An infectious disease refers to the disease that is caused by the invasion of pathogenic microbial agents found in the atmosphere, water, soil, animals and humans. Pathogenic microbial agents that cause infection include viruses (flu viruses, Noroviruses etc), Rickettsia (scrub typhus), bacteria (Enterohemorrhagic E. coli), parasites (pinworm), fungi (athletic foot). Infection can be communicable and non-communicable. The former refers to infectious diseases that can be communicated from one person to another; while the latter is the opposite.

Epidemical infectious diseases (pandemic)

Communicable infectious diseases have broken out in different times of history. These include the Black Death which killed nearly 30% of Europeans in the Mediaeval Age, the new-type flu called Spanish Flu which took the life of over 50 million people in 1918 etc.

HIV Yoshiwara Namiko
Professor
National Institute of sanitation control

There are many more on the list, such as AIDS which emerged in 1981 and kills about 3 million people a year; SARS which broke out in 2002 and killed 774 people within 9 months; and the recently emerged new-type infectious diseases known as the Emerging Infectious Diseases. At present, there are over 30 of them.

On the other hand, tuberculosis (TB) is an ancient infectious disease found in Egyptian mummies. Though it has been controlled with antibiotics, a new type of antibiotics-resistant TB has emerged as a result of repeated use of antibiotics. Today, over 2 billion people in the world are infected by this new-type of TB, and about 3 million were killed a year. Therefore, TB is a serious infectious disease at the moment. Infectious diseases which recur are called recurrent infectious diseases. Recurrent infectious diseases threaten both poorly developed and industrialized countries.

Severity of the pandemic of emergent new-type flu

Infectious diseases are like invisible killers breaking out into pandemics that have killed countless lives. As we are unable to overcome all infectious diseases, once a very powerful infectious disease breaks out, it will shortly turn into a pandemic.

Type A
Takeshi Sanekata, PhD

The 「 new-type influenza will probably develop into a pandemic infectious disease. The Spanish Flu was a pandemic that evolved from a weak H1N1 flu virus. Though it was not powerful it killed 50 million people in the world in 1918.

After communicating to humans, the new-type flu that evolved from the bird flu virus H5N1 will become a communicable infectious disease among people.

According to the estimates made by Lowy Institute for International Policy of Australia in February 2006, the worst case of H5N1 is 142 million casualties and US$4.4 trillion in damages (approx. ¥514 trillion) worldwide.

If it is true, 21 million people, 1.5% of the population, will be killed in Japan alone.
The forecast shows that man-to-man infection of the H5N1 virus will break out in the very near future. To modern people who travel by airplane, the avian flu may develop into a pandemic all of a sudden.
We may expect rescue or mitigation from other places for regional disasters like typhoons and earthquakes. If it is a pandemic, there is no foreign rescue or mitigation because it will become a disaster to all countries in the world.。