Sapovirus

Sapovirus is spread via the fecal/oral route. Infected individuals expel more than ${\displaystyle 10^{9}}$ particles/gram of feces or vomit. Particles from the infected individual remain viable for years, and an infectious dose can be as few as 10 particles. Contamination of work surfaces, hands, and etc. can cause a vast number of new infections. Infection may occur if the particles are inhaled, such as when the particles are aerosolized when those who are infected vomit, or when the toilet is flushed after an infected individual vomits. Other forms of transmission include the excessive handling of foods by an infected individual (this most commonly occurs in a restaurant setting), consumption of shellfish that lived in waters contaminated with infected fecal matter, and the ingestion of water that has been contaminated.[9]

After an incubation period of 1–4 days, signs of illness start to arise. Symptoms of sapovirus are very similar to those of norovirus. The most common symptoms are vomiting and diarrhea. However, additional symptoms may occur, including chills, nausea, headache, abdominal cramps, myalgia, and fever though it is very rare. While patients frequently start to show symptoms after the 1–4 day incubation period, there have been cases in which an individual is asymptomatic. Although the individual does not show symptoms, they are still capable of spreading the virus through the general mode of transmission, which is the oral-fecal route.[3]

General sanitary hygiene is the most important method of preventing sapovirus. This can be done by thoroughly washing hands after using the restroom and before eating/preparing food. Contaminated surfaces should be cleaned with disinfectant and or solutions containing bleach. Other preventative measures include avoiding contact and sharing drinks/food with infected individuals.

There is no specific medication for individuals infected with sapovirus. Sapovirus cannot be treated with antibiotics because it is not a bacterial infection. Treatments include symptom support such as rehydrating the individual.[9]

The exact replication cycle of sapovirus has not been determined; however, it is thought to have the same or similar cytoplasmic replication cycle that other caliciviruses display. The cytoplasmic replication cycle is as follows:

1. Entry into the host cell is achieved by attachment to host receptors, which mediates endocytosis of the virus into the host cell.
2. Uncoating and release of the viral genomic RNA into the cytoplasm.
3. VPg is removed from the viral RNA, which is then translated into a processed ORF1 polyprotein to yield the replication proteins.
4. Replication occurs in viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).
5. The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
6. Subgenomic RNA translation gives rise to the capsid protein and VP2.
7. Assembly of new virus particles and release by cell lysis."[10]

Using electron microscopy, the sapovirus was first seen in diarrheic stool samples from the United Kingdom in 1977 and was soon known as a gastroenteritis pathogen. While the virus was first seen in the United Kingdom, "the prototype strain of the genus Sapovirus was from another outbreak in Sapporo, Japan in 1982."[3] The first complete genome of sapovirus was interpreted from the Manchester strain in the United Kingdom in 1993. Formerly, sapoviruses were called "Sapporo-like viruses"; however, in 2002, they were changed to the species Sapporo virus, genus Sapovirus, in the family Caliciviridae. "Currently, the family Caliciviridae consists of five established genera: Sapovirus, Norovirus, Lagovirus, Vesivirus, and Nebovirus."[3]

Norovirus is most commonly associated with sapovirus. Norovirus and sapovirus genomes are very closely related; the distinction between the two can only be made from the differences in their coding strategy and reading frames. Noroviruses, along with sapoviruses, are the most common cause of gastroenteritis and therefore show the same symptoms as each other.[13]

Astrovirus, like sapovirus, causes gastroenteritis in children and the elderly, especially those who are immunocompromised. While sapovirus has two ORFs, Astrovirus has three. Astrovirus also has 6 recombinant strains. Astrovirus replicates within the cytoplasm and propagates readily in the GI tract.[9]

Rotavirus, like norovirus, astrovirus, and sapovirus, causes gastroenteritis. Rotavirus, however, is much more lethal, causing 37% of deaths in children with diarrhea and 215,000 deaths worldwide.[14]

Sapoviruses have been identified in bats, California sea lions, dogs, pigs and mink.[15][16]

• ICTV Report: Caliciviridae
• Viralzone: Sapovirus