Infectious Diseases: Causes and Symptoms.
                     INFECTIOUS DISEASES: 
CAUSES AND SYMPTOMS
Introduction
• Infectious diseases are disorders caused by organisms such as bacteria, viruses, fungi or 
parasites. 
• Many organisms live in and on our bodies. They're normally harmless or even helpful. But 
under certain conditions, some organisms may cause disease.
Source: www.mayoclinic.org
Expose to infectious diseases 
• Some infectious diseases can be passed from person to person. Some are transmitted by 
insects or other animals. And you may get others by consuming contaminated food or 
water or being exposed to organisms in the environment.
Source: www.mayoclinic.org
Symptoms
• Each infectious disease has its own specific signs and symptoms. General signs and 
symptoms common to several infectious diseases include:
– Fever
– Diarrhea
– Fatigue
– Muscle aches
– Coughing
Source: www.mayoclinic.org
When to consult a doctor
• Seek medical attention if you:
– Are having trouble breathing
– Have been coughing for more than a week
– Have severe headache with fever
– Have unexplained or prolonged fever
– Have sudden vision problems
Source: www.mayoclinic.org
Causes
• Infectious diseases can be caused by:
– Bacteria: These one-cell organisms are responsible for illnesses such as strep 
throat, urinary tract infections and tuberculosis.
– Viruses: Even smaller than bacteria, viruses cause a multitude of diseases ranging 
from the common cold to AIDS.
Source: www.mayoclinic.org
Causes cont.
• Infectious diseases can be caused by:
– Fungi: Many skin diseases, such as ringworm and athlete's foot, are caused by 
fungi. Other types of fungi can infect your lungs or nervous system.
– Parasites. Malaria is caused by a tiny parasite that is transmitted by a mosquito 
bite. Other parasites may be transmitted to humans from animal feces.
Source: www.mayoclinic.org
Direct contact
• Person to person: Infectious diseases commonly spread through the direct transfer of 
bacteria, viruses or other germs from one person to another. 
• Animal to person: Being bitten or scratched by an infected animal even a pet can make 
you sick and, in extreme circumstances, can be fatal. 
Source: www.mayoclinic.org
Indirect contact
• Disease-causing organisms also can be passed by indirect contact. Many germs can linger 
on an inanimate object, such as a tabletop, doorknob or faucet handle.
Source: www.mayoclinic.org
Food contamination
• 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. 
Source: www.mayoclinic.org
Risk factors
• 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:
– You're taking steroids or other medications that suppress your immune system, 
such as anti-rejection drugs for a transplanted organ
– You have certain types of cancer or other disorders that affect your immune system
Source: www.mayoclinic.org