The family Reoviridae (named after respiratotes enteric orphan – respiratory and intestinal orphan viruses) are viruses widespread in nature that infect vertebrates, invertebrates and plants. They are characterized by icosahedral symmetry of the capsid, are about 75-80 nm in size, and are not enveloped. Their genome, made up of dsRNA, is divided into 10-12 segments. They replicate in the cytoplasm of infected cells. The reovirus family consists of at least 9 genera; pathogenic for humans are: Reo virus, Orbivirus, Coltivirus and Rotavirus.
Reoviruses are widespread around the world. It is estimated that approximately 70% of children under the age of 5 have antibodies against these viruses. Primary infection occurs in early childhood, but is not associated with any particular symptom complex. The route of infection is not well understood, possibly faecal-oral or droplet infection. Primary infection is usually asymptomatic or mild. It has not been found that infection with these viruses could lead to the development of severe syndromes. The presence of antibodies in humans may indicate the prevalence of infection, which, due to its mild course, is usually not confirmed etiologically. Reoviruses have been found to be an etiological factor in colds, diarrhea, pharyngitis and rashes. Serological signs of infection have been found in isolated severe cases, e.g. in neonates with biliary atresia, in adults with cholestatic syndrome, aseptic meningitis and encephalitis. Tests confirming the etiological factor are not performed routinely. For research purposes, material from a patient with monkey kidney cell culture is passaged and the cytopathic effect is assessed. Serological tests can be performed: inhibition of haemagglutination, indirect immunofluorescence, immunoabsorbance and PCR testing of the genetic material. There is no causal treatment, symptomatic treatment is applied. There is no preventive vaccine.
Orbiviruses (Orbiviruses) and coltiviruses (Coltiviruses) are primarily animal pathogens. They differ from other reoviruses in their physicochemical properties and the fact that the infection is transmitted by arthropods. Coltiviruses cause Colorado tick fever. The vector for them are ticks (Dermacentor andersoni), living in the western states of North America and parts of Canada. Annually, there are 100-200 cases of the disease in these regions. The pathomechanism of Colorado fever infection is not fully understood. Coltiviruses are known to attack erythrocyte precursors in the bone marrow, and to lys or damage liver and heart muscle cells. The hatching period is on average 3-6 days. The disease is manifested by high fever, apathy, nausea, pain in the muscles and eyeballs. In about 50% of cases, fever is two-phase, with a blotchy rash and neurological symptoms common. The disease is rarely severe, complete recovery takes 7-10 days. Additional tests show a decreased number of leukocytes (2-3 thousand / mm3). Diagnostics consists in performing ELISA tests, direct and indirect immunofluorescence or testing with the use of PCR. It is possible to isolate the virus from cell culture. Treatment is symptomatic – antipyretic and analgesic. There is no preventive vaccine. In prophylaxis, it is important to use repellants and to quickly remove the tick from the skin. Patients must not donate blood for at least 6 months – there is a possibility of infection through transfusions. The virus is isolated from blood erythrocytes for 120 days after becoming ill.
Orbivirus infection affects animals more than humans. More than 100 orbivirus subtypes are known. Epidemiological data on the frequency and clinical course of infections are incomplete. It is known that human infection with only certain strains is associated with disease symptoms. They were named after the places where they caused disease cases. Patients usually have a history of a tick bite or stay in an endemic area. The most common symptoms are high fever, muscle aches, vomiting and stomach pain. Additional tests revealed leukopenia, thrombocytopenia and anemia. Kemerovo tick fever virus causes fever disease and encephalitis in eastern Europe (Our Country) and western North America – the vector is Ixodes persulcatus. Lipovnik virus has been found in patients with encephalitis in the Czech Republic and Slovakia, it is transmitted by Ixodes ricinus. Infections with other orbiviruses cause disease in different regions of the world – it is closely related to the ecological niches of arthropods. Changuinola virus is transmitted by the Phlebotomus fly and the disease occurs in Panama. Lebombo virus and Orungo virus carry Aedes and Anopheles mosquitoes that live in Africa.
Rotaviruses
Rotaviruses (Rotaviruses) belong to the Reoviridae family. They infect numerous vertebrates, including humans. They have icosahedral symmetry, about 100 nm in diameter. Their genome, which consists of 11 segments of double-stranded RNA, is surrounded by a triple-layer 20-walled envelope. Each of the 11 segments encodes a different protein – 6 structural and 5 non-structural proteins are formed. In an electron microscope, they resemble a wheel, hence their name (Latin rota – wheel). Differences in the structure of proteins within the layers forming the envelope allow for their differentiation, classification of strains and determine the antigenic response. Taking into account the antigenic properties of the VP6 protein within the inner envelope layer, the rotavirus genome is divided into different serogroups, from A to E, with the possibility of two additional groups F and G. Further classification is based on the genetic properties or seroactivity of the viral proteins VP4 and VP7 in the outer sheath layer. Each of these proteins stimulates the production of specific antibodies. The protease-sensitive VP4 protein determines the P serotype (23 P serotypes have been identified). The VP7 glycoprotein determines the G serotype (15 G serotypes have been isolated). Among rotaviruses infecting humans, 10 P genotypes and 10 G genotypes have been detected.
Definicja
Rotaviruses are the most common cause of serious, non-bacterial diarrhea in infants and children around the world, and adults can also suffer.
Epidemiology
Almost every child under the age of 5 has had rotavirus infection. Due to high incidence and mortality, these infections are the main health problem in all countries of the world. Annually, over 138 million children are ill worldwide. The number of deaths in children under the age of 5 is estimated at over 450. The clinical picture of the disease in developing and developed countries is different. The percentage of children with clinical symptoms is similar, but due to better medical care, significantly fewer deaths are observed in developed countries. Severe cases of diarrhea, with an unsuccessful outcome, affect children from parts of the world such as Southeast Asia, India, Africa and, to a lesser extent, South America. In the temperate climate, the highest incidence is recorded in the winter months, in the tropics – throughout the year. The peak incidence occurs in children between 4 and 36 months of age, newborns and adults can also suffer from the disease. The infection is transmitted through the ingestion, infection is possible through contaminated food and water. The presence of viral antigens in respiratory secretions suggests the possibility of droplet infection. Due to their high infectivity, rotaviruses are a common cause of nosocomial infections in children (approximately 20%). Surviving the primary infection gives partial immunity and protects against a severe course of the disease in 75% of cases in the next infection. You can get sick several times, natural immunity usually develops in the first 3 years of life. The most serious clinical significance is group A virus infections, which cause acute diarrhea in children under 2 years of age and are associated with high mortality. It was found that over 90% of all rotavirus strains causing diarrhea belong to the serotypes: P [8] G1, P [8] G3, P [8] G4 or P [4] G2. The dominant strains change, the most frequently isolated serotype is P [8] G9. The remaining strains cause less severe diarrhea, some only in certain regions of the world (e.g. Asia).
pathogenesis
The incubation period is short, about 2 days. Most viruses multiply in the small intestine, but signs of inflammation also occur in other parts of the digestive tract, including the stomach. Rotavirus infects and causes cell necrosis in the apical parts of the intestinal villi. Young cells that are renewing themselves do not have a fully functional absorption function. There is osmotic diarrhea, which is the result of impaired absorption of nutrients and water, and increased secretion of mucus. The virus is excreted in large amounts in the faeces within 2-5 days from the onset of symptoms. Local humoral immunity appears to play a decisive role in preventing infection, but mechanisms of cellular immunity are also involved.
Clinical symptoms
The clinical picture includes asymptomatic infections, mild diarrhea and severe course of the disease, occasionally leading to death. The asymptomatic course of infection is common in newborns and adults. Disease symptoms are usually observed within 24-48 hours of infection. Onset is usually sudden, with fever, vomiting and diarrhea. In 80% of children, vomiting precedes diarrhea. About one third of patients treated in hospital have a fever above 39 ° C. These symptoms may be accompanied by a runny nose, weakness, malaise and stomach pains. With a mild course of the disease, gastrointestinal symptoms last 2-6 days. There is mucus in the stool and leukocytes and red blood cells in about 15% of cases. The ailments disappear spontaneously. Some patients experience significant dehydration, the course of the disease is severe, and deaths have been reported. In some cases, the symptoms are not limited to the digestive system, but may include febrile seizures, anorexia or signs of meningeal irritation. Watery stools can be so common that they resemble cholera and lead to rapid dehydration. Assessing the state of dehydration is critical to deciding whether to treat in a home or hospital setting. Symptoms are poor in the early stages of the disease. With longer-lasting dehydration, there may be increased thirst, apathy or anxiety, skin elasticity decreases, eyeballs collapse, and fontanelles occur in infants. Rotavirus infection may be accompanied by various clinical syndromes, incl. Sudden Infant Death Syndromes, Reye’s, Schönlein-Henoch’s, Hemolytic Uremic Syndromes, Kawasaki’s and Crohn’s Diseases. Probably rotavirus infection is coincidentally associated with the above syndromes. In children with impaired innate, acquired and organ transplantation disorders, the course may be severe and even lead to death.
Diagnostics
Diagnosis is easy as rotavirus is excreted in large amounts in the stools. Immunoassays and latex agglutination are used to detect group A rotavirus antigen in the stool. Latex agglutination tests are cheap and are now widely used. In order to increase the sensitivity of ELISA tests, monoclonal antibodies are used. ELISAs for the diagnosis of non-A rotavirus infection also exist, but are not generally available. Testing of the genetic material of virus RNA is performed primarily for research purposes. Gel electrophoresis and electron microscopy evaluation are sensitive, but little available. Monoclonal antibody tests for particular serogroups and rotavirus serotypes are widely used in epidemiological studies.
Treatment
There is no causal treatment. It is important to replenish fluids initially orally, and in cases of more severe symptoms (vomiting, severe diarrhea) – also intravenously. Appropriately prepared fluids for rehydration by the oral route can be used. Their disadvantage is the taste that many children cannot tolerate. It is important to give fluids frequently, in small amounts, and then gradually add milk and solids to the diet. With a severe course of the disease, patients may require supplementation of electrolyte deficiencies (Na +, K +). Antibiotics and sulfonamides are not used. Probiotics and diosmectite can be administered.
Prevention
The basis of prevention is compliance with the rules of hygiene, washing hands after changing diapers in children and before each meal. There is also the possibility of active immunization. The first rotavirus vaccine was developed from a bovine strain in the early 80s and had little efficacy. In 1988, a vaccine containing the four serotypes of the human rotavirus and the rhesus monkey rotavirus was registered in the United States. It was a live, orally administered vaccine, but it caused intussusception in some infants, which led to its withdrawal. Currently, two oral live vaccines are available in Poland. One of them is a monovalent vaccine containing the RIX4414 strain grown on the Vero cell line. It is indicated for the active immunization of infants from 6 weeks of age. Two doses are used with an interval of at least 4 weeks. It was found that it stimulates the formation of cross-resistance and protects against rotavirus infections of the G1P [8], G3P [8] and G9P [8] types. Another is the pentivalent vaccine, which is used in a three dose schedule. The active substances contained in the RotaTeq vaccine are 5 strains of human-bovine rotavirus reassortants: G1-G4 and P1 [8]. Both vaccines are of comparable effectiveness.
Summation
Rotaviruses belong to the Reoviridae family. They are one of the most common causes of severe diarrhea in infants and children in the world. The peak incidence occurs in children between 4 and 36 months of age, newborns and adults can suffer from the disease. The infection is spread through the digestive tract, through contaminated food and water. The clinical picture includes asymptomatic infections, mild diarrhea and severe infections, occasionally leading to death. Symptoms develop within 24-48 hours of infection. The onset is sudden, with fever, vomiting and diarrhea, sometimes painful stomach cramps, runny nose, weakness, malaise. With a mild course, gastrointestinal symptoms last from 2 to 6 days. Treatment consists primarily of fluid replacement by the oral route and, in severe cases, by the intravenous route. The basis of prevention is compliance with the rules of hygiene, washing hands after changing diapers in children and before each meal. There is a possibility of active immunization of infants from the age of 6 weeks. Two live oral vaccines are available for immunization against the most common rotavirus strains.
Literature
1. Herrmann J.E.: Rotaviruses and other reoviridae, [ 1. w:] Gorbach S., Bartlett J., Blacklow N.R. (red.): Infectious diseases, Lippincott Williams & Wilkins, Philadelphia 2004, 2076-2082 (wyd. III).
2. Bernstein D.I., Ward R.L.: Rotaviruses, [w:] Feigin R.D., Cherry J.D., Demmler G.J. i wsp. (red.): Textbook of pediatric infectious diseases, Saundres, Philadelphia 2004; vol. II, 2110-2133.
3. Greenberg HE: Viral gastroenteritis, [in:] Fauci A., Braunwald E., Isselbacher K. et al. (Eds.): Interna Harrison, WydawnictwoCzelej, Lublin 1998, vol. II, pp. 1685- 1688 (XIV edition).
4. Bresee J.S., Parashal U.D., Widdowson M.A. i wsp.: Update on rotavirus vaccines, Pediatr Infect Dis J 2005; 24: 947-952.
Source: J. Cianciara, J. Juszczyk, Infectious and parasitic diseases; Czelej Publishing House