Microbiology and Immunology

Gastroenteritis WORLD OF MICROBIOLOGY AND IMMUNOLOGY

236

•

GGastroenteritisASTROENTERITIS

Gastroenteritis is an inflammationof the stomach and the

intestines. More commonly, gastroenteritis is called the stom-

ach flu.

The symptoms of gastroenteritis always include diar-

rhea. Fever, and vomiting can also be present. Typically the

symptoms associated with a bout of gastroenteritis typically

last only several days and are self-limiting. But sometimes the

malady can be more extended.

The diarrhea in gastroenteritis is very loose, even

watery. Also, bowel movements are frequent, occurring even

several times an hour as the body attempts to expel the offend-

ing microorganism. This large loss of fluid creates the poten-

tial for dehydration. Usually dehydration is not an issue in an

adult, unless the person is incapable of caring for themselves

and has no other caregiver. Dehydration is an important issue

in children. If a child is hospitalized because of diarrhea, it is

usually because of complications arising from dehydration,

rather than from the actual stomach and intestinal infection.

The other symptoms of gastroenteritis are especially

complicating in children. Vomiting makes it difficult to admin-

ister drugs to combat a bacterial infection. Also, the loss of

stomach contents can exacerbate dehydration.

Gastroenteritis-induced diarrhea is one of the major

causes of death in infants around the world. In Asia, Africa,

and Latin America millions of deaths in the newborn to four

years age group occurs every year.

Gastroenteritis can be caused by virusesand bacteria.

Viruses are the more common cause. Many There types of

virusescan cause gastroenteritis. These include rotaviruses,

enteroviruses, adenoviruses, caliciviruses, astroviruses,

Norwalk virus and a group of Norwalk-like viruses. Of these,

rotavirus infections are the most common.

Viral gastroenteritis tends to appear quickly, within

three days of ingestion of the virus, and diminishes within a

week. Those whose immune systemis compromised may

experience symptoms for a longer period of time.

Rotavirus is a virus that contains ribonucleic acidas the

genetic material. The genetic material is enclosed within a

double shell of protein. The virus is a member of the

Reoviridae family of viruses. There are three main groups of

rotavirus with respect to the antibodies that are produced

against them. These types are called groups A, B, and C.

Group A rotavirus is the cause of more than three million

cases of gastroenteritis in the United States every year. The

group B rotavirus causes diarrhea in adults, and has been the

cause a several major outbreaks of severe diarrhea in China.

Finally, the group C rotavirus can cause diarrhea in both chil-

dren and adults, but is encountered much less frequently than

groups A and B.

Rotavirus gastroenteritis is very contagious, spreading

from person to person in a fecal to oral route. Not surprisingly,

the virus is frequently encountered in day care facilities, where

the care of the soiled diapers of infants occurs regularly.

Improper hygiene, especially hand washing, contributes

directly to the spread of the virus. Infected individuals can

shed large numbers of virus in their diarrhea. Infection can

also be spread by the contaminationof eating utensils. Food

can become contaminated if the food handler has not properly

washed their hands after using the bathroom. Shellfish can

also be a source of the virus. Because shellfish feed by filter-

ing water through a special filter feeding apparatus, virus in

the water can become trapped and concentrated inside the

shellfish. Eating the shellfish, especially raw, spreads the

virus.

Gastroenteritis due to the Norwalk virus tends to be

more common in adults. However, more advanced immuno-

logical methods of detection have detected antibodyto the

virus in many children. Thus, children may be infected by the

virus but show no symptoms. Infection in the adult years pro-

duces gastroenteritis, for reasons that are as yet unknown.

Discovering the nature of the asymptomatic response of chil-

dren could led to a therapeutic strategy for the adult infection.

Bacteria also cause gastroenteritis. The bacteria of con-

cern include certain strains of Escherichia coli, Salmonella,

Shigella,and Vibrio cholerae. In developed countries, where

sanitary conditions and water treatment are established, bacte-

rial gastroenteritis is infrequent. But the bacterial form

remains problematic in the under-developed world, where

water is more vulnerable to contamination. Bacterial gastroen-

teritis can also be caused by the ingestion of contaminated

food. For example the presence of Salmonellain potato salad

that has been improperly stored or of E.coli O157:H7in

undercooked meat can cause the malady.

The protozoan Cryptosporidium parvumalso causes

gastroenteritis following the ingestion of contaminated water.

The bacterial and protozoan cases of gastroenteritis

account for well below half of the reported cases. The major-

ity of cases are of viral origin.

In the treatment of gastroenteritis it is important to

establish whether the source of the condition is bacterial, viral,

protozoan or another and non-biological factor. Intolerance to

the digestion of the lactose constituent of milk can also cause

gastroenteritis, for example. The need to establish the origin of

the malady is important, since bacterial infections will respond

to the administration of antibioticswhile viral infections will

not. Furthermore, the use of antibiotics in a viral infection can

actually exacerbate the diarrhea.

In August 1998, a vaccinefor rotavirus gastroenteritis

was licensed for sale in the United States. From September

1998 until July 1999, 15 cases of intussusception (a condition

where a segment of bowel folds inside an adjacent segment,

causing an obstruction) were reported among infants who

received the vaccine. Subsequently, the vaccine was with-

drawn from the market. No other vaccine has as yet been

licensed for use.

See also Enterobacterial infections; Transmission of

pathogens

GGene ENE

A gene is the fundamental physical and functional unit of

heredity. Whether in a microorganism or in a human cell, a

womi_G 5/6/03 3:18 PM Page 236