Heliobacteriosis

Helicobacteriosis refers to infection of the gastrointestinal tract with the bacteria, Helicobacter pylori (H. pylori). While there are other rarer strains of Helicobacter species that can infect humans, only H. pylori has been convincingly shown to be a cause of disease in humans. The organism was first documented to cause injury to the stomach in 1983, by two researchers in Australia, who ingested the organism to prove their theory. Since then, H. pylori has been shown to be the main cause of ulcer disease, and has revolutionized the treatment of peptic ulcer disease. It is also believed to be linked to various cancers of the stomach.

Description

H. pylori is a gram-negative, spiral-shaped organism, that contains flagella (tail-like structures) and other properties. In addition to flagella, which help the organism to move around in the liquid mucous layer of the stomach, H. pylori also produces an enzyme called urease, that protects it from gastric acid present in the stomach. As the production of this enzyme is relatively unusual, new diagnostic tests have enabled rapid identification of the bacteria.

H. pylori also produces two other chemicals: a cytotoxin called vacA, and a protein known as cagA. Patients with ulcer disease are more likely to produce the cytotoxin (vacA). The cagA protein not only occurs frequently in ulcer disease but also in cancer. It is still not known how these substances enable H. pylori to cause disease.

Causes and symptoms

Infection with H. pylori is largely dependent on two factors; age and income status. The bacteria is acquired mainly in childhood, especially in areas of poor hygiene or overcrowding. H. pylori is two to three times more prevalent in developing, non-industrialized countries. In the United States for example, the organism is believed to be present in about one third of the population.

The exact way in which H. pylori gets passed from one individual to another is uncertain, but person to person transmission is most likely. In most cases, children are felt to be the source of spread. Reinfection of those who have been cured has been documented, especially in areas of overcrowding.

The bacteria is well adapted to survival within the stomach. Not only does it survive there for years, but once infection begins, a form of chronic inflammation (chronic gastritis) always develops. In most individuals, initial infection causes little or no symptoms; however, some individuals such as the original researchers who ingested the bacteria, wind up with abdominal pain and nausea.

In about 15% of infected persons, ulcer disease develops either in the stomach or duodenum. Why some develop ulcer disease and others do not, remains unclear. Ulcer symptoms are characterized by upper abdominal pain that is typically of a burning or "gnawing" type, and usually is rapidly relieved by antacids or food.

Acid secretion increases in most patients with duodenal ulcers. This increase returns to normal once H. pylori is eliminated. It is now known that elimination of the bacteria will substantially decrease the risk of recurrent bouts of ulcer disease in the vast majority (85% or so) of patients.

In the last decade it has been shown that H. pylori is not only the prime cause of ulcer disease of the stomach and duodenum, but is also strongly associated with various tumors of the stomach. Bacterial infection is nine times more common in patients with cancer of the stomach, and seven times more common in those with lymphoma of the stomach (tumor of the lymphatic tissue), called a MALT tumor. It is believed that the prolonged inflammation leads to changes in cell growth and tumors. Eliminating H. pylori can lead to regression of some tumors.

In addition to the above damage caused by H. pylori, some individuals lose normal gastric function, such as the ability to absorb vitamin B₁₂.

Diagnosis

There are basically two types of tests to identify infection: one group is "invasive" in that it involves the use of an endoscopy to obtain biopsy specimens for evaluation, while the other "noninvasive" methods depend on blood or breath samples. Invasive tests can be less accurate because of technical limitations: the biopsy may miss the area where the bacteria hides.

Invasive studies make use of tissue obtained by endoscopic biopsy to identify the organism. The bacteria can be searched for in pieces of biopsy tissue or grown (cultured) from the specimen. However, H. pylori is not easy to culture. Another method uses the bacteria's production of the enzyme urease. Biopsy specimens are placed on a card that changes color if urease is present. Results are often available within a few minutes, but can take up to 24 hours.

Noninvasive tests are of two types: blood tests and breath test. Blood tests measure antibodies to make a diagnosis accurately within minutes. This can be done immediately in the doctor's office. In addition, antibody levels can be measured several months after treatment, to see if H. pylori has been eradicated.

The breath test uses radioactive or non-radioactive forms of a compound called urea, which the patient drinks. The method that uses a radioactive form urea is easier to perform, as the equipment is commonly available in x-ray departments. Radiation exposure is less than that of a chest x ray. The test that uses non-radioactive urea is safer for children. The breath test is the best way to be sure of elimination of H. pylori. The test can be used within 30 days after treatment. This is an advantage over following antibody levels that take six months or longer to diminish.

A light microscopic image of a stomach ulcer. Gastric and duodenal ulcers are usually caused by infection with the bacteria Helicobacter pylori. This bacterium is also believed to be a cause of various cancers of the stomach. (Photograph by J.L. Carson, Custom Medical Stock Photo. Reproduced by permission.)

Treatment

H. pylori peptic ulcers are treated with drugs to kill the bacteria, drugs to reduce stomach acid, and drugs to protect the lining of the stomach. The antibiotics most commonly used to kill the bacteria are: amoxicillin, clarithromycin, metronidazole, and tetracycline. Drugs used to reduce stomach acid may be histamine blockers or proton pump inhibitors. The most commonly used histamine blockers are: cimetidine, famotidine, nizatidine, and ranitidine. The most commonly used proton pump inhibitors are: lansoprazole and omeprazole. The drug bismuth subsalicylate (a component of Pepto-Bismol) is used to protect the stomach lining.

The most common drug treatment is a two-week course of treatment called triple therapy. This treatment regimen involves taking two antibiotics to kill the bacteria and either an acid reducer or a stomach-lining shield. This therapy has been shown to kill the bacteria, reduce ulcer symptoms, and prevent ulcer recurrence in over 90% of patients.

The main drawback of triple therapy is that some patients find it difficult to follow because it often requires taking as many as 20 pills a day. The antibiotics may also cause unpleasant side effects that may make certain patients less likely to follow the treatment protocol. These side effects include: dark stools, diarrhea, dizziness, headache, a metallic taste in the mouth, nausea, vomiting, and yeast infections in women.

Prognosis

The elimination of H. pylori and cure of ulcer disease is now possible in more than 90% of those infected. The finding that most ulcers are due to an infectious agent has brought a dramatic change in treatment and outlook for those suffering from that disease. Some patients will wind up with repeated infection, but this is most common in overcrowded areas.

Prevention

Attempts to develop a vaccine to protect against infection may be worthwhile in areas where the H. pylori infection rate and occurrence of cancer of the stomach is quite high, such as in Japan.