infective larvae (L3 stage) migrate to the lymphatic system where they mature into adult worms. The adult worms reside in the lymph nodes and vessels, leading to inflammation, lymphatic dysfunction, and eventual fibrosis. Chronic infection results in lymphedema, hydrocele, and in some cases, elephantiasis. The pathology is driven by both the parasite and the host immune response.

Filariasis may be asymptomatic for years. Acute symptoms can include adenolymphangitis, fever, and localized inflammation. Chronic cases may exhibit severe lymphedema, hydrocele, or elephantiasis, significantly impacting quality of life. In subcutaneous filariasis, migration of worms under the skin and eye involvement can occur, as seen in onchocerciasis.

Diagnosis is primarily achieved through microscopic examination of blood samples for microfilariae, typically collected at night due to their nocturnal periodicity. Antigen detection tests and molecular diagnostic techniques like PCR offer higher sensitivity. Ultrasound can also detect adult worms in lymphatic vessels.

Antifilarial medications such as diethylcarbamazine (DEC), ivermectin, and albendazole form the cornerstone of treatment. Mass drug administration (MDA) programs aim to reduce transmission by treating entire at-risk populations. Management of chronic conditions includes hygiene-based lymphedema care, surgical intervention for hydrocele, and disability support.
The Global Programme to Eliminate Lymphatic Filariasis (GPELF) was launched by WHO in 2000. The primary strategies include annual  Mass drug administration (MDA) and morbidity management. Success in several countries has led to the interruption of transmission, though challenges remain in areas with high endemicity and logistical constraints. Filariasis remains a formidable public health issue in many parts of the world. Effective control and elimination are achievable through sustained Mass Drug Administration, public education, vector control, and healthcare infrastructure development. Continued research into vaccine development, drug resistance, and novel diagnostic tools is crucial for achieving global eradication.