CLASSIFICATION

The family Parvoviridae consists of small, single-stranded DNA viruses, divided into three genera of the sub-family Parvovirinae.

Erythroviruses include B19 and related simian viruses.

Parvovirus is the classification for any other autonomous virus in the family.

Dependoviruses are adeno-associated viruses and cannot replicate without the co-infection of another virus.

 

VIRION AND GENOME STRUCTURE

The single strand of DNA present in members of the family Parvoviridae is usually the negative strand, but some viruses contain a mixture of both positive and negative nucleic acid chains. The strand is packaged in an 18-26nm icosahedral nucleocapsid. The icosahedron has a T value equal to 1, giving it a simple structure containing 60 molecules of capsid proteins.

VP2 (60kDa) is the main capsid protein.

VP1 (80kDa) and VP3 are present in lesser amounts.

The genome of the parvovirus is very simple and consists of two genes, one for replication and the other for the capsid protein, aligned in the same orientation so only one strand must be transcribed. The DNA is in a linear formation with palindromic sequences at the end, which fold back to form a stable hairpin turn structure. The hairpin is used as a primer for DNA replication - the 3' prime end elongates to form a double stranded intermediate that can continue replication. Replication occurs in the nucleus of the host cell, but due to the inability of parvoviruses to induce cells to enter the S phase, they can only replicate in already dividing cells.

Nucleotide sequence of parvovirus genome depicting hairpin turn, palindromic sequences, and linear form. http://www.tulane.edu/~dmsander/WWW/335/Parvoviruses.html

 

HISTORY

Parvoviruses were first apparent in feline populations in the beginning of the 1900's, when various epidemics of panleukopenia, congenital cerebellar ataxia and enteritis occurred and spread to the ranch mink in the 1940's. The agent of feline panleukopenia virus (FPV) was determined to be the same in both species. With the identification of a similar rat virus (RV) and hamster virus (H-1) in 1959, the three were declared to be related. The recognition of adenovirus stock contaminants as defective parvoviruses (AAV's) in the 1960's led to the formal acceptance of the "Small Virus" family in 1970.

More parvoviruses continue to be identified since the classification of the family. Canine parvovirus (CPV) spread across the world in the 1970's, causing myocarditis and enteritis in puppies and dogs. Aleutian disease, a chronic immune complex disease in mink was discovered in the 1980's to be caused by a parvovirus. RA-1, a parvovirus causing spinal and skeletal deformities in mice, was isolated in 1984.

B19, the only autonomous virus affecting humans, was found in the 1970's in false-positive assays for Hepatitis B. The blood bank code of a viremic donor was B19, giving the virus its name. In the early 1980's, the virus was further linked to several diseases including fifth disease, a common childhood exanthem, polyarthropathy, transient aplastic anemia, and erythroblastosis fetalis. 30% of the adult population carry antibodies for the virus, which is a common exposure in childhood. It was discovered that viruses similar to B19 may cause infections in simians after an outbreak of severe anemia in cynomolgus monkeys in the early 1990's.


This webpage was constructed by Kat Hoffman and Diane Tseng for Dr. Robert Siegel's Human Biology class (HumBio115a), Humans and Viruses, at Stanford University during autumn quarter 2005.