Filarial Worm (Filariae)

Filarial worm are tissue residing nematodes. Around the world, there

are eight species, which could infected human being.

Species Location Vector

Wuchereria bancrofti ( 班氏 ) lymphatic system mosquito

Brugia malayi ( 马来 ) lymphatic system mosquito

Brugia timori ( 帝汶布鲁 ) lymphatic system mosquito

Onchocerca volvulus ( 旋盘尾 ) subcutaneous tissue blackfly

Loa loa ( 罗阿罗阿 ) subcutaneous tissue horsefly

Dipetalonema streptocerca ( 链尾 ) subcutaneous tissue gnats

Dipetalonema perstans （常现） body cavities

Mansonela ozzardi （奥氏） body cavities

Wuchereria bancrofti & Brugia malayi

世界性分布，蚊是主要传播媒介They are the most widely distributed filariae that are transmitted

by mosquitoes.

Morphology

成虫 (adult)

They are elongated, thread-like worms. The adult female worm

of W.bancrofti is larger than B.malayi.

Female produce larvae known as microfilariae.

微丝蚴 (microfilariae)

头隙 , 体核 , 尾核

They are elongated and sheathed, with blunt anterior end

and pointed caudal end. A large number of nuclei could

be seen in the body after staining.

班氏微丝蚴与马来微丝蚴的区别

班氏 马来大小 较大 较小

体态 柔和 僵硬头隙 呈方形 长方形体核 圆形，大小一致， 卵圆形，大小不一

清晰可数 排列密集尾核 无 有

W.bancrofti B.malayi

Length ( m)

Diameter ( m)

Body curves

Cephalic space

Somatic nuclei

Caudal nuclei

200-300

8

regular, smoothly curved

small

well separate

none

220-250

6

irregular twisted

large

over lapped

two

Differential characteristics of microfilariae between W.bancrofti and B.malayi (1)

区别的意义1. 致病性不同 班氏大2. 分布不同 班氏分布广3. 药敏性不同 马来对药敏感

difference in pathogenicity

W.bancrofti more heavy

difference in distribution

W.bancrofti worldwide distributed

difference in drug sensitivity

B.malayi is more sensitivity in drug

在蚊体内有腊肠期蚴 ; 丝状蚴 ,

感染期幼虫为丝状蚴 (filariform larva)

microfilariae in the mosquito first into a rhabditiform larva

(Sausage shaped larva) then into an filariform larva------

infectious stage

Life cycleThe life cycle of two species are similar. The larvae develop in the mosquito which acts as vector, and the adults develop in the human.

adlut microfilariae sausage shaped larva filariform larvalymphatic peripheral thoracic musculature labium of system blood of mosquito mosquito

human infected

larva enter the lymphatic system

成虫 微丝蚴 腊肠期幼虫 丝状蚴( 淋巴系统 ) ( 血液 ) ( 蚊胸肌 ) ( 蚊下唇 )

蚊叮

吸血

在蚊体内的发育 , Development in the mosquito: The microfilariae ingested by the mosquito along with its blood meal migrate to its muscles.

After 6 to 14 days of development, the larva force their way out of muscles, migrate to the proboscis (labium).

During the blood meal the developed larva emerge from proboscis onto the skin of the new host.

# some factors effected the development of larva in mosquito vectorW.bancrofti: Culex 淡色库蚊 , 致倦库蚊B.malayi Anopheles, Aedes 中华按蚊 , 嗜人按蚊 , 东乡伊蚊

在人体内的发育 Development in the human

On penetrating the skin through the bite wound, the larva pass to the

lymphatic vessels and nodes

After copulation, the female produces microfilariae in about 3 months

infection

The microfilariae migrate from the parent worm the through the walls

of the lymphatics to the neighboring small blood vessels or are carried

in the lymphatic circulation to the bloodstream

Microfilariae appear in the greatest number in the peripheral blood

between 8 pm and 4 am

nocturnal periodicity-------- the microfilariae, present in very

small numbers or often undetectablein the peripheral circulation

during the daytime, then appear in the greatest density at night,

when absent from the peripheral circulation the microfilariae

are found in the capillaries of the lung

夜现周期性 (nocturnal periodicity)

微丝蚴白昼滞留于肺血管内，夜晚则出现在外周血液的现象。

Microfilariae of Wuchereria bancrofti

Nocturnal periodicity of microfilariae

W.bancrofti B.malayi

Location

nocturnal

periodicity

reservoir host

deep or near surface

lymphatic system

10 pm—2 am

-

near surface

lymphatic system

8 pm—4 am

+

Differential characteristics of microfilariae between W.bancrofti and B.malayi (2)

致病 (Pathogenicity) 　丝虫病主要是由成虫引起的

Filarial symptoms are caused mainly by the adult worms,

living as well as dead and degenerating

Microfilariae cause less pathology, although they have been associated

with tropical pulmonary eosinopholia granulomas of the spleen, and

allergic reactions following their destruction by drugs

Clinically, the disease can be divided into incubation, acute,

and chronic phase

Incubation phase: 1. asymptomatic and may last for a year or more 2. may include low-grade fever caused by lymphatic inflammation Acute phase: an allergic response to the products of dying and degenerating adult worms ------ lymphangitis, funiculititis, orchitis, epididymitis filarial fever

Chronic phase: repeated lymphangitis granuloma fibrosis obstruction of lymph vessels lymph varices rupture of lymphatic proliferation of connective tissues elephantiasis elephantiasis hydrocele testis W.bancrofti chyluria

淋巴 ( 结 ) 管炎 增生性肉芽肿 纤维化 ( 纤维组织增生 )

1. 淋巴液肿

(1)     象皮肿 (elephantiasis)

(2)     睾丸鞘膜积液

2. 乳糜尿

管道阻塞压力↑ 曲张破裂液体外溢

诊断

( 一 ) 病原诊断

1. 血检

2. 体液和尿液检查微丝蚴 Examination of blood thick blood film-----detected microfilariae lysed blood check -----concentrated Examination of aspiration ( induction) 3. 成虫检查　　直接或以活检 Detection of adult worm ( 二 ) 血清学检查

( 三 ) 其他 mAb, ELISA, PCR

流行因素 Epidemiology

( 一 ) 分布：

世界性分布 W.bancrofti is worldwide distributed

B.malayi is restricted to Asia

( 二 ) 流行环节

1. 传染源 Source of infection: patients, infected persons

2. 传播媒介 ：蚊是主要传播媒介，主要蚊媒如下：

Transmission: mosquito Culex Anopheles, Aedes

班氏丝虫 马来丝虫

W.bancrofti: B.malayi

淡色库蚊

致倦库蚊

嗜人按蚊

中华按蚊

东乡伊蚊

3. 易感人群

4. 影响因素

防治原则 Treatment & Prevention

( 一 ) 普查普治

海群生 diethylcarbamzine (DEC) hetragan 治疗Diethylcarbamazine(hetrazan) is the first choice in treatment of filarial worm. A single-dose treatment of ivermectin plus Diethylcarbamazine has also proven highly effective, producing a 99 % reduction in the number of microfilariae

( 二 ) 防蚊灭蚊

( 三 ) 加强监测　 Mass treatment coupled with the use of screens, insect repellents and insecticides has proven effective in the filarial control

Onchocerca volvulus

Onchocerciasis is considered by WHO the world’s second leading infectious cause of human blindness

Adult worms are found in fibrous nodules called onchocercomas in the subcutaneous connective tissues and viscera of humans

Adult worms may cause minor pathological alterations

When microfilariae invade the cornea, cause inflammation of the sclera, cornea, iris and retina, lead to impaired vision or the total blindness known as “ river blindness”

The presence of microfilariae in the connective of the skin, produces severe dermatitis

Worldwide, there are estimated to be 20 million (20000000) cases of onchocerciasis, approximately 96 % of the cases are in tropical Africa

Microscopically demonostration of microfilariae in dermal lymph of skin biopsyis proof of infection, or identification of adults in skin nodules

Ivemectin, administered in a single dose, the most effective treatment, Diethylcarbamazine(hetrazan) also, however, the drug does not affect adult worms------surgical

Loa loa

Loasis is limited to the African

The parasite usually cause no serious damage to the host

Adult worm in subcutaeous tissue, in eye, Calabar swelling

Microfilariae can be seen in unstained fresh prepared blood

Diethylcarbamazine(hetrazan) is the first choice in treatment of filarial worm.

Trichinella spiralis

旋毛虫 (Trichinella spiralis) 成虫寄生在小肠下部的肠壁，

幼虫寄生在人体横纹肌中，引起旋毛虫病 (Trichinellosis) ，

为人兽共患病。

食源性寄生虫病，特点：地区性、群体性、食源性、季节性

Trichinellosis is the disease among human and animal, a zoonosis.

The infection is endemic in many areas of the world where raw or undercooked meat, mainly pork is consumed.

形态 Morphology

成虫 Adult small & slender male: 1.5 mm X 0.04 mm female: 3.5 mm X 0.06 mm deposited larva

幼虫 Larva enveloped, 0.25-0.5 mm X 0.21-0.42 mm

生活史 Life cycle

成虫和幼虫均寄生在同一宿主体内

完成生活史需更换宿主

Human infection results from consumption of meat, most communly poorly cooked pork, containing encapsulated larva.

Life Cycle of Trichinella spiralis

交配4-6d

肠淋巴管或静脉 心 肺 全身各处

( 囊包 )

食入

脱囊

幼虫2-3days

成虫 幼虫 幼虫

4-6 days lymphatic vessels heart lung spread

Adult Larva Larva

another 2-3 days

LarvaLarvae can survive only in the skeltal muscle & become encysted in 2 to 3 weeks

致病 Pathogenicity

Trichinellosis, mainly result from larval invasio of muscle & othertissues and the hperimmune reaction of the host to the metabolic by-products and secretions of the larvae

1. 侵入期 肠道症状Invasion stage: due to penetration of adult female & larva into the mucosa & submucosa, begins 24 hrsafter infection and lasts for 1 to 7 days asymptomatic or transient gastrointestipational complaints

2. 幼虫移行期 全身症状、肌肉症状等一系列严重症状

Migration stage: begins about 1 week after infection and lasts after female worm die(4-6 wks) triad of myalgia palpebral edema eosinophilia fever

3. 成囊期Encystment stage:

诊断 Laboratory diagnosis

病原诊断 组织活检

免疫诊断

皮内试验、环蚴沉淀试验、皂土絮状试验、 ELISA 。

最近也将检测急性期的循环抗原作为手段之一。

•A parasitologic diagnosis is made by means of biopsy or at autopsy

•Serologic tests EIA dot immunobinding to detect circulating parasitic antigen

流行和防治 Epidemiology, treatment, prevention

主要预防措施：不食生肉

mebendazole 对成、幼虫均有效

This infection is much less common in Africa and Asia than in Europe and America.

The drug of choice is Mebendazole, which can kill both the larva and adult worms. ( albendazole is also effective)

No raw or undercooked meat