Infectious Diseases1
Despite advance in technology, one of the biggest threats to human survival comes from primitive life forms.
Infectious diseases are caused by microorganisms, such as bacteria, viruses and parasit.
These organisms have no access to education or technology, but they present a huge challenge to humanity.
That's because they are adaptable.
Just as a adaptability has helped humans survive, it makes more difficult to control infectious disease.
As conditions change, the organisms which cause these diseases adapted and become stronger.
what is the opposite of primitive?...advanced.
There are several kinds of infectious diseases.r
Bacterial infections, such as pneumonia(英[njuːˈməʊniə]肺炎), are caused by bacteria.
These infections can be treated by antibiotics(抗生素), which kill the bacteria.
Viral infections are caused by viruses(病毒), such as the influenza(流感=flu) virus.
These can sometimes be prevented by vaccines, such as the flu vaccines(疫苗).
An example of a parasitic(寄生的) infection is malaria（疟疾）.
Malaria is caused by parasites(寄生虫) transmitted to humans by infected(传染，使携带病菌)mosquitoes.
Once inside the body, the parasites can be difficult to kill or control.
And of course, the parasites are also adaptable.
What do antibiotics(抗生素) do?.... They attack and kill bacteria.
One of the biggest threats to human survival comes from primitive life forms.
Antibiotics attack and kill bacteria.
Viral infections are caused by viruses , such as the influenza virus.
How serious are infectious diseases?
Consider what happened in 1918, the influenza pandemic(流行病).
It started in the fall of 1918 with what seemed to be something no more serious than the common cold.
In the next 2 years however, it infected a fifth of the world's population.
In fact, it turned out to be the most deadly epidemic in history, killing between 20 and 40 million people.
In influenza virus that caused it was much stronger than previous influenza viruses.
Its mortality(死亡率) rate was 2.5% compared to 0.1% in previous influenza epidemics.
It struck quickly and without mercy sometimes killing people within hours.
Schools and businesses close in many places, and people were masked to prevent transmission of the virus through the air.
What was unusual about this pandemic was that it was most deadly for people aged 20-40, rather than the elderly and young children.
What was unusual about this pandemic?
....it was most deadly for people aged 20-40.
What did people do to prevent transmission of the virus through the air？
...They wore masks.
Consider what happened in 1918, the influenza pandemic
It started in the fall of 1918 with what seemed to be something no more serious than the common cold.
Once inside the body, the parasites can be difficult to kill or control.
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