Wuchereria bancrofti & Brugiya malayi

1. Wuchereria bancrofti
Bancroftian Filariasis
Filarial Elephantiasis
Lymphatic Filariasis
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2. Introduction
• Geographical distribution: It occurs in Asia including India,
Africa, Australia, Pacific and South America.
• Habitat
• Adult male and female worms reside in the lymph nodes and
lymphatic vessels of man. The microfilariae are found in blood.
Humans are the only known reservoir hosts
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3. Morphology
• Adult worms
• Adult worms are transparent, creamy white, long,
hair like structures.
• They are filiform in shape with both ends tapering.
The male and female worms measure 2.5-4 cm x
0.1 mm and 8-10 cm x 0.2-0.3 mm respectively.
• The posterior end of the female worm is straight,
while that of the male is curved ventrally and
contains two spicules of unequal length.
• Both male and female worms remain coiled
together and it is difficult to separate them.
• The female is viviparous and liberates sheathed
embryos (microfilariae) into lymph from where they
find their way into blood
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4. • Microfilaria
• It is transparent and
colorless with blunt head
and pointed tail. It is
covered by a hyaline
sheath which is much
longer (359 um) than the
microfilaria.
• It can move forwards and
backwards within the
sheath. The somatic cells
or nucleus appear as
granules in the central
axis of the microfilaria.
• The tail-tip is free from
nuclei
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6. Life cycle
• W. bancrofti passes its fife cycle in two hosts.
• Man is the definitive host and the female mosquitoes belonging to
the genera Culex, Aedes and Anopheles act as intermediate hosts
• Culex quinguefasciatus is the most important vector of W. bancrofti
being responsible for more than 50% of cases of lymphatic filariasis.
• In rural areas, Anopheles species are the primary vectors often
transmitting malaria as well.
• Adult worms reside in lymph nodes and lymphatics (usually inguinal,
scrotal and abdominal) of man.
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7. • The Lymph provides nutrition to the adult worms The male fertilizes
female and the gravid female gives birth to microfilariae through
lymphatics, they find their way into general circulation
• The appearance of micro- filariae in the peripheral blood shows
marked periodicity.
• The microfilariae appear for about 2 hours before and after midnight
(10 pm-2 am) and then disappear more or less completely for the
rest of the 24 hour period from the peripheral circulation and remain
in pulmonary circulation.
• This correlates with the nocturnal biting habit of the insect vector.
The periodicity may also be related to the sleeping habits of the
hosts.
• In Southeast Asia there are sub-periodical forms of W. bancrofti, in
which, althourgh microfilariae are present throughout the 24 hour
period, numbers in the blood are elevated at night.
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8. • Nocturnal Periodicity
• When the largest no. of microfilaria are occur in the blood at night
• Diurnal Periodicity
• When the largest no. of microfilaria are occur in blood during day
• Non-periodic
• When the microfilaria circulate at constant level during day and night.
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10. • In Pacific areas like a non-periodic or slightly diurnally
periodic form is present in which microfilariae are
present in the peripheral blood more or less constantly
throughout much of the 24 hour period.
• Sheathed microfilariae are ingested by the mosquito
during its blood meal and reach the stomach of the
mosquito
• They cast off their sheaths in 2-6 hours, penetrate the
stomach wall and in the course of 4-17 hours reach
thoracic muscles. In next 2 days they metamorphose
into short, sausage-shaped organisms with a short
spiky tail measuring 124-250 um in length by 10-17 um
in diameter (the first-stage larvae)
• In 3-7 days' time, they moult once or twice to become
second-stage larva measuring 225-300 um in length by
15-30 um in diameter.
• On the 10th or 11th day the metamorphosis become
complete, the tail atrophies to a mere stump and the
digestive system, body cavity and genital organs are
fully developed. These are the third-stage larvae and
are infective.
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11. • They measure 1,400-2,000 um in length by 18-23 um in diameter
and These larvae then migrate from thoracic muscles to the
proboscis sheath of the mosquito
• When the infected mosquito bites a human being the larvae, in its
proboscis, are deposited on the skin near the site of puncture.
• They then either enter through the puncture wound or penetrate
through the skin on their own. Thereafter, they enter into lymphatics
and settle down usually in inguinal, scrotal and abdominal lymph
nodes, where they develop into adult worms.
• In one year or more they become sexually mature. Male fertilizes
female, the gravid female gives birth to microfilariae and the cycle is
repeated.
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14. Pathogenicity
 Infection caused by W. bancrofti is known as Wuchereriasis or Bancroftian filariasis.
 It is mainly die to the presence of adult worms in the lymph nodes and vessels. The lymph nodes
become enlarged, firm and fibrotic
 Microscopically, lymph nodes show the presence of many (lymphocytes plasma cells, polymorphs.
eosinophils and there may be foci of necrosis
 Sections of adult worms can be see in the subcapsular Sinuses or the lumen of the lymphatic vessel.
In chronic disease the nodes and vessels may contain dead worms surrounded by fibrotic and
eventually calcified tissues.
 Mechanical irritation caused by the movement of adult parasites inside the lymphatic system,
liberation of metabolites by growing larvae, absorption of toxic products from dead worms and
secondary bacterial infection leads to lymphangitis with swelling, redness, and pain.
 Permeability of the walls of the lymphatics increases, which permits the leakage of fluid with high
concentration of protein into the surrounding tissue
 Lymphatic obstruction may result from mechanical blocking of the lumen by dead worms, obliterative
endo-lymphangitis, obliterative excessive fibrosis of the lymphatic vessels and fibrosis of afferent
lymph nodes draining particular area
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15. • Repeated leakage of lymph into tissues results first in lymphoedema, then to
Elephantiasis of one or more limbs, breasts, penis, scrotum or vulva, in which there is
non-pitting oedema with growth of new adventitious tissue and thickened skin and
secondary bacterial and fungal infections.
• In males hydrocele orchitis, funiculitis and epididymitis are common.
• The development of lymph scrotum results in Chyluria with lymph getting into the urine. In
some parts of the world, hydrocele is very common.
• In East Africa, it occurs in up to 50% of infected males. Dilatation of lymph vessels
(lymphngio-varices) commonly occurs in the inguinal, scrotal, testicular and abdominal
sites.
• Rupture of Iymph varices leads to the release of lymph or chyle.
• The biological incubation or prepatent period in areas of endemic filariasis lasts 1 year or
more. This is the period from the entry of the third-stage infective larvae into the skin until
microfilariae first appear in peripheral blood.
• In many patients, acute attacks of filarial fever ensue in a matter of a few months to
many years after patency.
• Patient develops intermittent recurrent fever lasting 3-15 days, with headache, malaise,
localized pain and tenderness with oedema and erythema above lymph vessels and
glands, accompanied by acute lymphangitis and lymphadenitis of the groin or axilla.
Examination of blood often shows high eosinophilia.
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17. Laboratory Diagnosis
• Detection of microfilariae
• Microfilariae of W. bancrofti circulate in the peripheral blood with a regular
nocturnal periodicity. Therefore, to diagnose bancroftian filariasis, blood must be
taken during night optimally between 10 pm and 2 am.
• adults blood should be obtained from the ear or finger and in infants from the heel
• Thin and thick smears are prepared. The thick smear is dehaemoglobinized
and both the smears are stained with haematoxylin or Giemsa Stan, The smears
are then examined under microscope tor the presence of characteristic micro-
filariae
• In cases of light infections or when samples are collected at suboptimal times,
membrane filtration. centrifugation and sedimentation are the techniques that
may help o detect circulating miro-filariae
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19. • Microfilariae can also be seen in microscopic mounts of
anticoaguated blood by their undutating motion, displacing the red
blood cells from side to side as they move
• Acridine orange-microhaematocrit tube technique can also be used
for the detection of microfilariae.
• A microhematocrit tube incorporating heparin, EDIA, and acridine
orange serves the basis tor this test.
• After centrifugation, parasites become concentrated in the buffy coat
and can be visualized through the clear glass wall of the tube.
• The acridine orange stains the DNA of the parasites, and the
morphologic characteristics, including the nuclear patterns the tail
Sections, can be examined by fluorescence microscopy making a
species identification.
• Knot Concentration method may also be used for the detection of
microfilariae in the blood
• Microfilariae may also be demonstrated in the Chylous urine exudate
of lymph and in the hydrocele fluid
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21. • Detection of adult worms
Adult worms can be seen in the biopsied lymph node
and the calcified worm may be seen on X-ray examination.
• Immuno-diagnosis
• Filarial antigen may be detected in the patient serum by enzyme
immunoassays, using monoclonal antibodies against micro-filarial
larval surface antigens.
• However, In because antigen shedding may be irregular, particularly
during times when circulating microfilariae may not be detected,
detection of antibody to larval antigens may be more appropriate.
• Molecular diagnosis
• Polymerase chain reaction is available for W. bancrofti and B.
malayi. This may be used for the diagnosis of infection caused by
these parasites.
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22. Treatment
• Diethylcarbamazine is the drug of choice for the
treatment of bancroftian filariasis.
• It is given orally in a dose of 6 mg/kg body weight daily in
divided doses for 12 days. It kills microfilaria but its action on
adult worms is much less dramatic.
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23. Prophylaxis
• Bancroftian filariasis can be prevented by control of vectors by
spraying residual insecticides such as DDT, malathon, etc. onto
common resting sites.
• A difficulty in this approach has been that many vector species
have become resistant to the available insecticides.
Insecticides can be effectively used against larval Stages.
• A film of oil may be sprayed over water Surfaces.
• Larvivorous fish may be added to the ponds.
• Open drains, septic tanks, soakage pits and flood pit
laterines should be adequately maintained.
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24. BRUGIA MALAYI
• Common name: Malayan filaria.
• Geographical distribution
• B. malayi is prevalent in India, the Far East and Southeast Asia.
In India it has been chiefly reported from Kerala, Assam, Orissa,
West Bengal and Madhya Pradesh.
• W. bancrofti and B. malayi may co-exist at one place.
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25. Habitat
• As in case of W. bancroffi, adult male and female B.malayi
reside in the lymph nodes and lymphatic vessels, and the
microfilariae in the blood of man.
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26. Morphology
• The adult woms of B. malayi bear a general resemblance to those of W. bancrofti, though
smaller in Size.
• Mature females vary from 43-55 mm in length and 130-170 Lm in breadth. Mature males
vary from 13-23 mm in length and 70-80 jum in breadth.
• Microfilaria malayi is enveloped, Like W. Bancrofti the sheath extends beyond the anterior
and posterior ends of the larvae.
• As compared to W. bancrofti, it is smaller in size measuring 177-230 um in length and 6
um in diameter.
• Tail-tip of B. malayi is not free from nuclei.
• There are two discrete nuclei, one at the extreme tip of the tail and the other midway
between the tip and the posterior column of nuclei Microfilaria of B. malayi, like those of
W bancrofti, are also released into the blood stream with nocturnal periodicity.
• Subperiodic forms also exist in B. malayi.
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27. Life cycle
Life cycle
• The life cycle of B. malayi is similar to that of W. bancrofti,
however, the intermediate hosts of B. malayi are mosquitoes of
the genera Mansonia, Anopheles and Aedes.
• The intermediate hosts in India are M. annulifera, M. indiana, M.
uniformis and Anopheles barbirostris.
• Larval development of B. malayi, in the mosquito, is completed
in 6-8 days and adult mature females develop in lymph vessels
of man in about 7 months
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28. Pathogenicity
• B. malayi causes brugian filariasis.
• The course of brugian fiiariasis is similar to that of bancroftian
filariasis but elephantiasis, when it occurs, is usyally restricted
to the legs and there is no chyluria and involvement of male
genitalia.
• Like W. bancrofti, it may also cause tropical pulmonary
eosinophilia.
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29. Laboratory diagnosis
• As in case of bancroftian filariasis, the diagnosis of brugian
filariasis can be made by the Demonstration of
microfilariae and adult worms of B. malayi. DNA probes
and PCR for B. malayi have also been developed.
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30. • Treatment
• Same as that of bancroftian filariasis.
• Prophylaxis
• Preventive measures of brugian filariasis are similar to those of
bancroftian filariasis.
• Larval Mansonia vectors obtain oxygen from the roots of underwater
aquatic plants, such as water lettuce (Pistia stratioides).
• In Sri Lanka and southern India, where M. annulifera is the chief
vector of B. malayi, the transmission of this parasite has been
effectively reduced by removal of these water plants.
• Herbicides have also been employed successfully to kill aquatic
plants.
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