Calicivirus - Replication, Pathogenesis, Clinical manifestation, Transmission, Lab Diagnosis
Replication of Calicivirus
The replication pattern of Calicivirus is similar to that of Picornavirus as they are of the same family. Replication occurs exclusively in the cytoplasm with the release of viral particles on cell destruction/lysis.
Pathogenesis of Calicivirus
Calicivirus is a non-invasive virus and infection is typically limited to the mucosal cells of the intestinal tract.
Infection is characterized by damage to the microvilli in the small intestine, causing malabsorption. It mediates changes in the gastric mucosa and delays gastric emptying causing vomiting. No histopathological lesions are seen in the gastric mucosa.
Clinical manifestation of Calicivirus
The incubation period of infection by Calicivirus is around 12-72 hours. The illness lasts for 1-4 days, with the excretion of a detectable number of virus particles for up to two weeks. In severely immunocompromised cases, persistent excretion of caliciviruses can take place.
Clinical manifestations of calicivirus include ‘gastric flu’ (i.e. diarrhea, headache, fever, aching limbs, and malaise), projectile vomiting, nausea, abdominal pain, etc. Stools do not contain blood or mucus. Symptoms are mild and rarely require hospital admission. But during outbreaks among elderly/infant patients with underlying problems, IV rehydration may be necessary
Epidemiology of Calicivirus
Epidemiological studies have confirmed that the calicivirus is worldwide in distribution.
Mode of transmission
Following are the mode of transmission of calicivirus
Fecal-oral route
>109 particles per gram
the virus can remain viable for several years
infectious dose: 10-100 particles
Respiratory route
inhalation of aerosols of vomit or fecal material
Contaminated food, and water
Cold foods such as sandwiches, iced cakes, melons, salads
Seafood that are eaten raw such as Shellfish
contaminated water
Asymptomatic excretion
Lab diagnosis
Specimen
feces (collected asap and stored at 4°C)
vomitus
contaminated food and drinks
Microscopy
Electron microscopy can be used. But they are difficult to recognize. The sensitivity of an electron microscope can be increased by solid-phase immune electron microscopy (IEM) or conventional IEM. IEM is also used to measure Ab responses
The virus reacts with antibodies in the fluid phase resulting in aggregates of particles. Masking of the virus by antibodies should be prevented.
Serodiagnosis
EIA is available to detect some Norovirus while EIA for Sapovirus is not available.
Molecular methods
RT-PCR has high sensitivity and specificity. Primers are designed to be directed to the highly conserved RNA polymerase region, the VPI region, or the area binding the two regions
Treatment
No specific treatment is available while severe dehydration managed with parenteral fluid replacement