Eli5: how do scientists know that someone can spread disease before showing symptoms of the disease? For example, being able to spread the flu before any symptoms start.
In: Biology
A pathogen only causes symptoms when it either negatively impacts function, or the body impacts function to respond to it. Simply because a pathogen hasn’t impacted function, to an extentent that is noticable no less, doesn’t mean that pathogen can’t be transmitted.
Take the flu for example. The flu is spread primarily through water vapor emitted from the lungs. That process can occur any time after the virus has reached the lungs and started reproducing. However, there will be a point when the viral content of your lungs is neither sufficient to cause an immune response, nor enough to cause a bad cough. During this period, the host is contagious, but not symptomatic.
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