Published on March 10, 2014
FILARIASIS PRAKASH DHAKAL Public Health Microbiology Tribhuvan University, Nepal
OUTLINE OF PRESENTATION Introduction Epidemiology Morphology Mode of transmission Life cycle Pathogenesis Signs and symptoms Laboratory diagnosis Prevention and Control Pictures
INTRODUCTION Filariasis is the pathological condition caused by infection of filarial nematodes transmitted by different vectors. Infection occurs in blood vessels, lymphatic system , connective tissues and serous cavities of man. Disease of tropical warm lands. Caused by different worms and are characterized by different clinical features.
EPIDEMIOLOGY Lymphatic filariasis is caused by infection with nematodes of the family Filarioidea: 90% of infections are caused byWuchereria bancrofti and most of the remainder by Brugia malayi. Humans are the exclusive host of infection with W. bancrofti. Although certain strains of B. malayi can also infect some animal species (felines and monkeys), the life cycle in these animals generally remains epidemiologically distinct from that in humans. The major vectors of W. bancrofti are mosquitoes of the genus Culex (in urban and semi-urban areas), Anopheles (in rural areas of Africa and elsewhere) and Aedes(in islands of the Pacific).
The parasites of B. malayi are transmitted by various species of the genusMansonia; in some areas, anopheline mosquitoes are responsible for transmitting infection. Brugian parasites are confined to areas of east and south Asia, notably India, Indonesia, Malaysia and the Philippines. An estimated 120 million people in tropical and subtropical areas of the world are infected with lymphatic filariasis; of these, almost 25 million men have genital disease (most commonly hydrocele) and almost 15 million, mostly women, have lymphoedema or elephantiasis of the leg. Approximately 66% of those at risk of infection live in the South-East Asia Region and 33% in the African Region. In Nepal the disease is endemic in 61 districts .The prevalence rate is 13 % ( from 0.1 % to 40 % )
An example in case of Nepal : A Sentinel surveillance study was carried out among 7,000 (Male- 3319, Female-3681) cases and tested for microfilaraemia. The total number of Microfilaraemia positive cases was 55, and the number were 20, 5,10,4,5,7 and 4 in Sindhupalchok, Nawalparasi, Rupandehi, Palpa, Tanahu, Syangja and Gorkha districts respectively. The total number of cases having symptoms and signs is 176 and the number were 138,0,28,4,1,5 and 0 in Sindhupalchok, Nawalparasi, Rependehi, Palpa, Tanahu, Syangja and Gorkha districts respectively. The highest microfilariae infection rate was 2.0% in Sindhupalchowk district which is significant in number as compared to other districts and lowest 0.40% in Palpa and Gorkha districts. The highest number of symptomatic cases was found in Sindhupalchowk district 138 (13.8%). One significant finding was that 55 persons were found to be microfilaraemia positive but only 41persons had symptoms of Lymphatic Filariasis and 14 microfilaraemia positive cases did not have symptoms and signs of filariasis. ( Source : Fiariasis Elimination Programme, World Health Organization/Epidemiological Disease Control Division, Teku, Kathmandu )
MORPHOLOGY Wuchereria bancrofti Adult worm are long hair like transparent nematodes, filariform in shape with tapering ends. Male measures 2.5 to 4 cm in length by 0.1 mm in thickness and female measures 8 to 10 cm in length and 0.3 mm in thickness. Tail end of male worm is curved ventrally while that of female worm is narrow and abruptly pointed.
Brugia malayi The adult females of B malayi resembles to W. bancrofti but the adult males differ . Brugia timori Similar to B. malayi . Loa loa The male measures 3 cm in length and 0.35 mm in breadth . The female measures 6 cm in length by 0.5 mm in breadth.
MODE OF TRANSMISSION Transmitted by vectors Bancroftian filariasis is transmitted by Culex, Aedes and Anopheles mosquito. Malayan filariasis is transmitted by Anopheles and Mansonia spp. Loiasis is transmitted by Tabonid or horse fly of Chrysops spp. When the vectors suck blood from infected person, the microfilariae reaches the of vector , which then enters the thorax where by development of larvae takes place. Infective larvae enters the mouth parts and are shed on the skin of healthy human host when the vectors takes blood meal.
LIFE CYCLE Life cycle of Wuchereria bancrofti
Life cycle of Loa loa
LABORATORY DIAGNOSIS Samples includes : Peripheral blood , Chylous urine, Exudate of lymph varix, Hydrocele fluid,Lymph node biopsy, skin specimen Microscopic examination : It deals with the detection of microfilariae. Macroscopic examination : detection of adult worm ( lypmh node biopsy ) Haematological examination : eosoinophilic count is done. Serological test : Complement fixation test is performed. Intradermal test : immediate hypersensitivity test. Filarial antigen is injected on skin. After 30 minutes a weal over 2 cm appears.
PREVENTION AND CONTROL Prevention : Destruction of breeding sites of vectors. Using bed nets while sleeping. Applying repellant creams on skin. Control Treatment : diethylcarbamazine against filarial worms. Paramethyl phenyl stibonate against infective larvae. Arsenical preparation against adult worm. Correction of lymphatic defect through surgery. Surveillance of disease in endemic areas.
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