Nobody enjoys getting sick, but in the case of most infections, the period of illness is short-lived. Some pathogens, however, have the ability to come back later on, sometimes even years after the initial infection, to once again wreak havoc on the body. In a recent YouTube video, the team at SciSchow gave us a recap of some of the most common “sleeper-agent pathogens.”

Varicella zoster, the virus that causes chickenpox, is perhaps the most common latent virus. Although there is now a chickenpox vaccine, most of us born before it was available are familiar with the itchy spots of the chicken pox. Although the spots do heal, the virus never leaves our body, and in some cases can come back with a vengeance in the form of shingles.

Measles is another virus that can lie dormant for years. If you are lucky enough to survive the initial measles infection, the virus can in rare cases reappear years later in the form of subacute sclerosing panencephalitis (SSPE), a serious condition that affects the central nervous system. Symptoms of SSPE include cognition and motor difficulties, coma, and even death. So if you needed another reason to get your child vaccinated, there you go.

As explained in the video, it's not just viruses that can lie dormant; bacteria do this as well.A well-known, although thankfully not popular virus infection that behaves this way is anthrax. Anthrax powder is actually a spore which protects the virus, allowing it to survive throughout extreme conditions, only to be reactivated once it is inside the warm moist body of a host. Thankfully there are treatments for anthrax infections, but if the infection is left untreated for too long, death is quite possible.

Mycobacterium tuberculosis, the bacteria that causes tuberculosis, can also lie dormant for years. According to the World Health Organization, one-third of the world’s population is estimated to be infected with the TB bacteria but show no symptoms. However, in about 5 to10 percent of these individuals, the bacteria can be reactivated years later, causing them to develop TB years after their initial infection.

To see other diseases that are able to lay low and hide out for years before causing disease, watch the SciShow video.

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Measles Vaccine Thwarts Other Infectious Diseases: Study: Read Here