狂犬病概論與防疫

中華民國獸醫師公會全聯會理事長 江世明2007.09.11

概述

•狂犬病是由 lyssavirus 病毒感染人與哺乳動物的人畜共通傳染病，其血清型共四型，基因型共有七型。

•防疫原則有： (1) 疫苗注射； (2) 減少接觸帶原動物，降低感染風險； (3) 全面撲滅感染源 (需要強烈的企圖心 ambitious task) 。

雖然有很多哺乳類可以傳播本病，但僅有少數的物種與防疫有關。在非洲、美洲、澳洲、歐洲， Chiroptera 綱的蝙蝠是重要的帶原者，共有十七科，種類繁多。在亞洲、非洲、美洲、歐洲，傳統典型的狂犬病 (血清型一 )主要是由肉食獸傳播 (帶原 )，病毒在這些肉食動物間傳播。偶有蝙蝠型病毒感染肉食動物，也不會在這些動物間繼續散佈。基因的研究顯示，全世界狗的狂犬病病毒都是源自於歐洲，其他地區的病毒也都是殖民時代從歐洲傳播過去的 (Smith 1992) 。

1.浣熊被狂犬動物(rabid animal) 咬到。

2. 狂犬病病毒進入浣熊體內

3. 狂犬病病毒透過神經進入浣熊脊髓與腦

4. 病毒在浣熊體內潛伏約 3~12 週，此時浣熊沒有任何狂犬症候出現。

狂犬病病原性與感染過程 infectious path

5. 病毒在腦內迅速繁殖，然後進入唾液腺。此時浣熊開始出現症狀。

6. 感染之動物通常在出現症狀後七天內死亡。

狂犬病病毒最特異處

There are two types of rabies:• ‘Furious’ rabies ( 狂暴型 ) causes the animal to

foam ( 口吐白沫 ) and drool ( 從嘴滴下 ) at the mouth. Animals behave unpredictably and may become vicious, snap ( 猛咬 ) at imaginary objects and attack without warning. The animal becomes progressively unco-ordinated, paralysed and usually dies in 4-5 days.

• ‘Dumb’ rabies ( 麻痺型 ) causes early paralysis, followed by drooling and death. Animals with dumb rabies remain quiet and only bite when provoked. They are unable to eat, but will frequently try to drink water.

A rabid dog, with saliva dropping out of the mouth. From Wikipedia

Rabies

• Ranks 12th on the WHO list of major killer diseases

• OIE list B disease• Occurs in developing countries

particularly in Asian countries

Etiology: What Causes Rabies? Rhabdovirus: Genus, Lyssavirus• Bullet-shaped

• 180nm in length• 80nm in width

• Enveloped • Single-stranded RNA• Major surface glycoprotein G with G1

and G2 subgroups

Stability: Very fragile

• viable for less than 24 hours in carcass @ 20°C

• destroyed by UV light• easily deactivated with soap and wate

r• can be preserved by refrigeration or fr

eezing

Transmission of Rabies

• Virus shed in saliva Direct contact with saliva of rabid animal Bites and scratches

• Fresh wounds (rare)• Mucous membrane penetration• Ingestion

• Aerosol transmission• Rare in high density bat caves

• Cornea transplant (2 cases in US)• Organ transplants (4 cases in 2004)• Transplacental- Skunks & Bats

Susceptibility of Animals

• Greatest: Foxes, Coyotes, Wolves • Moderate: Dogs, Sheep, Goats, Horses,

Non-human primates, Cats and Humans

• Low: Skunks, Raccoons, Bats, Cattle• Least: Birds, Opossums

Epidemiology • Most warm blooded animals and humans are susceptible -

almost 100% lethal after infection. Slow course of the virus assures its survival in the environment

• In nature, rabies virus cycles in concert with the population of its wildlife reservoir host life-cycle. (Sylvatic cycle)

• In undeveloped countries, cycle occurs primarily in dogs – then to humans.

• In developed countries, domestic animal exposure most often a result of spill-over from sylvatic reservoirs (Epizootics)

• Pathogenesis depends upon species, strain or ecotype of rabies virus, infective dose, and site of infection

Clinical Signs in Animals

• No clinical signs are observed until the virus enters the CNS

• Three distinct phases may be observed~Prodromal~Excitatory or Furious~Paralytic or Dumb

• Phases may overlap!• Timing of phases cannot be predicted

Clinical Signs of Rabies in Wildlife • Nocturnal animals come out during the day

• Irrational behavior• Fox with porcupine quills• Attack pets—foxes, raccoons, coyotes

• Lost fear of man• Ataxic (lack coordination), aggressive

• Be wary or any unafraid wildlife or any bats encountered• Bats resting on the ground• Bats fighting

Five Stages of Human Rabies

• Incubation Period • Prodromal and Early Symptoms• Acute Neurological Period

-Furious Rabies-Paralytic Rabies

• Coma• Death or Recovery (very rare)

A patient with rabies, 1959. from Wikipedia

美國本土境內感染病例主要是蝙蝠感染，狗咬感染僅二例， 2004 年共有8 例，其中四例是因器官移植感染狂犬病 ( 捐器官者都是被蝙蝠感染而死 ) 。

1990 2006美國 年至 年狂犬病境內感染來源(CDC資料）

34

2 4

0

10

20

30

40

蝙蝠咬 狗咬 (bat)器官移植

人死

亡案

例數

已開發國家人感染狂犬病之風險已開發國家人感染狂犬病之風險

容易被狗咬的年齡容易被狗咬的年齡 (( 防疫重點防疫重點 ))

From: http://www.in.gov/isdh/dataandstats/disease/2000/idrab.htm (Indiana State Dept. Health)

狂犬病防疫

一、掌握疫情二、狂犬病疫苗注射三、狗口控制

一、掌握疫情

• 中央必須要重視，全國獸醫中央機關必須要進行全國的疫情監控，其中實驗室技術十分重要，因為狂犬病最後的確認必須要靠實驗室診斷。

• 流行病學資料是從全國到地方所有防疫計畫的依據，故須要快速收集、彙整、分析，然後要儘速上網供全國各級單位做防疫參考。台灣是狂犬病非疫區，故目前實施狗貓血清力價調查，從這些資料可以知道台灣各地區狂犬病爆發後的風險。

二、狂犬病疫苗注射拉丁美洲的經驗是完成 85%狗的狂犬病疫苗注射，結果大幅降低狂犬病發生率。其成功經驗是：

(1) 必須各部門的通力合作(2) 需要媒體強力支持(3)社區參與，勵行社區教育，讓社區有足夠的人文深度

進行合作(4)政治承諾 (political commitment)(5) 全國性 (national) 、區域性 (subregional) 、地方性 (local) 三個層次都要通力合作

(6)完備的社會宣導教育(7) 地方的確實執行 (local commitment)(8)充分的疫苗供應 (supply of vaccine) 。

•在疫苗注射率方面，全國之總狗數 (含流浪狗 )預防注射率至少要 70%，才能杜絕疾病之擴散。

• WHO 對口服疫苗的建議：唯有在疫區且有大量無法近身的野狗 (roaming dogs)存在時方可使用。目前其安全性尚未確認。

三、狗口控制

• 狗數調查與寵物登記是極重要的措施，這是需要長期努力的。台灣已經有良好之基礎，但仍有進步空間。

☻ 以上三項是狂犬病防疫的黃金律。

Thanks for your attention!