Lymphatic filariasis, although rarely life threatening, has huge socioeconomic consequences in over 73 countries around the globe. It affects over 120 million people living in the tropics and subtropics. The parasitic worm lives in human lymphatics blocking flow and causing huge limb & genital swelling and the disparaging epithet, Elephantiasis.
What is lymphatic filariasis?
Lymphatic filariasis is a parasitic worm that, in its adult form, lives in human lymphatics. It infects people, often in early childhood, causing permanent damage to the lymphatic system ultimately leading to disability and disfigurement later in life. Adult worms can live for up to seven years continuously producing micro filaraiae. There are three types of filariasis species, the two main ones are:
- Bancroftian Filariasis – transmitted by Culex Quinquefasciatus anopheles and aedes species found in India, South East Asia and the Pacific Islands. This type of worm is responsible for over 90% of cases. Concentration of microfilariae in the blood is highest at night, to coincide with feeding times of mosquito species.
- Brugian Filariasis – transmitted by anopheles, this is a less common parasite of monkeys, living mainly in the swampy forests of Flores, Timor and Alor.
How is lymphatic filariasis spread?
The microfilariae produced by both types of parasitic worm live in the human bloodstream. Mosquitos ingest these when they feed on an infected person. The mosquitos incubate the microfilariae for 1-2 weeks before secreting them into a new human during a blood meal. Over the next year the microfilariae develop into adult worms and in a small percentage of infected people they block the lymphatics, causing elephantiasis.
Risk of transmission from a single mosquito bite is very low and methods of mosquito bite prevention can be useful to prevent the spread of infection.
Most tropical and subtropical countries across all continents have reported cases of lymphatic filariasis. The list includes Brazil, Guyana, Haiti, Myanmar, Thailand and Vietnam where the disease is endemic. Southeast Asian countries and the Western pacific regions account for over 90% of the worlds reported cases of lymphoedema.
In 2000, there were over 120 million reported cases of the disease which has fallen following a WHO initiative and widespread eradication programmes throughout the world.
The West African country of Benin was one of the first to introduce a national programme of eradication following a study in 2001 looking at the prevalence of the disease. A study published in the journal of parasitology and vector biology records the follow up data of their programme. In the study communes they met the WHO target of <1% prevalence following 5 rounds of preventative chemotherapy.
Signs and Symptoms
The majority of people who are infected will remain asymptomatic with subclinical lymphatic dilatation. In around 30% of infected individuals, the adult worm will completely block lymphatics causing huge swelling of limbs or genitals. Men may develop hydroceles, funiculitis, epididymitis and orchitis.
Blockage of lymphatics leads to recurrent bacterial infection of the affected limbs which ultimately thickens and hardens the skin akin to that of an elephant. If infected, you may experience recurrent low grade fevers and death of an adult worm will cause acute filarial lymphangitis. Tender nodules may appear under the skin where the dead worm is located.
In the Indian subcontinent, a few individuals will develop an immune hyperresponsiveness called tropical eosinophilia syndrome, characterised by coughing, wheezing and splenomegaly. These patients will require three weeks of intensive treatment.
Diagnosis of filariasis is by blood smear. Microfilariae are most likely to be circulating at night, so you should take blood samples then, in order to have the highest chance of detecting the organisms. You can visualise the microfilariae on examination after staining with giemsa or hamatoxylin.
Newer techniques involve immunological testing for filarial antigen, IgG1 and IgG4. For immunoassay, you can take the blood test at any time of day. Urinalysis may reveal microscopic proteinuria and haematuria.
Diethylcarbamazine (DEC), 6mg/kg/day, is the treatment for Lymphatic Filariasis. DEC is lethal to microfilariae, however, adult worms are only killed by long courses. Side effects include nausea, dizziness, fevers and headaches with severity directly correlating to the level of microfilariae in the blood. Blood microfilariae levels above 2500/mm³ can cause life threatening encephalitis and treatment should not be commenced.
The side effects and long courses of treatment often prevent adequate treatment with patients stopping treatment early. Additionally, patients often do not get complications of infection for years after they become infected. They often do not see the benefits of treatment until late stages at which point it can be too late.
Make sure to thoroughly examine for onchocerciasis, caused by the parasitic worm onchocerca volvulus. If co-infection exists, DEC treatment can cause severe eye exacerbations and blindness.
Until recently, treatment has focussed on mosquito bite prevention, including the use of mosquito nets, sprays and protective clothing. Another strategy is to destroy larval and pupal stages of mosquitos in aquatic vegetations.
Newer techniques include eliminating mosquito breeding sites with polystyrene beads and larvicides.
The WHO have labelled lymphatic filariasis and an eliminable disease. Endemic areas are being encourage to introduce treatment programmes where all members of the community will receive a single dose of ivermectin yearly for five years, aiming for a prevalence below 1% of the population once completed. By scaling up current efforts against LF across all endemic areas, a recent study in the BMJ estimated that over 4.38 million disability adjusted life years could be averted. Scaling up current elimination projects could save health systems over $483 million.
To find out more about the global programme to eliminate Lymphatic Filariasis, click here.
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