Rotavirus

Rotavirus is a genus of double-stranded RNA viruses in the family Reoviridae that is the most common cause of severe diarrhea in children up to 5 years of age. years old and neonates of different species of mammals. It is one of several viruses that often cause infections called gastroenteritis. In humans, the vast majority of infants under 5 years of age have been infected with rotavirus at least once. In cattle, for example, rotavirus diarrhea affects calves in the first weeks of life, which generates great economic losses.

There are 8 groups, called: A, B, C, D, E, F, G, and H. Rotavirus A, the most common, causes more than 90% of infections in humans and animals. The virus is transmitted by the fecal-oral route. It infects and damages the cells lining the small intestine, causing gastroenteritis.

Rotavirus is a virus that is easily resolved in healthy patients (those who are not immunocompromised), but around 450,000 children still die worldwide every year, most of them in developing countries, and almost two million more become seriously ill. In cattle, this virus is part of the Neonatal Calf Diarrhea complex that can affect up to 70% of these animals.

The most effective way to prevent rotavirus infection is through vaccination. In children, this is mandatory, mainly in developed countries, and also in some developing countries such as Argentina. In bovines, the vaccination strategy is to immunize the mother before calving to then transmit her defenses to the calf at birth.

History

In 1943, Jacob Light and Horace Hodes demonstrated that a filterable agent in the feces of children with infectious diarrhea also caused diarrhea in cattle. Three decades later, preserved samples of the agent proved to be a rotavirus. In the following years, the virus inoculated into mice demonstrated the relationship between the virus and diarrhea. In 1973, Ruth Bishop and her colleagues described the virus associated with childhood gastroenteritis.

In 1974, Thomas Henry Flewett suggested the name rotavirus after observing it under an electron microscope, where he saw that it resembled a wheel (rota in Latin); the name was officially recognized by the Committee International Taxonomy of Viruses four years later. In 1976, the virus related to other species was described. The virus was recognized as an infectious agent for humans and animals throughout the world. Rotavirus serotypes were described by for the first time in 1980, and the following year, its production in cell cultures derived from simian kidneys was achieved by the addition of trypsin (an enzyme found in the mammalian duodenum and known to be essential against cell replication). rotavirus) in culture medium. The ability to grow rotavirus in culture accelerated the pace of research, and the first vaccines began to be evaluated in the mid-1980s.

In 1998, the rotavirus vaccine was approved for use in the United States. Clinical trials were conducted in the United States, Finland, and Venezuela that were 80-100% effective in preventing severe diarrhea caused by rotavirus A. However, investigators found statistically significant serious adverse effects. It was withdrawn from the market in 1999 when it was discovered that the vaccine may have contributed to an increased risk of intussusception, a type of intestinal obstruction, in one in 12,000 vaccinated children. The experience sparked intense debate about the risks and benefits relative to rotavirus vaccine. In 2006, two new rotavirus A vaccines appeared that were shown to be safe and effective in children, and in June 2009 the World Health Organization recommended that rotavirus vaccination be included in all national immunization programs to provide protection against this virus.

Symptoms

Rotavirus gastroenteritis is an illness that can be both mild and severe and is characterized by: vomiting, watery diarrhea, and mild fever. When a child is infected with the virus, there is an incubation period of approximately two days before symptoms appear. These usually begin with vomiting followed by four to eight days of profuse diarrhea. Dehydration is more common in rotavirus infection than in most infections caused by pathogenic bacteria and is the most common cause of death related to rotavirus infection.

A rotavirus A outbreak can occur at any time in life: the first infection usually produces symptoms, but subsequent infections are usually mild or asymptomatic, as the immune system provides some protection. Consequently, symptomatic infections are more frequent in children under two years of age and decrease progressively with age. Infections in infants, while common, are often associated with mild or asymptomatic disease; the most severe symptoms tend to occur in children six months to two years of age, the elderly, and the immunocompromised. Due to immunity acquired in childhood, most adults are not vulnerable to rotavirus; gastroenteritis in adults usually has a cause other than rotavirus, but asymptomatic infections can sustain transmission of infection in the community.

Transmission

Rotavirus in the feces of an infected child

Rotavirus is transmitted primarily by the fecal-oral route, but it can also be transmitted through dirty hands, surfaces, and objects, and it can also be transmitted through the respiratory system. An infected person's droppings may contain more than 10 trillion infectious particles per gram; fewer than 100 of these particles being enough to infect another person.

Rotavirus is stable in the environment and samples have been found in estuaries at levels as high as 1-5 infectious particles per US gallon. Proper sanitation measures for the removal of bacteria and parasites appear to be ineffective in rotavirus control, since the incidence of rotavirus infection in countries with high and low sanitary levels is similar.

Mechanisms of infection

Photograph obtained with an electronic microscope of an enterocyte infected by a rotavirus (top) compared to an uninfected cell (low).

Diarrhea is caused by multiple activities of the virus. Malabsorption is due to the destruction of intestinal cells called enterocytes. The toxic rotavirus protein NSP4 disrupts the SGLT1 transporter involved in water reabsorption, appears to reduce disaccharidase activity, and possibly activates calcium ion-dependent secretion reflexes in the enteric nervous system. healthy enterocytes secrete lactase in the small intestine; milk intolerance caused by lactase deficiency is a symptom of rotavirus infection, which can persist for weeks. Mild recurrent diarrhea is often followed by the reintroduction of milk into the child's diet, due to to bacterial fermentation of the disaccharide lactose in the intestine.

Diagnosis and detection

A diagnosis of rotavirus is usually a diagnosis of gastroenteritis as a cause of severe diarrhea. Most children admitted to hospital for gastroenteritis are tested for rotavirus A. Specific diagnosis for rotavirus A infection is made by looking for the virus in the stool of children using a linked immunosorbent assay. to enzymes, ELISA for its acronym in English. There are several licensed test kits on the market that are sensitive, specific, and detect all rotavirus A serotypes. Other methods, such as electron microscopic visualization and polymerase chain reaction, are used in testing laboratories. research. Reverse transcription polymerase chain reaction (RT-PCR) can detect and identify all human rotavirus species and serotypes.

Treatment and prognosis

Treatment of acute rotavirus infection is non-specific, consisting of managing symptoms and, most importantly, maintaining hydration. If left untreated, children can die from severe dehydration. Depending on Due to the severity of the diarrhoea, treatment consists of rehydrating orally, giving the child an excess of water to drink that contains small amounts of salts and sugars, or giving fluids intravenously by drip or nasogastric tube, while monitoring the electrolytes of the diarrhoea. child and blood sugar. Rotavirus infections rarely cause other complications and for a well-controlled child, the prognosis is excellent.

Virology

Types of rotaviruses

There are eight groups of rotaviruses, designated A, B, C, D, E, F, and G. Humans can only be infected with types A, B, and C, primarily A. All species attack some animal. Within type A there are variations, called serotypes. As with the influenza virus, a double classification system is used, based on two types of capsid proteins. The VP-7 glycoprotein defines the G type and the VP-4 protease sensitive protein defines the P type. The P type is defined as a number for the P serotype and as a number in square brackets for the P genotype. The G serotypes they have a similar nomenclature, with the number of the G serotype being the same as that of the G genotype. For example, the Wa chain is denoted as P1A[8]G1. Because the two genes that determine type G and type P can be transmitted separately, different combinations are found in the progeny of the virus.

Structure

Rotaviruses (from Latin rota: wheel) have a characteristic wheel-like appearance when viewed under an electron microscope. Rotaviruses are non-enveloped (naked) viruses, in their capsid 3 layers are observed (External, Middle and Internal layer). The genome is composed of 11 double-stranded RNA segments, which code for six structural and six non-structural proteins (one of its segments codes for 2 proteins). The virus is stable in the environment. They can measure up to 76.5 nm in diameter.

Protein

The virion is made up of seven proteins (VP). These structural proteins are called VP1, VP2, VP3, VP4, VP5, VP6 and VP7. Apart from the structural proteins, there are six more non-structural proteins (NSPs), produced only in infected cells. They are named NSP1, NSP2, NSP3, NSP4, NSP5, and NSP6. At least six of the twelve proteins encoded by the viral genome carry associated RNA, and the function of these proteins in rotavirus is not well explained; they are believed to be involved in RNA synthesis and packaging, transport of mRNA to the replication zone of the genome, and in mRNA translation and regulation of gene expression.

Structural Proteins

VP1 is located in the core of the virus and is an RNA polymerase. In an infected cell, it produces mRNA transcripts to synthesize viral proteins and replicates the genome to produce new viral particles.

VP2 is part of the innermost layer of the virion and is attached to the RNA genome.

VP3 is also part of the inner layer of the virion and is an enzyme called guanylyl transferase. It is an enzyme that produces the cap on the 5' of RNA (capping enzyme), during post-transcriptional modification of messenger RNA. This cap stabilizes the 5' of the messenger and prevents it from being attacked by nucleases, enzymes that break down nucleic acids.

VP4 is located on the outside of the virion and forms a bulge, which is capable of binding to cell receptors on the cell to enter its interior. VP4 must be modified by an intestinal protease, to give rise to VP5* and VP8*, before the virus particle is infectious. The structure of VP4 determines the virulence of the virus and whether it is P-type.

VP6 is the major capsid protein. It is highly antigenic and can be used to determine the rotavirus species. It is used in clinical trials to determine the existence of rotavirus A infection.

VP7 is a glycoprotein that forms part of the outer layer of the virion. Apart from its structural functions, it determines the G type of the chain, and together with VP4, it is involved in the immune response to the virus.

Nonstructural Proteins

NSP1 is transcribed by gene 5 and is a nonstructural RNA-binding protein.

NSP2 is an RNA-binding protein, which accumulates in cytoplasmic inclusions (viroplasm) and is necessary for genome replication.

NSP3 is bound to mRNA in infected cells and is responsible for the termination of cellular protein synthesis.

NSP4 is a viral enterotoxin that induces diarrhea and was the first viral enterotoxin to be discovered.

NSP5 is encoded by segment 11 of the rotavirus A viral genome, and in infected cells accumulates in the viroplasm.

NSP6 is a nucleic acid binding protein that is encoded by gene 11, in an open reading frame that is out of phase.

Multiplication

They replicate mainly in the intestine and infect enterocytes of the intestinal villi, causing functional and structural changes in the epithelium. Its triple protein layer (not to be confused with capsid) makes it resistant to the pH of the stomach and the digestive enzymes of the intestine.

The virus enters cells by receptor-mediated endocytosis and forms a vesicle called an endosome. Proteins in the third layer (VP7 and VP4) break the endosome membrane, creating a difference in calcium concentration. This results in the rupture of the VP7 trimers into a single protein subunit, leaving the VP2 and VP6 envelope around the viral RNA.

The 11 double-stranded RNA segments remain under the protection of two protein coats, and RNA polymerase creates mRNA transcripts of the RNA genome. By remaining in the capsid, the viral RNA evades the immune response of RNA interference, an RNA molecule that suppresses the expression of specific genes, which is triggered by the presence of the double-stranded RNA.

During infection, rotavirus produces mRNA for protein biosynthesis and gene replication. Most of the proteins accumulate in the viroplasm, where the RNA is replicated and virions are assembled. Viroplasma forms around the cell nucleus within 2 hours of infection, and consists of viral factories believed to be made up of two non-structural proteins: NSP5 and NSP2. Inhibition of NSP5 by RNA interference results in a marked decrease in rotavirus replication. The virions migrate to the endoplasmic reticulum where they obtain their third layer formed by VP7 and VP4. The progeny are released from the cell by lysis.

Rotavirus Infections

The nature of the disease

Rotaviruses cause acute gastroenteritis and severe abdominal pain. "Childhood diarrhea", "winter diarrhea", "acute non-bacterial infection" and "acute viral gastroenteritis" are the other names with which this condition is called. The infective dose is presumed to be 10-100 infectious viral particles, since a person with rotavirus frequently excretes a large number of viral particles: on the order of (10⁸-10¹⁰ infectious particles/ml of feces). The route of contagion occurs through contact with contaminated hands, objects or utensils. The incubation period for rotavirus disease is approximately 2 days but this is not known with certainty. The illness is characterized by vomiting and watery diarrhea for 3 to 8 days, and fever with abdominal pain occurs frequently. Immunity occurs after infection. Subsequent infections tend to be less severe than the original infection.

Prognosis and prevention of the disease

Usually the development of the infection resolves spontaneously. Acute dehydration due to diarrhea is one of the major complications. The use of electrolytes is advisable, although it is advisable to consult your doctor beforehand.

The best way to prevent it is to use clean utensils and wash your hands after using the bathroom. Care must also be taken when handling diapers so as not to promote further contagion.

Important Vaccinations

In 2006, two rotavirus vaccines were shown to be safe and effective in children: the Rotarix monovalent vaccine developed by GlaxoSmithKline laboratories and is created based on live attenuated viruses and the RotaTeq pentavalent vaccine developed by Merck and is created with recombinant human and bovine viruses. Both are administered orally and contain live attenuated virus. Vaccination with Rotarix is 90% effective in preventing severe rotavirus diarrhea during the first 2 years of life in countries with low infant mortality and 35% in countries with high infant mortality, while the figures for RotaTeq are 96%. and 44% respectively. Two other vaccines have been developed (Rotavac monovalent and Rotasil pentavalent) that have been approved for use in India and have been shown to have similar levels of effectiveness to Rotarix and RotaTeq.

In 2006, the FDA approved RotaTeq for use in the United States, announcing a price of $187.50 for the standard three-dose regimen. Therefore, it is one of the most expensive childhood immunizations, despite the discounts it becomes an unaffordable option for infants in the third world. However, the WHO strongly recommends the inclusion of the rotavirus vaccine in immunization programs in all regions of the world. As of April 2020, 107 countries have introduced rotavirus vaccine into their national vaccination systems.

A first approved rotavirus vaccine, Rotashield, developed by Wyeth-Ayerst, was withdrawn from the market in the late 1990s when it was found in very rare cases to be linked to intussusception; however, subsequent evaluations demonstrated that the risk of intussusception increased with increasing age at the first dose and that the risk was very low if vaccination was started at an early age. Likewise, none of the four currently approved vaccines have been associated with an increased risk of serious adverse events or intussusception when administered as recommended.

Complications

Repeated rotavirus infections may increase the risk of developing Celiac disease in generally susceptible children. Intestinal infections have long been believed to contribute to its development, a common digestive disorder triggered by eating wheat-based products and other foods that contain the protein gluten. Some studies, however, have reviewed the role of specific infectious agents in disease development. As participants in a study of environmental triggers of the disease, 1,931 children from the Denver metropolitan area - who were genetically susceptible to celiac disease - were monitored from infancy for rotavirus and the development of celiac disease later.

Conclusions

Rotavirus is a preventable and highly contagious infectious disease that can be fatal in children if not treated in time. Data obtained by the WHO say "Diarrheal diseases are the second leading cause of death in children under 5 years of age". It is important to highlight that these types of infections are preventable and treatable; educating parents and the general population on hygienic-dietary habits, emphasizing vaccination, remembering that it is free and within everyone's reach.