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Vital Signs is a monthly program bringing viewers health stories from around the world.
(CNN)It takes eight to 10 years to take hold and once symptoms emerge, it can leave people permanently disabled and disfigured in its wake. With a signature symptom of legs and feet swollen to enormous proportions, this parasite continues to infect 120 million worldwide and put almost 1.4 billion people at risk of infection, 500 million of whom are in India.
The disease is lymphatic filariasis -- commonly known as elephantiasis -- and its symptoms leave images in the mind you may never forget.
It is caused by a parasitic worm that is transmitted between people by mosquitoes. The worms lodge inside a person's lymphatic system, affecting the regulation of body fluids and causing hugely swollen limbs and organs. The obstructions can affect the immune system and the swelling of tissues extends in some cases beyond the limbs to the face, neck and scrotal tissue, as well as other regions of the body.
The disease may not be fatal, but the social and economic cost to those left disfigured leaves them in a life of poverty and isolation.
"The largest number globally are in India," says Neeraj Mistry, managing director of the Global Network for Neglected Tropical Diseases. Three in five of the Indian population remains at risk of becoming infected with lymphatic filariasis, despite the country having the longest-running control program in the world. Mistry says the national control program reaches 300 million people -- but in a country with more than 1.2 billion residents it will take more to bring an end to this disease.
In December 2014, the country's Ministry of Health and Family Welfare (MOHFW) launched a new public health campaign to provide more than 400 million people with free medication. It is part of India's ambitious target to eliminate the disease by 2015 -- five years before the target date set by the rest of the world.
Drugs for everyone
The main strategy used globally to control lymphatic filariasis is the widespread distribution of the de-worming drugs diethylcarbamazine (DEC) and albendazole, which kill the worms found in the blood to prevent people transmitting the disease once infected -- known as mass drug administration.
"(The drugs) cause a reduction in the parasite so when the mosquito bites the person it doesn't transmit the disease," says Mistry. The two drugs have a limited impact in terms of killing the adult worms which form nests inside the lymph nodes and vessels, but instead kills the young (microfilariae) larvae released by adult females into the blood, which are then picked up by mosquitoes as they feed.
"The more people we cover, the lower the parasite load gets -- to the extent that we can actually break the transmission cycle," continues Mistry -- fewer parasites in the blood of the population, mean a lower likelihood of mosquitoes transmitting them.
Of the 120 million people infected worldwide, 40 million of them are disabled, or disfigured, according to the World Health Organization. There is no vaccine and no treatment, only these drugs to prevent further transmission of the disease.
Of all the people in the world in need of this preventative treatment, over 40% of them live in India. "To go from control to elimination, we need to expand drug coverage," says Mistry.
The goal is to provide the drugs for free annually to everyone living in high-risk populations -- whether they have the infection or not. Pharmaceutical giants EISAS and GSK now donate the drugs for use in global control making this a much cheaper approach than diagnosing individuals.
The new campaign is targeting 17 states in India but particularly the states of Uttar Pradesh, Jarkhand, Bihar and West Bengal, where almost two-thirds of the country's disease burden occurs.
Convincing the masses
The majority of lymphatic filariasis infections fail to cause symptoms and in those that do, symptoms can take eight to 10 years to manifest, which is where the greatest challenge arises in terms of disease control. People don't know, or believe, they could be infected, making them less inclined to take the drugs provided to them.
The MOHFW has launched a series of public service announcements across the country to overcome this and spread the word in communities where the disease is plaguing their population.
"One of the challenges of the India program has been treatment compliance," agrees Simon Brooker, professor of epidemiology at the London School of Hygiene and Tropical Medicine, who also founded the Global Atlas of Helminth Infections, which maps infections including lymphatic filariasis.
In 2000, the WHO launched the Global Program to Eliminate Lymphatic Filariasis, for which mapping of the disease has been crucial. "When targeting elimination you need to know where transmission occurs," says Brooker.
Many districts in India believed to have stopped transmission of the parasite. The challenge remaining is in rural hotspots.
On the way to elimination
By mapping the disease geographically over set periods of time, the progress of control programs can be seen directly and hotspots of disease easily identified. "We can look at the shrinking of the map," says Brooker, who has seen the improvement since elimination was first targeted both in India, and globally. "Regions that were endemic (for disease) are no longer endemic ... but what India is seeing is more and more hotspots of transmission."
Hotspots are thought to arise from people not taking the drugs but also environmental factors aiding mosquito survival and breeding. In a country as populous as India, factors like overcrowding also come into play and anything that promotes contact with mosquitoes can increase your chance of being infected.
The final challenge then lies in catching the last worms.
"In catching those last few cases, that's when diagnostics become important," says Mistry and the recent development of a rapid diagnostic blood test should enable this faster and cheaper to truly monitor the presence of the parasite in the smallest of communities. "[Then we can] know if the parasite has been completely eliminated from the population."
