Wuchereria bancrofti Filariasis a Microbiology topic for MBBS

1. Wuchereria bancrofti &
Brugia malayi –
• Pathogenesis
• Clinical Features
• Lab Diagnosis
• Prevention
• Treatment

2. Geographical Distribution Of Wuchereria
bancrofti

3. Wuchereria bancrofti
Pathogenesis
 Mode of infection – inoculative method – Mosquito bite.
 Transmitting agent – female mosquitoes ( Culex, Aedes, Anopheles )
• In India – Culex pipens fatigans ( C. p. quinquefasciatus)
 Infective form – 3rd stage larvae.
 Portal of entry – skin.
 Site of localisation – lymphatic system.
 Biological incubation period – 8 to 12 months.

4.  In endemic areas, infection is mostly asymptomatic .
• Tolerate microfilaria, immune response being inhibited.
 Infective larvae enter thru bite → lymphatics → moult, releasing their
body proteins, secretions & other products.
• In some, they cause irritation – directly or hypersensitivity.
 Typical manifestations produced by the adult worms.
 Living microfilaria circulating in blood – not known to produce any
pathogenic effect, except in Occult filariasis.

5.  Response from RE system only when worm dies / undergoes
degenerative changes.
 Area invaded by macrophages & giant cells appear in order to engulf &
absorb fragments of dead worm.
 Eosinophilic infiltration gradually disappears.
 Fibroblasts appear & laid down in concentric layers.
 Hyalinised scar tissue – tombstone of dead worm
 Basic lesion – a/c inflammation followed by an epitheloid granuloma
surrounding adult worm & fibrous scar.

6. Histopathological changes
1. Males & females of W.bancrofti lodged in lymph node.
2. Lymphoedema / Lumph varices.
3. Obliterative endolymphangitis
4. Occlusion of lymph vessel
 Strangulating the parasite – degeneration
5. A parasitic onion developing around degenerated
parasite.
6. Hyaline scar

8. Causes of Lymphatic obstruction
1. Mechanical blocking.
2. Obliterative endolymphangitis.
 Endothelial proliferation & inflammatory thickening of walls.
3. Excessive fibrosis of lymphatic vessels.
4. Fibrosis of afferent lymph nodes.
5. Allergic inflammatory reactions.

9. Causes of Lymphangitis
1. Mechanical irritation
2. Liberation of metabolites of growing larvae &
secretion of some toxic fluid by fertilised females
3. Absorption of toxic products liberated from dead worms
undergoing disintegration.
4. 2° bacterial infection

10.  Inflammatory changes damage the valves , aggravating
lymph stasis.
 Increased permeability of vessel walls → leakage of protein
rich lymph into the tissues.
 Brawny edema / hard pitting edema.
 Fibroblasts invade → laying down fibrous tissue → non
pitting gross edema of elephantiasis.

11. Occult Filariasis
Occult filariasis Classical filariasis
Lesion by microfilarias Developing worms & Adults
Lesion not only in lymph nodes, but
lungs, liver, spleen
Lymph nodes, lymphatic system
Eosinophilic granuloma a/c inflammation followed by epitheloid
granuloma
Microfilaria present in affected tissues,
but not in blood
Microfilaria present in blood
Complement fixation test highly
sensitive
Not so sensitive

12. Clinical manifestations
Asymptomatic
Filariasis
Symptomatic
Filariasis
Inflammatory Phase Obstructive Phase

14. Wuchereriasis
 Does not kill, but cause great suffering, disfiguration & disability.
 Metabolites of growing larvae in highly reactive individuals →
allergic manifestations -
• malaise, headache, nausea, vomiting , low grade fever,
urticaria, pruritis, fugitive swellings, lymphoedema.
 Fugitive swellings – raised, painless, tender, diffuse, red areas
on skin
 Symptoms may appear much earlier.
 Fails to demonstrate microfilaria in blood.

15. Lymphadenitis
 Inguinal lymph nodes most often affected.
 Swollen nodes may be painful and tender.

16. Lymphangitis
 Red streaks underneath the skin.
 Lymphatics of testis & spermatic cord are frequently involved
→ Epidymo-orchitis and Funiculitis

18. Filarial fever
 High fever of sudden onset, often with rigor, lasting for 2 or 3
days.
 Temperature comes down by crisis with profuse sweating.
 Associated with localizing sign of inflammation of lymphatic
vessel.
 Examination of blood → transient leukocytosis, increased
neutrophils, presence of microfilaria.

19. Lymphangiovarix
 Dilatation of lymph vessels ; varicosity.
 Results from collateral circulation & lymph stasis.
 Commonly occur in inguinal, scrotal, testicular & abdominal
sites.

20. Lymphorrhagia
 Rupture of lymph varices → release of lymph / chyle.
 Depends on the sites involved.
 Lymph scrotum, lymphocoele, chyluria, chylous diarrhoea, chylous
ascites, chyothorax.
 Chyluria :-
 Due to rupture of varicose chyle vessels thru mucous membrane
of urinary tract.
 Milk white in colour.
 Contains fat particles, albumin, fibrinogen.
 Microscopical examination – microfilaria, few RBCs &
lymphocytes.

21. Hydrocoele
 Due to obstruction of lymph vessels of spermatic
cord & also by exudation from the inflamed testes
and epididymis.
 Fluid – clear & straw coloured ,
sometimes – cloudy, milky or haemorrhagic.

22. Lymphoedema
 Starts as swelling around the ankle, spreading to the back of the
foot & leg.
 Also effect arms, breast, scrotum, vulva…
 Hard & Non Pitting

24. Elephantiasis
 Affected part becomes enormously enlarged, producing tumour
like solidity.
 Most commonly in leg, but may also involve arm, breast,
scrotum, penis & vulva.
 Causes –
1. Fibrotic constriction of all afferent lymphatics.
2. Recurrent attacks of lymphangitis over years.
3. Hypertrophy & Hyperplasia – result of excess protein in exudate.

25.  Pathological Anatomy -
• Surface of skin – rough, fissured & even papillomatous.
• On section – skin cuts like an unripe pear, is thickened, dense &
fibrous.
• Subcutaneous tissues – edematous ( blubbery ) appearance – dilated
& thickened lymphatics & veins seen.
Histology – granulation tissue.
 Blood Microfilaria – generally absent

28. Occult Filariasis
(Meyers – Kouwenaar Syndrome)
 Clinical conditions not due to lymphatic involvement,
but due to hypersensitivity reactions to filarial antigens.
 Massive eosinophilia, > 3000cells/mm3.
 Generalised lymph node enlargement, Hepato-splenomegaly,
pulmonary symptoms & absence of microfilaria in blood.
 Microfilaria does not reach peripheral blood, because they are
destroyed in tissues.
 Host reaction – Eosinophil granuloma

29.  Filarial complement fixing antibody present in high titre.
 Serological tests with filarial antigens are strongly positive.
 Non specific antibody production → biological false positive
reaction in serological tests for syphilis.
 Prompt response to DEC confirms the diagnosis.
 Also reported to cause arthritis, glomerulonephritis,
thrombophlebitis, tenosynovitis & dermatoses.

30. Tropical Pulmonary Eosinophilia
( Eosinophilic Lung / Weingarten’s Syndrome )
 A manifestation of Occult filariasis.
 Low fever, loss of weight, paroxysmal cough with scanty
sputum, dyspnoea, asthmatic wheezing & splenomegaly.
 Blood eosinophil count – above 3000/mm3. IgG levels ↑.
 Chest Xray – increased bronchovascular markings, diffuse
mottled shadows resembling Miliary TB.

31. Lab Diagnosis
Direct Evidence Indirect Evidence
Microfilaria Adult Allergic tests Immunological
tests
A sheathed
microfilaria having
pointed tail tip
free of nuclei
1. In peripheral
blood.
2. In chylous
urine
3. In exudate of
lymph varix.
4. In hydrocoele
fluid.
1. In biopsied
lymph node.
2. Calcified worm
by X ray.
1. Blood
examination –
Eosinophilia.
2. Intradermal
test.
( wheal over
2cm after 30
min )
1. Demonstration
of antibody to
filarial
antigens
2. Demonstration
of filarial
antigens in
blood.

34.  Microfilariae not found in peripheral blood in following
cases :-
1. During early allergic manifestations
2. In occult filariasis
3. Case of Elephantiasis – due to lymphatic obstruction
4. After an attack of lymphangitis, due to death of adult worm.
 Nocturnal periodic – Night blood samples, collected
between 10pm to 4am

35. Unstained Film
 Examination under low power microscope –
• actively motile microfilariae lashing the blood cells around.
 May be conveniently made next morning –
• as microfilariae retain their viability & motility for a day or two
at room temp.
 By using a simple counting chamber, microfilaria in the wet
mount can be counted.

36. Stained Film
 A Thick & Thin blood smear.
 Dehaemoglobinised by applying distilled water.
 Fixed with methanol.
 Stained with Giemsa, Leishman, Delafield’s haematoxylin or
Polychrome methylene blue stains.
 Microfilaria seen under light microscope in thick film.
 Morphology studied in thin film.
 Species identification made.

37.  By using a measured quantity of blood for preparing smears, for
e.g, 20mm3 pipette and counting the total no. of microfilariae in
the smear ---- microfilaria counts can be obtained.

38. Features Mf. bancrofti Mf. malayi
Length 250 – 300 µm 175 – 230 µm
Appearance Graceful , sweeping
curves
Kinky, with secondary
curves
Cephalic space Length = breadth Length = 2 x breadth
Stylet at anterior
end
Single Double
Excretory pore Not prominent Prominent
Nuclear column Discrete nuclei Blurred
Tail tip Pointed; free of nuclei 2 distinct nuclei, one
at tip, other sub
terminal
Sheath Faintly stained Well stained

41. Concentration Techniques
 Employs venous blood.
 When microfilaria density is low – larger volumes of blood,
 Two Methods –
1. Sedimentation method –
 Sample of blood first lysed with acetic acid, saponin or other lytic
substances or by freeze thawing & then centrifuged.
 Sediment is stained & microfilariae is counted.

42. 2. Filtration Method –
 A measured quantity of blood (1-5 ml) is collected
into an anticoagulant solution → passed through
membrane filters.
 Millipore & Nucleopore Filters.
 Blood cells & proteins sticking on to the filter are
washed away by repeatedly passing saline thru it.
 Filter is removed, placed on a slide, stained &
examined.
 Much more sensitive - collected even during
daytime.
 Disadvantages – cost , need for venepuncture

43. DEC Provocation Test
 Oral administration of Diethyl Carbamazine (100mg or 2mg/kg body
weight) induces microfilariae to appear in peripheral blood, even during
daytime.
 Blood collected 20-50 min after.
 Great advantage for surveys.
 But may cause febrile reactions, esp. in Brugiasis.
 Cannot be used in areas endemic for Onchocercasis – severe reactions.

44. Treatment
 DEC (Hetrazan) – drug of choice.
• Dose – 6mg/kg orally in 3 divided doses for 12 days.
• Adverse effects – due to host response to dying
microfilariae
o Fever, headache, nausea, vomiting, arthralgia &
prostration.
o Anti-histamines/corticosteroids to control.
 Other drugs - Ivermectin

45. Prevention & Control
 Eradication of vector mosquito
 Detection & treatment of Carriers
• DEC -6mg/kg daily for 12 days.
• Repeated in endemic areas , every 2 yrs or so.
 DEC medicated salt
 Morbidity Control –
• Improved hygiene measures
• Proper treatment of 2º infection
• Proper care of the limb

46. Global Eradication Programme
 Whole population at risk – annual dose of 2 drugs-
• Ivermectin & Albendazole in countries of Africa- co endemic
for Onchocercasis.
• DEC (6mg/kg) with Albendazole (400mg) in other parts of world.
• Continued for 5-6 yrs for interruption of transmission.
(150µg/kg) (400mg)

47. Brugia malayi
 In India, Kerala is the largest endemic area.
 Pathogenicity –
 Intermediate hosts – various species.
• Mansonia species & One species of Anopheles ( A.barbirostris).
 Like W.bancrofti, causes lymphangitis & elephentiasis ( Primarily of
lower limbs).
 Malayan Filariasis – absence of chyluria & rarity of scrotal swellings.

48.  By finding characteristic Microfilariae in peripheral blood.
• 175 – 230 µm
• Kinky, with secondary curves
• Length = 2 x breadth
• Double stylet
• Prominent excretory pore
• Blurred nuclear column
• Blunt tail tip - 2 distinct nuclei, one at tip, other sub terminal
• Sheath - Well stained
Lab Diagnosis

51.  Treatment –
 Same as for Wuchereriasis.
 Prevention –
 Same as for Wuchereriasis.
 Certain water plants ( Pistia, Water hyacinth, Swamp grass) –
necessary for growth of Mansonoides --- remove those.

52. Brugia timori
 Natural vectors – Anopheles barbirostris.
 Clinical manifestations milder than other lymphatic filariasis.
 Lymphangitis, Lymphadenitis, Lymphoedema ( confined below
knee) & abscess along lymph trunk/nodes.
 Draining abscess – lead to scar formation

53.  Lab Diagnosis :
 By finding characteristic Microfilariae in peripheral blood.
• Larger than Mf. malayi ( overall length- 310µm ).
• Cephalic space : length = 3 x breadth
• 5 to 7 terminal nuclei
• Sheath not stained with Giemsa stain
 Treatment & Prevention :
 Same as for B. malayi