Infectious mononucleosis. Light micrograph of blood cells obtained from an inflamed lymphatic ganglion in a case of infectious mononucleosis (glandular fever). Caused by Epstein-Barr virus (EBV), infectious mononucleosis (mono) is transmitted through saliva. It is often referred to as the 'kissing disease'. It is characterised by enlarged, atypical lymphocytes, a type of white blood cell. These are hyperbasophilic lymphocyte cells (red). The other cells here are red blood cells (orange).