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Gastroenteritis (Common Causes)

Gastroenteritis (Common Causes)

Introduction

Disease History, Characteristics, and Transmission

Scope and Distribution

Treatment and Prevention

Impacts and Issues

BIBLIOGRAPHY

Introduction

Gastroenteritis is an inflammation of the stomach and the intestines that is produced by the immune system's response to an infection that can be caused by a number of bacteria or viruses. Gastroenteritis is sometimes referred to as the stomach flu, but is not caused by influenza viruses.

The symptoms of gastroenteritis include a stomach or intestinal upset, vomiting, and often the production of watery feces that is called diarrhea. In developing regions of the world, and especially among children, gastroenteritis-induced diarrhea is a killer. Millions of deaths of newborns and children due to gastroenteritis occur each year in Asia, Africa, parts of the Indian sub-continent, and Latin America.

Disease History, Characteristics, and Transmission

Gastroenteritis is caused mainly by viruses, but can also be caused by infection with bacteria and protozoa. The viruses that cause gastroenteritis include rotaviruses, enteroviruses, adenoviruses, caliciviruses, astroviruses, Norwalk virus, and a group of Norwalk-like viruses. Rotavirus infections are the most common.

The symptoms of viral gastroenteritis usually appear quickly, within a few days of ingesting the virus in contaminated water or food. The illness tends to pass quickly, usually being over within the same week. But, people whose immune system function is inefficient such as the young and the elderly, people who are ill with another ailment such as acquired immunodeficiency syndrome (AIDS, also cited as acquired immune deficiency syndrome), or someone whose immune system has been deliberately subdued (such as someone who has received an organ transplant, to reduce the chances of organ rejection) can be ill for a longer time.

Rotavirus is a member of the Reoviridae family of viruses, which contain ribonucleic acid (RNA) as the genetic material. When the virus infects a host cell, the host's genetic machinery is used to make deoxyribonucleic acid (DNA) from the viral RNA; the viral DNA can then be transcribed and translated with host DNA to produce the components that will make new virus particles. There are three main groups of rotavirus that differ from each other slightly in the composition of the protein shell that surrounds the genetic material. These differences mean that a host's immune system will produce different antibodies to the different viruses. Group A rotavirus causes over three million cases of gastroenteritis in the United States annually. Group B rotavirus causes diarrhea that is more prevalent in adults; it has caused several large outbreaks in China. Group C causes diarrhea in children and adults, but is less common than the other two types of rotaviral gastroenteritis.

Rotavirus gastroenteritis hospitalizes 70,000 children every year in the United States. The main reason that rotaviral gastroenteritis is so common is the contagious nature of the virus. Rotavirus easily is spread from person to person, usually when fecal material gets into the mouth. This is known as the fecal-oral route of transmission. Not surprisingly, this type of gastroenteritis occurs frequently in day care facilities, where touching of soiled diapers and hand-to-mouth contact are common. In older children and adults, improper hygiene, particularly washing of the hands, is the main reason for the spread of the virus. People who are infected can excrete (or shed) very high numbers of virus in the watery diarrhea, and spread the infection. Also, handling of utensils and preparation of food with hands that are soiled spreads the virus to the diner. Another route of transmission that is not related to hygiene is the consumption of shellfish. Shellfish are filter feeders— they filter water through an apparatus that traps small food particles. The filter can also trap rotavirus that is present in fecal-contaminated water. As the shellfish feeds, more and more virus can accumulate, until the shellfish becomes toxic to anyone eating it. The danger is especially pronounced in shellfish such as oysters, which some people prefer to eat raw.

Another virus that causes gastroenteritis is the Norwalk virus. This form of the illness tends to be more common in adults, although surveys of children using sophisticated molecular techniques of viral detection have revealed the presence of Norwalk antibodies in children, meaning they have been exposed to the virus, or to a protein that is very similar to the Norwalk viral protein.

Bacteria also cause gastroenteritis. Common examples include certain strains of Escherichia coli, Salmonella, Shigella, and Vibrio cholerae. Bacterial gastroenteritis occurs less in developed countries, as the treatment of drinking water, and treatment and disposal of sewage water tends to be much better than in underdeveloped regions. In developing nations, bacterial gastroenteritis due to contaminated water remains a significant concern. Bacterial gastroenteritis can also be caused by eating contaminated food. Examples include foods such as potato salad that has been left at room temperature for some time prior to the meal and contaminated with Salmonella, and the presence of a type of E. coli designated O157:H7 in undercooked meat; a toxin produced by O157:H7 damages the cells lining the intestinal tract, causing bloody diarrhea.

A protozoan called Cryptosporidium parvum, which resides in the intestinal tract of some animals, also causes gastroenteritis when it contaminates drinking water. This type of gastroenteritis is becoming more prevalent in the United States. One reason is the continuing expansion of urban areas into regions that were previously wild, which brings humans into closer contact with wildlife and the C. parvum they carry. Another reason is that the protozoans can form an environmentally hardy form called a cyst that allows the protozoan to persist through water treatments such as chlorination and, because of the small diameter of the cysts, to pass through filters used in water filtration. Once inside a person, the cyst can rejuvenate into the growing form that is the cause of the illness.

The symptoms of gastroenteritis always include diarrhea. Fever and vomiting are also common. Typically, these symptoms last only several days and progressively lessen over the next few days as the infection abates. The diarrhea in gastroenteritis is very loose and watery. Bowel movements occur frequently, even several times an hour, as fluid pours out of the cells lining the intestine as a consequence of the infection and as an attempt to flush out the infecting bacteria or virus. Dehydration is not usually a problem in an adult, who will instinctively drink water. If dehydration occurs very quickly or if the individual is so sick that they are unaware or unable to take care of themselves, then they can become very ill. Hospitalization of a child for diarrhea is usually because of complications of the excessive fluid loss rather than any direct effect of the stomach and intestinal infection.

WORDS TO KNOW

ANTIBODY: Antibodies, or Y-shaped immunoglobulins, are proteins found in the blood that help to fight against foreign substances called antigens. Antigens, which are usually proteins or polysaccharides, stimulate the immune system to produce antibodies. The antibodies inactivate the antigen and help to remove it from the body. While antigens can be the source of infections from pathogenic bacteria and viruses, organic molecules detrimental to the body from internal or environmental sources also act as antigens. Genetic engineering and the use of various mutational mechanisms allow the construction of a vast array of anti-bodies (each with a unique genetic sequence).

FECAL-ORAL ROUTE OF TRANSMISSION: The spread of disease through the transmission of minute particles of fecal material from one organism to the mouth of another organisms. This can occur by drinking contaminated water, eating food that was exposed to animal or human feces (perhaps by watering plants with unclean water), or by the poor hygiene practices of those preparing food.

ORAL REHYDRATION THERAPY: Patients who have lost excessive water from their tissues are said to be dehydrated. Restoring body water levels by giving the patient fluids through the mouth (orally) is oral rehydration therapy. Often, a special mixture of water, glucose, and electrolytes called oral rehydration solution is given.

VIRAL SHEDDING: Viral shedding refers to the movement of the herpes virus from the nerves to the surface of the skin. During shedding, the virus can be passed on through skin-to-skin contact.

Scope and Distribution

Gastroenteritis is global in distribution. However, it most affects people living in the developing world, and most of these are children. Estimates put the death toll of children due to gastroenteritis-related diarrhea at 1–2 million each year, and the great majority of these deaths occur in developing countries. Still, this is much less than the near five million deaths that occurred annually until the 1980s, and the introduction of what is called oral hydration therapy—drinking a solution containing salts and sugars that helps replenish the body's essential electrolytes (salts and sugars) and fluids that are lost due to diarrhea.

The differences in the severity of the infection and the death rates in the developed versus developing worlds highlight the influence of living conditions, hygiene, and cultural practices on the consequences of gastroenteritis. Age is another factor; the very young and the elderly are particularly susceptible as they may be physically unable to seek prompt relief from the dehydration of diarrhea.

Treatment and Prevention

In the treatment of gastroenteritis it is important to distinguish whether the infection is due to bacteria, virus, protozoan or some other non-biological factor. An example of the latter is lactose intolerance. It is important to know the cause, as antibiotics are effective against bacteria, but are not useful against viruses and can actually make the disease worse since antibiotics can remove normal intestinal bacteria that can help clear the viral infection.

Antibiotics such as fluroquinolone are useful in treating bacterial forms of gastroenteritis, and over-the-counter compounds that lessen diarrhea can also be beneficial. Making sure a person is receiving plenty of fluids is a very important part of the treatment.

A vaccine for rotaviral gastroenteritis was approved for use in 1998, however complications in some children who received the vaccine resulted in its withdrawal from the market a few years later. In 2006, two rotavirus vaccines were licensed for use by the European Medicines Agency and the U.S. Food and Drug Administration (FDA). Both are taken orally and consist of a weakened version of the virus—it is incapable of causing an infection, but stimulates the immune system to develop protective antibodies against rotavirus.

Impacts and Issues

The overwhelming impacts of gastroenteritis are its prevalence and the high death toll among children in under-developed and developing countries due to the debilitating effects of diarrhea. Diarrheal diseases are the second most common cause of death each year in children aged five years or less, according to the World Health Organization (WHO), resulting in over two million child deaths. Earlier and larger death tolls have been reduced by the use of oral rehydration therapy, which is spearheaded by organizations such as UNICEF.

Despite the availability of vaccines against rotavirus, the diarrheal gastroenteritis that is caused by this virus still kills over 600,000 children each year and over two million children require hospitalization because of the severity of their infection. Overwhelmingly, the deaths are in developing countries, where the vaccines and treatment are not as readily available as in developed countries.

Beginning in 2003, a number of agencies including the WHO and the U.S. Centers for Disease Control and Prevention initiated the Rotavirus Vaccination Program, which has sought to make rotavirus vaccines more widely available. As well, beginning in 2005, the Pan American Health Organization commenced an annual campaign of immunization that includes the FDA-licensed rotavirus vaccine.

See AlsoBacterial Disease; Cholera; Escherichia coli O157:H7; Food-borne Disease and Food Safety; Norovirus Infection; Salmonella Infection (Salmonellosis); Sanitation; Shigellosis; Water-borne Disease.

BIBLIOGRAPHY

Web Sites

Centers for Disease Control and Prevention (CDC). “Cholera.” <http://www.cdc.gov/ncidod/dbmd/diseaseinfo/cholera_g.htm> (accessed May 25, 2007).

World Health Organization. “International Network to Promote Household Water Treatment and Safe Storage.” <http://www.who.int/household_water/en/> (accessed May 25, 2007).

Centers for Disease Control and Prevention (CDC).

“Viral Gastroenteritis.” <http://www.cdc.gov/ncidod/dvrd/revb/gastro/faq.htm> (accessed May 25, 2007).

Brian Hoyle

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