首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
医学
Avian influenza is an infectious disease of birds caused by type A strains of the influenza virus. The disease, which was first
Avian influenza is an infectious disease of birds caused by type A strains of the influenza virus. The disease, which was first
admin
2015-01-26
77
问题
Avian influenza is an infectious disease of birds caused by type A strains of the influenza virus. The disease, which was first identified in Italy more than 100 years ago, occurs worldwide.
All birds are thought to be susceptible to infection with avian influenza, though some species are more resistant to infection than others. Infection causes a wide spectrum of symptoms in birds, ranging from mild illness to a highly contagious and rapidly fatal disease resulting in severe epidemics. The latter is known as "highly pathogenic avian influenza". This form is characterized by sudden onset, severe illness, and rapid death, with a mortality that can approach 100%.
Fifteen subtypes of influenza virus are known to infect birds, thus providing an extensive reservoir of influenza viruses potentially circulating in bird populations. To date, all outbreaks of the highly pathogenic form have been caused by influenza A viruses of subtypes H5 and H7.
Migratory waterfowl — most notably wild ducks — are the natural reservoir of avian influenza viruses, and these birds are also the most resistant to infection. Domestic poultry, including chickens and turkeys, are particularly susceptible to epidemics of rapidly fatal influenza.
Direct or indirect contact of domestic flocks with wild migratory waterfowl has been implicated as a frequent cause of epidemics. Live bird markets have also played an important role in the spread of epidemics.
Recent research has shown that viruses of low pathogenicity can, after circulation for sometimes short periods in a poultry population, mutate into highly pathogenic viruses. During a 1983-1984 epidemic in the United States of America, the H5N2 virus initially caused low mortality, but within six months became highly pathogenic, with a mortality approaching 90%. Control of the outbreak required destruction of more than 17 million birds at a cost of nearly US$ 65 million. During a 1999-2001 epidemic in Italy, the H7N1 virus, initially of low pathogenicity, mutated within 9 months to a highly pathogenic form. More than 13 million birds died or were destroyed.
The quarantining of infected farms and destruction of infected or potentially exposed flocks are standard control measures aimed at preventing spread to other farms and eventual establishment of the virus in a country’s poultry population. Apart from being highly contagious, avian influenza viruses are readily transmitted from farm to farm by mechanical means, such as by contaminated equipment, vehicles, feed, cages, or clothing. Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low. Stringent sanitary measures on farms can, however, confer some degree of protection.
In the absence of prompt control measures backed by good surveillance, epidemics can last for years. For example, an epidemic of H5N2 avian influenza, which began in Mexico in 1992, started with low pathogenicity, evolved to the highly fatal form, and was not controlled until 1995.
From the passage we can infer that rapid mutation of low to highly pathogenic viruses______.
选项
A、has led to evolution of the highly fatal form H5N2 viruses
B、makes it impossible for scientists to develop more effective vaccines against the viruses
C、helps to prevent spread from farm to farm by mechanical means
D、proves to be protective of the extensive reservoirs
答案
B
解析
推理题。根据原文只能推断出B是正确的:病毒由低致病性迅速转向高致病性便已使科学家们难以及时研制出有效的疫苗。
转载请注明原文地址:https://kaotiyun.com/show/5FT3777K
本试题收录于:
医学博士外语题库考研分类
0
医学博士外语
考研
相关试题推荐
Justbeforedawnwereceivedacallthatanunresponsiveinfantwasbeingbroughtbyemergencymedicalservicestoourhospital.
Scienceisthe4-yearpursuitofknowledgethateveryhighschoolteenagermustlivethrough.Ioftenaskmyself,whenwillIev
Thedoctorsuggeststhatagoodholidayinthecountryshould______him______nicelyafterhisoperation.
RobertSpring,a19thcenturyforger,wassogoodathisprofessionthathewasabletomakehislivingfor15yearsbyselling
A、Settingagoodexamplefortheirchildren.B、Discipliningtheirchildren.C、Reflectingthenatureofmodern-daylife.D、Changi
I’m______passinganewlawthathelpspoorchildrengetbettermedicine.
Theautomaticdoorsinsupermarkets______theentryandexitofcustomerswithshoppingcarts.
Ididn’tneedanyspecificmedicalinputor______control,althoughIwasinamessphysicallyandIdidneedtorest,relax,a
Themostinterestingarchitecturalphenomenonofthe1970’swastheenthusiasmforrefurbishingoldbuildings.Obviously,thisw
Thebrainisorganizedintodifferentregions,eachresponsiblefordifferentfunctions,andinhumansthisorganizationisvery
随机试题
子由①书孟德事见寄。余既闻而异之,以为虎畏不惧己者,其理似可信。然世未有见虎而不惧者,则斯言之有无,终无所试之。然曩余闻忠、万、云安②多虎。有妇人昼日置二小儿沙上而浣衣于水者,虎自山上驰来,妇人仓皇沉水避之。二小儿戏沙上自若。虎熟视久之,至以首抵触,庶几其
男性,28岁,右上腹撞伤伴剧烈腹痛半小时入院。查体:血压82/45mmHg,脉率13次/分,呼吸25次/分。神志清楚,面色苍白,胸廓无畸形,呼吸音清,腹部膨隆,腹式呼吸减弱,全腹压痛,以右上腹最重,伴有肌紧张和反跳痛,肝区叩痛(+),肝浊音界无缩小,肠暝音
【2015年广西.单选】品德结构的四个要素中具有催化剂作用的是()。
1/44,1/42,1/40,1/38,()
下列关于医学常识的表述,正确的是:
A地区与B地区相邻。如果基于耕种地和休耕种地的总面积计算最近12年的平均亩产,A地区是B地区的120%;如果仅基于耕种地的面积,A地区是B地区的70%。如果上述陈述为真,最可能推断出以下哪项?
经过对最近十年的统计资料分析,大连市因癌症死亡的人数比例比全国城市的平均值要高两倍。而在历史上大连市一直是癌症特别是肺癌的低发病地区。看来,大连最近这十年对癌症的防治出现了失误。以下哪项如果为真,最能削弱上述论断?
A、 B、 C、 D、 B
A、 B、 C、 B
WhydidthewomangotoHongKong(SAR)?
最新回复
(
0
)