Epidemiology and Clinical Manifestations of Lymphatic Filariasis
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Epidemiology and Clinical Manifestations of Lymphatic
Filariasis
Dr. Dilip Kumar DasAssociate Professor, Community Medicine
R. G. Kar Medical College, Kolkata, West Bengal
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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
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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
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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
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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
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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.
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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
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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.
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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.
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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
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How is LF transmitted?
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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)
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Clinical ManifestationsClinical Manifestations
Lymphatic Filariasis
Stage of invasion Asymptomatic/carrier stage Stage of acute manifestations Stage of chronic manifestations
Ocult Filariasis
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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
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Acute Filarial LymphangitisAcute Filarial Lymphangitis
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Acute dermatolymphangioadenitis
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After the “acute attack”
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Entry lesions common in LymphoedemaLymphoedema
Injury CandidiasisPyoderma ParonychiaFissure foot EczemaInsect bites
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Entry lesions can cause acute attacks
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Chronic obstructive lesions:Elephantiasis
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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
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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
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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
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Microfilariae in peripheral blood
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Filaria Survey
Prevalence of Filariasis can be Prevalence of Filariasis can be estimated byestimated by
Clinical Survey Parasitological Survey Entomological Survey
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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
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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