綜說：口蹄疫

口蹄疫（FMD）是偶蹄類動物的高度惡性傳染病，一直都受到國際上的重視。此病毒是Picornaviridae的aphthovirus屬。病毒顆粒極小，約22nm，結構蛋白VP1的βG-βH環是決定抗原性的重要區域。此病毒以交叉保護及血清學等試驗可分為O、A、C、SAT-1、SAT-2、SAT-3及Asia 1七型，另可分成不同的亞型有80種之多。各血清型之間幾乎無任何交叉保護力，同一血清型之不同亞型則有不同程度的保護作用。此病毒的變異性極大，在牛SAT-2為毒VP1基因上1D的變異頻率可高至1.64 X 10^（-2）取代/核苷酸/年，而一般細胞DNA的變異頻率則為10^（-9）。針對FMD病毒的診斷有許多方法，但目前較為人接受的仍然是病毒分離。型別的鑑定，則可使用ELISA, CF, Liquid-phase blocking ELISA等。臨床及病理上，FMD的感染不易與豬水疱疹、水疱性口炎及豬水疱病區別，必須使用病毒分離及鑑定進行鑑別診斷。FMD病毒經由呼吸道或皮膚傷口感染後，首先在咽喉或扁桃腺繁殖利用病毒表面之RDG胺基酸序列或其他方式附著于細胞上，再經由胞飲作用（Endocytosis）進入細胞，在細胞內繁殖。由Langerhan's前驅細胞經血液或其他方式送至身體各處，主要在上皮細胞胞質內進一步生長，或感染哺乳豬心肌細胞造成肌肉的壞死。此時皮膚如受到壓力，外傷或其他因素的影響，則形成水泡，否則病毒即逐漸消失。此病毒會感染所有的偶蹄類動物。自然宿主在家畜方面包括牛、豬、山羊、綿羊、鹿及駱駝，也會感染許多野生偶蹄類動物及實驗動物包括兔、鼠等。此病毒感染到其他動物主要以接觸為主，然空氣也是重要的傳染途徑之一，感染動物的水泡液、唾液、乳汁、精液、所呼出的空氣及糞尿均含有高量的病毒（每日排毒10^8-10^10 TCID50），人可經由機械性的攜帶傳播給其他動物。目前為止只有反芻動物會保毒，豬感染恢復後14-28天病毒即由體內消失，保毒動物會間歇性排毒，但排毒量會逐漸減少，保毒時期牛約1-3年，水牛22個月，綿羊9個月，而山羊約4個月。本病撲滅策略的選擇有二種，撲殺清場及免疫策略，前者的使用多在只有少數場發病，且有完備疫情通報系統的地區使用。如屬常在性疾病，或通報及監控無法落實的地區則多半採階段性免疫策略。我國於今年三月份爆發口蹄疫至今已9個月，自6月份受到控制後，12月初又出現新病症。雖然我國在爆發後執行前所未有的嚴格措施，但仍然在6個月後再次出現疫情，可見要面對此病時所須考慮的問題不能等閒視之。

關鍵字

口蹄疫；病毒；致病機制；流行病學；預防控制

並列摘要

Foot-and-mouth disease (FMD) is an internationally important contagious disease infected cloven-hoofed animals. The causative agent is an aphthovirus belonging to Picornaviridae. It is a minute virus with a size about 22nm, the βG-βH loop in the structural protein VP1 is an antigenic decisive site. By cross protection and serological tests, seven serotypes are designated, they are O、A、C、SAT-1、SAT-2、SAT-3 and Asia 1, with over 80 subtypes. Cross protection between serotypes is minimal; however, variable protection is present between subtypes among the same serotype. The mutation frequency (MF) of FMD virus is tremendous, the MF of the ID gene in SAT-2 virus in cattle is 1.64 X 10^(-2) replacement/nucleotide/year, in comparison to a normal cell DNA, the MF is only 10^(-9). Virus isolation is so far the most reliable method to definitively diagnose the disease. In differentiating serotypes, ELISA, CF, liquid-phase blocking ELISA are usually employed. Clinically and pathologically, FMD infection is difficult to differentiate from infection of other vesicular diseases, such as swine vesicular disease, vesicular stomatitis and vesicular exanthema, virus isolation and associated antigens detection are also the only officially acceptable methods for a confirmative diagnosis of these diseases. The viruses first adhere on the target cells through RDG or other mechanism after infecting animals by ways of respiratory tract or skin, they then enter the cells via endocytosis and multiply intracellularly. The viruses are replicated in tissues adjacent to pharyngeal region and in tonsil, thereafter, they are transported to other parts of body by Langerhan's cells through blood or other vehicles, but mainly to the cytoplasm of epithelial cells, they may also infect myocardiocytes causing cell necrosis. Vesicles are developed as factors such as pressure, trauma or other unknown reasons are applied to the skin; otherwise, the viruses are slowly disintegrated. They naturally infect cattle, pig, goat, sheep, deer, camel and many wild cloven-hoofed animals, rabbits and mice are experimentally infected. Horizontal transmission through direct contact is the major way of transmission; however, air is another significant media for the spread of the viruses. High titre of viruses (10^8-10^10 TCID50/day) are present in vesicular fluid, saliva, milk, semen, breath and manure of infected animals. Human beings are a consequential mechanical means of transporting the virus. The only known reservoir animals for the viruses are ruminants, the viruses will not be detected in pigs in 14-28 days after recovery. The carrier animals shed viruses intermittently with diminishing amount, the carrier period for cattle is about 1-3 years, water buffalo for 22 months, sheep for 9 months and goat for 4 months. Normally there are two eradication strategies, stamping out and vaccination. Stamping out policy is usually chosen for areas with minimal number of outbreaks, and where routinely practices securely reporting program and tight surveillance system, otherwise, the vaccination policy is constantly executed. The FMD outbreak in Taiwan had been nine months since this past March; nevertheless, new cases recurred six months after the first outbreak in spite of stringent action implemented countrywide all the way along the whole period. It is therefore our duty to put forth unequivocally special precaution while operating the control and eradication programs for FMD virus infection.

並列關鍵字

Foot-and-mouth disease ； Virus ； Pathogenesis ； Epidemiology ； Prevention and control

國際替代計量

綜說：口蹄疫

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