A pathogen is defined as an organism causing the disease to its host, with the severity of the disease symptoms referred to as virulence. Pathogens are taxonomically widely diverse and comprise viruses and bacteria as well as unicellular and multicellular eukaryotes. Every living organism is affected by pathogens, including bacteria, which are targeted by specialized viruses called phages.
The number of viruses and bacteria on earth is staggering and they occupy essentially every environment. A liter of surface seawater typically contains in excess of ten billion bacteria and 100 billion viruses. The number of viruses on Earth is estimated to be around 1031, which corresponds to roughly ten billion times the number of stars in the universe. An average human is made up of about 30 trillion cells but carries a similar number of bacteria, mostly in the gut.
The vast majority of viruses and bacteria we are exposed to have no negative effect and some can even be beneficial, though a tiny fraction of these can severely affect our health. Specifically, about one in a billion microbial species is a human pathogen. Indeed, approximately 1400 human pathogens have been described, whereas it has been estimated that there are one trillion microbial species on Earth, the vast majority of which remain uncharacterized.
Modes of Transmission
Most people work outside their homes. This increases the risk of exposure to pathogens that cause infectious diseases. Pathogens can be transmitted through direct or indirect transmission. Direct transmission can occur through direct contact or droplet spread. Indirect contact occurs when pathogens are transferred through airborne transmission, vehicles, or vectors.
- Direct Contact: Direct contact refers to contact with surfaces that contain pathogens. Direct contact includes person-to-person contact. For example, a worker who has coughed into their hand can directly transfer pathogens by shaking hands with their coworkers.
- Droplet Spread: Droplets from a cough, sneeze, or talking can spread an infectious disease. This type of transmission requires people to be within close proximity. For example, droplets from sneezing can spray over a few feet and fall on a person who is not infected.
- Airborne Transmission: This type of transmission occurs when pathogens are carried by dust or droplet nuclei that are suspended in the air. This can cause pathogens to remain in the air for longer periods of time and travel longer distances than droplets. For example, if an ill person coughs, the pathogens from their cough can remain suspended in the air if they fall onto dust or droplet nuclei.
- Vehicles: A vehicle is an object or material that can carry pathogens. Common vehicles are water, food, and blood. Pathogens can infect a person when they touch or ingest a vehicle. For example, a person may contract the stomach flu if they consume food that was not handled with care.
- Vectors: A vector is any insect or animal capable of transmitting pathogens known to cause disease in humans. Mosquitoes, fleas, and ticks are examples of vectors.
In the case of workplace hygiene, the most common modes of transmission are direct contact, droplet spread, and airborne transmission.