What Is an Infectious Disease?
According to the World Health Organization, an infectious disease is any disease caused by pathogenic microorganisms, like bacteria, parasites, or viruses, that can be spread directly or indirectly between people. The name may sound alarming – the idea of contagious conditions that spread through microorganisms implies serious illnesses that can cause widespread problems – but the reality is a little more benign; the common cold or the flu, for example, are considered infectious diseases. However, there are a number of infectious diseases that can be extremely contagious and challenging to treat, so proper detection is critically important.
The nature of a particular disease can play a large role in treatment options and containment. In general, most infectious diseases come in one of three forms: bacteria, viruses, or parasites.
Simply put, pathogenic bacteria refers to any one-celled bacterial organism that can cause disease. There is no parameter on severity or intensity; any bacteria that has the ability to transmit a disease of any kind qualifies. Despite the significant number of infectious diseases that can affect humans, there are thought to be fewer than 100 strains of bacteria that contribute to these kinds of conditions.
Bacteria can be transmitted in numerous ways, including in the air, by touch, through sexual activity, and in a cut or opening in the skin. Bacterial diseases come in many forms, ranging from largely inconsequential to deeply serious, with common conditions including:
- Tuberculosis, caused by the bacterium Mycobacterium tuberculosis
- Pneumonia, caused by the bacteria Streptococcus and Pseudomonas
- Foodborne illnesses, caused by bacteria like Salmonella and Shigella
Many bacterial pathogens can be treated with antibiotics like penicillin and amoxicillin. In addition, bacteria can be killed with the use of antiseptic disinfectants, like bleach.
A viral pathogen refers to any disease-causing virus, or a microscopic infectious agent that replicates only within the cells of other living organisms. Viruses are extremely common, and can cause influenza, colds, Ebola, AIDS, and SARS. Viruses can also be causative agents, contributing to initial diseases that can eventually evolve into more serious conditions. Some forms of virus can cause chronic or long-term illnesses that are challenging or impossible to treat. Transmission is generally either vertical, from mother to child, or horizontal, from person to person.
Viruses cannot be killed with antibiotics but must be treated with antiviral drugs or prevented via vaccines. These kinds of conditions are often harder to treat than bacterial infections as more complex biological processes are required to address the presence of a virus.
A parasitic pathogen refers to a parasite that can cause disease in humans. Parasites come in many forms in nature, but only several are able to infect humans. Parasite transmission most commonly occurs via insect bites or contaminated food and water and are most common in tropical and sub-tropical locations. Unlike viruses and bacteria, parasites are generally not contagious between humans. While there are no vaccines for parasites currently, most can be treated easily with antiparasitic drugs. Common parasites include: