Filariasis – Lymphatic Filariasis (Elephantiasis)

Lymphatic filariasis parasitic disease, considered as a neglected tropical disease (NTD), caused by microscopic, thread-like filarial worms.

Filariasis is tropical, parasitic disease that affects the lymph nodes and lymph vessels of human.

Lymphatic filariasis is caused by parasites classified as nematodes (roundworms) of the family Filariodidea.

The two species of worms most often associated with infection are; Wuchereria bancrofti and Brugia malayi.  Wuchereria bancrofti, which is responsible for infection 90% of the cases.

Lymphatic filariasis is spread by infected mosquitoes to human. Their bites deposit a parasite that travels to the lymph system of body and adult worms only live in the lymph nodes and lymph vessels (human lymph system). Lymphatic filariasis is spread from person to person by bite of mosquitoes.

Epidemiological Triad

Agent – The causative agent of filariasis is microfilariae of wuchereria bancrofti (W. bancrofti) and Brugia malayi (B. Malayi) in india.

Lymphatic filariasis is a vector-borne disease, being transmitted by infected mosquitoes (e.g. Culex quinquefasciatus, Anopheles and Aedes mosquitoes)and several black fly species. The main vector is Culex quinquefasciatus in india.

Host factor- All ages is susceptible, but infection rate is more with age of 20-30 years.Human is the (definitive host) and mosquito is the (intermediate host).

Environmental factors-  Bad drainage or ill maintained drainage, Inadequatesewage disposal, Septic tanks, Open ditches drainage, Breeding place such as cess pools, soakage – pits, Poor environmental sanitation.

Causes of Filariasis

Filariasis is a tropical infectious disease caused by the round worm parasites (nematode); Wuchereria bancrofti or Brugia malayi.

The infection spreads from human to human by infected mosquito bites. The adult worm lives in the human lymph node and lymph vessels and produces a number of microscopic worms, known as microfilariae. Microfilariae circulate in the human blood and infect the mosquito when bites a human who is infected.

Mode of Transmission

Culex mosqitos or Mansonia mosquito pick up the microfilaria of Wuchereria  Bancrofti, Brugia malayi when bites an infected person.

Microfilariae (the minute larva of a filaria ) grow and develop in body of mosquito vector.  When bites a healthy person, the larval worms pass from the mosquito into the human skin, and circulating to the lymph vessels.

Filariasis disease spreads from man to man by mosquito bites. When a mosquito bites a person who infected with  lymphatic filariasis, microscopic worms circulating in the person’s blood enter and infect the mosquito.

1.  Man  To  mosquito   To     man

2. Infected man    bitten by   Culex mosquito

3. Mosquito     infects       man

Lymphatic filariasis disease, is a vector-borne disease and being transmitted by mosquitoes (e.g. Culex, Anopheles and Aedes mosquitoes). 

Incubation Period

The incubation period is can be vary, short as about 4 weeks or as long as about 8-16 months. 

Life Cycle

1. When a mosquito bites to a man who has lymphatic filariasis.

2. Microfilariae grow and develop mature into infective larvae within the mosquito.

3. When infected mosquitoes bite to man, mature parasite larvae are deposited on the skin from where they can enter the body.

4. The larvae then circulate to the lymphatic vessels where they develop into adult worms. 

5. The larvae matures in a six to twelve months period into the adult filariae which can live up to fifteen years and producing microfilariae.

6. The adult worms release millions of microfilariae into the blood of people. People with microfilariae in their blood can be the source of infection to others, thus continuing a cycle of transmission.

1. Culex mosquitos

2. Infected a person having microfilariae in peripheral blood

3. microfilariae are picked up by mosquito by bite

4.  Mosquito bites to healthy human

5.  After an incubation period

6. Cause filaria in the human host

Pathophysiology of Filariasis

The pathogenic effect are produced by adult worm (living/dead) of parasite –

1. The larval form of the parasite transmits the disease to humans by the bite of a mosquito

2. Larvae then enters the patient’s blood through the skin wound

3. Spread to the different sites such as lymphatic vessels

Affected lymph node and lymph vessel

4. Cause obstruction and Dilation of Lymphatic vessels, cause granulomatous lesions

5. Infections of lymphatics (Lymphangitis)

6. Obstruction of the lymph nodes, obstruction of the lymph flow

7. Chronic inflammation may lead to hardening of the lymphatic vessels (fibrosis)

8. Swell especially the legs and external genitals

9. Lymphoedema pitting (Grade 1)

10. Lymphoedema non- pitting (Grade 2)

11. Elephantiasis (Grade 3)

Clinical Manifestation

In the early stages of the infection, the patient clinical manifestation are –

1. High Fever

2. Shaking chills

3. Body aches

4. Headaches

5. Skin lesions

6. Swollen lymph nodes

7. Hypersensitivity reactions

Chronic Conditions

1. Lymphadenitis –  Enlargement one or more lymph node

2. Swelling in the legs, arms and genitalia especially, legs and external genitals

3. Lymphangitis is an inflammation of the lymphatic system

4. Lymphoedema – localized swelling of the body caused by an abnormal accumulation of lymph

Attacks may also be associated by acute inflammation of the genitalia in males –

1. Inflammation, pain and swelling of the testes (orchitis)

2. Sperm track (funiculitis)

3. Sperm ducts (epididymitis)

4. Scrotum may become abnormally swollen and painful

5. Epididymo-orchitis  – Inflammation of tube that carries and stores sperm, and/or of the testicle

When fibrosis and obstruction of lymphatic vessels occur due to chronic stage, which develop after 10-15 years after acute attack, in such cases, clinical manifestation are-

1. Hydrocele- accumulation of fluid in the scrotum

2. Elephantiasis – enlargement of an area of the body,  enlarged due to obstruction of the lymphatic vessels, causing accumulation of fluid, arms and  legs are the areas most often affected.

3. Chyluria – presence of lymphatic fluid in the urine

4. Abnormally enlarged lymphatic vessels (varices)

Progressive edema (elephantiasis) can affect in Female  –

Female external genitalia; (vulva), breasts, and/or arms and legs. Chronic edema may result abnormally thick skin.

Types of Filaria Infection

1. Lymphatic filariasis

 A.  Asymptomatic microfilaremia – patients remain asymptomatic for months and/or for years.

B. symptomatic filariasis – presents with the symptoms 

a. Acute manifestation

b. Chronic manifestation (lesion manifestation) 

2. Occult filariasis 

Associated characteristic histological changes. such as Hypersensitivity reaction

Diagnostic Evaluation

Filariasis is diagnosed in microfilaraemic cases primarily through direct observation of microfilariae in the peripheral blood.

Microfilariae cause lymphatic filariasis that circulate in the blood at night (called nocturnal periodicity).

1. Thick blood film

2. Serological tests – detect antobodies to microfilariae

ELISA  – Enzyme-linked immunoassay

IFAT – Immuno – Fluorescence Antibody Test

CFT – Complement fixation test

IHAT – Indirect hemagglutination test           

Now a days,  antigen are detected in blood or urine

3. DEC (diethyl- carbamazine)  provation test – detect microfilariae in day time

4. Filariasis Antigen Test

Urine examination- urine sample of chyluria

5.Lymph node sample from an infected individual.

6. PCR

Treatment of Filariasis 

Currently there is no vaccine available to prevent cure for lymphatic filariasis infection in human.

Antiparasitic drugs may be effective in eliminating the worm. If the disease is left untreated, obstruction of the lymph flow will cause swell to particular areas of the body especially the legs and external genitals. Symptoms are primarily a response to adult worms that cause inflammation and obstruction of the lymph flow.

Drugs Treatment of Filariasis

Di-Ethyl- Carbamazine (DEC) . This medication causes the disappearance of microfilariae from circulation and is effective in killing microfilariae.

More drugs are: Ivermectin, Albendazole, and Diethylcarbamazine. These drugs get from rid of the larval worm, to inhibit reproduction of the adult worm, or to kill the adult worm.

Surgical Treatment of Filariasis

Surgery may be performed to treat some people with filariasis who develop an abnormal accumulation of fluid in the scrotum (hydrocele).

Note – DEC should not be administered to patients who may also have onchocerciasis (river blindness) as DEC can worsen onchocercal eye disease.

 In patients with loiasis (related to Loa loa microfilarial density; skin and eye disease), DEC can cause serious adverse reactions, including encephalopathy.

Drug of choice – Where onchoceriasis is present, Ivermectin is the drug of choice to treat lymphatic filariasis.

Prevention and Control

In the tropical areas, mosquito control is an important part of prevention of filariasis. 

The best way to prevent lymphatic filariasis is to

1. Identification of cases and carriers

a. Clinical parameters-  Incidence and prevalence rate

b. Parasitological parameters – Measures microfilarial rate

2. Control of mosquito

a. Anti-larval measures

b. Anti-adult measures

3. Personal protection- Prevent from mosquito bites

4. Environmental sanitation

Know the signs and symptoms of Malaria, caused by Plasmodium parasites, transmitted to human through the bites of infected female Anopheles mosquitoes.