When it comes to what viruses there are, you may count them all: Ebola, rabies, smallpox, HIV ...... These viruses are basically related to human diseases.

However, there are very few viruses that actually consider humans as their only host, such as smallpox virus and polio virus, the "culprit" of polio.

Viruses can infect all forms of life; in addition to plants and animals, they infect bacteria, archaea, and even viruses themselves. Viruses are everywhere, and in staggering numbers - 10 million viruses per milliliter of seawater.

In the long struggle with viruses, humans have also enriched their own knowledge of viruses.

One peculiar virus, carried by 90 percent of the population but causing no disease, is the haplo-cyclic virus, which was first discovered in 1997 in a Japanese hepatitis patient but has never been confirmed to be associated with any disease. Studies have shown that this is a virus that is found all over the world and infects people of all ages. There is no significant association between carrying the virus and age, gender or personal history of disease.

However, there is a correlation between the amount of the virus in the human body, and the level of suppression of the immune system in people: in immunosuppressed people, the viral load is higher. Therefore, this virus can be used as a marker of immune suppression. For example, a patient receiving an organ transplant needs to suppress the patient's immune system with drugs to reduce the rejection reaction. At this point, the fine ring virus acts as a sensitive detector that can be used to detect the effectiveness of the drug.