ZT为什么蚊子不会传播肝炎呢？

天使的羽毛

Why Mosquitoes Don't Spread Hepatitis

By Charles Daniel, About.com
Updated: August 22, 2008
http://hepatitis.about.com/od/prevention/a/mosquitoes.htm
About.com Health's Disease and Condition content is reviewed by the Medical Review Board


It's a beautiful day and you're outside enjoying the fresh air. You feel a small prick on your arm and notice that a mosquito is getting a free meal. Without realizing, you kill it with a quick slap of your hand, but notice a little blood on your arm where the mosquito was. Along with the nuisance of a mosquito bite, you might be worried about possible infections you can catch, including hepatitis.
It's intuitive to think that when a mosquito bites someone infected and then bites another person, the second person could be exposed to viral hepatitis. Fortunately, viral hepatitis isn't spread from mosquitoes. Let's look at some reasons why.

Mosquitoes Inject Saliva, Not Blood
Because hepatitis B and hepatitis C are spread by contact with infected blood, it's very tempting to think of mosquitoes as flying hypodermic needles. However, the "needle" that mosquitoes feed with, called the proboscis, is actually a complex structure that has separate channels. When a mosquito bites, it injects saliva through one channel. The saliva functions as a lubricant to help the mosquito feed easier. The blood it sucks as a meal flows in a completely separate channel and only in one direction: toward the mosquito. So, it's biologically unlikely for infected blood to be spread to another person.

But, Wait! Mosquitoes Spread Malaria and Yellow Fever. Why Not Hepatitis?
Since mosquitoes can spread some diseases, such as malaria and yellow fever, it is tempting to think they can spread other blood-borne diseases like HIV and hepatitis. The answer is in the saliva! When a mosquito bites, it injects its own saliva into whatever it is biting. The diseases spread by mosquitoes are actually spread through the mosquito's saliva. Hepatitis, however, is spread through blood.

Need More Proof? Viruses are Fragile
The hepatitis viruses are very picky about what they infect and where they can survive. They really like livers, and mosquitoes don't have livers! This means that the mosquitoes aren't really a good home and the viruses wouldn't survive long enough to be spread, even if they could be. Also, people who study mosquitoes have noticed they usually don't bite two people consecutively. After they bite, they will fly away to let their food digest and then after a period of time, they will feed again. Because the hepatitis viruses don't last long in a harsh environment, they wouldn't survive long enough to infect.

So, Is this Just Mosquitoes? How about Insects and Spiders?
Mosquitoes are part of a very diverse biological classification called arthropods, which include a variety of life. Some types of arthropods include insects, spiders, centipedes, shrimp and crayfish. Experts agree that arthropods don't spread viral hepatitis. A fair bit of scientific study has gone into how arthropods spread disease, especially since HIV emerged in the 1980s.

If Not Mosquitoes, What Does Spread Hepatitis C?
Hepatitis C is spread by direct contact with infected blood. So, some things that could expose you to infected blood would be razors, needles (not mosquitoes!) and toothbrushes. Also, certain actions are at higher risk for spreading hepatitis C. Examples of these would include injecting street drugs without sterile needles and works and having sex with someone who is infected (though this doesn't happen often).

Question: How long does the hepatitis virus live outside the body?
Answer: Many viruses cause hepatitis, but only five common viruses share an affinity for infecting the liver. These are known as hepatotrophic viruses and are usually what people mean when they talk about hepatitis viruses. While they cause similar symptoms in the body, they are separate viruses and have different characteristics. All of these viruses can be infectious outside of the body for certain periods of time. However, a good rule of thumb is that wet material is infectious and dried material is much less infectious.

The hepatitis A virus, or HAV, is relatively hardy. In good conditions, it can survive outside the body for months. HAV can survive certain acids and some heat. For a period of time and under certain conditions, HAV can survive in sea water, dried feces and live oysters.
Hepatitis B Virus
The hepatitis B virus, or HBV, can still be infectious for up to a week outside the body.
Hepatitis C Virus
The hepatitis C virus, or HCV, can live outside the body for up to 4 days. However, many experts think it usually survives up to 16 hours at room temperature.
Hepatitis D Virus
This virus needs help from the hepatitis B virus to be infectious, so it only infects someone with hepatitis B.
Hepatitis E Virus
This virus is spread similar to the hepatitis A virus and causes acute disease similar to the others.

天使的羽毛

蚊子为何不传播病毒性肝炎

遇上一个好天，你总想去户外呼吸点新鲜空气。感觉到一点点刺痛，你发现一只蚊子在你的手臂上享用免费大餐。你不加思索一巴掌拍死了它，会留意有一点血迹留在原处。除了对蚊子叮咬的厌恶之外，你也许会担心会不会被感染，其中就包括肝炎。

当蚊子叮咬一个肝炎病人，然后又叮咬另外一个人的时候，很自然地，你会想到第二个人会不会感染上病毒性肝炎。幸运的是，病毒性肝炎不会通过蚊子传播。让我们看看这是为什么。

叮咬人的时候，蚊子注射唾液而不是血液

由于乙型和丙型肝炎都是通过接触感染血液传播，人们禁不住把蚊子看作飞行的注射针头。然而，蚊子的用来进食的“针头”，称为口器，实际上具有复杂的结构，它有2个独立的管道。叮咬人时，蚊子从一个管道注射唾液，唾液的功能像是润滑剂，可以帮助蚊子吮吸更容易些。它吮吸的血液，作为食物流是在一个完全独立的管道内，并且是单向的：流向蚊子。因此，这种方式下，将污染血液传播给别人在生物学上是不大可能发生。

但是，等等，蚊子不是会传播疟疾和黄热病吗？为什它不会传播病毒性肝炎呢？诚然，蚊子可以传播某些疾病，如疟疾和黄热病，很自然地，也会认为它能传播其他的血源性传播疾病，像HIV和病毒性肝炎。答案还是蚊子的唾液！蚊子在叮咬时会在它叮咬的任何地方注入自己的唾液。蚊媒疾病实际上是通过蚊子的唾液传播，而病毒性肝炎是通过血液传播。

还需要更多证据吗？病毒很脆弱

肝炎病毒对感染对象和生存环境非常挑剔，它们喜欢生活在肝脏，蚊子是没有肝脏的。这就意味着蚊子实际上不是很好的宿主，肝炎病毒在蚊子体内不会存活足够长的时间让它得到传播，即使它能传播的话。研究蚊子的专家们也注意到，蚊子实际上不会连续叮咬2个人。叮咬一次后，它们会飞走以消化吸食的血液，过了一段时间才会再次叮咬进食。因为肝炎病毒在这样的恶劣环境下存活时间不长，它们不会活到有机会感染他人。

仅仅蚊子是这样？昆虫和蜘蛛又会怎样

蚊子属于非常多样的一个生物分类—节肢动物，该类中包括了很多不同的物种。一些典型的节肢动物包括：昆虫、蜘蛛、蜈蚣、虾和小龙虾等。专家认为节肢动物不会传播病毒性肝炎。关于节肢动物如何传播疾病的科学研究还相当少，尤其从1980年代HIV开始出现以后。

如果不是蚊子，哪又会是什么传播丙型肝炎呢？

丙型肝炎通过血液直接接触传播，可能让你暴露感染血液的东西有剃刀、针头（不是蚊子）和牙刷。某些行为也是丙型肝炎传播的高危因素。这样的例子包括用未经消毒的针头街头注射毒品以及与丙型肝炎感染者一道工作或发生性接触（虽然这种情况不是经常发生）。

问：肝炎病毒在体外能够存活多久？

答：有很多病毒引起肝炎，但是只有5种普通的病毒对肝脏有亲和性并导致感染。它们被称为嗜肝性病毒，就是通常人们所说的肝炎病毒。虽然它们在人体引起的症状相似，它们却各不相同，具有不同特点。所有这些病毒都可以在一定时间内在体外具有传染性，简单的判断方法是湿的物品感染性强，干的物品较少具有感染性。

甲肝病毒，HAV，相对耐活。在较好的条件下，体外能存活数月。HAV能够耐某种程度的酸度和热。在某些条件下，HAV能在海水、干燥的粪便和活的贝类体内生存一段时间。

乙肝病毒
乙肝病毒，HBV，在体外能够保持最多一周时间的传染性。

丙肝病毒
丙肝病毒，HCV，在体外能够存活最多4天。但很多专家认为，在室温下丙肝病毒最多能存活16小时。

丁肝病毒
这种病毒需要乙肝病毒存在才具有传染性，所以只能感染乙肝患者。

戊肝病毒
这种病毒的传播类似于甲型肝炎病毒，引起急性肝炎也与其他病毒引起的相似。