Lymphatic Filariasis

Lymphatic filariasis (LF) commonly known as elephantiasis is a painful and profoundly disfiguring disease. Lymphatic filariasis is caused by three species of thread-like nematode parasitic worms known as filariae.

Male worms are about 3–4 centimeters in length, and female worms 8–10 centimeters. The male and female worms together form “nests” in the human lymphatic system, which cause huge swellings of the limbs and other parts of the body.

In communities where filariasis is transmitted, all ages are affected. While the infection may be acquired during childhood, its visible manifestations may occur later in life, causing temporary or permanent disability.

These parasitic worms responsible for filariasis are

• Wuchereria bancrofti
• Brugia malayi
• Brugia timori

The vectors of these parasitic worms are mosquitoes - Anopheles, Culex, Aedes, Ochlerotatus and Manson mosquitoes.

Wuchereria bancrofti is transmitted throughout the tropics in Africa, Asia, the Pacific and the Americas while B. malayi and B. timori are found in east and south Asia.

Bancroftian filariasis, caused by Wuchereria bancrofti, is mainly transmitted by Culex quinquefasciatus and by some Anopheles and Aedes species.

Brugian filariasis, caused by Brugia malayi and B. timori is transmitted by Mansonia and Anopheles species.

Although the disease causes much suffering and disability it is rarely life-threatening.

Humans are definitive hosts and mosquito is the intermediate host.

An estimated 120 million people in tropical and subtropical areas of the world are infected with lymphatic filariasis; of these, almost 25 million men have genital disease (most commonly hydrocoele) and almost 15 million, mostly women, have lymphoedema or elephantiasis of the leg.

A recent estimation of the impact of MDA during the past 13 years suggests >96.71 million cases were prevented or cured, yet as many as 36 million cases of hydrocoele and lymphoedema remain.

Of the total population requiring preventative chemotherapy, 57% live in the South-East Asia Region (9 countries) and 37% live in the African Region (35 countries).

As one of the leading causes of global disability, LF accounts for at least 2.8 million DALYs; this does not include significant co-morbidity of mental illness commonly experienced by patients and their caregivers.

In Africa, 34 countries are endemic, and Nigeria is believed to bear the highest burden of LF, with an estimated 80 to 120 million people at risk.

Nigeria is the third most endemic country in the world with about 22.1% of the population infected.

The adult worms live in the lymphatic vessels in the human body and produce embryos called microfilariae, which circulate in the bloodstream and are picked up by biting mosquitoes.

After developing for several days in the mosquito, infective larvae is transmitted through the skin when the mosquito feeds, migrate to the lymph nodes and develop into adult worms in the lymph vessels.

• Estimated 2/3 people “asymptommatic”
• Inflammation of the lymphatic system
• Acute recurrent fever.
• Lymphedema and elephantiasis, the characteristic swelling of the limbs, genitalia and breasts (with thickening of the skin and underlying tissues).

Microscopy: examination of thick smears of 20–60 μl of finger-prick blood. The microfilariae that causes LF circulate in the blood at night (called nocturnal periodicity). Blood collection should be done at night to coincide with the appearance of the microfilariae, and a thick smear should be made and stained with Giemsa or hematoxylin and eosin.

Immunochromatographic card test (ICT): The test requires 100 μl of finger-prick blood drawn at any time, day or night. ICT has high sensitivity and specificity for detecting Wuchereria bancrofti infection.

Ultrasonography: using a 7.5 MHz or 10 MHz probe can locate and visualize the movements of living adult worms of W.bancrofti in the scrotal lymphatics of asymptomatic males with microfilaraemia. The constant thrashing movements described as “Filaria dance sign” can be visualized.

In 1997, WHO classified lymphatic filariasis, along with five other infectious diseases, as eradicable or potentially eradicable.

In 2000, WHO launched the Global Programme to Eliminate Lymphatic Filariasis (GPELF).

The elimination strategy has two components:

1. To stop the spread of infection (interrupting transmission)
2. To alleviate the suffering of affected populations (controlling morbidity).

Stop the spread of infection – MDA

In order to interrupt transmission, districts in which lymphatic filariasis is endemic must be mapped and a strategy of preventive chemotherapy called mass drug administration (MDA) implemented to treat the entire at-risk population.

The following drug regimens are recommended for use in annual MDA for at least 5 years with a coverage of at least 65% of the total at-risk population.

• 6 mg/kg of body weight diethylcarbamazine citrate (DEC) + 400 mg albendazole; or
• 150 µg/kg of body weight ivermectin + 400 mg albendazole (in areas that are also endemic for onchocerciasis);
• 400 mg albendazole preferably twice per year (in areas that are also endemic for Loa loa).

An alternative and equally effective community-wide regimen in endemic regions is the use of common table salt or cooking salt fortified with DEC. DEC fortified salt has been used in only a few settings.

Alleviate suffering – MMDP

Successful MDA will prevent new infections and no new cases of clinical disease. To achieve the second aim of GPELF, a core strategy of morbidity management and disability prevention (MMDP) is needed.

Suffering caused by the disease can be alleviated through a minimum recommended package of care to manage lymphedema and hydrocele. These services should be available within primary health care systems in all areas of known patients.

China and the Republic of Korea were declared to have eliminated lymphatic filariasis as a public health problem in 2007 and 2008, respectively.

In 2015, Togo was declared a LF free country by WHO and it’s the first sub-saharan African country to eliminate LF.

Of 73 countries listed by WHO as being endemic for lymphatic filariasis, 18 countries have completed interventions and are conducting surveillance to validate elimination.

An additional 22 countries had delivered MDA in all endemic areas and are also on track to achieve elimination.

The remaining 33 countries have not been able to achieve 100% geographical coverage; 10 of these are yet to initiate preventive chemotherapy or submit evidence that MDA is not required.

Mass treatment is ongoing in 45 countries. Ten countries have not started treatment or submitted evidence indicating treatment is not required.

Lymphatic filariasis (LF) is still a major public health problem. The disease is ranked by the World Health Organization (WHO) as the second leading cause of permanent and long-term disability, and has been targeted for elimination by 2020.

Effective diagnosis LF is required for treatment of infected individuals, for epidemiological assessment and for monitoring of the control program. Conventional diagnosis of LF depends on detection of microfilariae (Mf) in blood specimens.

In order to achieve the goal of LF elimination by 2020, National LF elimination program of Nigeria needs to scale up MDA in all the states of the federation.