Novak virus gastroenteritis

　　One, the cause of the disease

　　1. The Novak virus is spherical with a diameter of about 27nm. It has no envelope, is a single-stranded positive-sense RNA, and replicates in the host cell nucleus. Its genome includes 3 open reading frames (ORF), ORF1 encodes a non-structural protein precursor with RNA polymerase properties, ORF2 encodes a capsid protein with a relative molecular weight of about 57kD. This protein has antigenicity and can produce antibodies. ORF3 encodes a protein with a molecular weight of about 22.5kD, whose function is not yet clear.

　　2. There is no systematic classification and naming for Novak and Novak-like viruses. Novak virus is the most representative one in this group. It was initially classified as small round structured viruses (small round structured viruses, SRSVs) because the particle diameter is about 30nm, and they cannot be distinguished in morphology, and the clinical conditions are similar. However, many studies by scholars have shown that the virus is most similar to caliciviruses in terms of genomic structure, coding proteins, and the morphological structure of the virus, so it has been classified into the Caliciviridae family in terms of virus classification.

　　3. Novak-like viruses are at least divided into 3 genotypes based on the nucleotide sequence of the RNA polymerase region or the amino acid sequence encoded by it, with the representative strains being NV, SMA, and Sapporo. The SMA genotype can be divided into two subgroups, SMA and HWA forming one subgroup, and the other subgroup including MXV, Minireovirus, Oth-25, and Bristolvirus. The Sapporo group in the 3 genotypes is more similar to the morphological features of caliciviruses and is also more similar to animal caliciviruses in nucleotide sequences, while having low similarity with the other two groups of viruses. The typing of Novak-like viruses still needs further study.

　　4. The virus is acid-resistant, ether-resistant, and heat-stable. It cannot be completely inactivated at 60℃ for 30 minutes. It can survive for 3 hours in an environment with a pH of 2.7, and its buoyant density in cesium nitrate is 1.36-1.41 g/cm3.

　　Second, Pathogenesis

　　The site of Norovirus infection is mainly the mucosa of the proximal small intestine, replicating in the nucleus of cells. Due to the invasive infection of the virus, the enzyme activity of the epithelial cells is altered, causing malabsorption of carbohydrates and lipids, leading to increased osmotic pressure in the intestinal lumen, and fluid entering the intestines, resulting in symptoms of diarrhea and vomiting. Pathological tissue examination shows that the villi of the intestinal mucosal epithelial cells become thicker and shorter, the mitochondria within the cells swell and deform, no cell necrosis is observed, and there is infiltration of monocytes in the lamina propria of the intestinal wall, but no viral particles are found. The stomach and large intestine do not show lesions.

　　A few severe cases may develop complications such as dehydration and shock. A few patients may develop intussusception, rectal bleeding, hemolytic uremic syndrome, encephalitis, and Reye syndrome, etc. Dehydration caused by diarrhea and vomiting is a serious complication of gastroenteritis, and young infants are very likely to experience dehydration. Other complications include electrolyte imbalance, intestinal perforation, sepsis, etc.

　　The incubation period is 24-48 hours, with an acute onset, mainly manifested by diarrhea and vomiting. There is often marked nausea, with diarrhea occurring several times or more than ten times a day, watery or loose stools, non-hemorrhagic diarrhea, and sometimes severe colicky abdominal pain. Accompanied by decreased appetite, general weakness, headache, low fever, etc. Children with the disease first exhibit vomiting of watery substances, followed by diarrhea. The course of the disease is generally 3 days, with self-limiting characteristics. Elderly patients may have a longer course of the disease.

　　Pay special attention to the management of food and drinking water hygiene, maintain personal hygiene and good living habits, and pay attention to the disinfection of shellfish aquatic products, avoiding the consumption of raw shellfish aquatic products. Currently, there is no effective vaccine available to prevent Norovirus infection. Early detection and isolation of patients; disinfection of patient feces, disinfection of utensils; strict disinfection and isolation system should be established in baby rooms; breast-feeding infants is recommended; oral attenuated vaccines containing various types of rotavirus can be administered to children aged 6-24 months, which can stimulate the production of IgA antibodies locally, and is currently the most effective preventive measure.

　　1. The peripheral blood white blood cell count is mostly normal or slightly elevated, with a few cases showing a decrease in white blood cell count.

　　2. Stool examination usually shows no abnormalities in fecal microscopy, and no pathogenic bacteria grow in culture.

　　3. Within 24 hours after the onset of the disease, the feces can be detected for the virus using immunoelectron microscopy, which is often difficult to find due to the low amount of virus.

　　3. Radioimmunoassay (RIA) method for detecting viral antigens in feces has higher sensitivity than immunoelectron microscopy, but it is difficult to obtain norovirus antigens and antisera.

　　4. Spot hybridization technique for detecting viral RNA by molecular biological detection technology, or RT-PCR method for amplifying viral RNA in specimens, has good sensitivity and specificity. The experiment shows that the RT-PCR method with the highest sensitivity is not as good as detecting other certain viruses in the actual detection of Norwalk virus infection, which may be due to the large variation in the genomes of different strains. The use of multiple primers and/or primers targeting more conservative regions of the viral gene may increase the positive rate of PCR detection, but this still needs further exploration.

　　No special abnormal findings.

　　The key to preventing infection with norovirus is to do a good job in prevention. Controlling the disease from the mouth is crucial; do not eat raw and cold foods and uncooked or undercooked foods, especially banning the consumption of raw shellfish and other marine and aquatic products. Do not dine at unlicensed street stalls and restaurants. Wash fruits and vegetables thoroughly before eating.

　　Pay attention to personal and environmental hygiene, wash hands before and after meals, and develop good hygiene habits. Once an outbreak of norovirus is found, patients, suspected patients, and carriers should be isolated and treated separately; the vomit, diarrhea, and contaminated items of patients and suspected patients, as well as toilets, should be disinfected.

　　1. Treatment

　　Currently, there is no specific effective treatment for this disease. Treatment is mainly symptomatic and supportive, with attention to correcting dehydration, acidosis, and electrolyte disorders. Mild dehydration can usually be corrected by oral rehydration (ORS), while moderate to severe dehydration requires intravenous fluid therapy. Six-sided montmorillonite (Smecta) is an intestinal mucosal protective agent that can cover the mucosa of the digestive tract, adsorb bacteria, viruses, and their toxins, shorten the duration of diarrhea, reduce the frequency of defecation, and at the same time prove that the drug does not affect the treatment of ORS and normal feeding, and has no side effects. The trial results were good.

　　NLV and infantile diarrhea are generally recommended to have light food due to the damage to the function of the small intestine.

　　2. Prognosis

　　The course of the disease is usually 1-3 days, showing self-limiting characteristics with a good prognosis.