Pathogens are organisms that cause disease in other organisms. The most common pathogens are bacteria, viruses, and fungi. In addition to common ailments such as a cold or cough, pathogens are also responsible for more serious illnesses like food poisoning, HIV, and tuberculosis. All pathogens act differently, and some are easy to get rid of, while others are much more difficult. While treatment varies, simple things like washing your hands can often prevent the spread of serious, pathogen-caused illness.


Viruses are unique pathogens that can only replicate inside a living host. They are composed of genetic material surrounded by protein and use biological mechanisms inside their host to replicate themselves. Viruses are smaller than bacteria and can mutate during replication, which is one reason treating a viral infection is so difficult: the virus can change from host to host. That said, many viruses are host-specific, meaning they are usually capable of infecting only humans or specific animal species.

Virus protein genetics sitox / Getty Images



Bacteria are diverse, single-celled living organisms that can reproduce. They are found almost everywhere on the planet. While many are harmful and cause a variety of diseases, some bacteria are beneficial, such as those that live in the gut and help with digestion. There are five basic bacterial shapes: comma-shaped, rod-shaped, spherical-shaped, spiral-shaped, and flagellated.

Bacteria Petri dish AndreasReh / Getty Images



There are more than 140,000 types of fungus in the world. These pathogens can live in soil or water while others have a symbiotic or parasitic relationship with plants or animals. Some are beneficial — for example, certain fungi produce chemicals used in statin drugs that lower cholesterol. Others, though, cause serious problems when they come in contact with the human body.

Fungus Fungal Infection BeholdingEye / Getty Images


Hepatitis B Virus

One of the most common viral pathogens in the world is hepatitis B, which is caused by the hepatitis B virus or HBV. Most people with hepatitis B recover completely, but infants and children are more likely to get a chronic infection that can lead to significant liver damage. Vaccines are available to prevent contraction, but there is no cure. HBV is passed from one person to another through sexual contact, sharing of needles or accidental needle sticks, or mother to baby in utero.

Hepatitis B Liver alexskopje / Getty Images


Herpes Simplex Virus

Herpes simplex virus is categorized into two types: herpes simplex 1 or HSV-1 and HSV-2. Both are prevalent worldwide. HSV-1 infects about 3.7 billion people and is primarily spread through oral contact; HSV-2 has around 417 million cases and is transmitted through sexual contact. Both types of this virus are lifelong conditions; most infections are asymptomatic, however, with occasional outbreaks consisting of blisters at the infection site.

Herpes Simplex Virus Hailshadow / Getty Images



Staphylococcus is a bacteria commonly found on the skin. Normally, these pathogens do not cause any problems or only lead to minor skin infections. When staph enters the body, though, it can cause life-threatening infections in the heart, lungs, or bloodstream. The symptoms depend on where the infection occurs and can include boils, impetigo, cellulitis, toxic shock syndrome, blood poisoning, and infection of the heart, lungs, and brain. Staph is also the most common cause of food poisoning. Antibiotics are the most common treatment, but some strains have become antibiotic-resistant.

Staph Staphylococcus Bacteria ksass / Getty Images



There are multiple varieties of streptococcal bacterial pathogens, but they do not all causes infections in humans. Group c typically only affects horses and group H only canines. In humans, group A is commonly found on the skin and in the throat. It can cause scarlet fever, strep throat, bacteremia, and necrotizing fasciitis or flesh-eating disease. Group B strep lives in the GI and genital tracts and can cause significant problems when it moves to other areas of the body. This migration is responsible for sepsis, meningitis, and pneumonia. Most strep infections are treatable with antibiotics.

Strep Streptococcus Infection cdascher / Getty Images



One of the most common fungal pathogens causes ringworm, a skin infection that appears as a red, ring-shaped rash that expands outward. The inside of the ring may be clear or have scales or red bumps. Ringworm spreads from direct contact with another infected person or animal. It is closely related to jock itch and athlete's foot and commonly responds to topical antifungal creams.

Ringworm Itchy Fungus Tharakorn / Getty Images



Another common fungal pathogen is Candida. Normally, Candida lives in the mouth, nose, gut, and skin without causing any problems but in people with certain conditions, it can cause thrush, an infection of the esophagus, throat, and mouth. Thrush appears as white patches in the mouth and throat, with associated redness and pain. Thrush usually responds to oral anti-fungal medications.

Candida Thrush Candidiasis designer491 / Getty Images


Preventing Illness

Medication can treat some pathogens that cause disease, while other infections can lead to chronic, life-long illness. To prevent infection in the first place, it is important to practice good hygiene, including handwashing, covering your mouth and nose when you cough or sneeze, and not sharing utensils, cups, or household items. Cook foods thoroughly and avoid cross-contamination. Practicing safe sex is essential, too. There are are also vaccinations available for protection from many of these pathogens.

Wash Hands Good Hygiene AfricaImages / Getty Images


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