Infections of the Small Intestine

The major function of the small intestine is to digest, absorb and propel food along its length. Most clinically important infections of the small intestine will interfere with these functions. Diarrhea is common; other symptoms include bleeding, bloating, nausea, vomiting, abdominal pain, and even features of complete abdominal obstruction. Some infections have characteristic features.

Electron micrograph showing Salmonella Typhimurium.
Color-enhanced scanning electron micrograph
showing Salmonella Typhimurium (red)
invading cultured human cells.

Salmonella Infections

Salmonella appears in many forms. The so called non-typhoidal Salmonella species is the most common cause of food poisoning outbreaks in the United States. These organisms are extremely common in meat products, but have also been traced to pet turtles and iguanas. Chickens and eggs are probably the most common cause of infection.

Patients will develop symptoms 10 to 48 hours after eating contaminated food. They may have a wide range of symptoms ranging from mild gastroenteritis to a severe diarrheal illness with dehydration and profound infection. Patients with malignancies, sickle-cell anemia, aortic aneurysms, and heart valve disease appear to be more predisposed to getting a disseminated type of infection (i.e. spread to the blood).

Patients may get better without the use antibiotics. Antibiotics are recommended for very ill patients. A small percentage of individuals may develop a chronic carrier state; they are asymptomatic, but excrete salmonella in the stool for a year or longer.

Illustration of a typhoid bacteria.
Typhoid fever is a common worldwide bacterial
disease transmitted by the ingestion of food
or water contaminated with feces from an
infected individual.

Typhoid Fever – An infection from a particular species of Salmonella (usually Salmonella typhi), typhoid fever is characterized by prolonged fever, bacteria in the blood and multiple organ dysfunctions, including inflammation of the kidney and brain. Typhoid fever is becoming rare in the United States. Immunization is useful. Treatment requires powerful antibiotics and specific treatments for other organ involvements.

Staphylococcus Aureus – Staphylococcus aureus is probably the second most common cause of bacterial food poisoning in the United States. The bacteria multiply in the food and produce the toxin. The toxin that is produced by the food is not inactivated by heating. Symptoms develop within six to eight hours and are dominated by vomiting and abdominal cramping. Usually patients make a full recovery within 24 to 48 hours.

Bacillus Cereus – Bacillus cereus is an organism that produces an intestinal toxin. This infection is associated with the consumption of fried rice. Vomiting usually occurs within six hours of ingesting the food. Some patients may develop diarrhea, but most improve spontaneously without specific treatment.

Other Infections – There are many other bacterial infections that can cause acute symptoms. These include the various E-coli, Clostridium, Campylobacter, Yersinia, and Vibrio (cholera). There are also viral infections of the intestine that can cause acute diarrheal illnesses which usually resolve spontaneously. Dehydration is the biggest problem.

An image of a species of protozoa in a bone marrow cell.
A species of protozoa in a bone marrow cell.

Protozoal Infections

Giardia Lamblia – Giardia lamblia is a common parasitic pathogen which can contaminate water supplies, and often occurs in travelers to underdeveloped countries. Children in day care centers (and adults working in them) have a higher incidence of contracting Giardiasis.

Symptoms vary but can include bowel disturbance, gas, bloating and features of malabsorption. Patients may have significant weight loss and some steatorrhea. Diagnosis can be made by doing a specific stool analysis, or by examining a duodenal biopsy specimen which is obtained during upper endoscopy.

Giardia is usually easily treated with a short course of antibiotics. Infections can recur, and the intestine may remain "irritable" for some weeks or months after the infection is eradicated.

Intestinal Worms

While true that many intestinal worms can be found in the United States, they are, in fact, a global problem with most instances occurring outside the USA.

Hookworm – Hookworms attach themselves to the lining of the small intestine. They are the most common cause of iron deficiency anemia worldwide, and can also result in abdominal pain and diarrhea. Occasionally severe protein loss can occur from the intestines. The diagnosis is made by stool examination. Medication is effective.

Tapeworm – There are numerous types of tapeworms that can be found in various meats, such as pork, beef or fish. Infection occurs when poorly cooked meats are ingested. The most common type of tapeworm in the United States is thought to be transmitted through contact with human feces.

Tapeworms can cause obstruction to the intestine, but usually cause few symptoms apart from non-specific abdominal pains and occasional diarrhea. The fish tapeworm can cause vitamin B12 deficiency. Diagnosis is made by stool examination, and effective medication is available.

Pin Worm – Quite often seen in young children, the most common symptom of pin worms is itching in the anal area, though many infected individuals are asymptomatic. The diagnosis is made by finding the eggs or the actual worms around the peri-anal area by placing a transparent sticky tape to the anal area early in the morning. The sticky tape is then examined under a microscope slide.

Although specialized therapy is both available and effective, testing and treatments may still need to be conducted on other members of the household to prevent reinfection.

Strongyloides Stercoralis – Strongyloides Stercoralis is most common in Africa, Asia and Latin America but is found also in the southern part of the United States. This worm enters the body by penetrating through the skin and migrating through the venous system to the lungs and finally reaches the small intestine.

Patients may develop symptoms from lung involvement such as cough, shortness of breath and wheezing. Chronic infection can cause intermittent abdominal pain, vomiting, malabsorption and weight loss.

Patients with organ transplant or underlying malignancies such as leukemia, lymphoma or those who are taking corticosteroid therapy can develop a life threatening infection manifested by severe gastrointestinal and pulmonary symptoms. The diagnosis is made by careful stool examination and specific medication is prescribed.

Echinococcosis – Echinococcus worm is found in the intestine of dogs and sheep. Humans become infected with the cystic form. This infection is found in areas where dogs, sheep and humans live in close proximity, particularly under conditions of poor hygiene. Humans become infected when they ingest the eggs in fecally contaminated food such as vegetables, wild fruits and water.

Once the eggs enter the human intestine the larvae invade the bowel wall and circulate to various organs such as the liver and lung where they form cysts.

Diagnosis is made by X-ray studies. A special blood test can detect specific antibodies. Although some patients will also require surgery, all will be treated with medications.