Primary Infection

Antibodies attacking a virus, artwork
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What is a Primary Infection?

A primary infection refers to the first time you are exposed to (and infected by) a pathogen. During a primary infection, your body has no innate defenses against the organism, such as antibodies. Antibodies take time to develop after you have been exposed to an infectious organism, although they can help to prevent future infections with the same disease. Vaccination, before exposure to a disease, works by causing your body to produce antibodies.

Those antibodies then improve the body's ability to fight off a primary infection.

For diseases such as genital herpes, which persist in the body, the primary infection occurred at the time when you were initially exposed to the herpes simplex virus. That's true whether or not you had an outbreak at that time. This is important to understand, since different herpes blood tests have differing abilities to pick up new, primary infections. Some are much better at detecting long-standing or recurring infections. Herpes IgM tests are a better marker of early primary infections.Herpes IgG tests are better at detecting chronic or recurrent infections.

Similarly, early, primary HIV infections may not show up on blood tests. That's because HIV tests usually look for antibodies rather than virus. Therefore, someone may test negative even though they still have enough virus in their bodies to infect their partners.

Early HIV transmission, which takes place during the time before people begin to test positive, is a significant public health problem. Many such infections take place. Some of them could be avoided with more consistent use of universal screening

Note: The term secondary infection has a specific meaning that does not refer to the second time you are infected with an organism.

Also Known As: initial infection, early infection

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