The word filaria derives its origin from Latin filum, that means thread-like. These worms are really thin. Even grownup or adult worms that are about 2-4cm long, are less than a tenth of a millimeter wide. Its offspring or microfilaria are even more tiny. Seen only under a microscope, they can travel inside our bodies. While adult worms find solace in lymph channels or below the skin, microfilaria travel through blood. Mosquito bites help microfilaria move from one human body to another. This sets them apart from all other worms, that enter humans through skin or mouth.
Elephant like limbs
While filarial diseases are age-old, our realization that these are spread through mosquitoes or caused by tiny worms, came later. A common form of filarial disease is Lymphatic filariasis. In this form, adult worms clog lymph channels to lead to abnormal enlargement of a body part. One limb (usually leg) may get so swollen, with thickening of the skin, that we call it “elephantiasis” or an elephant like limb. Some others develop swollen scrotum or “hydrocoele”. These manifestations were not only described but also illustrated by the ancient Egyptians Greeks, Japanese and in India.
Discovery of the worms
In 1863, Jean-Nicholous Demarquay found microfilariae in hydrocele liquid of a Cuban national. Three years later Otto Wucherer found thread like microfilariae in urine of a patient in Brazil. Over the next decade, Timothy Lewis, J Bancroft, found microfilaria, and adult worms in humans with elephantiasis. In 1877 Patrick Manson completed the life cycle of the organism when he found microfilariae in the stomach of blood-sucked mosquito. This was a good twenty years before a similar discovery was made for malaria. In fact Manson mentored Ronald Ross in 1890s, and suggested that he should search for malarial parasites in mosquitoes.
The most common species of filaria is named as Wuchereria bancrofti, in honour of Otto Wucherer and Joseph Bancroft. In 1927 a Dutch parasitologist Steffen Lambert Brug (1879–1946) identified a new filarial species, while working in Malaya (now Malaysia). He initially called it Filarial malayi. This species was later renamed as Wuchereria malayi, before its current name Brugia malayi. Thus the organisms that cause Lymphatic filariasis are named after its discoverers.
Treatment
In 1947, Yellapragada Subbarow discovered a drug called DEC or Diethylcarbamazine. From the time of its discovery till 1990s, it was only useful drug for filariasis. Today DEC is joined by ivermectin albendazole for filaria control. As Lymphatic filariasis affects about 40 million individuals, who live in 39 countries across the world, mass drug administration (to all those living in the affected areas) is one of the key elimination strategy.
River blindness
Another filarial species Onchocerca volvulus, causes blindness and skin lesions. This is prevalent in river beds across central Africa, South and Central America. The disease was known as “river blindness”. In 1890, a German missionary in Ghana detected its organism. This was initially named Filaria volvulus.
In 1910. Raillet and Henry renamed the parasite as Onchocerca (for hook and tail)Later in 1915 R. Robles reported the new distribution of this filarial parasite in Guatemala. He also discovered that the organism causes nodules in eye, and denodulization improved the symptoms remarkably. This is the reason that the Government of Guatemala launched denodulization campaign in the endemic areas since 1935. Since, this disease is spread by blackflies, vector control, drug administration (DEC and Ivermectin) and removal of nodules are mainstays in its treatment.
Worm in eye – Loa Loa
In 1778, a French surgeon named Guyot described the parasite in the eyes of West African slaves on a French ship to America. Guyot named the parasite “Loa”, the word for “worm” used by the indigenous population. On 26 May 1781 Guyot submitted a report on his findings to the “Académie Royale de Chirurgie” in Paris. In 1890, ophthalmologist Stephen McKenzie identified microfilariae, and next year Patrick manson found microfilariae in blood. Like other filarial organisms, Loasis is also treated with drugs like diethylcarbamazine and ivermectin. The endemic countries are Angola, Cameroon, Congo Brazzaville, Gabon, Equatorial Guinea, Nigeria, Democratic Republic of Congo (DRC), South Soudan, and Chad
Public Health action
In 1997, WHO and its Member States made a commitment to eliminate Lymphatic Filariasis (LF) as public health problem by 2020 Indian national Health Policy (2002) had also set the goal of Elimination of Lymphatic Filariasis in India by 2015, which was later extended to 2021. Meanwhile a Global Alliance to Eliminate Lymphatic Filariasis (GAELF) was formed in 2000. The filariasis however is yet to be eliminated.
At the start of GPELF, 81 countries were considered endemic for lymphatic filariasis. 21 countries and territories (Bangladesh, Brazil, Cambodia, the Cook Islands, Egypt, Kiribati, Lao People’s Democratic Republic, Maldives, Malawi, Marshall Islands, Niue, Palau, Sri Lanka, Thailand, Timor-Leste, Togo, Tonga, Vanuatu, Viet Nam, Wallis and Futuna, and Yemen) are now acknowledged as achieving elimination of lymphatic filariasis as a public health problem. By 2023, 14 countries had successfully implemented recommended strategies, and are under surveillance to demonstrate that elimination has been achieved. Preventive chemotherapy is still required in 39 countries.
Five countries have been verified by WHO as free of onchocerciasis after successfully implementing elimination activities for decades: four in the region of the Americas: Colombia (2013), Ecuador (2014), Mexico (2015) and Guatemala (2016), and one in Africa: Niger (2025). The elimination battle in other countries continues.
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