The Cause And Effects Of Rotavirus Biology Essay

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This is a report based on the study of Public Health and Awareness. The main focus of this study is on a particular virus called the Rotavirus.

Rotavirus is the most common cause of severe diarrhea among infants and young children, and is one of several viruses that cause infections often called stomach flu, despite having no relation to influenza.

It is a double stranded RNA virus from the family Reoviridae. By five years of age, nearly every child in the world has been exposed to the pathogen named Rotavirus at least once. However, with each infection, immunity is developed and subsequent infections are furthermore less severe in action. Usually adults are rarely affected by the rotavirus and there are five groups of this virus named; A, B, C, D, & E; with A being the most common or prevalent type of affecting humans.

The means of contamination happen through the oral-fecal route. It damages and infects the cells of the lining of the small intestine causing gastroenteritis. Rota virus was discovered in 1973, and although this was some time ago people today still don't understand its importance. Rota virus is responsible for 50% of all severe diarrhea hospitalizations. Also an important thing to note is that it is a pathogen in which it may attack other animals, and most dangerously a livestock pathogen.

Rotavirus is considerably simple to treat, but unfortunately over 500,000 children under the age of five die from rotavirus infect annually, with an addition 2 million more becoming severely ill. In America, before the initiation of rotavirus vaccine over 2.7 million cases were found every year with a mortality rate of approximately 37 children per year.

Public health campaigns to combat rotavirus focus on providing oral rehydration therapy for infected children and vaccination to prevent the disease.

A brief History

Jacob Light and Horace Hodes proved in 1943, that a filterable agent in the feces of children with infectious diarrhea also caused scours or livestock diarrhea in cattle. Thirty years later, samples that were preserved of the agent were shown to be rotavirus. In the following years, a virus in mice was shown to be related to the virus causing scours. In 1973, Ruth Bishop described related viruses found in children with gastroenteritis.

In 1974, Thomas Henry Flewett suggested the name rotavirus after observing that, when viewed through an electron microscope, a rotavirus particle looks like a wheel or "Rota" in Latin; the name was officially recognized by the International Committee on Taxonomy of Viruses four years later. In 1976, related viruses were described in several other species of animals. These viruses, all causing acute gastroenteritis, were recognized as a collective pathogen affecting humans and animals worldwide. Rotavirus serotypes were first described in 1980, and in the following year, rotavirus from humans was first grown in cell cultures derived from monkey kidneys, by adding trypsin which is an enzyme found in the duodenum of mammals and now known to be essential for rotavirus to replicate to the culture medium. The ability to grow rotavirus in culture accelerated the pace of research, and by the mid-1980s the first candidate vaccines were being evaluated.

In 1998, a rotavirus vaccine was licensed for use in the US. Clinical trials in the United States, Finland, and Venezuela had found it to be 80 to 100% effective at preventing severe diarrhea caused by rotavirus A, and researchers had detected no statistically significant serious adverse effects. The manufacturer however, withdrew it from the market in 1999, after it was discovered that the vaccine may have contributed to an increased risk for intussusceptions, a type of bowel obstruction, in one of every 12,000 vaccinated infants. The experience provoked intense debate about the relative risks and benefits of a rotavirus vaccine. In 2006, two new vaccines against rotavirus A infection 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

Mechanism of Action

The diarrhea is caused by multiple activities of the virus. Firstly malabsorption occurs due to the destruction of intestinal cells called enterocytes. The toxic rotavirus protein NSP4 induces age and calcium ion dependent  chloride secretion, disrupts SGLT1 transporter mediated re-absorption of water, which apparently reduces activity of brush border membrane disaccharides, and possibly activates the calcium ion dependent secretory reflexes of the enteric nervous system. Healthy enterocytes secrete lactase into the small intestine; milk intolerance due to lactase deficiency is a particular symptom of rotavirus infection, which can persist for weeks. A recurrence of mild diarrhea often follows the reintroduction of milk into the child's diet, due to bacterial fermentation of the disaccharide lactose in the gut.

Electron micrograph of a rotavirus infected enterocyte (top) compared to an uninfected cell (bottom)

Mode of Transmission

Rotavirus is transmitted by the fecal-oral route, through contact with contaminated hands, surfaces, objects, and possibly by the respiratory route. The feces of an infected person can contain more than 10 trillion infectious particles per gram; only 10 - 100 of these are required to transmit infection to another person.

Rotaviruses are stable in the environment and have been found in estuary samples at levels as high as 1-5 infectious particles per United States gallon.  Sanitary measures adequate for eliminating bacteria  and  parasites seem to be ineffective in control of rotavirus, as the incidence of rotavirus infection in countries with high and low health standards is similar.

Rotavirus A from the feces of an infected child

Signs & Symptoms

Rotavirus gastroenteritis is a mild to severe disease characterized by nausea, vomiting, watery diarrhea, and mild fever. Once a child is infected by the virus, there is an incubation period of about two days before symptoms appear. Symptoms often start with vomiting followed by four to eight days of profuse diarrhea. Dehydration is more common in rotavirus infection than in most of those caused by bacterial pathogens, and is the most common cause of death in relation to the rotavirus A infection.

Rotavirus A infections can occur all throughout life: the first usually produces symptoms, but post infections are typically asymptomatic, as the immune system provides differential protection. Consequently, symptomatic infection rates are highest in children under two years of age and decrease progressively towards 45 years of age. Infection in newborn children, although common, is 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 those with compromised or absent immune system functions. Due to immunity acquired in childhood, most adults are not susceptible to rotavirus; gastroenteritis in adults usually has a cause other than rotavirus, but asymptomatic infections in adults may maintain the transmission of infection in the community. Symptomatic re-infections are often due to a different rotavirus A serotype.

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