Cytomegalovirus infection after transplant (NORD)

Cytomegalovirus, or CMV, is an enveloped double-stranded DNA virus that belongs to the herpesviridae family. It's one of the most common viruses to cause severe infection in individuals undergoing transplantation of bone marrow or solid organs like the liver or kidney. It can affect almost every organ in the body resulting in encephalitis, retinitis, pneumonia, hepatitis, gastroenteritis, and of course, transplant rejection.

In the post-transplantation period, the recipient is usually given immunosuppressive medication in order to prevent their immune system from recognizing the transplanted tissue as foreign and causing rejection. However, one major disadvantage of this approach is that the weakened immune system is unable to protect the body against pathogens like CMV.

CMV can be transmitted through blood and other body fluids like saliva, genital secretions, and urine of an infected person; or from the transplanted organ itself!

During the primary infection, the virus usually invades the epithelial cells, like those that make up the oral, GI, or urinary mucosa; and starts to multiply. CMV damages the infected cells by breaking down the cytoskeletons which maintain the cell structure. That results in enlarged cells with intranuclear viral inclusion bodies, giving it the typical owl's eye appearance.

CMV also infects monocytes in the blood and sets up a latent infection, which means that the virus remains dormant for long periods of time. The dormant virus can reactivate at times when the immune system weakens, causing disease.

Most of the time primary infection occurs years before the transplant with resultant  reactivation of the virus during immunosuppressive therapy. In about 25% of transplants primary infection occurs which is usually much more severe compared to reactivation.