Norwalk virus gastroenteritis

Introduction to Norwalk Viral Gastroenteritis Norwalk virus is one of the main causes of acute gastroenteritis, and children and adults in many countries around the world can be infected with Norwalk virus, which can cause epidemics. basic knowledge The proportion of illness: 0.003% Susceptible people: no special people Mode of infection: non-infectious Complications: dehydration shock

The cause of Norwalk viral gastroenteritis

(1) Causes of the disease

Novak is spherical, about 27 nm in diameter, and has no envelope. It is a single-stranded positive-stranded RNA that replicates in the host cell nucleus (Fig. 1). Its genome includes three open reading frames (ORFs), and ORF1 encodes an RNA polymerase. The non-structural protein precursor of nature, ORF2 encodes a capsid protein with a relative molecular weight of approximately 57 kD. This protein is antigenic and can also produce antibodies. ORF3 encodes a protein with a molecular weight of approximately 22.5 kD, the role of which is unclear.

At present, there is no systematic classification and naming of Norwalk virus and Norwalk-like virus. Novak virus is the most representative one of these viruses and began to be classified as small round structured viruses (SRSVs). Because the particle diameters are all about 30nm, and they are morphologically indistinguishable, the clinical situation is similar, but many scholars have shown that the virus is most similar to the calicivirus in the genomic structure, the encoded protein and the morphological structure of the virus. Therefore, it has been attributed to the Caliciviridae in the classification of viruses.

At present, according to the nucleotide sequence of the RNA polymerase region or the similarity of the encoded amino acid sequence, the Norwalk-like virus is divided into at least three genomes, and the representative strains of each group are NV, SMA and Sapporo components, respectively. The genome can be divided into two subgroups, SMA and HWA are a subgroup, and the other subgroup includes MXV, Minireovirus, Oth-25 and Bristol virus. The Sapporo group in the three genomes is more morphologically like a calicivirus. The nucleotide sequence is also closer to the animal calicivirus, and the similarity with the other two groups of viruses is low. The typing of the Norwalk-like virus remains to be further studied.

The virus is acid-resistant, ether-resistant, heat-stable, incompletely inactivated at 60 ° C for 30 min, survives for 3 h in a pH 2.7 environment, and has a buoyant density of 1.36 to 1.41 g/cm 3 in tantalum nitride.

(two) pathogenesis

The Norovirus infection site is mainly in the proximal mucosa of the small intestine and replicates in the nucleus. Due to the infection of the virus, the enzymatic activity of the epithelial cells changes, causing the absorption of carbohydrates and lipids, resulting in increased osmotic pressure in the intestinal lumen. Entering the intestine, the symptoms of diarrhea and vomiting appear. Histopathological examination showed that the villus of intestinal mucosal epithelial cells became thicker and shorter, the mitochondria in the cells were swollen and deformed, no cell necrosis was observed, and the lamina propria of the intestinal wall was infiltrated by mononuclear cells. Virus particles were found, and no lesions occurred in the stomach and large intestine.

Novak viral gastroenteritis prevention

Pay attention to the management of food and drinking water hygiene, maintain personal hygiene and good living habits, pay attention to the disinfection of shellfish aquatic products, and avoid raw shellfish aquatic products. There is no effective vaccine to prevent Norwalk virus infection.

Norwalk viral gastroenteritis complications Complications dehydration shock

A few severe cases can be complicated by dehydration and shock.

Norwalk virus gastrointestinal symptoms common symptoms fatigue nausea watery stool diarrhea loss of appetite low fever abdominal pain

The incubation period is 24 to 48 hours. The onset is urgent. The main symptoms are diarrhea and vomiting. There are often obvious nausea. The diarrhea is several times or more than 10 times a day. The watery stool or yellow stool is diarrhea, and the diarrhea is non-blood. It may have abdominal pain and sometimes abdominal pain. Severe colic, with loss of appetite, general malaise, headache, low fever, etc., children with vomiting water-like substances first, then diarrhea, the course of the disease is generally 3 days, self-limiting, older patients with longer course.

Check of Norwalk viral gastroenteritis

1. Peripheral blood leukocytes are mostly normal or slightly higher, and a small number of white blood cell counts are also reduced.

2. Fecal examination There are no abnormalities in stool examination, and no growth of pathogenic bacteria is cultivated.

3. The feces can be detected by immunoelectron microscopy 24 hours after immunoelectron microscopy, which is often difficult to detect due to the small amount of virus.

4. Radioimmunoassay (RIA) method for detecting viral antigens in feces is more sensitive than immunoelectron microscopy, but Norwalk virus antigens and antiserum are more difficult to obtain.

5. Molecular biological detection technology The dot blot hybridization method detects viral RNA, or RT-PCR amplification of viral RNA in specimens has good sensitivity and specificity. Experiments show that the most sensitive RT-PCR method is used for The actual detection of WACKER virus infection does not result in a high positive rate as some other viruses, which may be due to the large variation of the genome between different strains, using multiple pairs of primers and/or using Primers targeting more conserved regions of the viral gene may increase the positive rate of detection by PCR methods, but this needs further exploration.

No special abnormalities.

Diagnosis and diagnosis of Norwalk viral gastroenteritis

Diagnostic criteria

1. Epidemiology mainly understands the history of exposure, the season of onset, and whether there is a similar epidemic in the area.

2. Clinical manifestations of short-lived watery diarrhea and vomiting.

3. Laboratory examinations and other auxiliary inspections.

Differential diagnosis

The disease is not difficult to distinguish from bacterial and parasitic diarrhea; the identification of other viral gastroenteritis is mainly based on specific diagnostic experiments.

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