Epidemiology and

Control of Filariasis

ABU UBAIDA FAZAA

ABDULRAZZAQ

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What is Lymphatic Filariasis

What is Lymphatic Filariasis

Lymphatic filariasis is a vector-borne

parasitic disease that is endemic in

many tropical and subtropical

countries. The disease is caused by

thread-like, parasitic filarial worms:

Wuchereria bancrofti, Brugia

malayi, and Brugia timori.

W. bancrofti is most widely spread

and is responsible for more than 90%

of the infections.

Classification

Can be classified depending on their habitat in human tissues

Lymphatic filariasis

Body cavity filariasis

Connective tissue

filariasis

Most Important Filariae

SpeciesGeographic

distributionPathogenicity

site of

infection

Microfilariae

(characteristics)Vector

Wuchereria

bancrofti

Asia, Pacific,

Tropical Africa,

Americas

Lymphangitis,

fever,

elephantiasis

hydrocoele,

and

chyluria

Lymphatics

Found in blood,

sheathed,

periodicity

variable

Culicidae

(mosquitoes)

Brugia malayiSouth and East

Asia

Lymphagitis,

fever, and

Elephantiasis

Lymphatics

Found in blood,

sheathed,

nocturnally

periodic or

subperiodic

Culicidae

(mosquitoes)

LIFE CYCLE The adult worms (macrofilaria) are located in the lymphatic system

of the human host, where they live for 5-10 years.

During their lifespan, after mating, female worms bring millions ofimmature microfilariae (mf) into the blood.

Some of these mf may be engorged by mosquitoes taking a blood

meal.

Inside a mosquito, mf develop in about 12 days into L3 stage larvae

(L3). These L3 are infectious to human: they can enter the human

body when a mosquito takes a blood meal. Some will migrate to the

lymphatic system and develop into mature worms.

LIFE CYCLE Maturation takes 6-12 months.

Mf cannot develop into adult worms without

passing through the developmental stages in

the mosquito.

life span of mf in the human body is estimated at

6-24 months.

WHY FILARIASIS NEVER CAUSES EXPLOSIVE

EPIDEMICS

There are three reasons

1- The parasite does not multiply in the insect vector.

2- The infective larvae do not multiply in the human host.

3- The life cycle of the parasite is relatively long, 15 years or more.

These factors favor the success of a control program.

Symptoms Most people infected with Brugian or

Bancroftian filariasis in endemic areasare asymptomatic, since thedevelopment of symptoms relates tothe cumulative acquisition ofincreasing numbers of worms.

The clinical course of lymphaticfilariasis includes three distinct phases:

1. Asymptomatic microfilaremia.

2. Acute episodes of adenolymphangitis(ADL). Which is reversible.

3. Chronic lymphedema disease(irreversible lymphedema), which isoften superimposed upon repeatedepisodes of ADL.

Axillary

lymph

nodes

Inguinal

lymph

nodes

Parasites White, slender, roundworms.

Three types. the most common are:

Wuchereria bancrofti.

Brugia malayi.

Brugia timori.

Live for 5-7 years, produce millions of

microfilaria.

EPIDEMIOLOGY

W. bancrofti occurs in the following regions:

Africa, Southeast Asia, the Indian subcontinent,

many of the Pacific islands, and focal areas in

Latin America.

B. malayi occurs mainly in China, India, Malaysia,

the Philippines, Indonesia, and various Pacific

islands.

B. timori is limited to the Timor Island of Indonesia.

EPIDEMIOLOGY

It is estimated that more than 120 million people

worldwide are infected with one of these three

microfilariae.

More than 90 percent of these infections are due to W.

bancrofti, and the remainder are mostly due to B. malayi.

Estimates suggest that more than 40 million infected

individuals are seriously incapacitated and disfigured by

the disease.

Infected regions

Control How can the menace of filariasis be controlled?

Addition of DEC to salt for mass treatment: It is also a cheap and safe

method. Common salt medicated with 1–4 g of DEC per kg.

Mosquito control measures: This is achieved by spraying insecticides which

are lethal to the larvae of the mosquitoes.

Environmental issues in the control of filariasis: The filariasis problem largely

arises as a result of poor sanitation and hygiene. The emphasis should be on

improving existing sanitary conditions. In the case of Mansonia mosquitoes,

breeding is best controlled by removing supporting aquatic vegetation

such as the Pistia plant from all water collections and converting the ponds

to fish or lotus culture. Larvicidal operations are complemented activities

such as filling up of ditches and cesspools, drainage of stagnant water,

adequate maintenance of septic tanks and soakage pits etc.

Control Filarial Surveys: Firstly, in order to control the disease, an estimate of

the problem by conducting surveys has to be undertaken. There are

many elements in the survey. The survey can either entail theexamination of patients for the symptoms of filariasis, or the

examination of blood samples, particularly at night time to

demonstrate the parasite. Many times, the parasite is difficult to

detect in the blood, and tests which measure antibodies against the

parasite may have to be employed.

Entomological survey: This comprises general mosquito collectionfrom houses, dissection of female vector species for detection of

developmental forms of the parasite, a study of the extent and typeof breeding places. The data is assembled, analyzed and used for

the compilation of certain filarial statistics.

Control

Preventive measures for travelers:

Avoid outbreaks: Travelers should avoid known

foci of epidemic disease transmission.

Be aware of peak exposure times and places.

Wear appropriate clothing: Travelers can

minimize areas of exposed skin by wearing long-

sleeved shirts, long pants, boots, and hats.

Control Check for ticks: Travelers should inspect themselves and

their clothing for ticks during outdoor activity and at the

end of the day.

Bed nets: Bed nets are essential in providing protection

and reducing discomfort caused by biting insects.

Insecticides and spatial repellents: These products,

containing active ingredients that help kill the mosquitos.

Optimum protection can be provided by applying the

repellents to the exposed skin.

TREATMENT Diethylcarbamazine — DEC with or without corticosteroieds.

Ivermectin — Studies have established that ivermectin given as asingle dose in Bancroftian filariasis reduces microfilaremia byapproximately 90 percent even one year after treatment.

Albendazole — has also been used in filarial infections. Prolonged

courses of high dose albendazole have a significant macrofilaricidal

effect and result in a gradual decrease in microfilarial levels.

Doxycycline — Initial studies suggested that doxycycline, which has

good activity against filaria spp, leads to sterility of adult worms.

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