Infectious diseases are disorders that are often caused by organisms such as bacteria, viruses, fungi or parasites. Organisms live in our bodies and are typically harmless, however, certain conditions may cause the organisms to spread infectious diseases that can be spread from person to person.
Some infectious diseases can be spread by insects or animals.
These health threats are called zoonotic infectious diseases, and recent outbreaks include COVID-19 and Ebola.
“In the age of COVID-19, it is understandable that many people may not realize how many outbreaks of other infectious diseases are caused by complex, intertwined ecological and socioeconomic conditions,” lead author Patrick Stephens, an associate research professor at the University of Georgia’s Odum School of Ecology in Athens says.
His team analyzed 4,400 zoonotic disease outbreaks worldwide since 1974. They identified the 100 largest, all of which infected thousands to hundreds of thousands of people. These were compared with 200 outbreaks that included 43 or fewer cases.
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Causes of infectious diseases
1. Water
Contaminated water is the leading cause of large-scale outbreaks of infectious diseases that can be transmitted from animals to people, researchers say.
Water contamination was the most common cause of large outbreaks and the second most common cause of smaller ones. Examples of these water-associated diseases include hepatitis E, typhoid and dysentery.
Protect yourself from waterborne illnesses with the following tips from the CDC:
- Flushing your faucets and showerheads if they have not been used recently
- Cleaning, disinfecting, and maintaining all devices that use water
- Communicating with your water utility
- Keeping private water sources safe
- Checking with your building manager, owner or landlord
2. Viral pathogens
Large outbreaks were also much more likely to be caused by viral pathogens such as SARS coronavirus, influenza virus and Japanese encephalitis virus.
3. Travel and zoonotic pathogens
“We know that factors like exposure to wild mammals, habitat disruption, international trade and travel and contact with contaminated food and water are important considerations,” Stephens says in a university news release.
“Perhaps two-thirds of future infectious disease outbreaks are expected to be caused by zoonotic pathogens, and the number of these diseases is growing worldwide,” he adds. “Our research is an extremely important first step to better understand global variation in the drivers of outbreaks.”
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Smaller vs larger outbreaks
Smaller outbreaks were associated with food contamination, local livestock production and human-animal contact.
The researchers also found that large outbreaks tended to be caused by a greater variety of factors than small outbreaks, according to findings recently published in the journal Philosophical Transactions B.
Symptoms, treatment and prevention
Signs and symptoms of infectious diseases vary depending on the organism causing the infection, but often include fever and fatigue. Mild infections often respond to rest and home remedies. However, life-threatening infections may require hospitalization.
General signs and symptoms common to a number of infectious diseases include:
- Fever
- Diarrhea
- Fatigue
- Muscle aches
- Coughing
Many infectious diseases, such as measles and chickenpox, can be prevented by vaccines. Frequent and thorough hand-washing will also help protect you from most infectious diseases.
When to see a doctor
If you experience any of the following, you should consult with your doctor:
- Have been bitten by an animal
- Are having trouble breathing
- Have been coughing for more than a week
- Have severe headache with fever
- Experience a rash or swelling
- Have an unexplained or prolonged fever
- Have sudden vision problems