Caliciviridae

Electron micrograph of a calicivirus

The Caliciviridae is a family of viruses that infect a wide range of hosts, including humans and animals. Members of this family are known for their small, non-enveloped, icosahedral structure and single-stranded RNA genome. The family includes several genera, with notable members such as the Norovirus and Sapovirus, which are significant causes of gastroenteritis in humans.

Structure

Diagram of the calicivirus structure

Caliciviruses are characterized by their small, round, non-enveloped virions, typically 27-40 nm in diameter. The capsid is composed of 180 copies of a single protein, arranged in an icosahedral symmetry. The surface of the virion displays a distinctive cup-shaped depression, which is a hallmark of the family and gives the family its name (from Latin "calyx" meaning cup).

Genome

The genome of caliciviruses is a single-stranded, positive-sense RNA molecule, approximately 7.4 to 8.3 kilobases in length. It is organized into three open reading frames (ORFs). ORF1 encodes a polyprotein that is processed into non-structural proteins, including the RNA-dependent RNA polymerase. ORF2 encodes the major capsid protein, and ORF3 encodes a minor structural protein.

Replication

Calicivirus replication occurs in the cytoplasm of the host cell. The virus attaches to the host cell surface receptors and is internalized. The viral RNA is released into the cytoplasm, where it is translated into viral proteins. The RNA-dependent RNA polymerase synthesizes a complementary negative-sense RNA strand, which serves as a template for the production of new positive-sense RNA genomes. These genomes are packaged into new virions, which are then released from the host cell to infect new cells.

Pathogenesis

Caliciviruses are known to cause a range of diseases in humans and animals. In humans, noroviruses are the leading cause of viral gastroenteritis, characterized by acute onset of vomiting and diarrhea. Sapoviruses also cause gastroenteritis, primarily in children. In animals, caliciviruses can cause diseases such as feline calicivirus infection in cats and rabbit hemorrhagic disease in rabbits.

Epidemiology

Caliciviruses are highly contagious and can spread rapidly in closed environments such as cruise ships, nursing homes, and schools. Transmission occurs primarily through the fecal-oral route, either by direct contact with an infected person or by consuming contaminated food or water. The viruses are resistant to many common disinfectants, which contributes to their ability to cause outbreaks.

Prevention and Control

Preventing calicivirus infections involves good hygiene practices, such as regular handwashing, especially after using the bathroom and before eating. In outbreak settings, thorough cleaning and disinfection of contaminated surfaces are crucial. Vaccines are available for some animal caliciviruses, such as the feline calicivirus, but there are currently no vaccines for human caliciviruses.

Related pages

• Norovirus
• Sapovirus
• Feline calicivirus
• Rabbit hemorrhagic disease virus

Calicivirus particles under electron microscopy