Epidemiology and Clinical Manifestations of Lymphatic

Filariasis

Dr. Dilip Kumar DasAssociate Professor, Community Medicine

R. G. Kar Medical College, Kolkata, West Bengal

What is Lymphatic Filariasis?

Lymphatic filariasis is a disfiguring, disabling communicable human disease caused by the thread like nematode parasitic filarial worms.

A leading cause of permanent and long-term disability in the world

A cause of major social and economic burden

Global Burden

World Health OrganizationGlobal Programme for Elimination of Lymhatic Filariasis

Countries with lymphatic filariasis

LF status of countries as of May 2000

endemic

non-endemic

post-endemic or uncertain

Globally………Globally………

Affects 83 countries in the worldAffects 83 countries in the world About 1.2 billion people at risk of infectionAbout 1.2 billion people at risk of infection 120 million people have some form of the 120 million people have some form of the

disease disease 40 million are incapacitated/disfigured40 million are incapacitated/disfigured SEAR: 60 million infected, 31 million have SEAR: 60 million infected, 31 million have

clinical manifestationsclinical manifestations More than one third of the infected people in More than one third of the infected people in

IndiaIndia

Filarial Endemicity in India

Endemic districts with MF rate 1% and above

Low endemic districts with MF rate below 1%

Districts under survey

Non-endemic districts

In India…….In India…….

250 districts in 20 states/UTs are endemic 600 million people are at risk of infection 6 million attacks of acute filarial disease per

year 20 million one or more chronic filarial lesions

Highly endemic states: Uttar Pradesh, Bihar, Jharkhand, Andhra

Pradesh, Orissa, Tamilnadu, Kerala, Gujarat.

Basic Epidemiology of LF

Agent :

– Filarial parasite: Nematode– 3 of 8 species cause Lymphatic Filariasis– Wuchereria bancrofti, Brugia malayi, Brugia timori– In India: W. bancrofti (99.4%) and B. malayi (0.6%) cause LF

– Develops in two hosts: Man – Primary (definitive) host Mosquito – Secondary (intermediate) host

Periodicity

Nocturnally Periodic Diurnally Sub-periodic

Basic Epidemiology of LF…

Host :

- Man is the natural host.

- All ages are susceptible to infection.

- Adults are more frequently and more heavily infected than children

- Mf rate is higher in men

- Filaria disease appears in a small percentage of infected individuals.

- Urbanization, industrialization, migration of people and specific habits are some of the social factors associated with filariasis.

Basic Epidemiology of LF…

Vectors : Bancroftian Filariasis (nocturnally periodic): Culex quinquefasciatus. Brugian (Malayan) Filariasis: Mansonoides annulifera, M. uniformis, M. indiana. Bancroftian Filariasis (Diurnally sub-periodic): Ochlarotatus (Finlaya) niveus group

C. quinquefasciatus generally breed in dirty and polluted water (stagnant drains, cesspools, septic tanks, burrow pits etc).

Mansonoides breed in water bodies containing certain aquatic plants

C. quinquefasciatus is highly anthrophilic, an indoor rester (endophilic) and bites at midnight.

Basic Epidemiology of LF…

Environment:

Prevalent both in urban and rural areas

Climate influences the breeding and longevity of vector mosquitoes and also determines the development of parasite in the vector

Bad drainage, inadequate sewage disposal, lack of town planning increase vector breeding

How is LF transmitted?

Incubation PeriodIncubation Period

Extrinsic incubation period: Time interval for microfilariae to develop

inside the mosquito to 3rd stage infective larvae.

(10 – 14 days)

Pre-patent period: Time interval between introduction of

infective larvae and the first appearance of detectable Mf in the peripheral blood.

(12 –18 months)

Clinical incubation period: Time interval from invasion of infective larvae

to the development of clinical manifestations. (8 – 16 months)

Clinical ManifestationsClinical Manifestations

Lymphatic Filariasis

Stage of invasion Asymptomatic/carrier stage Stage of acute manifestations Stage of chronic manifestations

Ocult Filariasis

Clinical featuresClinical features Recurrent attacksRecurrent attacks Filarial feverFilarial fever LymphangitisLymphangitis LymphadenitisLymphadenitis Epididymo-orchitis in malesEpididymo-orchitis in males Mastitis in femalesMastitis in females LymphoedemaLymphoedema

ElephantiasisElephantiasis HydroceleHydrocele ChyluriaChyluria

Acute Filarial LymphangitisAcute Filarial Lymphangitis

Acute dermatolymphangioadenitis

After the “acute attack”

Entry lesions common in LymphoedemaLymphoedema

Injury CandidiasisPyoderma ParonychiaFissure foot EczemaInsect bites

Entry lesions can cause acute attacks

Chronic obstructive lesions:Elephantiasis

LF is a social evil…LF is a social evil…

Disfigurement of limbs and genitalia leads to

Stigma Anxiety Ostracization Psychological trauma Sexual dysfunction

The disease impedes

Mobility Travel Educational opportunities Employment opportunities Marriage prospects

LF drains the economy…

Global economic loss at US $ 2 billion per annum

India loses 1.2 billion man days annually

Estimated economic loss in India alone is US $ 850 million per year

The economic loss is equivalent to 0.05% of GNP

A major cause of poverty in the regions

How can LF be diagnosed?How can LF be diagnosed?

Clinical examination for filarial symptomsClinical examination for filarial symptoms

Detection of microfilariae in mf carriersDetection of microfilariae in mf carriers - Thick blood film (20 c.mm) microscopy at night (8-30 PM – 12

AM) - MFC method - DEC provocation test

Antigen detection Immunochromatographic test (ICT):

Field friendly, sensitive and specific, easy to perform and can be done at any time during the day or night

DNA based molecular techniques

Microfilariae in peripheral blood

Filaria Survey

Prevalence of Filariasis can be Prevalence of Filariasis can be estimated byestimated by

Clinical Survey Parasitological Survey Entomological Survey

Parasitological indices

Microfilaria rate:

No of slides +ve for mfNo of slides +ve for mf Total number of slides examinedTotal number of slides examined Average mf density

Total number of mf among +ve blood smearsTotal number of mf among +ve blood smears Number of +ve blood smearsNumber of +ve blood smears Disease rate No of persons +ve for diseaseNo of persons +ve for disease Total number of persons examinedTotal number of persons examined

x 100x 100

x 100x 100

Entomological indices

10 man hour density No of male & female Cx. Quinquefasciatus collected

Time (in hours) spent on mosquito collection Vector infection rate - Percentage of female vector mosquitoes +ve for

L-1/L-2/ L-3 stage larvae Vector infectivity rate - Percentage of female vector mosquitoes +ve for

infective larvae (L-3 stage) Average number of infective larvae

per infective mosquito

x 10x 10