Lymphatic Filariasis: Toward Elimination

Introduction & Epidemiology : Lymphatic system is the network of lymph nodes and lymph vessels that maintains the fluid balance between the tissues and the blood which is an essential element of the body’s immune defense system. Filaria worms are living in the vessels of the lymphatic system and creating damages.

99. bancrofti, B. malayi and B. timari are round, coiled and threadlike parasitic namatode worms belong to the family filaridae. In India 99.4% infections are caused by W. bancrofti and 90% W. bancrofti infection results to Lymphatic Filariasis from subclinical stages to Elephantiasis. 20 million people are suffering from the disease globally.

It is a disease of the tropic and sub tropics ranging from Asia to Africa to Latin America and Pacific Region where heat and humidity along with heavy rainfall prevail vis a vis endemicity of the disease.

The disease in transmitted through bites of infected female Culex, Mansonia and Anopholes mosquitoes where adult worms are living in human lymphatic vessels and microfilariae (Mf) are circulated at peripheral blood.

Acute and chronic manifestations are fever, pain, lymphangitis, adeno lymphadenitis, funiculitis (inflammation of the spermatic cords), epididymitis (inflammation of the testes); swelling of the legs, arms, genitals (scrotum, vulva, breasts); pitting or non-pitting oedema, hydrocele, chyluria (a rare condition when lymphatic fluid leaks into the kidneys and turns the urine millky white) and elephantiasis causing considerable suffering, deformity and disability as well as social stigma.

Scrotal pain is common and microfilariae may be found in hydrocele, chyluria and blood. Hypersensitivity state may cause Tropical Pulmonary Eosinophilia and Atypical Filarial Arthritis.

Lymphatic Filariasis is a public health problem. Reducing prevalence of microfilariae in human to <1% may stop the transmission. Therefore to reduce the transmission Govt. of India (GOI) introduced Mass Drug Administration (MDA) in endemic states, UTs and districts since 2004 with an annual single dose of DEC and Albendazole.

Agent Factors:

Human Filarial Infection

Characteristic nocturnal periodicity :

The Worms become active at night and microfilariae appear in large number in the blood stream at night and retreat during the day time. Maximum density of Mf in blood from 10 pm to 02 am (upto 04 am as per Prof. K. D. Chatterjee). Interestingly the biting habits of the vector mosquitoes are biologically adapted at night.

Life Cycle of the agents :

Man is the definitive and mosquito is the intermediate hosts, i.e., sexual cycle occurs in man and asexual cycle occurs in mosquito.

1. a) Human Cycle : Infected larvae come through mosquito bites and they grow to adult male and female worms. bancrofti adult male and female worms are 40 mm and 50-100 mm long respectively. Female worms are viviparous (which produces live offspring rather than eggs) giving birth about 50,000 Mfs per day which find their way into blood circulation via lymphatic system. Lifespan of Mfs is usually one year and more. Adult worms survive for 15 years and more. In a case adult worm survived 40 years.
2. b) Mosquito Cycle : Mfs are picked up during feeding. (i) Unsheathing happens inside the stomach of mosquito when larvae come out from sheaths within 1-2 hours. (ii) First stage of larva: They penetrate the stomach wall and come to thoracic muscle within 6-12 hours. (iii) Second stage of larva: Larvae molt and mature and (iv) Third stage of larva: After the final molt they become infective. Mosquito Cycle is also called Extrinsic Incubation Period and it lasts 10-14 days.

Host Factors: Mf infestation is found higher in males and it is related with migration, urbanization, poverty, illiteracy, poor sanitation etc. After many years of exposure some people may develop a kind  of resistance.

Environmental Factors:  Hot humid climate with 22⁰C – 38⁰C temperature and 70% humidity is optimal for living of the Culex mosquitoes. Intermittent rain and water logging; stagnant polluted water, poor drainage system; unplanned habitats with unattended water storage and ill maintained cesspools, open ditches, soak pits, septic tanks, burrow pits, water bodies etc. are favourable for breeding of mosquitoes.

Vectors:

Mode of transmission : Bite of infected female mosquito.

Incubation Period : The time interval between inoculation of infective larvae and the first appearance of detectable Mf is known as ‘Pre patent period’

The time interval from invasion of infected larvae to the development of clinical manifestations is known as ‘Clinical Incubation Period‘ which is 8 to 16 months or more.

Clinical Manifestations : Small portions of cases exhibit clinical manifestations whereas most of the cases show Inapparent Infection and act as Carrier. Those cases which exhibit clinical manifestations exhibit in two ways, mostly (1) Lymphatic Filariasis and (2) Occult Filariasis in limited cases.

(1) Lymphatic Filariasis :

1. a) Stage of asymptomatic amicrofilaraemia –
2. b) Stage of asymptomatic microfilaraemia – These carriers are usually detected by night blood sample examination.
3. c) Stage of acute manifestation –

Recurrent episodes of acute inflammation, lymphangiectasia and lymphatic dysfunction in lymph glands and vessels due to mechanical irritation; liberation of metabolites and toxic fluid by larvae and fertilized female worms, absorption of toxic products from dead worms and bacterial infections.

Filarial fever, pain, urticaria, fugitive swelling, lymphangitis, lymphadenitis, lymphadenoma of various parts of the body and  epididymo-orchitis are common signs and symptoms.

Those who have circulating microfilariae but outwardly healthy may transmit infection to others through mosquitoes.

1. d) Stage of chronic obstructive lesions –

Usually 10-15 years after the onset of the disease. Mechanical blocking of lumens by dead worms, endothelial proliferation and inflammatory thickening of afferent lymph nodes lead to chronic filariasis, obstruction of lymph vessels and varicosity of lymph nodes causing permanent structural changes and hypertrophy of affected parts, viz., Hydrocele, Chyluria and Elephantiasis.

The persons with chronic filarial swellings suffer severely from the disease but no longer transmit the disease.

2) Occult Filariasis :

It results from a hypersensitivity reaction to filarial antigens derived from Mfs., e.g., Tropical Pulmonary Eosinophilia exhibiting low grade fever, loss of weight, paroxysmal cough, dyspnoea and splenomegaly turns to Interstitial Fibrosis and Chronic Restrictive Lung Disease. Mfs may be found in lungs, liver and spleen.

Diagnosis : i) Preparation of thick film and microscopy to find Mf.

Filaria Survey : Night mass blood collection from endemic areas.

Management :

1. a) Lymphadenoma Management :

Early detection, care of the skin, washing and drying of the affected area or limb, elevation of limbs, exercise, wearing proper foot wears etc. and to follow WHO guidelines.

1. b) Chemotherapy
2. i) Diethylcarbamazine or DEC: 2mg/kg BW thrice daily x 21 days. Sometimes toxic reactions which usually subside. Pregnant women and children under two years are exempted.
3. ii) Albendazole: 400 mg, single dose.iii) Ivermectin: 150-200 mg/kg BW

1. c) Drainage of hydrocele, plastic and reconstruction surgery etc.

Control Measures :

1. a) Vector Control :
2. i) Anti larval measures: Using Mosquito larvicidal Oil (MLO) like Pyrethrum, Temophos, Fenthion etc.; De-weeding, De-silting, Pisciculture of larvivarous fishes like guppy and gumbuscia; source reduction, land filling; proper sanitation and drainage; proper water storage practice etc. Better to introduce Integrated Vector Management through environment friendly multi-prong approaches.
3. ii) Anti adult measures: Space spray etc. using DDT, HCH, Dieldrin etc.

iii) Individual protection: Wearing full sleeve dresses, covered shoes and shocks; using mosquito nets, repellants etc.

National Filaria Contral Programme :

• Introduced in 1955.
• In 1978, Operation Component of NFCP was merged with urban malaria scheme. Anti-larval measures, source reduction, detection of cases, treatment of Mf carriers, morbidity management, IEC etc.
• In 2000, Global Alliance to eliminate LF (GAELF) was formed.
• In 2002, under National Health Policy (NHP) LF was targeted to be eliminated by 2015. Later it was extended up to 2021.

MDA (a single dose of DEC 6 mg/kg BW and Albendazole 400 mg) was initiated along with home based management of lymphadenoma cases and up scaling hydrocele operations at CHC and above.

• In 2002, LF is included in National Vector Borne Disease Control Programme (NVBDCP) and in 2005 it was integrated with National Rural Health Mission (NRHM).
• In 2017, Transmission Assesment Survey (TAS) was introduced to assess the programme.
• In 2018, Triple drugs IDA (DEC, Albendazole and Ivermectin) was initiated for endemic districts for next five years along with ‘Morbidity Management & Disability Prevention (MMDP)’
• 1st November is the National Filaria Day and November is the Filaria Month.
• During 2018 to 2021, as many as 256, 272, 328 and 333 endermic districts were identified respectively where >1% mf rate were present.

>90% LF burden in India is contributed by 12 endemic states – Bihar (17%), Kerala (15.7%), Uttar Pradesh (14.6%), Andhra Pradesh (10%), Kerala (10%), Jharkhand, Odisha, Chhattisgarh, Madhya Pradesh, Maharashtra, West Bengal and Assam. they have contributed 86% of Mf cases and 97% disease cases of the country.

0.55 million Lymphadenoma and 0.15 million Hydrocele cases were detected in 2022.

• Like all neglected tropical diseases (NTD) Lymphatic Filariasis (LF) is also targeted to be eliminated by 2030 under Sustainable Development Goals (SDG).