"Virus particles" refers to extremely minuscule components of a virus that are too small to be seen by the naked eye. They are responsible for infecting cells and causing diseases like the flu or COVID-19. Full definition
The puppy will shed virus particles in enormous amounts for 3 weeks, but it's possible even up to 6 weeks. (pethelpful.com)
Once this happens, the cell makes new virus particles. (pethelpful.com)
Cats can become infected by direct contact with an infected cat or with objects that have been contaminated with virus particles such as food and water dishes or litter boxes. (rachelebaker.com)