Filariae
Filariasis is one of the five major parasitic
disease in China and also one of the six major
tropical diseases to which WHO devotes much
attention (malaria, shistosomiasis, filariasis,
leishmaniasis, trypanosomiasis) . Wuchereria
bancrofti and Brugia malayi are found in
China.
Eight Species of Filariae Parasitizing Humans
_____________________________________________________________________________
Species
Site of inhabitation
Vector
Pathogenesis
Distribution
_______________________________________________________________________
W. bancrofti lymphatic tissues
mosquito
lymphatic damage
worldwide
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Brugia malayi lymphatic tissues mosquito
lymphatic damage
Asian
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Brugia timori lymphatic tissues
mosquito
lymphatic damage Island of timor
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Onchocerca subcutaneous; eye black fly蚋 river blindness
Africa
volvulus
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Loa loa
subcutaneous
deer fly斑虻 skin swellings
Africa
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Dipetalonema subcutaneous
midge库蠓
indefinite
Africa
streptocerca
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Dipetalonema thoracic and
midge库蠓
indefinite
Middle and
perstans
abdominal cavities
South America
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Mansonella
peritoneal cavity
midge库蠓
indefinite
South America
ozzardi
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I. Morphology
1. The adults are white and thread-like worms.
The female is about 5-10 cm and the male 2.5-4 cm.
2. The microfilaria ranges from 177-296µm in
length. They are encased in a sheath.
number of body nuclei
A large
are seen in the stained
specimen. A nerve ring with no nuclei can be seen
at the anterior 1/5 of the body. The morphological
differences between bancroftian and malayan
microfilariae are the following:
Adult worm of filaria
Morphological Differences of Microfilariae between W. bancroti and B. malayi
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Species
W. bancrofti
B. malayi
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Appearance
graceful, sweeping curves
irregular, stiff curves
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Size
larger 244-296× 7 µm
smaller 177-230 × 6 µm
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Cephalic space shorter(1:1 or1:2)
longer(2:1)
(length:width)
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Nuclei
body nuclei equal sized, clearly unequal sized, coalescing,
defined, countable
uncountable
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Terminal nuclei
no
two
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Microfilaria of W. bancrofti and B. malayi
Microfilaria of W. bancrofti
Anterior part and posterior part
of bancroftian microfilaria
Microfilaria of W. bancrofti showing it’s appearance
Bancroftian microfilaria:body nuclei equal
sized, clearly, defined, countable without
caudal nucleus
Microfilaria of W. bancrofti
Microfilaria of B. malayi: the body nuclei is
unequal sized, coalescing,uncountable. The cephalic
space is longer with two caudal nuclei.
Microfilaria of B. malayi
II. Life Cycle:
1.Biohelminth: intermediate hosts(vector) are
mosquitoes, bancroftian filaria is transmitted by
Culex pipiens pallens in which the larval
development takes 10-14 days, the development
of malayan filaria in Anopheles sinensis requires
6-6.5 days;
2. Infective stage: filariform larva(L3);
3. Infective route: by skin( the wound bitten by
mosquito );
4. Site of inhabitation: lymphatic tissue;
5. Life span: 4-10 years;
6. Microfilariae may survive 1-3 months;
7. Viviparous;
8. Nocturnal periodicity: The microfilariae
present in the peripheral blood during
daytime is very low in density. The
number of microfilariae gradually
increase from evening to midnight.
Proboscis of a mosquito containing
filariform larvae
A large number of 3rd stage larvae
of a filarial sp emerging from the
proboscis of a mosquito.
III. Clinical manifestation
1. Acute stage:
The symptoms are due to allergic reaction. It
begins with a chill followed by a high fever. It is
called filarial fever. The lymphangitis（淋巴管
炎 ） , lymphadenitis( 淋 巴 结 炎 ） may occur,
orchitis （ 睾 丸 炎 ） and inflammation of
spermatic cord are only found in infection of W.
bancrofti.
2. Chronic stage:
The manifestations are caused by
lymphatic lesion.
(1) Elephantiasis: Lymph edema may
occur in the limbs, scrotum, breast, vulva
and etc.
(2) Chyluria only caused by W. bancrofti.
(3) Hydrocele is only found in infection
of W. bancrofti.
A patient of
elephantiasis
Elephantiasis of leg due to filariasis
Elephantiasis due
to Brugia malayi.
Pitting
does
not
occur in this stage
(solid edema)
 Elephantiasis due to
Brugia
malayi,
complicated by severe
dermatitis
and
secondary
bacterial
infection
 This
lady
has
elephantiasis of the
right leg and edema
in the left
Hydrocele is only
found in infection
of W. bancrofti.

elephantiasis of the left leg
and scrotum
IV. Diagnosis
The diagnosis depends on the symptoms,
signs and history of living in endemic areas, but
the confirmative diagnosis depends on the
demonstration of microfilariae.
1. First choice method is thick blood
smear, taking blood at night from 9pm-2am.
2. Millipore membrane filtration is used for
screening the patients or checking curative effect
in the endemic areas with the low infective rate.
3. Fresh blood smear used for mass education.
4. Immunological tests are only made reference
of the diagnosis.
V. Treatment and Prevention
Elimination the source of infection and control
mosquitoes.
1. First choice drug is diethylcarbamazine ( DEC,
Hetrazan ).
2. DEC table salt (3:1000 ) are sold in endemic
areas. People take this salt over 6 months, resulting
in an elimination or great reduction of microfilariae
in the blood stream, for treating and preventing
filariasis.
3. Remove the giant elephantiasis of the scrotum,
chest and limbs.
4. Eradicate mosquito breeding place and control
mosquitoes.It is important to protect people from
mosquito biting for controlling filariasis.
VI. Epidemiology
 1. Source of infection: The people harbor microfilariae
in the blood stream.
 2.
Vector: Culex pipiens pallens, C. fatigans for W.
bancrofti, Anopheles sinensis, Anopheles anthropophagus
transmitting B. malayi.
 3. Distribution: Filariasis of W. bancrofti is world-wide
distribution, while filariasis of B. malayi is in Asia. In
China, W. bancrofti distributes in south of Yellow River
16 provinces and city, while B. malayi in south of Yellow
River 13 provinces and city. B. malayi is not in Shandong,
Hainan and Taiwan.
 4. Reservoir host: W. bancrofti is no reservoir host, while
cat, monkey may be the reservoir host of B. malayi.
Trichinella spiralis
T.spiralis
is
the
smallest
human
nematode and a biohelminth. The adults
and juveniles (larvae) live in the same
host, but they have to change a host to
complete their life cycle.They cause
trichinosis, a zoonosis, which is spread
by mammals kill each other. Human
infections result from eating raw meat.
I. Morphology
♂1.5mm, ♀3-4mm, both have a
single set of reproductive organs and
stichocytes surrounding the esophagus. The
secretions of stichocytes are relative to
digestion and pathogenesis.
2. Juvenile: 124×6 µm, one or more coil
in a cyst in the skeletal muscle fibers. The
cyst is about 0.25-0.5 ×0.21-0.42mm in
size. This is infective stage. There are
stichocytes around the esophagus.
1. Adults:

Trichinella spiralis
encysted larva

T. spralis – posterior end, male &
female
II. Life cycle
1. Infective stage: juveniles in cyst
2.
Site
of
inhabitation:
adults
in
small
intestine(mainly in duodenum and jejunum),
juveniles in skeletal muscles
3. Route of infection: by mouth
4. Life span of female: 1-2 months
5. Final host and intermediate host: person
6. Reservoir host: pigs, cats, dogs, mice etc
swallowed by man
Juveniles in raw meat
duodenum
digestive juice
cysts rupture
penetrate mucosa, develop and molt
Larvae
Mate
free from the cysts
die
return to intestinal lumen
♂burrow into mucosa
give birth to
♀
Liver
R.H
lungs
L. H
juveniles
♂adults
♀
portal vein
skeletal muscle cells
III. Clinical manifestation
The process of the pathogenesis may be divided into 3
stages:
1. Invading stage(about 1 week): The damage is
mainly found in the intestine. In this stage,
abdominal pain, nausea,vomiting,diarrhea and fever
may occur.
2. Migrating stage of the juveniles(2-3weeks):The
damage is mainly in the skeletal muscles. In this
stage, muscular pain with high fever is main
symptoms, especially in active muscles. Wandering
juveniles may also cause pneumonitis, pleurisy,
encephalitis, nephritis and myocarditis etc.
3. Encysted stage(4-16 weeks): In this stage, only
muscular pain present without other symptoms.
IV. Diagnosis
1. Muscular biopsy; 2. Examination of left food and
xenodiagnosis; 3.Immunodiagnosis:(1) CPT(circumlarval
precipitin test) (2) ELISA (3) IHA
V. Treatment:
Albendazole and Mebendazole
VI. Epidemiology:
Worldwide distribution. Lots of mammals can serve as
reservoir hosts. The spread of trichinosis is due to mammals
killing each other. Humans get the infection by eating raw
meat.
VII. Prevention
1. Quarantine of meat; 2. Avoid eating raw meat and feeding
animals on raw meat.