When you touch a doorknob handled by someone ill with the flu or a cold, for example, you can pick up the germs he or she left behind. If you then touch your eyes, mouth or nose before washing your hands, you may become infected.
Some germs rely on insect carriers — such as mosquitoes, fleas, lice or ticks — to move from host to host. These carriers are known as vectors. Mosquitoes can carry the malaria parasite or West Nile virus. Deer ticks may carry the bacterium that causes Lyme disease. Disease-causing germs can also infect you through contaminated food and water. This mechanism of transmission allows germs to be spread to many people through a single source. Escherichia coli E. While anyone can catch infectious diseases, you may be more likely to get sick if your immune system isn't working properly.
This may occur if:. In addition, certain other medical conditions may predispose you to infection, including implanted medical devices, malnutrition and extremes of age, among others. Most infectious diseases have only minor complications. But some infections — such as pneumonia, AIDS and meningitis — can become life-threatening. A few types of infections have been linked to a long-term increased risk of cancer:.
In addition, some infectious diseases may become silent, only to appear again in the future — sometimes even decades later. For example, someone who's had chickenpox may develop shingles much later in life. Prepare food safely. Keep counters and other kitchen surfaces clean when preparing meals. Cook foods to the proper temperature, using a food thermometer to check for doneness. For ground meats, that means at least F 71 C ; for poultry, F 74 C ; and for most other meats, at least F 63 C.
Also promptly refrigerate leftovers — don't let cooked foods remain at room temperature for long periods of time. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission.
This content does not have an English version. This content does not have an Arabic version. Overview Infectious diseases are disorders caused by organisms — such as bacteria, viruses, fungi or parasites.
Request an Appointment at Mayo Clinic. Viruses can pass from person to person in various ways, including:. There are thousands of species of fungi, some of which cause disease in humans. These conditions are contagious and can spread through person-to-person contact.
A study in Trends in Microbiology found that fungal pathogens are evolving a capacity for memory. They can use signals in the body to anticipate imminent threats to their survival, against which they can then prepare themselves.
These single cell organisms cause disease in their host. They infect other organisms to survive and reproduce. Protist pathogens affect plants and food crops. Foods containing protists can cause dysentery , which is an infection of the intestines that causes diarrhea. Protist pathogens can also be parasitic and live in other organisms, such as mosquitoes.
Protists cause malaria through mosquito bites. Parasitic worms, also known as helminths, are large enough for people to see with the naked eye, and they can live in many areas of the body. Some worms include:. Pathogens can cause a variety of different diseases, with some being more severe than others.
Human bodies are nutrient-rich and can provide a pathogen with an ideal environment in which to grow and multiply. The severity of infections that pathogens cause will vary. Some infections may be mild, while others can be life threatening. For example, the common cold is a mild viral infection compared with the lethal Ebola virus disease.
Some scientists believe that viruses are not living organisms. Some reasons for this include :. About species of fungi are pathogenic to humans. As with bacteria and viruses, they can have a significant effect on human health. Protozoa are responsible for most protist diseases. Protozoa are single cell microorganisms that feed on other microorganisms, organic tissues, and debris.
Protist diseases include:. Parasitic worms cause many diseases, which include :. There are millions of different fungal species on Earth.
Just or so are known to cause sickness. Fungi can be found just about everywhere in the environment, including indoors, outdoors, and on human skin. They cause infection when they overgrow.
Fungi cells contain a nucleus and other components protected by a membrane and a thick cell wall. Their structure can make them harder to kill.
Some new strains of fungal infections are proving to be especially dangerous , such as Candida aurus , and have prompted more research into fungal infections. Parasites are organisms that behave like tiny animals, living in or on a host and feeding from or at the expense of the host. Though parasitic infections are more common in tropical and subtropical regions, they can occur anywhere.
They can be spread several ways, including through contaminated soil, water, food, and blood, as well as through sexual contact and via insect bites. Viruses can cause a number of infections, many of which are contagious. Examples of viral diseases include:. Pathogens have the ability to make us sick, but when healthy, our bodies can defend against pathogens and the illnesses they cause.
Treatments are available for many of the illnesses caused by the different types of pathogens. Bacterial meningitis is a serious disease that can lead to paralysis, stroke, and even death. Read more on how to treat and prevent it.
Airborne diseases spread easily and are difficult to prevent. Learn more about the types of airborne diseases and how to protect yourself. The 5-second rule gives you permission to eat something that fell on the floor, as long as it's picked up within five seconds. But is it safe? Boils are caused by bacteria building up in a hair follicle and pushing up to the surface of the skin.
Recurring boils happen for a number of reasons…. Certain E.
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