犊弓首蛔虫 Toxocara vitulorum 动医 07 （ 2 ）班 王晶 吕嘉敏 卢沛兰.

犊弓首蛔虫Toxocara vitulorum

动医 07 （ 2 ）班 王晶 吕嘉敏 卢沛兰

Introduction

Kingdom Animalia （动物界）Phylum Nemathelminthes （线形动物门）Class Secernentea （尾感器纲）Order Ascaridata （蛔目）

Family Toxocaridae （弓首科）Genus Toxocara （弓首属）

Scientific classification

Host: cattle and buffalo

Site: small intestine （小肠）

Morphology

Size: large

The largest intestinal parasite of cattle

Shape :

it has a cylindrical( 圆柱状 ) form ， taper

ing at either end( 两端尖 ), and the body is

covered by a colorless, somewhat transluc

ent( 半透明的 ), layer, the cuticle ( 角皮 ).

11 ～ 26cm

14 ～ 30cm

70~80 μm ｘ 60 ～ 66 μm

Egg( 卵 )

Life cycle

Adult nematodes develop only in the small

intestines （小肠） of young calves under 6

months of age.The eggs do not hatch in the environment, but

larvae in the eggs develop to the infective second

stage larvae （ L2 ） .Direct Life Cycle( 直接型生活史 )

Egg Infective egg (with L2)

L2 在母牛小肠孵化

适宜的温度、湿度

移行

至肝、肺、肾等发育成 L3

L4

移行至子宫 胎牛吞入体内

犊牛小肠 Adult

经粪便排出

进入胎盘羊水液

Transmission from mother to fetus ( 胎儿 )across the placenta （胎盘）

Egg

L3进入小肠

乳腺乳汁

Adult

Infective egg (with L2)

移行

适宜的温度、湿度 L2 在母牛小肠孵化

L4

Transmission by the milk of the dam

至肝、肺等发育成 L3

移行

In some parts of the world calves may be

come infected ingesting infective eggs fr

om the environment ， for example, in th

e southern part of Africa.

Egg 适宜的温度和湿度

肝脏 L3

门静脉

心 肺动脉

细支气管、支气管、气管

肺泡

进入口腔

小肠

Adult 经粪便排出

咽部

Infective egg (with L2)

L2 在犊牛小肠孵化

Ingestion of infective eggs

后腔静脉 肝静脉

肺 L4

Epidemiology

cattle and buffalo Bos ( 牛属 ) calves seem to be less suscepti

ble than Bubalus ( 水牛属 ) calves Toxocara vitulorum is found mostly in trop

ical and subtropical climates worldwide

Calves can be infected both transplacental

ly （经胎盘地） before birth and via milk

after birth, while they may also become inf

ected ingesting infective eggs from the env

ironment.

Transmission through milk is the major

route of infection of calves in Southeast

Asia. But studies in the southern part of

Africa have indicated that the ingestion of

infective eggs from the environment is the

most common route of infection there.

Larvae develop into adults in the small

intestines of young calves, and then begin

shedding eggs in the feces contaminating

the environment and other animals.

The thick-walled eggs are very resistant to adverse climatic and environmental conditions.

At temperatures between 20 and 30ºC they can remain infective for a long period of time (several years).

Prevalence of Toxocara vitulorum in beef cattle in North Central Florida

(Davila ， et al 2010)

Calf age Prevalence

<3 months 29/165 = 17.6%

3–4 months 5/113= 0.4%

5–6 months 1/108 = 0.9%

7–9 months 0/47 = 0%

The prevalence( 感染率 ) in most countries is between 5 and 50% and has been influenced by animal species, sex and seasonal variations.

Prevalence can reach 100%, when uncontrolled in the field, since each female worm can lay up to 100 000 eggs per day.

Lesions

punctate hemorrhage 点状出血 eosinophilia 嗜酸性粒细胞增多 hemorrhage 出血 ulcer 溃疡 intestinal obstruction 肠阻塞 intestinal perforation 肠穿孔

Signs enteritis 肠炎 emaciation 消瘦 lethargy 嗜睡 fever, couch, dyspnea( 呼吸困难 ) a stink smell likes acetone( 丙酮 ) diarrhea 腹泻 stomachache 腹痛 exhaustion 衰竭 intestinal obstruction 肠阻塞

intestinal perforation 肠穿孔

Diagnosis

Epidemiological analysis 流行病学分析 history of disease ( 病史 ) 、 age 、 feeding and manage

ment practices （饲养管理方式）、 season of occurrenc

e （发病季节）、 climate , etc.

Clinical signs 临床症状 Faecal examination: by flotation method

Post-mortem examination( 死后剖检 )

Diagnosis for treatment ( 治疗性诊断 )

Control

The principle of control is to prevent the

parasites from having an effect on the

calves and from contaminating the

environment with eggs.

anthelmintics( 驱虫药 )

盐酸左旋咪唑 Levamisole 8mg/kg po/im

丙硫苯咪唑 Albendazole 10~15mg/kg po

伊维菌素 Lvermectin 0.3mg/kg sc/po symptomatic treatment 对症治疗

1 、 Treatment 治疗

2 、 prevention 预防 preventative deworming 预防性驱虫 Eliminating the immature parasites before they can h

arm the calves and start egg production ； Calves under 20 days of age Sanitation 卫生 e.g. Harmless disposal of feces 粪便无害化处理 isolated feeding 隔离饲养

It is advised that all calves under 6

months of age should be used anthel

mintics( 驱虫药 ) in endemic area.

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