Infectious diseases are disorders caused by organisms such as bacteria, viruses, fungi or parasites. Many harmless organisms live in and on the human body; however, under certain conditions, some organisms may cause disease.

Some infectious diseases can be passed from person to person. Others are transmitted by bites from insects or animals and some are acquired by ingesting contaminated food or water or through exposure to organisms in the environment.

Symptoms may vary relative to the organism that is causing the infection; however, symptoms commonly include fever and fatigue. Mild infections may respond to rest and home remedies, while other infection may be life threatening and require medical care.

Vaccines can prevent many infectious diseases, including measles and chickenpox. Frequent and thorough hand washing can also help to prevent infectious diseases.



Symptoms of each infectious disease vary. However, the general symptoms common to numerous infectious diseases include:


  • Fever
  • Diarrhea
  • Fatigue
  • Muscle aches



Possible causes of infectious disease include:


  • Bacteria: One-cell organisms that cause illnesses such as strep throat, tuberculosis and urinary tract infections.
  • Viruses: Viruses can cause a wide range of diseases from the common cold to AIDS.
  • Fungi: Fungi cause many skin diseases such as ringworms and athlete’s foot. Other types of fungi can infect the lungs or nervous system.
  • Parasites: Parasites are transmitted through insect and animal bites or animal feces and can cause diseases such as Malaria.


Direct contact

Infectious diseases can be spread through direct contact in three ways:


  • Person to person: Transmission of bacteria or viruses from person to person can occur if the infected person touches, coughs on or kisses on another person who is not infected. The same germs can also spread through the exchange of body fluids during sexual contact or a blood transfusion.
  • Animal to person: Being bitten or scratched by an infected animal can cause illness or be fatal in extreme circumstances. Handling animal waste such as cleaning a cat’s litter box can also be hazardous.
  • Mother to unborn child: A woman can pass germs that cause infectious diseases to her unborn child during pregnancy.


Indirect contact

Germs can also be passed through indirect contact because germs can linger on objects such as a tabletop, doorknob or faucet handle.


Insect bites

Some germs are passed through insect carriers such as mosquitoes, lice, fleas or ticks that move from host to host. The carriers are known as vectors. For instance, deer ticks carry the bacterium that causes Lyme disease, while mosquitoes may carry the malaria parasite or the West Nile virus.


Food contamination

Infectious diseases can occur from germs that live in contaminated food and water. The mechanism of transmission involves one single source that allows germs to spread to many people.


Risk factors

Anyone can get infectious diseases; however, the risk may be higher if the immune system is not functioning properly. The reason for this may be:


  • Use of steroids or other medications that suppress the immune system such as anti-rejection medications.
  • HIV or AIDS diagnosis
  • Certain types of cancer or other disorders that affect the immune system.
  • Other medical conditions such as implanted medical devices, malnutrition among others.



Most infectious diseases have minor complications. However, some infections such as pneumonia, meningitis and AIDS can become life threatening. Several types of infections are associated to long-term increased risk of cancer:


  • Human papillomavirus (HPV) is associated with cervical cancer
  • Helicobacter pylori is linked to stomach cancer
  • Epstein-Barr virus is associated with lymphoma



The following tips may help reduce the risk of infections:


  • Frequent hand washing: Especially before and after preparing food, before eating and after using the toilet.
  • Avoid touching the eyes, nose or mouth before washing hands
  • Getting vaccinated against common infections and diseases
  • Staying home when sick
  • Preparing food properly
  • Practicing safe sex
  • Avoid sharing personal items such as toothbrush, comb and razor
  • Inquire about vaccinations when travelling to other countries