Papilloma and Polyoma viruses

They are in the Papovavirus family. They cause some easily identifiable diseases.

Human Papillomavirus or HPV

It is widely known for causing cervical cancer and is the reason behind routine cervical pap smear screenings. E6 and E7 proteins of HPV are essential for oncogenesis. E6 binds to and targets p53 for degradation by ubiquitin ligase. E7 binds to the Rb tumor suppressor protein family and interferes with the function of E2F transcription factors. Infection is thought to occur in cells of the basal layer of stratified epithelia where viral genomes are established as episomes and are replicated synchronously with chromosomal DNA. Infection is transmitted by skin to skin and genital contact.

Clinical features: HPV types 1,2,3 and 4 cause benign warts on hands and feet. Types 6 and 11 cause laryngeal papillomas and genital warts or condyloma acuminata which may become malignant. Types 16 and 18 are most commonly associated with cervical cancer, anal cancer, penile cancer and some cases of oral cancer. HPV 31, 33 and 45 are also associated with cervical cancers. Remember that histologically it is a squamous cell carcinoma.

Laboratory diagnosis of HPV infections: Koilocytes are vacuolated squamous cells which can be seen in lesions. DNA hybridization can also be used to detect viral DNA. E 6 and 7 mRNA detection assays are being used recently to predict risk of developing cervical carcinoma.

Polyoma Virus

Important ones are JC and BK viruses. They become latent in immunocompetent individuals after primary infection. They have been loosely associated with oncogenesis and also autoimmune disorders. JC virus causes progressive multifocal leukoencephalopathy in AIDS and other immunodeficiencies. BK virus causes hemorrhagic cystitis in bone marrow transplant recipients, transplant nephropathy causing renal allograft failure.

Diagnosis is made by quantification of polyoma virus DNA in blood, CSF and urine. Urine can be screened for typical “decoy” cells which are infected epithelial cells with intranuclear inclusions. They can be detected in urine cytology by Papanicolaou stain or phase contrast microscopy. Brain or renal biopsy specimens will show glassy, basophilic intranuclear viral inclusions.