MANIFESTATION OF ROTAVIRUS INFECTION ON HUMANS
Human rotavirus has been reported as the cause of the most severe, acute gastroenteritis in infants and young children in both developed and developing countries.
Rotavirus is a non-enveloped double-stranded RNA virus. It is a member of the family Reoviridae and it has seven different antigenic groups A-G. Group A viruses are known to be the primary causative agents of rotavirus diarrhoea and groups B and C can cause gastroenteritis in adults (Flewett etal, 1974). The virus looks like a wheel when viewed by electron microscopy. The appearance of intact particles is suggestive of a wheel with a wide hub, short spokes and a well-defined rim, hence the name rotavirus (Flewett et al; 1974).
Morphologic and biochemical characteristics shared by members of the rotavirus genus include the following: mature virus particles are nonenveloped and possess a multi-layered icosahedral protein capsid, approximately 75 nm in diameter, composed of an outer layer, an inner layer, and a core; the virus genome consists of 11 segments of double-stranded RNA (dsRNA); particles contain an RNA-dependent RNA polymerase and other enzymes capable of producing capped RNA transcripts; virus replication occurs in the cytoplasm of infected cells; the viruses are capable of genetic reassortment;virus cultivation in vitro is facilitated by treatment with proteolytic enzymes, which enhances infectivity by cleavage of the outer capsid polypeptide Viral Protein 4;virus particles are formed by budding into the endoplasmic reticulum (ER), and enveloped particles are evident transiently at this stage of morphogenesis; and mature particles are liberated from infected cells by cell lysis.(Flewett etal,1974)As stated by Estes and cohen,1989 the outermost shell contains two important proteins—Viral protein 7(VP7), or G-protein, and Viral Protein 4(VP4), or P-protein. VP7 and VP4 define the serotype of the virus and induce neutralizing antibody that probably involved in immune protection.
Human rotaviruses were discovered 36 years ago—a decade after the first animal rotaviruses were visualized (Adams and Krat, 1963).The World Health Organization estimates rotavirus cases globally 215 000 (197 000 – 233 000) child deaths occurred during 2013 due to rotavirus infection compared to 528 000 (465 000 – 591 000) in 2000(Word Health Organisation,2018)Rotaviruses are highly contagious. Transmission of rotaviruses is mostly by the fecal–oral route, which can happen directly from person to person, or indirectly via contaminated fomites. The infectious dose is low (as few as 10 particles by patients with diarrhoea(Ward etal;1986) The virus is shed in large quantities (as many as 1011 particles per gram of stool) both before the onset of symptoms and for several weeks afterward(Richardson etal:1998).It can easily contaminate the environmental objects. A respiratory mode of transmission has also been suggested.Rotavirus outbreaks show a seasonal pattern such that they occur around winter months.
Pathogenesis refers to the ability of a microorganism to cause disease. The outcome of disease depend on virus virulence factors and host,the most host factor being age. Rotavirus infects the cells of the small intestinal villi, especially those cells near the tips of the villi. Because these particular cells have a role in the digestion of carbohydrates and in the intestinal absorption of fluid and electrolytes, rotavirus infections leads to malabsorption by impaired hydrolysis of carbohydrates and excessive fluid loss from the intestine (Flewett 1974). Virulence is associated with the expression of genes 3, 4, 5,9 and 10(Greenberg and Estes,2009) according to Greenbrg and Estes they found some evidence suggests that one non-structural protein, NSP4, may behave as an enterotoxin in a manner similar to the heat-labile enterotoxin of Escherichia coli and cholera toxin explaing the excess ?uid and electrolyte secretion in the acute phase of illness. NSP4 has been observed to the cause release of Ca2+ ions from the endoplasmic reticulum. The increase in intracellular Ca2+ concentration results in a number of cellular processes, including disruption of the microvillar cytoskeletal network, lowered expression of disaccharidases and other enzymes at the apical surface, general inhibition of the Na+-solute cotransport systems, and necrosis (Lundgren and Svensson, 2001). NSP4 appears to be released specifically by a Ca2+-dependent pathway due to cell lysis. This as a result leads to a malabsorption component of the diarrhoea through reduction in absorptive capacity of the epithelium, reduced activity of Na+-solute cotransporters, and reduction of digestive enzyme expression on the epithelial surface.Viral excretion usually lasts 2 to 12 days but can be greatly prolonged in malnourished or immunode?cient patients, with persistent symptoms (Ryan etal; 2018)
Rotavirus can be detected in stool specimens from children with gastroenteritis by several techniques, including electron microscopy, polyacrylamide gel electrophoresis, antigen detection assays, and reverse transcription polymerase chain reaction (RT-PCR), and virus isolation. Polyacrylamide gel electrophoresis detects rotavirus RNA extracted directly from stool specimens; the electrophoretic migration pattern of the 11 segments of the double stranded RNA genome permits analysis of the relatedness of circulating strains (Herring etal; 1982). RT-PCR is widely used in research laboratories to detect the viral genome. It provides data on the VP7 and VP4 genotypes that form the basis of binary classification (G and P type, respectively) of rotavirus strains (IturrizaGómara, 2004)
The enzyme-linked immunosorbent assay (ELISA) is an immunological assay which is commonly used to measure antibodies, antigens, proteins and glycoproteins in biological samples. ELISA tests are very precise tests. They are considered highly sensitive and specific. Antibodies are proteins that recognize and reduced the effect of toxins produced by microorganisms. Cells that make antibodies are B lymphocytes. The substance or molecule identified by antibodies or that can cause antibody response is called an antigen. There are differenttypes of ELISA being direct, indirect, and competitive and sandwich ELISA test.
The Sandwich Enzyme-Linked ImmunoSorbent Assay (ELISA) is a highly sensitive method which measures the antigen concentration from microorganisms in an unknown sample. According to the Boster Antibody and Elisa Expert handbook, to detect antigen, the wells of microtiter plates are coated with specific (capture) antibody followed by incubation with test solutions containing antigen. Unbound antigen is then washed out and an antigen-specific antibody conjugated to enzyme (i.e., developing reagent) is added, followed by another incubation. An enzyme labelled antibody can be produced in the same animal that produced passively adsorbed antibody. The unbound conjugate is then washed out and the substrate is added. Once incubation process is complete, the degree of substrate hydrolysis is measured. The amount of substrate hydrolyzed is equal to the amount of antigen in the test solution therefore,identifying the microorganism causing the illness.
The World Health Organization (WHO) recommends global use of rotavirus vaccines Rotarix, or RotaTeq, , to prevent severe gastroenteritis due to rotavirus.
Rotarix® , is a live vaccine that contains the attenuated monovalent G1, P8 human rotavirus strain. This vaccine is orally administered in 2 doses to infants at ages 2 and 4 months. Rotarix ® efficacy has been evaluated 83.0%
RotaTeq® is a pentavalent bovine–human, reassortant vaccine (produced by Merck and Company, Whitehouse Station, New Jersey). RotaTeq® has five reassortant rotaviruses made from human and bovine rotavirus strains that have human rotavirus outer capsid proteins of five common circulating strains (G1, G2, G3, G4, andP8 (subgroup P1A). Three doses of this vaccine are adivised to be given orally to infants at ages 2, 4, and 6 months,togetherwith other vaccines given at this age. (World Health Organisation,2014)