Lymphatic filariasis

EPIDEMIOLOGY AND PREVENTION OF LYMPHATIC FILARIASIS

1. LYMPHATIC FILARIASIS 1 BRIG DR HEMANT KUMAR PROF &HOD

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3. Filariasis  has been a major public health problem in India next only to malaria.  The disease was recorded in India as early as 6th century B.C. by the famous Indian physician, Susruta in his book  Susruta Samhita . In 7th century A.D.,  Madhavakara  described signs and symptoms of the disease in his treatise ' Madhava Nidhana ' which hold good even today.  3

4. Contd… In 1709, Clarke called elephantoid legs in Cochin as  Malabar legs .  The discovery of microfilariae (MF) in the peripheralblood was made first by Lewis in 1872 in Calcutta(Kolkata) 4

5. Filariasis is caused by several round, coiled and thread-like parasitic worms belonging to the family filaridea . These parasites after getting deposited on skin penetrate on their own or through the opening created by mosquito bites to reach the lymphatic system. 5

6. Based on pathogenicity and habitat it classified into : 1) Lymphatic filariasis 2) Subcutaneous filariasis 3) Serous cavity filariasis 4) Zoonotic filariasis 6

7. LYMPHATIC FILARIASIS 7

8. Lymphatic Filariasis, commonly known as elephantiasis , is a neglected tropical disease . Infection occurs when filarial parasites are transmitted to humans through mosquitoes. Infection is usually acquired in childhood causing damage to the lymphatic system 8

9. The painful and profoundly disfiguring visible manifestations of the disease , lymphedema, elephantiasis and scrotal swelling occur later in life and can lead to permanent disability . These patients are not only physically disabled, but suffer mental, social and financial losses contributing to stigma and poverty. 9

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11. It is endemic in many tropical & subtropical countries like Africa, Asia, Western Pacific and parts of America. 11

12. More than 1.4 billion people are at risk, and approximately 65% reside in WHO’s South East Asia Region. Over 120 million people are currently infected , and about 40 million disfigured and incapacitated by the disease.   12

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15. INDIAN SCENARIO 15

16. The overall microfilaria rate has reduced from 1.24% in 2004 to 0.29% in 2015 at the national level. Out of 255 districts, 203 have reported overall microfilaria rate of less than 1%. Out of remaining 52 districts, 31 need high priority as these districts have been persistently reporting microfilaria rate above 1%, 16

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18. 18 Heavily infected areas include UP, Bihar, Jharkhand, Andhra Pradesh, Orissa, TN, Kerala and Gujarat.

19. Epidemiology 19

20. \ AGENT FACTORS There are at least 8 species of filarial parasites that are specific to man . They are Wuchereria bancrofti , Brugia malayi , Brugia timori , Onchocerca volvulus , Loa loa , T perstans , T streptocerca , Mansonella ozzardi Out of these, the first 3 cause lymphatic filariasis . 20

21. PERIODICITY Both the microfilaria( Mf ) of W. bancrofti and B. malayi occurring in India display nocturnal periodicity . The maximum density is reported between 10pm to 2am . This is a biological adaption to the nocturnal biting habits of the vector mosquitoes . 21

22. LIFE CYCLE 22

23. DEFINITIVE HOST- MAN, INTERMEDIATE HOST- MOSQUITO The adult worms ( macrofilaria ) are found in the lymphatic system of man, where they may survive for 15 yrs or more . During their lifespan, after mating, female worms ( viviparous ) give birth to 50,000 immature microfilariae (mf) per day into the blood circulation via lymphatics . They may survive up to a year or more. Some of these microfilariae may be ingested by the mosquitoes during their blood meal. 23

24. STAGES IN THE MOSQUITO EX-SHEATHING- The larva comes out of the sheath in which it was enclosed in stomach of the mosquito. FIRST STAGE LARVA -The larva penetrates the stomach wall of the mosquito, and migrate thoracic muscles where it develops into a short thick form SECOND STAGE LARVA - The larva moults and increase in length THIRD STAGE LARVA (INFECTIVE ) -The larva moults and develops into a long thin form which migrates to the proboscis of the mosquito. The mosquito is said to be infected . 24

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27. RESERVOIR OF INFECTION Although filarial infection occurs in animals, human filariasis is not usually a zoonosis . In man , the source of infection is a person with circulating Mf in peripheral blood. In filarial disease (late obstructive stages), Mf are not found in the blood. 27

28. VECTORS OF LYMPHATIC FILARIASIS Culex - vector for Bancroftian filariasis Mansonia - vector for Brugian filariasis Culex breeds in polluted water Mansonia is associated with certain aquatic plants (such as Pistia stratiotes ) 28 Culex Mansonia

29. HOST FACTORS Man is a natural host . a) AGE : All ages are susceptible to infection. The infection rates rise with age up to 20-30 yrs and then level off b) GENDER In most endemic areas, Mf rate is higher in men c) MIGRATION Migration led to the extension of filariasis into non-endemic areas 29

30. D) IMMUNITY develops only after years of exposure E) SOCIAL FACTORS Lymphatic filariasis is associated with poor sanitation, urbanization, migration of people , etc. 30

31. ENVIRONMENTAL FACTORS a) CLIMATE – It influences the breeding of mosquitoes , their longevity and the development of parasite in insect vector.(22-38 °C , RH - 70% b) DRAINAGE – Vectors breed profusely in polluted water. c) TOWN PLANNING – Inadequate sewage disposal and lack of town planning have aggravated the problems of filariasis in India.The common breeding places are open ditches, septic tanks, ill-maintained drains . 31

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43. FILARIA SURVEY 5-7% of the population for routine surveys and 20% for evaluation studies . It consists of- Mass blood survey Clinical survey Serological tests Xenodiagnosis Entomological survey 43

44. DEC PROVOCATION TEST Mf can be induced to appear in blood in the daytime by administering DEC100mg orally . Mf begin to reach their peak within 15minutes and begin to decrease 2hrs later . 44

45. 2) Clinical Survey People are examined for clinical manifestations of filariasis . 3) Serological tests To detect antibodies to Mf and adults using immunoflorescent and complement fixing techniques. But , CANNOT DISTINGUISH between past and present infection , and heavy and light parasite loads . 45

46. 4) Xenodiagnosis Mosquitoes are allowed to feed on the patient, and then dissected 2weeks later. 5) Entomological survey It consists of: general mosquito collection from houses dissection of female vector species for detection of developmental forms of the parasite Study of the extent and type of breeding places . 46

47. ASSESSMENT OF FILARIAL CONTROL PROGRAMMES It can be assessed using : Clinical parameters Parasitological parameters Entomological parameters 47

48. CLINICAL PARAMETERS Incidence of acute manifestations and prevalence of chronic manifestations are measured. PARASITOLOGICAL PARAMETERS i . Microfilaria rate- It is the % of people showing Mf in their peripheral blood in the sample population. 48

49. ii. Filarial endemicity rate- It is the % of people examined showing microfilariae in their blood , or disease manifestation or both . iii. Microfilarial density- It is the no. of Mf per unit volume of blood in samples from individual people.It indicates the intensity of infection iv. Average infestation rate- It is the average no. of Mf per positive slide .It indicates the prevalence of microfilaraemia in the population. 49

50. ENTOMOLOGICAL PARAMETERS They comprise Vector density per 10 man-hour catch % of mosquitoes positive for all stages of development % of mosquitoes positive for infective larvae Annual biting rate Types of larval breeding places 50

51. Control Measures 51

52. The current strategy is based on- Chemotheraphy Vector control 52

53. CHEMOTHERAPY 53

54. 1) DEC It is safe and effective . Given in divided doses after meals Rapidly absorbed Reaches peak blood levels in 1-2hrs Rapidly excreted 54 Filariasis Dose 1) Bancroftian filariasis 6 mg/kg body weight per day orally for 12 days 2) Brugian filariasis 3-6 mg/kg body weight per day orally for 12 days

55. 2) Filaria control in the community 55

56. Mass therapy- DEC is given to everyone in the community irrespective of whether they have microfilaraemia , disease manifestation or no signs of infection; except children under 2yrs, pregnant women and seriously ill patients. Dose: DEC 6mg/kg body weight Indicated in highly endemic areas 56

57. Selective treatment DEC given only to those who are Mf positive .More suitable in low endemicity areas.Dose : 6mg DEC per kg body weight daily for 12 doses In endemic areas, it should be repeated every 2yrs 57

58. Vector Control Vector control is beneficial when used in conjunction with mass treatment . The most important step is to reduce the target mosquito population to stop or reduce the transmission. It consists of: Anti-larval measures Anti-adult measures Personal prophylaxis 58

59. NATIONAL FILARIA CONTROL PROGRAMME It is operational since 1955 In June 1978 , it was merged with malaria scheme .Filaria control strategy includes vector control through anti-larval operations Source reduction Detection and treatment of microfilaria carriers Morbidity management 59

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