Infectious diseases can be caused by many pathogens, including bacteria, viruses, fungi, and parasites that may cause illness and disease. For humans, the transmission of pathogens may occur in a variety of ways: spread from person to person by direct contact, water or foodborne illness, or aerosolization of infected particles in the environment and through insects (mosquitoes) and ticks.
Signs and symptoms and treatment of infectious diseases depend on the host and the pathogen.
Anyone can get an infectious disease. People with a compromised immune system (an immune system that doesn’t work at full strength) have a greater risk for certain types of infections. Those at higher risk include:
People with suppressed immune systems, such as those going through cancer treatment or who have recently had an organ transplant
Those who are unvaccinated against common infectious diseases
People travel to at-risk areas where they may be exposed to mosquitoes that carry pathogens such as malaria, dengue virus and Zika viruses.
Infectious diseases are extremely common worldwide. Some infectious diseases strike more often than others. For instance, in the United States, 1 out of every 5 people is infected with influenza (flu) virus each year.
What complications are associated with infectious diseases?
Many infectious diseases cause complications. These can range from mild to severe. For some conditions, complications may include wheezing, skin rash, or extreme fatigue. Mild complications usually disappear as the infection resolves.
Certain infectious diseases may cause cancer. These include hepatitis B and C (liver cancer), and human papillomavirus (HPV) (cervical cancer).
SYMPTOMS AND CAUSES
What are the symptoms of infectious diseases?
Symptoms of infectious disease are particular to the type of disease. For example, symptoms of influenza include:
- Muscle aches and headache
Other infectious diseases, such as Shigella, cause more serious symptoms, including:
- Bloody diarrhea
- Dehydration (lack of fluid)
You may experience one or several symptoms of an infectious disease. It’s important to see a doctor if you have any chronic (ongoing) symptoms or symptoms that get worse over time.