Once invasion is successful and pathogens gain access to the blood stream, they can cause various illnesses ending in **–emia**, including:
- Bacteremia
- Pyemia
- Viremia
- Toxemia
- Septicemia

Illnesses Caused by Pathogens in The Blood

Once adhesion is successful, invasion can proceed. Invasion involves the wide spread of a pathogen throughout local tissues or the body. Pathogens may produce exoenzymes or toxins, which serve as virulence factors that allow them to colonize and damage host tissues as they spread deeper into the body. 

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There are four stages of pathogenesis. The pathogen must be able to gain entry to the host, travel to the location where it can establish an infection, evade or overcome the host’s immune response, and cause disease to the host.
- exposure (contact)
- adhesion (colonization)
- invasion
- infection.

Stages of Pathogenesis

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An encounter with a potential pathogen is known as exposure or contact. The food we eat and the objects we touch are ways that we can be exposed to potential pathogens. For a pathogen to cause disease, it needs to be able to gain access into host tissue. An anatomic site through which pathogens can pass into host tissue is called a portal of entry. 

Exposure

Following the initial exposure, the pathogen adheres at the portal of entry. Adhesion refers to the capability of pathogens to attach cells of the body using adhesion factors. Different pathogens use various mechanisms to adhere to the cells of the body.

Adhesion

Invasion

Following invasion, successful multiplication of the pathogen leads to infection. Infection is the final stage of pathogenesis.

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