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, lei

shmaniasis, trypanosomiasis) . Wuchereria ba

ncrofti 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____________________________________________________________________ Brugia malayi lymphatic tissues mosquito lymphatic damage Asian_______________________________________________________________________ Brugia timori lymphatic tissues mosquito lymphatic damage Island of timor __

__________________________________________________________________ Onchocerca subcutaneous; eye black fly 蚋 river blindness Africa volvulus_______________________________________________________________________ Loa loa subcutaneous deer fly 斑虻 skin swellings Africa_______________________________________________________________________ Dipetalonema subcutaneous midge 库蠓 indefinite Africa streptocerca _______________________________________________________________________ Dipetalonema thoracic and midge 库蠓 indefinite Middle and perstans abdominal cavities South America_______________________________________________________________________ Mansonella peritoneal cavity midge 库蠓 indefinite South America ozzardi _______________________________________________________________________

I. Morphology

1. The adults are white and thread-like worms. T

he female is about 5-10 cm and the male 2.5-4 cm.

2. The microfilaria ranges from 177-296µm in len

gth. They are encased in a sheath. A large number

of body nuclei 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 bet

ween 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 ________________________________________________________________

Cephalic space shorter(1:1 or1:2) longer(2:1)

(length:width)

________________________________________________________________ Nuclei body nuclei equal sized, clearly unequal sized, coalescing,

defined, countable uncountable

________________________________________________________________

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 cau

dal nucleus

Microfilaria of W. bancrofti

Microfilaria of B. malayi: the body nuclei is unequal sized, coalescing,uncountable. The cephalic space i

s 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 develop

ment takes 10-14 days, the development of malay

an filaria in Anopheles sinensis requires 6-6.5 da

ys;

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 p

resent in the peripheral blood during dayt

ime is very low in density. The number of

microfilariae gradually increase from eve

ning 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 be

gins with a chill followed by a high fever. It is c

alled filarial fever. The lymphangitis （淋巴管炎） , lymphadenitis(淋巴结炎） may occur, o

rchitis（睾丸炎） and inflammation of sperma

tic cord are only found in infection of W. bancr

ofti.

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, sign

s 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 mo

squitoes. 1.  First choice drug is diethylcarbamazine ( DEC,

Hetrazan ). 2.   DEC table salt (3:1000 ) are sold in endemic are

as. 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 i

n the blood stream. 2.   Vector: Culex pipiens pallens, C. fatigans for W. banc

rofti, 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 nemato

de and a biohelminth. The adults and juv

eniles (larvae) live in the same host, but t

hey have to change a host to complete th

eir life cycle.They cause trichinosis, a zoo

nosis, which is spread by mammals kill e

ach other. Human infections result from

eating raw meat.

I. Morphology

1. Adults: ♂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.

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(mainl

y in duodenum and jejunum), juveniles in skeletal mu

scles

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 digestive juice Juveniles in raw meat duodenum cysts rupture penetrate mucosa, develop and molt

Larvae free from the cysts ♂adults return to intestinal lumen ♀ die Mate give birth to portal vein ♂burrow into mucosa juveniles ♀ Liver R.H lungs L. H 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 xeno

diagnosis; 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 reser

voir 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 a

nimals on raw meat.