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EPIDEMIOLOGY OF FILARIASIS Dr. P ritesh patel Resident Community medicine dept.


What is lymphatic filariasis? Lymphatic filariasis, also known as elephantiasis, is a disease of the tropics that causes grotesque swelling of the limbs and male genitalia. The disease is caused by thread-like, parasitic filarial worms, Wuchereria bancrofti , Brugia malayi that live almost exclusively in humans. These worms lodge in the lymphatic system, the network of nodes and vessels that maintains the delicate fluid balance between the tissues and blood, and which is an essential component for the body’s immune defence system. They live for 4-6 years, producing millions of immature microfilariae (minute larvae) that circulate in the blood.

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Epidemiology One hundred and twenty million people in at least 80 countries of the world are infected with lymphatic filarial parasites, and it is estimated that 1.2 billion (20% of the world's population) are at risk of acquiring infection. One third of these infected live in India, one third in Africa and most of the remainder in Asia , the Pacific and the Americas .

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Cont…. Ninety percent of these infections are caused by Wuchereria bancrofti , and most of the remainder by Brugia malayi . For W. bancrofti , humans are the exclusive host, and even though certain strains of B. malayi can also infect some feline and monkey species, the life-cycles in humans and in these other animals generally remain epidemiologically distinct, so that little overlap exists.

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Cont.. The major vectors for W. bancrofti are Culex mosquitoes in most urban and semi-urban areas, Anopheles in the more rural areas of Africa and elsewhere, and Aedes species in many of the endemic Pacific islands. For the Brugian parasites Mansonia species serve as the major vector, but in some areas anopheline mosquitoes are responsible for transmitting the infection. Brugian parasites are confined to areas of east and south Asia, especially India, Malaysia, Indonesia, the Philippines, and China.


Mapping LF Distribution In Endemic Countries 54 countries completed

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India and Global Filariasis is a major public health problem next only to malaria.As per recent estimates, about 428 million people with 28 million mf carriers and 21 million clinical cases are spread in 13 States and 5 Union Territories. India contributes about 74% of endemic population and 81% of the disease burden in the Region. W.bancrofti is the most predominant infection comprising 99.4% of the problem in the country while B.malayi is confined to the western coast of Kerala and a few pockets in six other States. Both the infections are nocturnally periodic. In Nicobar Group of Islands, diurnally subperiodic infection of W.bancrofti transmitted by Aedes ( Finlaya ) niveus group was detected about three decades back.


Cont.. The first pilot project in the world for the control of LF was undertaken in Orissa from 1949-54 and in the subsequent year the National Filaria Control Programme was launched with the following objectives:   i .    to delimit the problem, ii.      to undertake large scale control operations and iii.      to train the professionals and ancillary staff to run the Programme. At present, the Programme is confined to urban areas only covering 11% of the endemic population

What is lymphatic filariasis? :

Cont.. After affecting many changes in the Programme during the last four-and-a-half decades the country adopted a revised strategy in 1997 for elimination of LF. A National Filaria Day (NFD) is being observed with a single dose mass DEC therapy once a year and morbidity control through IEC in 13 highly endemic districts in six States having a total population of about 41 million.

Epidemiology :

Agent Factor Wuchereria bancrofti Brugia malayi Brugia Timori Mansonella streptocerca Loa loa Onchocerca vovulus Mansonella ozzardi Mansonella perstans


Causal Agents: Filariasis is caused by nematodes (roundworms) that inhabit the lymphatics and subcutaneous tissues.  Eight main species infect humans .  Three of these are responsible for most of the morbidity due to filariasis: Wuchereria bancrofti and Brugia malayi cause lymphatic filariasis, and Onchocerca volvulus causes onchocerciasis (river blindness).   The other five species are Loa loa , Mansonella perstans , M. streptocerca , M. ozzardi , and Brugia timori .  (The last species also causes lymphatic filariasis.)


Dr.GCSahu/ROHFW/A'bad 12 Charehterstics Mf of W.bancrofti Mf of B. malayi 1. General appearance Graceful,sweeping curves Crinkled, secondary curves. 2. Length 244 to 296 mu 177 to 230 mu 3. Free cephalic space As long as broad Nearly twice as long as broad 4. Excretory pore Not prominent Prominent 5. Caudal end Uniformly tapering to a delicate poin. No terminal nuclei. Kinkled and two terminal nuclei present. 6. Nuclear column Nuclei discrete smudged Difference betwwen Mf of W. Bancrofti and B. malayi .

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LIFE CYCLE OF W. bancrofti IN HUMANS The definitive host is the human,in whose lymphatic system the adult worms are harboured.live embryos( microfilariae ) are discharged which find their way to blood stream. The microfilariaeare capable of living in the peripheral blood for a considerable time without undergoing any developmental metamorphosis.They are subsequently taken up by the female culicine mosquitoes during a blood meal. The intermediate host is a mosquito, in which the microfilariae undergo further development,after which they become infective to human. A large number of species of mosquito belonging to the genus Culex,Aedes and Anopheles act as intermediate hosts for W.bancrofti and Brugia malayi .


MODE OF INFECTION :- Innoculative method, through the bite of certain culicine mosquitoes. TRANSMITTING AGENT :- Female mosquitoes of the species Culicine / Aedes /Anopheles depending upon their geogrophical prevalence. INFECTIVE FORMS :- Third stage larvae of developing microfilariae . PORTAL OF ENTRY :- Skin SITE OF LOCALISATION :- Lymphatic system of the host, superior or inferior extremities according to the site of bite., most commonely of inguino -scrotal region.


Mode of transmission :-Transmitted by the bite of an infected mosquito.The parasite(infective larvae) is deposited near the site of the puncture,gets attractedby the warmth of the body,penitrates the skin on its own and enters the lymphatic system through the capillaries. Biological incubation period(pre patent period ):- This lasts for one to one and half years During this period the infective larvae(third stage) grows to adult forms and becomes sexually mature. Patent period:- Being viviparous,gives birth to microfilarae which subsequently appear in peripheral blood. Periodicity:- The mf of W.bancrofti and B. malayi may display a nocturnal periodicity and appear in large numbers at night and are either absent or scarce during the day. The maximum density of mf in blood is reported between (10 pm) to (2 am to 4 am) which may be due to the blood searching activities and biting rhythm of the vector during the time.

Agent Factor :

HOST FACTORS Man is the natural host Age :- All ages are susceptible to infection. Infection rates tend to rise up to age 20-30,but not there after- may be due to the fact that some of the persons developing the disease become – ve for mf. Sex :- Sex does not appear to influence the infection rate. Density of infection :- It is reported to be one mf per40 c.mm of blood is infective to 2.6 percent of mosquitoes feeding on him.

Causal Agents: :

Cont… Migration of people :- This has led to extension of the disease into areas previously non endemic. Immunity :- Man may develop resistanse to infection and superinfection -- immunological basis still unknown. Social factors :- Rapid unplanned urbanization, population movement and sleeping habits. The swelling of legs and other parts of body causes suffering,stigma and reduced working capacity of the patients.

PowerPoint Presentation:

ENVIRONMENTAL FACTORS Climate is an important factor in the epidemiology of fileriasis . It influences the breeding of vector mosquitoes, their longevity and determines the development of parasite in mosquitoes. Temperature :- The maximum prevalence of culex spp is observed when the temperature ranges between 22 to 38 deg. Centigrade. Humidity:- It influences the longevity of the mosquitoes ant the longevity is optimum when the relative humidity is around 70 percent. Drainage :- Fileria is associated with poor drainage as the vector breeds profusely in clogged and polluted water. Town planning :- Inadequate sewage disposal and lack of town planning aggravate the problem by providing more breeding sites nearer to human dwellings.



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