Caliciviridae

A family of viruses that includes important pathogens of humans and animals

The Caliciviridae is a family of viruses that are non-enveloped, positive-sense single-stranded RNA viruses. This family includes several genera that are significant pathogens in humans and animals, causing a range of diseases from gastroenteritis to systemic infections.

Structure

File:Calicivirus structure.png

Diagram of a calicivirus structure.

Caliciviruses are small, round viruses with a diameter of approximately 35-40 nm. They have a simple icosahedral capsid structure composed of 180 copies of a single capsid protein. The capsid displays a characteristic "cup-shaped" depression, which is a hallmark of the family and gives the family its name (from the Latin "calyx" meaning cup).

Genome

The genome of caliciviruses is a single-stranded, positive-sense RNA molecule of approximately 7.4 to 8.3 kilobases in length. The genome 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, VP1.
• ORF3 encodes a minor structural protein, VP2, which is involved in the assembly and stability of the virus particle.

Replication

Caliciviruses replicate in the cytoplasm of host cells. The virus attaches to specific receptors on the host cell surface and enters the cell via endocytosis. Once inside, the viral RNA is released and 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 responsible for a variety of diseases in humans and animals. The most well-known human pathogens in this family are the Norovirus and Sapovirus, which cause acute gastroenteritis. In animals, caliciviruses can cause diseases such as feline calicivirus infection in cats and rabbit hemorrhagic disease caused by Lagovirus.

Norovirus

File:Norovirus virions.png

Electron micrograph of norovirus particles.

Noroviruses are a leading cause of viral gastroenteritis worldwide, affecting people of all ages. They are highly contagious and can spread rapidly in closed environments such as cruise ships, hospitals, and schools. Symptoms include nausea, vomiting, diarrhea, and abdominal pain, typically lasting 24 to 48 hours.

Sapovirus

Sapoviruses also cause gastroenteritis, primarily in children. The symptoms are similar to those caused by noroviruses but are generally milder.

Vesivirus

The Vesivirus genus includes the Feline calicivirus, which is a common pathogen in domestic cats. It causes respiratory disease, oral ulcers, and sometimes systemic infections.

Lagovirus

Lagoviruses are known for causing rabbit hemorrhagic disease, a highly contagious and often fatal disease in rabbits. This disease is characterized by fever, lethargy, and bleeding.

Epidemiology

Caliciviruses are distributed worldwide and can infect a wide range of hosts. Human caliciviruses, particularly noroviruses, are a major cause of foodborne illness. They are transmitted via the fecal-oral route, often through contaminated food or water, or by direct person-to-person contact.

Prevention and Control

Preventing calicivirus infections involves good hygiene practices, such as regular handwashing, proper food handling, and sanitation. In healthcare settings, isolation of infected individuals and thorough cleaning of contaminated surfaces are important to prevent outbreaks.

Related pages

• Norovirus
• Viral gastroenteritis
• Feline calicivirus
• Rabbit hemorrhagic disease