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疫苗与自闭症无关：防腐汞在体内快速排泄不会造成蓄积
Infant study casts doubt on vaccine-autism link
WASHINGTON (Reuters) - The mercury in a vaccine preservative is pumped out of a baby's body too quickly for it to do any damage, researchers reported on Wednesday in a study they say should further absolve shots of causing autism.
The study in the journal Pediatrics reinforces what many vaccine experts have said for years -- that the form of mercury found in the preservative is handled differently by the body than the kind found in pollution and contaminated fish.
\"It takes a certain amount of time and a certain concentration ... to make it into the brain,\" Dr. Michael Pichichero of the University of Rochester in New York, who led the study, said in a telephone interview.
Thimerosal is widely used to preserve vaccines and is made from a kind of mercury called ethyl mercury. It allows vaccines to be distributed in multi-dose containers.
\"The World Health Organization has continued to sanction the use of thimerosal in vaccines because it has proven to save many lives by preventing bacterial contamination,\" said Pichichero, who has served as a consultant to several vaccine manufacturers and the WHO.
Many studies have shown thimerosal is safe, but some vocal groups have continued to lobby against its use and it has been removed from all childhood vaccines in the United States except for some influenza vaccines.
Pichichero's team studied 216 infants from R. Gutierrez Children's Hospital in Buenos Aires, Argentina, where thimerosal is still routinely used in vaccines.
They were divided into three age groups to have their blood-mercury levels tested before and after they were immunized at their newborn, 2- or 6-month checkups.
Blood tests showed the half-life of ethyl mercury -- the time it takes for the body to dispose of half of it -- was 3.7 days. The more dangerous methyl mercury, known to damage nerves, has a half-life of 44 days.
GONE TOO FAST
\"Until recently, that longer half-life was assumed to be the rule for both types of mercury,\" Pichichero said. \"Now it's obvious that ethyl mercury's short half-life prevents toxic build-up from occurring. It's just gone too fast.\"
The blood tests also showed most of the infants had methyl mercury in their blood, at safe levels, before they were ever vaccinated, he said.
Autism is marked by a variety of difficulties in social interaction and behavior, from the awkwardness of Asperger syndrome to severely debilitating repetitive behaviors and an inability to speak.
The U.S. Centers for Disease Control and Prevention estimates that one in 150 children has autism or a related disorder in the United States.
Experts know genes play an important role. Because autism is often diagnosed in toddlers, who also have undergone a battery of childhood immunizations, some advocacy groups argue that the vaccines may have caused the condition.
The U.S. Institute of Medicine reported in 2004 that no link could be found between vaccines and autism and took the unusual step of urging researchers to look elsewhere for a cause.
The U.S. debate was renewed because ABC television is planning to debut a new legal drama this week with an episode in which a jury finds that a mercury-based preservative in a vaccine caused a child's autism.
The American Academy of Pediatrics asked ABC to cancel the show but the network has refused.
In a separate study on Wednesday, a team at the University of Washington's Autism Center reported that children with autism have normal-size heads at birth but develop accelerated head growth between six and nine months of age.
http://www.reuters.com/article/healthNews/idUSN3050545420080130
华盛顿（路透社）-----研究人员周三报道用于疫苗防腐的汞制剂能快速的从孩子身体排泄而不造成任何伤害，其与自闭症的形成原因无关。儿科学杂志的这项研究再次支持了疫苗专家们多年来所主张的观点----该观点认为用于人体的防腐汞与被污染的鱼中的那种汞明显不同。领导该研究的纽约罗彻斯特大学的Michael Pichichero先生在一次电话采访中说，“需要一定的时间和浓度才能够进入大脑”。硫柳汞被广泛用于保存疫苗，它是由一种称为乙基汞的汞制成，可以允许疫苗分布在多剂量器皿中。担任多个疫苗生产厂家和世界卫生组织的顾问Pichichero先生说：“世界卫生组织继续核准应用于疫苗的硫柳汞的使用，因为它已经被证明可以预防细菌污染，保护生命”。很多研究已经证实硫柳汞是安全的，但是一些组织继续去游说反对它的使用，而且在美国它已经不用于除了一些流感疫苗外的所有儿童疫苗。Pichchero的小组研究了来自于阿根廷Buenos Aires的R.G儿童医院的216个婴儿。在那里硫柳汞仍然被常规用于疫苗防腐。他们被分成三个年龄组，在他们刚出生时，2或6个月被动免疫的前后测定他们的血汞水平。血液试验表明硫柳汞的半衰期（身体代谢其半量的时间）是3.7天。而更危险的甲基汞（可损伤神经）的半衰期是44天。
快速排泄
Pichichero说，“直到最近，长半衰期仍被认为是各种类型的汞所普遍具有的。现在可明显看出，硫柳汞的短半衰期避免了毒性的积累并发生。它能很快地排泄。”这血液试验也表明大多数婴儿在他们没有接种任何疫苗之前血中甲基汞含量在正常水平。自闭症表现为各种社交和行为困难，可表现为阿斯佩格综合症的笨拙，也可是严重双重行为和说话障碍。美国国家疾控中心估计在美国150个儿童中就有一个患有自闭症或相关的紊乱。专家认为基因起了重要的作用。因为自闭症经常在幼儿群体中被诊断，这些幼儿也经历了一组儿童期免疫，一些鼓吹组织则据此人认为疫苗导致了这种状况的发生。美国医学研究所在2004年报道认为在疫苗与自闭症之间没有发现关联，并且采取不寻常的措施敦促研究者们到其它方面去寻找病因。美国的这种辩论重新开始了，因为ABC电视台计划这周播出一个新的合法的节目，其中的事件是一个陪审员发现了一种汞制剂的疫苗防腐剂导致一个孩子自闭症。美国儿科学会要求ABC取消该节目，但是该公司拒绝了。在周三的独立研究中，华盛顿自闭症研究中心的小组报道自闭症儿童在出生时有正常的头围，但在六到九个月年龄，头围加速生长。 |
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发表于 2008-3-5 23:54:36