Viremia is a condition in which viruses are present in the bloodstream. From the point of view of a virus, this is great news, because it means that the virus has access to a highly efficient distribution system which will spread it throughout the body. From the point of view of the owner of the body, of course, viremia is not good news at all.
Viruses can enter the bloodstream in a wide variety of ways, ranging from slipping into an open wound to being introduced by a puncture wound. Once in the bloodstream, the viruses can start to replicate, and as they replicate, they will spread through the body. This can create a situation known as secondary viremia, in which the virus has colonized other areas of the body and it is feeding new copies of itself back into the bloodstream.
A number of viruses are passed specifically through the blood, with the human immunodeficiency virus (HIV) being a very well known example. Other viruses will make the leap into the bloodstream if they see an opportunity to do so. For example, a viral infection of the respiratory tract could enter the bloodstream through cuts in the mouth.
This condition is diagnosed by taking a blood sample and examining it in a lab. The blood can be run against viral antibodies which will react if a virus is present and flag the blood, and it can also be examined under a microscope to look for copies of the virus. Microscopy can also allow a lab technician to identify a virus when a test is not available.
The treatment for viremia is administration of antiviral drugs to kill the virus. Not all viruses can be treated with medications; some have resisted the best efforts of drug developers. If no antiviral drug is available, the focus is on managing the patient's symptoms and keeping the patient as strong and healthy as possible in the hopes that the immune system will fight off the virus.
People can have chronic viral illnesses, in which they always have some copies of a virus in their blood. In these cases, doctors monitor the patient's viral load, looking at how many copies are present. If the load is low, it suggests that the patient's body is keeping the virus in check. If it is high, it means that the patient is not controlling the virus, or that secondary viremia is occurring.