[ti:Bats and the Origins of Outbreaks]
[by:www.21voa.com]
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[00:00.04]Scientists have long suspected
[00:02.80]that the rate of new infectious diseases could speed up.
[00:08.44]This is especially possible in developing countries
[00:12.24]where human and animal contact is increasing.
[00:17.40]Changes in the environment are moving many species of animals
[00:22.08]into new living spaces.
[00:25.84]Those movements, combined with more human contact with animals
[00:30.68]as people move deeper into forests,
[00:33.64]increases the chances of a virus jumping species.
[00:39.84]Diseases that can jump from animals to humans
[00:43.92]are called zoonotic diseases.
[00:47.84]These diseases can be problematic because the human body is not
[00:52.44]designed to defend against this kind of invasion.
[00:57.40]The host animal species often shows no signs of disease.
[01:03.60]This is because the animal’s body has already learned to deal with the virus.
[01:10.08]However, when such viruses or other disease-causing microorganisms
[01:16.88]jump from animals to humans, the effects can be deadly.
[01:22.64]Many scientists believe bats were the first carriers
[01:27.20]of the coronavirus that causes COVID-19.
[01:31.12]The animals have been linked to past outbreaks of coronaviruses in humans.
[01:38.20]Studies have shown that bats are natural hosts to many other viruses as well.
[01:45.88]One example is the Ebola virus,
[01:49.40]which caused deadly outbreaks in Western Africa.
[01:53.80]The Nipah virus, also carried by bats,
[01:57.84]has caused human outbreaks across South and Southeast Asia.
[02:03.80]Health experts say Nipah is serious enough
[02:08.16]to possibly cause a “serious epidemic.”
[02:12.68]The coronavirus family of viruses also includes diseases
[02:18.04]such as Severe Acute Respiratory Syndrome (SARS)
[02:21.80]and Middle East Respiratory Syndrome (MERS).
[02:25.08]Scientists have discovered that SARS and MERS
[02:30.40]were caused by viruses that started in bats,
[02:34.48]with other animals serving as intermediate hosts.
[02:39.92]The only other animals coming close
[02:42.84]to hosting as many viruses as bats are rodents.
[02:47.68]There are about 2,300 species of rodents,
[02:53.12]making up about 40 percent of all mammals.
[02:58.00]While rodents are believed to have more viruses as a group,
[03:03.52]bats host more viruses per species.
[03:08.08]Scientists believe the many types of species in both groups
[03:14.56]can create more possibilities for viruses.
[03:18.80]Some bats live in forests while others are found in caves.
[03:25.64]Most eat insects such as beetles, moths and mosquitoes.
[03:32.80]Some bats eat fruit, nectar, seeds and pollen from flowers.
[03:40.12]Others eat small animals such as birds, fish, frogs and lizards.
[03:48.28]A small number of bats feed on blood.
[03:52.72]Bats also provide many benefits to the environment.
[03:58.44]Some bats play important parts in plant pollination and spreading seeds.
[04:04.72]Bats can pollinate more than 500 species of plants
[04:09.88]including avocados, bananas, dates and mangoes.
[04:16.24]In Southeast Asia, durian, a highly valued fruit,
[04:21.84]can be effectively pollinated only by the Dawn Bat.
[04:26.92]In this way, bats are important economically for people.
[04:33.04]Insect-eating bats also serve
[04:36.40]to naturally control insect populations.
[04:40.28]These bats eat millions of insects at night,
[04:44.72]including some that cause severe damage to crops.
[04:49.76]I’m Jonathan Evans. 更多听力请访问21VOA.COM