Infectious diseases are caused by the invasion of pathogenic microorganisms in the environment (including the air, water, soil, and animals) into the human body. Many invisible microorganisms (bacteria, viruses, fungi (molds, yeasts, etc.) are present around us. Among them, the microorganisms that cause infectious diseases are called pathogens. Also, parasitic diseases caused by parasites such as ascaris and pinworms are one of the infectious diseases.

In addition, parasitic disease caused by parasites such as roundworm and helminth is one of the infectious diseases

Infection is caused by the invasion, establishment, and multiplication of pathogens in the human body. Infection may cause symptoms (overt infection) or may not cause obvious symptoms (subclinical infection). Latently infected people are often problematic because they are unknowingly carriers (carriers) who shed the pathogen and are likely to spread the infection as a source of infection.
It is important to know where (source) and how (path) invisible pathogens and parasites invade.

[On the Source of Infection].

People (infected individuals), animals, and insects infected with pathogens, and foods and foods contaminated with pathogens are sources of infection. These include foods and foods touched by carriers and infection animals, such as bodily waste, vomitus, blood, and body fluids from infected individuals and infected animals. Isolating or disinfecting the source of infection is an effective measure.
However, some carriers (such as those with bacterials and viruses) who are not infected with a pathogen may not be able to take adequate measures.

[On the Route of Infection].

For an infection to occur, a pathogen must enter humans from a source. Blockade of the route of infection is therefore an important measure.
In everyday life, the three main routes of infection to be cautioned are contact (oral) infection, droplet infection, and airborne infection (droplet nucleus infection).

Contact infections are infections caused by direct contact with the skin or mucous membranes or by the attachment of pathogens through contact with surfaces such as hands, door handles, handrails, toilet seats, switches, and boutons. It invades the body mainly through the mouth through food, objects, fingers, and dirt and vomit contaminated with pathogens. Infectious gastroenteritis caused by noroviruses, rotaviruses, enterohemorrhagic Escherichia coli (O157), Salmonella, or Staphylococcus aureus is the most common cause.
Sexually transmitted diseases, such as HIV-associated AIDS and chlamydia, can cause contact infections that can be transmitted through the blood, body fluids, and mucous membranes.
Animals and insects can also be transmitted as vectors, such as rabies and toxoplasma, which are acquired by biting, scratching, or touching the body or feces, and malaria and Japanese encephalitis, which are acquired by biting mosquitoes, fleas, and ticks.
Droplet infections are infections caused by inhalation of pathogens in the splashes or splashes (droplets) that have been splashed by coughing, sneezing, or conversation. Droplets are more than 0.005mm in diameter and contain water, so they are said to reach about 1 to 2 m from the source of infection. Therefore, wearing a mask or taking a distance from the source of infection is an effective measure. Influenza, cold syndrome, mumps, and rubella are among the most common diseases caused by droplet infection.
Particles with a diameter of 0.005 mm or less on which water contained in droplets has been vaporized are called droplet nuclei, which float in the space and spread widely. Pathogens also float with dust and spread by inhalation are called airborne or droplet nuclear infections. Noroviruses, measles virus, and Mycobacterium tuberculosis are transmitted by airborne infection.
Other infections are transmitted directly from the mother to the fetus or newborn through the placenta or breast milk (vertical transmission).