1. Filarial Worms
Rumala Morel
Dept. of Parasitology
Peradeniya
Y2S2

2. Teaching Learning Objectives:
 Name the major tissue nematodes of humans indicating their
location in the human body.
 List the major characteristics of the filarial parasites of
humans indicating those found in Sri Lanka
 Name the vectors of those parasites found in Sri Lanka
 Outline the life cycle of a typical filarial parasite
 Describe the life cycle of Wuchereria bancrofti
Describe the phenomenon ‘Periodicity of microfilaria’
 State the stages that cause pathogenic effects
 Identify stages of diagnostic importance
 Outline laboratory methods of visualization/identification of
parasites/products
 Identify points in the life cycle where preventive measures
are applicable

3. FILARIAL WORMS: Filariasis
 tissue nematodes
 adults thread like;
 female embryos (early first stage larvae)
microfilariae (mf)
• transmitted by insect vectors
• adults in different habitats in body
• mf in blood/ subcutaneous tissue

4. Human filarial parasites grouped according to
HABITAT of the ADULT WORM in man
 Lymphatic filariae
 Subcutaneous filariae
 filarial infections of the body cavities
& associated tissue

5. LIFE CYCLE
MAN
2 moults Adults
mf in blood /
subcutaneous tissue
INSECT VECTOR
2-moults
NO multiplication
Infective larva-L3

6. Microfilaria- periodicity
In some species mf in peripheral blood only
during certain times during 24 h period.
 Non periodic
 Periodic - nocturnally
- diurnally
 Sub periodic- mf present at all times
but peak nocturnally or during daytime

7. Periodicity of microfilaria
physiological adaptation to biting habits of vector
Mf bld
patency
6h 12h 24h 2h 6h
Nocturnally
periodic
Non
periodic
Diurnally
periodic
Sub periodic

8. LYMPHATIC FILARIAE
mosquito borne
adults in lymphatics / mf in blood
 Wuchereria bancrofti-widespread tropics
 Brugia malayi- SE Asia, India
 Brugia timori- Timor island,
other islands nearby

9. Hydrocoele
Lymphoedema

10. Distribution of lymphatic filariae
Sub periodic W. b

11.  Dog filarial worm
Dirofilaria repens- zoonosis in Sri Lanka
Filarial infections of Man in Sri Lanka
 Bancroftian filariasis- W bancrofti
(nocturnally periodic)

12. Wuchereria bancrofti (nocturnally periodic)
High prevalence in hot,humid, tropics.
associated with ‘poor’ urbanization
Vector-common urban mosquito
Culex quinquefasciatus
In E Africa- vector rural-Anopheles gambiaePacific islands- diurnally sub periodic
vector day biting -Aedes spp

13. life span 7-16 yrs

14. Larva developing in the
mosquito thoracic muscle

15. Infective larvae L3 emerging from proboscis
of mosquito

16. Adults of
Wuchereria bancrofti
are long and threadlike.
MALES (left) measure
up to 40 mm long
and FEMALES (right)
are 80-100 mm long.

17. tail nuclei
Wuchereria bancrofti -mf Brugia malayi
300 x10 µm 260 µm
Lie- graceful curves kinked (acute angles)
head space- short long
nuclei- countable, overlapping,tail nuclei+
head space

18. Laboratory Diagnosis of Filariasis:
Direct Detection of mf in blood
Thick film- 10pm-2 am (20-60µl)
wet mount/ stain Giemsa
Concentration-
•Knott’s method-1ml blood +2% formalin, centrifuge,
examine deposit for mf
•Membrane filtration- pore size 5µm
Detection of adults in biopsy- rare
Detection of Filarial Specific Ab
Detection of Circulating Filarial Ag.
Indirect

19. A). Detection of filarial antibodies in serum
 Indirect immunofluorescent test- IFA/FAT
Antigen used - microfilariae of W bancrofti
sections of adult worms (cattle filariae)
 ELISA (enzyme linked immunosorbent assay)
Disadvantage: Ab long lasting
B). Detection of Circulating Filarial Ag
•Antigen detection ELISA
•Immunochromatographic [ICT] Card Test
INDIRECT TESTS

20. Antigen detection strip (card) tests- RDTs
Sample origin
(whole blood
serum/plasma)
polyclonal Ab
+ colloidal gold
Mab
W bancrofti
T C
absorbent pad
test control
RDT = Rapid Detection Tests
Immunochromatographic Card Test
=

21. Immunochromatographic
Card Test
Ag detection
ELISA plate

22. ICT card test
Immunochromatographic card test-
detects specific circulating W bancrofti Ag
in serum/whole blood using monoclonal Ab IgG4
 simple, no equipment required
 quick results <15 min
 no need for night blood
 100% sensitive in mf +s
 Not quantitative (+/-)
But disease severity not dependant on mf density
Disadvantage: High cost > Rs. 1600/test

23. Filariasis in Sri Lanka-
1937-39: Brugia malayi predominant
1947: Anti Filariasis Campaign
1960’s: Brugian filariasis eradicated
control of larval breeding
residual action of DDT on adults
treatment with DEC
Bancroftian filariasis is the ONLY
lymphatic filariasis in SL now

24. LF is endemic
in eight of the
25 districts.
Confined to
urbanized
coastal belt:
9.5 million
(50%)
population
exposed
inland foci:
Gampaha,
Warakapola
Veyangoda

25. Global Elimination of Lymphatic
Filariasis
• Global Programme to Eliminate Lymphatic Filariasis -
WHO 1998
• Global Alliance to Eliminate Lymphatic Filariasis - 2000
– public-private partnership
– WHO, national Ministries of Health,
– Private drug companies donating albendazole &
ivermectin (Mectizan®)
– NGOs
• 1 billion at risk population
• > 120 million people are already infected
• > 40 million incapacitated or disfigured

26. Bancroftian filariasis control in Sri Lanka
vector control:
prevent mosquito breeding
clear drains, cess pits, sealing of septic tanks
larviciding with insecticides, larvivorous fish
 Selective treatment of mf + cases
with 2-week DEC (6 mg/kg)
 Mass chemotherapy- eradication of parasite by
killing mf and disrupting transmission- continued for
4-5 years
Morbidity control clinics – disability management
training

27. Culex quinquefasciatus breeding sites
Dirty water in blocked drains, cess pits etc.

28. Brugia malayi - Confined to Asia
Not detected in Sri Lanka since 1962
a
d
u
Adults in lymphatics of lower limbs, groin. Rare in genitalia.
Mf sheathed, characteristic morphology
Pre patent period- 1-3 months
Sub periodic form
- SE Asia-zoonoses
(monkeys,dogs & cats)
B malayi- nocturnally periodic
Vector: Mansonia species
Female mosquito of Mansonia spp
lays eggs on the under surface of
leaves of water plants
eg. Pistia, Salvinia, Eichonia

29. Subcutaneous filariasis of humans
different fly vectors
mf in blood / subcutaneous tissue
biting habits of vector
Onchocerca volvulus- Onchocerciasis
Major public health problem - tropical Africa
vector- black flies, mf – subcutaneous
Loa loa- Tabanids, mf in blood
Body cavities:
Mansonella spp- culicoides, mf in blood

30. Dirofilaria repens - Dirofilariasis
Zoonotic filariasis in Sri Lanka
a common subcutaneous filarial infection of dogs in
Sri Lanka
Transmitted by several species of mosquitoes
Aedes, Armigeres & Mansonia spp.
Human disease common
Causes subcutaneous nodules
due to granulomatous reaction
to adult worm
but
not known to
produce microfilariae
in humans
D.repens adult

31. Cross-sections of Dirofilaria sp. from a subcutaneous nodule
stained with hematoxylin and eosin (H&E).
100x 200x

32. Onchocerciasis = River Blindness
Simulium (black fly)
fast flowing rivers
River Volta-W Africa

33. mff causes eye lesions:
blindness
In skin: itching, depigmentation
loss of elasticity
Adults cause subcutaneous nodules

34. Loa loa- loasis
Adults in subcutaneous tissue
Mf in blood- diurnally periodic
transmitted by blood sucking day-biting flies
Vectors: Tabanid flies
Confined to Tropical Africa where vectors are
found
Mf in blood
Adult worm under
the conjunctiva- 10 mm
Transient swellings-days

35. Tabanid fly
adult worm under
the conjunctiva

36. Filarial worms
- Wucheraria bancrofti [SRI LANKA]
Brugia malayi
• Subcutaneous filariae
- Onchocerca volvulus [River blindness]
- Loa loa
- Dirofilaria repens [ZOONOSIS in SRI LANKA]
• filarial infections of the body cavities
& associated tissue
•Lymphatic filariae