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What is an infection?

Infectious diseases are illnesses resulting from microorganisms called pathogens invading and proliferating in the body and causing symptoms.Pathogens include viruses, bacteria, fungi, and parasites, which differ in size and structure.
Most of them are so small that they are invisible to the naked eye and are always present around us in the air, water, soil,
and animals.

Types of pathogens and
routes of infection

Types of pathogens

  • Parasites

    Parasites

    Roundworms,
    lice, etc.

  • Fungi

    Fungi

    Mold, yeast,
    etc.

  • Bacteria

    Bacteria

    E. coli,
    cholera bacteria,
    etc.

  • Viruses

    Viruses

    Influenza virus
    Etc.

Source: Gakken Manga de Wakaru Series 176:
Secrets of Immunity

The main pathogens that cause infections are viruses and bacteria. The differences between the two pathogens are as follows.

Size Structure Way of
proliferating 		Pathogens
(and infections caused) 		Pharma­ceuticals
Virus -So small that they cannot be seen by the naked eye. They are approximately 10 to 200 nanometers in size, one-tenth to one-hundredth the size of bacteria.
-Not visible with an optical microscope, but visible with an electron microscope.		 Non-enveloped viruses Capsid/Nucleic acid enveloped viruses Envelope/Nucleic acid -Do not have cell membranes. Since they have no cells, they enter human or animal cells and make copies of themselves to proliferate. -Influenza virus (the flu)
-Coronavirus (COVID-19)
-Norovirus (infectious gastroenteritis [food poisoning])
-Measles virus (measles)
-Rubella virus (rubella)
-Herpes virus (herpes zoster)
-HIV (AIDS), etc.		 Antibiotics do not work.
Bac-
teria 		-So small that they cannot be seen by the naked eye, ranging in size from about 0.5 to 3 micrometers.
-Visible under an optical microscope.		 -Have cell membranes. Cell wall/Flagellum/Nucleoid/Cilium/Ribosome/Cell membrane Since they are cells, they make copies of themselves (through cell division) to proliferate. -Streptococcus pneumoniae (pneumococcal infection)
-E. coli (infectious gastroenteritis [food poisoning])
-Mycobacterium tuberculosis (tuberculosis)
-Bacillus tetani (tetanus)
-Plague bacteria (The Plague)
-Cholera bacteria (cholera)
-Bordetella pertussis (whooping cough)
-Dysentery bacillus (dysentery), etc.		 Antibiotics are effective.

Source: Gakken Manga de Wakaru Series 176:
Secrets of Immunity

Infection routes

The route by which pathogens enter the body is called the "route of infection," and the 4 main routes are described below.

  • 1.
    Airborne infection

    Inhalation of airborne bacteria or viruses causes infection.

  • 2.
    Droplet infection

    Inhalation of spray (droplets) from coughing or sneezing causes infection.

  • 3.
    Contact infection

    Infections are spread by touching an infected person, or touching something with bacteria or viruses on it.

  • 4.
    Vector-borne infection

    Transmitted through contaminated water, food, blood, animals, or insects.

History of
Infectious Diseases

Timeline

For all of history, infectious diseases have spread throughout the world and claimed many lives.
Let us unravel the history of the battle between humankind and infectious diseases.

Year
Event
About
3,000
years ago
Tuberculosis and smallpox epidemics occur in ancient Egypt.
2nd
century
Malaria epidemic in ancient Rome.
6th
century
A plague epidemic breaks out in Constantinople.
8th
century
Smallpox epidemic in Japan (Nara Period).
14th
century
A plague epidemic sweeps across Europe, killing more than one-third of the population.
16th
century
Smallpox is introduced from Europe to Mexico and Central America, resulting in a pandemic.
17th
century
A plague epidemic breaks out in London (England).
Leeuwenhoek discovers bacteria.
1796
Edward Jenner successfully inoculates against smallpox.
1810s
A worldwide cholera epidemic begins.
1882
Robert Koch discovers Mycobacterium tuberculosis.
1883
Robert Koch discovers the cholera bacteria.
1885
Louis Pasteur develops a rabies vaccine.
1894
Alexandre Yersin and Shibasaburo Kitasato discover the plague bacteria.
1897
Kiyoshi Shiga discovers dysentery bacillus.
1905
Fritz Schaudinn discovers syphilis treponema.
1909
Charles Jules Henri Nicolle discovers that epidemic typhus is transmitted by lice.
1910
Paul Ehrlich and Sahachiro Hata develop Salvarsan, a treatment for syphilis.
1918
A worldwide epidemic of Spanish flu (influenza) begins.
1928
Alexander Fleming discovers the first antibiotic, penicillin.
1933
Wilson Smith and others discover the influenza virus.
1944
Selman A. Waksman and others develop streptomycin, a treatment for tuberculosis.
1980
The World Health Organization (WHO) declares the eradication of smallpox.
1980
onward
AIDS (Acquired Immune Deficiency Syndrome) becomes widespread in the world.
2003
SARS (Severe Acute Respiratory Syndrome) epidemic occurs.
2009
A novel influenza pandemic occurs worldwide (through 2010).
2012
MERS (Middle East Respiratory Syndrome) epidemic occurs.
2019
onward
A novel coronavirus infection epidemic spreads worldwide.

Source: Gakken Manga de Wakaru Series 176: Secrets of Immunity

  • 1.Smallpox

    An infectious disease caused by the smallpox virus.Infection causes high fever, rashes all over the body, and in severe cases, death.

  • 2.The
    plague

    An infectious disease caused by the plague bacteria and transmitted to humans when infected fleas suck their blood. It is also called the Black Death because the skin turns black and the person dies.

  • 3.Cholera

    It is caused by drinking water or eating food contaminated with cholera bacteria.
    Symptoms include severe diarrhea and nausea.

  • 4.Tuberculo
    -sis

    An infectious disease caused by Mycobacterium tuberculosis.
    When it develops, it causes cold-like symptoms such as cough, phlegm, and fever.

  • 5.Polio

    It is an infectious disease caused by the poliovirus. Children under 5 years of age are most often affected, and in severe cases, paralysis of the hands and feet may develop. In Japan, it is also called "pediatric paralysis".

  • 6.Measles

    An infectious disease caused by the measles virus, occurring most often in children. Symptoms include fever, runny nose, severe cough, bloodshot eyes, and red, itchy rash.

  • 7.Viral
    hepatitis

    An infectious disease caused by the hepatitis virus.The disease causes gradual breakdown of liver cells and can lead to cirrhosis and liver cancer.

  • 8.COVID-19

    An infectious disease caused by a novel coronavirus.When the disease develops,
    it causes fever, fatigue, and other cold-like symptoms, and in severe cases, it leads to pneumonia.

Source: Gakken Manga de Wakaru Series 176:
Secrets of Immunity

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