Astrovirus - Molecular diagnosis (RT-PCR)
Astrovirus is a Astroviridae virus family. This family is divided into two kinds: gender Mamastrovirus that infects humans and gender Avastrovirus that infects birds. Genus species include bovine Mamastrovirus A., A. feline, human A., A. sheep, pigs A., A. vison. Avastrovirus gender, which causes infection in birds, including species A. chicken, duck and A. A. turkey. Human astrovirus (HastV) are a major cause of acute gastroenteritis (GEA) worldwide, reaching in some geographical regions constitute the second leading cause of GEA, behind the Rotavirus.
Astrovirus has a size of 28 to 35 nm in diameter, with icosahedral symmetry and a characteristic surface structure shaped star five or six points when observed by electron microscopy. It is one of the most resistant virus physical and chemical agents, while maintaining their infectivity even after exposure to 60 for 10 minutes after exposure to pH 3.Tienen a positive single - stranded RNA genome and therefore are included in the Group IV classification of Baltimore. RNA strand has a poly-A end at the 3 'end, but lacks 5'-CAP. Excluding polyadenylation at the 3', the genome is 6.8 kb long 7.9 and is organized into three open reading frames (ORF: Open Reading Frame), with an overlap of about 70 nucleotides between ORF1b ORF1a and. The remaining ORF is known as ORF2. 8 and HastV serotypes, of which HastV-1 serotype / most frequent genotype known.
In people, astrovirus infection is transmitted by the fecal-oral route , usually through ingestion of contaminated food and water, but can also be transmitted by person-person contact. Because infected individuals generally excrete large amount of HastV (Human astrovirus) in the stool, these viruses easily contaminated wastewater. HastV have been detected in water sources and water supply systems of consumption. Once in the body, Astrovirus infects intestinal epithelial cells and multiply in the mature enterocytes in most of the apical portion of the villi. Inside the infected enterocytes viral accumulations are observed in lysosomes and intracytoplasmic vacuoles, or as intracytoplasmic inclusions in different vacuoles. This agent causes alterations of the cell as the nucleus degeneration, inflammatory response and enzymatic changes.
The incubation period is 3 to 4 days and the symptoms usually persist for 2 to 3 days, but can persist up to 12 days. In humans, the clinical manifestations of astrovirus infection include diarrhea, nausea, vomiting, fever, malaise, headache, abdominal pain and anorexia. The approximate duration of these symptoms is approximately 4 days. In some cases, the infection is more severe and accompanied by lactose intolerance. Astrovirus infection is not usually a serious situation and only in rare cases cause dehydration. People of all ages are susceptible to infection by astrovirus, but children, the elderly, and immunocompromised people are more prone to infection, which can cause serious and chronic diarrhea. In children it is considered the second leading cause of viral diarrhea. It is estimated that most children acquire antibodies around 5 years old, giving them protection in adult stages, until the antibody titer starts to decrease over time. At 10 years of age 80% of the population has serologic evidence of having had a previous infection. Likewise, it is estimated that the incidence of astrovirus infection varies depending on the season. In geographic areas with temperate climates infection is highest during the winter months, while in tropical regions the prevalence is highest during the rainy season. They described outbreaks of this virus as children 's centers and elderly care adult day care facilities.
Recommended tests for diagnosis:
This virus can not be grown in conventional cell culture, so the only alternative possible for clinical diagnosis are:
- Culture isolation: this virus is not isolated in culture generally. It can infect cell cultures of Caco-2 cells treated with trypsin, or HT-29 (Human Colon Adenocarcinoma) cells but is not a method used in diagnosis. Cell cultures in order to isolate several enteric virus as BGMK (Buffalo Green Monkey Cells) cells, can isolate Adenovirus types 40 and 41, although not produce cytopathic effect in these cells, and other enteric viruses, but however, Astrovirus, It does not replicate in these cells.
- Observation by electron microscopy virus: virus detection in faecal samples by observing stool purified by electron microscopy. This observation requires sample preparation and equipment that are unusual for clinical diagnosis.
- Detection of viral antigen: to detect viral antigen are several formats immunoenzymatic reaction (ELISA or immunochromatography) or passive agglutination. In general, these methods have low sensitivity.
- Detecting its nucleic acid (RNA), by methods of RT-PCR (Reverse Transcriptase Polymerase Chain Reaction), PCR in real time (Real Time PCR) or Luminex xMAP technology platforms. These tests are considered the most sensitive and most useful in diagnosis.
Tests in IVAMI:
- Molecular diagnosis (RT-PCR: Reverse transcriptase polymerase chain reaction).
- Stool (10 mL og).
- Vomiting (10 mL og).
Preservation and shipment of sample:
- Refrigerated (preferred) for less than 2 days.
- Frozen: over 2 days.
Being RNA viruses, it should be stored frozen, refrigerated or at least the shortest time possible, avoiding repeated freezing if frozen.
- Molecular diagnosis (RT-PCR): 24 to 48 hours.
Cost of the test: