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The Patient With Protozoan Illness
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The Case: A 5-year-old boy is brought to your office by his mother with a history of foul smelling, watery loose stools several times daily, accompanied by crampy abdominal pain and nausea for the past 3 days. For the past 24 hours, he has been fatigued and complains that his arms and legs ache. He has been able to drink liquids, but milk makes the cramps and diarrhea worse. The mother reports that he had been on a camping trip with his father about 2 weeks ago. Blood studies reveal that his CBC, BUN, and electrolytes are normal. He presently attends preschool and lives with his mother and two younger siblings. Stool specimen is positive for Giardia lamblia.
Key Supporting Information
Protozoa are microscopic, one-celled organisms that can be free-living or parasitic in nature. They are able to multiply in humans, which contributes to their survival and also permits serious infections to develop from just a single organism. Transmission of protozoa that live in a human’s intestine to another human typically occurs through a fecal-oral route (eg, contaminated food or water or person-to-person contact).
Pathogenic intestinal protozoa produce diarrhea and other intestinal symptoms by colonizing the human small and/or large intestine. Infections are found worldwide both in developing countries and the industrialized world. Intestinal protozoa are most prevalent in the developing world, where they are responsible for substantial morbidity and mortality. With continuing emigration from endemic countries, screening for parasitic infections remains a priority in United States (US) communities serving refugee and immigrant populations.
In developed settings, enteric protozoa are often ignored as a cause of diarrheal illness due to better hygiene conditions, and as such, very little effort is used toward laboratory diagnosis. Although these protozoa contribute to the high burden of infectious diseases, estimates of their true prevalence are sometimes affected by the lack of sensitive diagnostic techniques to detect them in clinical and environmental specimens. In many developed countries, only a few or no parasitic protozoa are included in operational surveillance systems because the major focus is on bacterial and viral infections. Where these systems exist, they are used mainly as indicators for identifying outbreaks of foodborne and waterborne diseases and in institutional settings. In many cases, the sick person in a developed setting may not seek medical attention, and even if he or she does, a stool specimen is not routinely requested from persons with diarrheal illnesses. For example, during an outbreak of gastroenteritis linked to a water supply in Austria in 2006, there was no identification of pathogenic microorganisms in stool samples from affected patients, and no parasite etiology was considered in this large outbreak. This could have been due to the fact that test requests by general practitioners may not have complied with existing knowledge of the gastroenteritis etiology at that time. There is evidence that climate-related changes will contribute to the burden of protozoan illness due to displacement of ecosystems and human and animal populations, increases in atmospheric temperature, flooding and other environmental conditions suitable for transmission, and the need for the reuse of alternative water sources to meet growing population needs.
Despite recent advances in the epidemiology, molecular biology, and treatment of protozoan illnesses, gaps in knowledge still exist, requiring further research. The development of technologies that can simultaneously detect several protozoa in stool is desirable in industrialized settings. This includes the development of molecular markers for the detection of outbreaks, for source attribution, and to estimate their contribution to the overall burden of infectious diseases.
The small intestinal protozoa Giardia lamblia and Cryptosporidium parvum have their major impact in children, whereas the large-bowel pathogen Entamoeba histolytica infects all age groups but has its most profound effects in adults. For many of the protozoa, the host immune response remains poorly defined, as do the mechanisms involved in their eradication and the development of protective immunity. As yet, there is no candidate vaccine for any of the intestinal protozoan infections. It is likely that the next decade will produce great advances in the understanding of many of these areas because of the research currently being undertaken on pathogenetic mechanisms and immune responses, with commensurate progress in treatment and prevention.
The mode of transmission is mainly horizontal, through physical contact with an infected person or with their excretions. Horizontal transmission can occur through direct contact with siblings, parents, or health care workers. Some cases of transmission through the ingestion of contaminated water or infant formula are also reported. Waterborne protozoan parasites such as cryptosporidium and giardia induce enteritis through their membrane-associated functional structures and virulence factors that alter host cellular molecules and signaling pathways, leading to structural and functional lesions in the intestinal barrier.
Cryptosporidium parvum has a high infectivity with significant enteric disease and rarely is asymptomatic. There have been reported cases of infection in the first month of life, although the passage of the maternal antibodies and breastfeeding are a protective factor against infection. Cryptosporidiosis is one of the most important diarrheal pathogens affecting people worldwide. Effective methods to control and treat cryptosporidiosis among high-risk groups present an ongoing problem in need of attention. Molecular methods provide a clearer understanding of cryptosporidiosis epidemiology. The major determinants of severity still are host immune status and parasite species. Children and immunosuppressed individuals, especially those with HIV/AIDS, are disproportionately affected.
Giardiasis is one of the intestinal protozoa that cause public health problems in most resource-constrained nations, as well as some resource-rich countries. Many infected persons can be asymptomatic, leading to difficulties in the eradication and control of this parasite due to the number of potential carriers, such as school children. Giardia lamblia is observed almost three times more in asymptomatic children than in symptomatic children. The first signs of acute giardiasis include nausea, loss of appetite, and an upper gastrointestinal uneasiness, followed or accompanied by a sudden onset of explosive, watery, foul-smelling diarrhea. Stools associated with giardiasis are generally described as loose, bulky, frothy, and/or greasy with the absence of blood or mucus, which may help distinguish giardiasis from other acute diarrheas. Other gastrointestinal disturbances may include flatulence, bloating, anorexia, or cramps. The acute stage usually resolves spontaneously in a few days. Occasionally, an acute infection will persist and lead to malabsorption, steatorrhea, loss of strength, and weight loss. It has been estimated that about 200 million people are infected each year in Africa, Asia, and Latin America. In the resource-rich countries, the prevalence rate of giardiasis is 2% to 5%. However, in resource-constrained countries, Giardia lamblia infects children early in life, thus a prevalence rate of 15% to 20% in children younger than 10 years is common. Children who are malnourished are more frequently infected.
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Learning Objectives
Upon successful completion of this educational activity, participants should be better able to evaluate protozoan infectious diarrhea in children.
Overview
Author(s)/Faculty: Ronald A. Codario, MD, FACP, FNLA, RPVI, CCMEP
Source: Healio Gastroenterology Education Lab
Type: Monograph
Articles/Items: 4
Release Date: 6/15/2015
Expiration Date: 6/15/2016
Credit Type: CME
Number of Credits: 0.25
Cost: Free
Provider: Vindico Medical Education
CME Information
Provider Statement: This continuing medical education activity is provided by Vindico Medical Education.
Support Statement: No commercial support for this activity.
Target Audience: This activity is designed for infectious disease specialists and other health care professionals involved in the treatment of patients with infectious diseases.