Infectious Human Diseases of the Intestine

Mary E. Miller

• Publisher: Momentum Press
• Year: 2018
• ISBN:
  9781944749880
• Topic: Ciencias biológicas
• Subtopic: Genética y genómica

This book describes the current understanding of symptoms, diagnosis, mode of transmission, and treatments of four important intestinal diseases, taking into consideration the molecular interactions between host cells and infectious agents.

Intestinal diseases are a significant health issue worldwide, with varying causative infections resulting in symptoms that range from mild or asymptomatic to death within hours. Understanding the cause of the different forms of intestinal disease is a critical aspect of proper management of these diseases that can save lives.

This book describes the current understanding of symptoms, diagnosis, mode of transmission, and treatments of four important intestinal diseases, taking into consideration the molecular interactions between host cells and infectious agents. Specifically, dysentery caused by infection with Entamoeba histolytica, giardiasis caused by infection with Giardia, shigellosis caused by infection with Shigella, and cholera caused by infection with Vibrio cholera, are discussed in each chapter.

The author also discusses future work related to prevention and treatment of these critical infectious diseases, given that the eradication of these diseases is unlikely. Awareness of how these diseases are spread and how they can be contained is a growing public health concern, particularly after natural and human-made disasters where public hygiene may be compromised.

CHAPTER 1

Symptoms and Diagnosis

Symptoms and Diagnosis of the Dysentery

Dysentery is a disease of the intestines that results in severe diarrhea with blood or mucus in the stool. Symptoms can include pain in the abdomen, fever, and a feeling of incomplete defecation. Symptoms are coupled to an inflammatory response in the colon that occurs because of infection by a microorganism. Several different types of microorganisms can cause dysentery, including the bacteria Shigella, the eukaryotic amoeba Entamoeba histolytica, and some strains of the bacteria Escherichia coli. Depending on the type of infecting microorganism, progression can cause severe disease of other organs in the body, such as the liver, lungs, or brain.

When a patient suffers from gastrointestinal disease caused by Shigella, it is called shigellosis. There are an estimated 164.7 million Shigella infections worldwide each year that include both endemic occurrences and epidemic outbreaks. Symptoms may include diarrhea, fever, stomach cramps, and the feeling that they need to pass stool when their bowels are empty. Shigella are able to infect the epithelial cells of the mucosa in the colon. As the infection spreads, it can cause ulcer, bleeding, and inflammation. In more serious forms of the disease, visibly bloody diarrhea can occur. Symptoms typically begin about 2 days after the infection occurs and subside within 5 days. While infected, people can spread Shigella to others which is particularly concerning when patients have very mild or undetectable symptoms, so they unknowingly spread the disease. In severe cases, Shigella can be spread to the blood system resulting in a blood-borne disease. Blood-borne shigellosis is life-threatening with a fatality rate of 46 percent. Complications associated with shigellosis include hemolytic-uremic syndrome that can lead to kidney failure and is one of the most common causes of kidney failure in children (though not necessarily because of Shigella infections). In rare cases associated with Shigella dysenteriae infections, the colon can become paralyzed so that it is unable to pass feces or gas, which causes swelling, fever, pain, weakness, and disorientation. Other complications of shigellosis can include hypoxia (low oxygen levels), reactive arthritis, and some neurological problems. Hyponatremia (abnormal electrolyte balance) and pneumonia can also occur, but these two diseases are uncommon consequences of Shigella infections.

Dysentery can also be caused from an infection by Entamoeba histolytica, and when this occurs the disease is called amebiasis. E. histolytica is distributed worldwide though it is more common in tropical regions. Approximately 50 million infected individuals experience gastrointestinal symptoms, and approximately 100,000 deaths occur per year. Most individuals who are infected with E. histolytica do not show symptoms, with only 10 to 20 percent getting sick. Long-term travelers (more than 6 months) are at higher risk of contracting amebiasis than short-term travelers (less than 1 month). Risk also increases for pregnant, immunocompromised, diabetic, and alcoholic individuals and patients taking corticosteroids. If symptoms occur, they usually develop 2 to 4 weeks after infection, though some cases take longer to become symptomatic. Symptoms include loose feces, stomach pain, and stomach cramping. More severe cases, such as amebic dysentery, cause stomach pain, bloody feces, and fever. In rare cases, infection spreads to the liver, and in even more rare cases it can spread to other parts of the body such as the lung or brain.

Diagnosis of both shigellosis and amebiasis involves identifying the infecting microorganism in the patient’s feces. Detection of Shigella infection involves sampling patient feces and allowing bacteria in the sample to grow in the laboratory for identification. These tests can be designed to distinguish Shigella species and antibiotic resistant forms of the bacteria, which can aid in treatment. Molecular tests designed to detect specific regions of the bacterial genome can also be used to diagnose specific species and drug resistance. For amebiasis, identification may involve concentrating microorganisms present in a stool sample and looking for the presence of E. histolytica cysts. Visual detection can be aided with the use of stains, such as trichome, which can help visualize the parasites when using a microscope. Since amoebas have a complex life cycle, it can be difficult to diagnose the disease based on histological approaches, and these approaches may not distinguish between pathogenic and nonpathogenic parasites. Improved methods include antibody-based and DNA tests to ensure that protozoan cysts identified in patient samples are capable of triggering dysentery.

Symptoms and Diagnosis of Cholera

Cholera is a serious gastrointestinal disease caused by infection of the bacteria Vibrio cholerae. A major health concern worldwide, cholera can cause death within hours of the onset of symptoms. Worldwide, approximately 21,000 to 143,000 deaths occur from cholera each year, and between 1.3 and 4 million individuals contract the disease. Cholera cases are not well documented sometimes, and reporting of cholera cases is not mandatory in many areas. In many areas, cholera is considered endemic and thus is a constant health concern. Outbreaks of cholera can be seasonal, or sporadic, frequently associated with heavy rainfalls. Outbreaks can vary in scale. If a region has not had a case in at least 3 years and one new case occurs, it would be considered an outbreak. In 2018 outbreaks have been recorded in Somalia (March 29, 2018); Kinshasa, Democratic Republic of the Congo (March 2, 2018); Mozambique (February 19, 2018); and United Republic of Tanzania (January 12, 2018). In 2017, 35 partners in the Global Task Force on Cholera Control developed a strategy to reduce deaths by 90 percent before the year 2030.

Most infected individuals show mild-to-moderate cholera symptoms that include acute watery diarrhea with dehydration. Severe dehydration causes lethargy, dry mouth, weak or absent pulse, low blood pressure, and low amounts of urine. Symptoms usually occur between 12 hours and 5 days after infection. Since many diseases cause diarrhea, diagnosis of cholera requires identification of V. cholerae in the patient’s feces. Identification of V. cholerae in feces can be performed using rapid diagnostic tests, but should be confirmed in a laboratory setting where bacteria are isolated and grown from patient samples. Subtyping, or serotyping, isolates is done using molecular tests that identify the O antigen or specific regions of the bacteria’s genome. The O antigen is a sugar expressed on the surface of the bacterium that can vary between different strains and be used to distinguish between pathogenic and nonpathogenic bacteria. Rapid tests can identify V. cholerae but are less able to identify serotypes or drug susceptibility; hence, slower molecular diagnosis methods are required for optimal treatments. In some areas, molecular tools are not available, so rapid tests such as Crystal VC dipstick can give an early warning to public health professionals of a potential outbreak. Positive rapid test results should be followed up by culturing the bacteria from patient fecal samples. The WHO recommends that instances involving children younger than 2 years of age experiencing acute diarrhea with dehydration, or instances of death from diarrhea, should be considered a suspected case of cholera. In areas where a cholera outbreak has been confirmed, any aged person with similar symptoms should be suspected of having cholera. Confirmed cases of cholera would include those cases where V. cholerae O1 or O139 antigens are confirmed by molecular tests.

Symptoms and Diagnosis of Giardiasis

Giardia is the one of the most common global causes of intestinal disease in people. Giardia infects approximately 2 percent of adults and 6 to 8 percent of children in developed nations, and 33 percent of individuals in developing countries. Infection by Giardia results in an intestinal disease called giardiasis. Though some people show no symptoms, most people with giardiasis experience a combination of symptoms that include diarrhea, gas that smells like rotten eggs, greasy stools that might float, stomach cramps, abdominal cramps, nausea, and dehydration. In rare cases, itchy skin, hives, and swollen eyes/joints might occur. Symptoms normally appear one to three weeks after infection. Sometimes symptoms...