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
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
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
=
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
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
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