Why does disease spread

Spread through the air by aerosol Some infections are spread when an infected person talks, breathes, coughs or sneezes tiny particles containing infectious agents into the air. Examples of airborne spread diseases: chickenpox measles tuberculosis TB Spread through faeces and then the mouth faecal-oral spread Some infections are spread when microscopic amounts of faeces poo from an infected person with symptoms or an infected person without symptoms a carrier are taken in by another person by mouth.

The faeces may be passed: directly from soiled hands to the mouth indirectly by way of objects, surfaces, food or water soiled with faeces. Examples of diseases spread from faeces: Campylobacter infection Cryptosporidium infection Giardia infection hand, foot and mouth disease hepatitis A meningitis viral rotavirus infection Salmonella infection Shigella infection thrush viral gastroenteritis worms Yersinia infection.

Spread by skin or mucous membrane contact Some infections are spread directly when skin or mucous membrane the thin moist lining of many parts of the body such as the nose, mouth, throat and genitals comes into contact with the skin or mucous membrane of another person. Examples of diseases spread by skin or mucous membrane contact: chickenpox cold sores herpes simplex infection conjunctivitis hand, foot and mouth disease head lice molluscum contagiosum ringworm scabies school sores impetigo Staphylococcus aureus infection warts.

Spread through blood or other body fluids Some infections are spread when blood or other body fluids for example for example, urine, saliva, breastmilk, semen and vaginal secretions from an infected person comes into contact with: the mucous membranes the thin moist lining of many parts of the body such as the nose, mouth, throat and genitals , such as through kissing, breast-feeding or sexual contact or the bloodstream of an uninfected person, such as through a needle stick injury or a break in the skin.

Examples of diseases spread through blood or other body fluids: hepatitis B - blood, saliva, semen and vaginal fluids hepatitis C - blood human immunodeficiency virus HIV infection - blood, semen and vaginal fluids, breastmilk cytomegalovirus CMV infection - saliva, semen and vaginal fluids, urine, etc. Sexual contact means: genital to genital oral to genital genital to anal.

Examples of sexually transmitted infections: Chlamydia infection genital herpes genital warts gonorrhoea hepatitis B human immunodeficiency virus HIV infection non-specific urethritis NSU pubic lice crabs syphilis trichomoniasis. Spread through food or water These diseases result from ingestion of water or a wide variety of foods contaminated with disease-causing germs or their toxins. Examples of food or waterborne diseases: botulism Campylobacter infection cholera Cryptosporidium infection haemolytic uraemic syndrome Listeria infection Salmonella infection Shigella infection typhoid and paratyphoid Yersinia infection.

Spread from a mother to her unborn child Some infections can be spread through the placenta from a mother to her unborn child or during delivery, or both. Examples of diseases spread from a mother to child in this way: chickenpox congenital cytomegalovirus hepatitis B rubella.

Diseases where person-to-person spread occurs rarely, if ever Some infectious diseases are almost never spread by contact with an infected person. Examples of diseases spread by contact with animals : cat-scratch disease hydatid disease psittacosis Q fever rabies toxoplasmosis. Examples of diseases spread by insects, and in the examples listed below, specifically by mosquitoes: Barmah Forest virus infection dengue fever malaria Ross River virus infection.

Examples of diseases spread by contact with water or soil : amoebic meningitis legionella infection - Legionella pneumophila and Legionella longbeachae tetanus. Related information You can search through to find related information. Services Documents Links. You've Got What? Preventing Disease And Infection Provides information on taking care of yourself and ways you can improve your health. Emergency departments are for emergencies Is it really an emergency? More about Emergency Departments.

More about Mental health support. 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. What are superbugs and how can I protect myself from infection?

Share on: Facebook Twitter. Show references Facts about infectious disease. Infectious Disease Society of America. Accessed May 29, Jameson JL, et al. Approach to the patient with an infectious disease. In: Harrison's Principles of Internal Medicine. Not only are people and goods traveling farther and at a greater volume and speed than any other time in history, but people are also more likely to live in densely populated urban environments.

More than half of the world's population now lives in cities, and just about every country on the planet is becoming more urbanized. Global health researchers have called the trend "an emerging humanitarian disaster. That's because most people don't live in relatively clean cities like Washington, DC, or Munich. Cities can be perfect breeding grounds for disease to spread. Consider the ongoing Zika outbreak in Brazil.

Not only was this an old virus in a new country that caught health officials off guard but Brazil's many cities also happened to be extremely hospitable to the virus.

The Aedes aegypti mosquito, which carries Zika, thrives alongside people. As Gubler wrote in this paper , "[It's] a highly domesticated urban mosquito that prefers to live with humans in their homes, feed on humans and lay eggs in artificial containers made by humans.

Across Latin America, million people nearly one in five live in slums. Many of these slums lack a clean and steady water supply, so people keep buckets filled with water around their homes — ideal mosquito breeding grounds. Not to mention the fact that air conditioning isn't common, leaving bodies and homes warm and making them even more hospitable to the disease-carrying bugs. Globally, unprecedented population growth following World War II has meant that not only are more people living in cities than ever before but populations are also exploding into areas that were once inhabited only by other animals.

Anytime humans interact with animals, there's a chance that a pathogen could make the leap across species and sicken them. Today about three-quarters of new emerging infectious diseases are spread to humans by animals — a health threat that came with the rise of agriculture. As the historian Yuval Harari writes in his sweeping history of humankind, Sapiens : "Most of the infectious diseases that have plagued agricultural and industrial societies such as small pox, measles, and tuberculosis originated in domesticated animals and were transferred to humans only after the Agricultural Revolution.

Today, this is still the case, whether it's chicken sellers sitting on the streets of China risking exposure to bird flu or hunters in Guinea eating bushmeat that could be infected with the Ebola virus.

When new viruses strike impoverished or weakened health systems, they have a much greater chance of thriving and killing people. The '15 Ebola epidemic offers another illustrative example here. Every American infected with Ebola during that period survived. The same wasn't true for the affected West Africans, 11, of whom died. The stark difference in outcomes had to do with money and access to health care: Patients with Ebola can be kept alive through tried-and-true health measures — kidney dialysis, IV rehydration, antibiotics — and hour hospital care.

While that's possible at the National Institutes of Health in Bethesda, Maryland, it wasn't in many of the places where Ebola struck, like Gueckedou, Guinea.

We're seeing a similar story play out right now with an outbreak of yellow fever in Angola. More than 2, people have been infected with the virus, and have died, in an ongoing outbreak.

This outbreak could have been prevented. While there's no cure for yellow fever, a vaccine was developed in , and it's highly effective. Within three or four weeks after receiving the shot, nearly all people are protected from the virus. But in order for the vaccine to really prevent outbreaks, many people need to be immunized. That's not happening in many parts of Africa, including Angola, where the virus is endemic.

Starting in , the World Health Organization, with support from Gavi an international organization focused on improving vaccine access , ramped up efforts to make sure at-risk communities got vaccinated. But many countries on the continent still have vaccine coverage rates that are much too low to make the vaccine effective. So because of poverty and weak health systems, even when we have the technology to stop disease spread, we don't get to use it.

But we sure as heck can prevent the pandemic. When we think about health, experts say, we need to start thinking about how environmental factors like climate change can matter as much as — or sometimes even more than — our personal behaviors. They argue that "[t]he implications of climate change for a global population of 9 billion people threatens to undermine the last half century of gains in development and global health," including the spread of disease vectors.

For example, Zika, dengue, and chikungunya are all spread by the Aedes mosquito.