Papilloma and Polyoma Viruses | Sherris Medical Microbiology, 6e | AccessBiomedical Science

INTRODUCTION

Historically, the papillomaviruses and polyomaviruses have been discussed together in microbiology textbooks, lumped under the category of papovaviruses. Papovaviruses are now split into two separate families: Papillomaviridae and Polyomaviridae. The unique characteristics that distinguish them from each other are shown in Table 19–1.

TABLE 19–1Characteristics of Papilloma and Polyoma Viruses

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TABLE 19–1 Characteristics of Papilloma and Polyoma Viruses

VIRUS SIZE	HUMAN SUBTYPES	TRANSMISSION	DISEASE	TREATMENT	PREVENTION
Papilloma 55 nm	HPV-1–3, 10	Close contact, occupational exposure, public shower/swimming pool	Skin warts	Topical cytotoxins or surgical removal
Papilloma 55 nm	HPV-6, 11	Close contact, sexual contact	Oral, laryngeal papillomatosis Genital warts (condylomata accuminata)	Treatment of laryngeal lesions is complex, varied	Vaccine
Papilloma 55 nm	HPV-16, 18 (several others are also increasingly implicated)	Sexual	Cervical, other neoplasias	May be removed by electrocautery	Vaccine
Polyoma 45 nm	BKV	Respiratory or oral (?)	Hemorrhagic cystitis in transplant recipients; postrenal transplantation nephropathy	Cidofovir may be used, but is not proven
Polyoma 45 nm	JCV	Respiratory/oral (?)	Progressive multifocal encephalopathy (PML)	Reduce immune suppression

BKV, BK virus; HPV, human papillomavirus; JCV, JC virus.

PAPILLOMAVIRUSES

VIROLOGY

Papillomaviruses are small, naked capsid (unenveloped), double-stranded, circular DNA viruses exhibiting cubic (icosahedral) symmetry of 55 nm in diameter (Figure 19–1). The icosahedral capsid comprises two capsid (structural) proteins, L1 (major capsid protein) and L2 (minor capsid protein). The 8 kb, circular, double-stranded DNA genome of human papillomavirus (HPV) encodes seven or eight early genes (E1-E8) and two late structural capsid genes (L1 and L2). The early genes are required for regulation of viral replication and transformation. The virus does not encode any polymerases and, therefore, is dependent on host cell transcription and replication machinery. Based on DNA homology, there are over 100 genotypes of HPVs. Papillomaviruses cause epidermal papillomas and warts in a wide range of higher vertebrates. Different members of the group are generally species specific. For example, bovine papillomaviruses and HPVs infect only the hosts reflected in their names. In some cases, lesions caused by these agents can become malignant, and the role of these agents as causes of certain human cancers is increasingly recognized. Papillomaviruses have been difficult to grow in tissue culture, and most of the virologic information has been derived from molecular and gene expression studies.

FIGURE 19–1.

Electron micrograph of human papillomavirus (HPV) particles isolated from a plantar wart (×300 000). (Reproduced with permission from Connor DH, Chandler FW, Schwartz DQ, et al: Pathology of Infectious Diseases. Stamford CT: Appleton & Lange, 1997.)