Predominance of Gastrointestinal Protozoan Parasites in Children: A Brief Review

Intestinal parasitic infections caused by intestinal helminths and protozoa are among the most common human infections endemic throughout the world especially in tropical and subtropical countries including India. About 3.5 billion persons are infected with intestinal parasites and nearly 450 million suffer from clinical morbidity [3]. The protozoan parasites are the more common cause of gastrointestinal disorders compared to helminthes especially in developing countries. A number of intestinal protozoan parasites are reported in different parts of the world like Giardia lamblia, Dientamoeba fragilis, Entamoeba histolytica, Blastocystis homini, Isospora belli, Cyclospora cayetanensis and Microsporidia. Among them Entamoeba, Giardia and Cryptosporidium are the major protozoan parasites of global public health concern. Protozoan parasites being single celled can rapidly multiply inside the body leading to the development of the serious infection. Most of the protozoan infections tend to be asymptomatic. However, the common symptoms associated with it include abdominal discomfort, vomiting and dysentery [4]. When burden of infection is pronounced, it may cause several complications like diarrhea, malaise, bloating, fatigue, epigastric discomfort, malnutrition, mal-absorption, intestinal ulceration, gastroenteritis, weight loss, abscesses, mental retardation and even death. Protozoan infections can also lead to structural and functional abnormalities of small intestines in humans and can be misdiagnosed as appendicitis or other inflammatory diseases of gastrointestinal tract. Children are the primary victims of gastrointestinal protozoan parasites. So the disease control interventions need to be focused towards the pediatric group.


Introduction
Intestinal parasitic infections caused by intestinal helminths and protozoa are among the most common human infections endemic throughout the world especially in tropical and subtropical countries including India. About 3.5 billion persons are infected with intestinal parasites and nearly 450 million suffer from clinical morbidity [3]. The protozoan parasites are the more common cause of gastrointestinal disorders compared to helminthes especially in developing countries. A number of intestinal protozoan parasites are reported in different parts of the world like Giardia lamblia, Dientamoeba fragilis, Entamoeba histolytica, Blastocystis homini, Isospora belli, Cyclospora cayetanensis and Microsporidia. Among them Entamoeba, Giardia and Cryptosporidium are the major protozoan parasites of global public health concern. Protozoan parasites being single celled can rapidly multiply inside the body leading to the development of the serious infection. Most of the protozoan infections tend to be asymptomatic. However, the common symptoms associated with it include abdominal discomfort, vomiting and dysentery [4]. When burden of infection is pronounced, it may cause several complications like diarrhea, malaise, bloating, fatigue, epigastric discomfort, malnutrition, mal-absorption, intestinal ulceration, gastroenteritis, weight loss, abscesses, mental retardation and even death. Protozoan infections can also lead to structural and functional abnormalities of small intestines in humans and can be misdiagnosed as appendicitis or other inflammatory diseases of gastrointestinal tract. Children are the primary victims of gastrointestinal protozoan parasites. So the disease control interventions need to be focused towards the pediatric group.

Giardia lamblia
It is a flagellated protozoan parasite of phylum Sarcomastigophora that colonise and reproduce in small intestines of humans, causing disease Giardiasis. Giardia is most frequently reported as a cause of diarrhea worldwide. Giardiasis can be responsible for severe malabsorption syndrome causing malabsorption of fat, proteins, folic acid, Vitamin A and vitamin B12 and these nutritional deficiencies in turn may lead to serious organ damage [5]. Giardia intestinalis results in stunted growth and poor psychomotor development of children [6]. Giardia infection also results in rEducced Hb level [7] and hypoalbuminemia [8,9]. It sometimes infects gall bladder leading to jaundice and colic.

Global burden
Giardia lamblia is the most prevalent protozoan parasite worldwide currently infecting about 200 million people [10]. G. lamblia is known to infect 2% to 5% of population in developed countries and 20-40% in developing countries, majority of which are children [5,11,12] (Table 1).

Entamoeba histolytica
It is a protozoan parasite of phylum Sarcomastigophora that colonizes and reproduces in large intestines of humans, causing disease Amoebiasis. The disease may remain restricted to intestinal lumen or invade intestinal lining causing Amoebic dysentery. It not only causes severe diarrhea but can also result in extra intestinal manifestations including rectal bleeding, amoeboma, toxic megacolon, pneumatosis coli, peritonitis and abscesses in the intestine, liver, lung and other organs. Entamoeba histolytica is reported to be responsible for deaths of approximately 1,00,000 persons per year, second only to another protozoan infection, malaria [1].

Global burden
Nearly 10% of the world's population is infected with E. histolytica, the majority being in developing countries. Most of the infected individuals tend to be asymptomatic while the minority of cases develops clinically apparent disease. E. histolytica is known to result in 50-100 million cases of colitis or liver abscesses per year and up to 100,000 deaths annually [13]. Amoebiasis is the third leading cause of death from parasitic diseases world-wide with its greatest impact on people of developing countries (

Control and Prevention
In view of high prevalence of protozoan infection and the morbidity they cause, the measures aimed at their control and prevention need to be strengthened. Steps should be taken to rEducce the infection rate to the levels at which they cease to be of public health significance. The prevention and control of protozoan diseases can be primarily achieved through improvement in personal as well as environmental hygiene [75]. The most effective control can be achieved by involving the community to participate in its own disease control. For this purpose, mass awareness programmes should be conducted to make the people aware about the various infectious agents and their modes of transmission, encourage hygienic practices, recommend use of safe drinking water, avoid defecation in open areas, and prioritize primary health care. Moreover, standard techniques should be used by clinical microbiologists for screening the stool samples to increase the chances of detection of parasites and chemotherapy option should be used for treatment of individuals diagnosed with protozoan infections.

Conclusion
Gastrointestinal disorders caused by various protozoan parasites impose a great burden on human populations in the developing world, particularly among children. The need of the hour is that we should have enough epidemiological information on the prevalence of gastrointestinal protozoan infections and their associated risk factors in different localities which are a prerequisite to develop quality control measures.

Cryptosporidium parvum
It is a small coccidian protozoan parasite belonging to Phylum Apicomplexa that infects the microvillous region of epithelial cells of the digestive tract in humans. Cryptosporidium causes moderate to severe diarrhea in the immunocompetent individuals due to malabsorption and increased secretion. In the immunocompromised individuals, the condition can be prolonged and dangerous. Cryptosporidium infection of the intestinal epithelium is associated with villous atrophy, hyperplasia of intestinal crypt cells, and inflammation of the lamina propia. Cryptosporidiosis can sometimes lead to extra-intestinal complications like respiratory cryptosporidiosis, cholecystitis, hepatitis and pancreatitis [48].

Global burden
Global statistics on prevalence of Cryptosporidium parvum shows that it infects 2-50% of population worldwide [3]. In Asia and Africa, the infection rate ranges from 5-10% (Table 3).

Intestinal Protozoan Infections in Kashmir Valley
In Kashmir valley the studies conducted so far demonstrate the presence of protozoan parasites Giardia intestinalis, and Cryptosporidum parvum among chidren. Besides this a number of helminth parasites have also been reported especially Ascaris lumbricoides, Trichuris trichiura, Enterobius vermicularis Taenia saginata Hymenolepis and Ancylostoma [64,65] (Table 4).

New Approach for Parasite Detection
Diagnosis of intestinal protozoa is made usually by microscopy after staining fecal smears with iodine or any other stain. This technique is being widely used for diagnosis of intestinal protozoa [10,[70][71][72][73][74]. However nowadays molecular diagnostic tests are increasingly being used for both clinical as well as research purposes. They involve identification of specific antigen or DNA of parasite in stool or serum samples through Enzyme linked immunoassay (ELISA) [22][23][24] or direct fluorescent antibody assay [25][26][27]. These molecular methods besides having high sensitivity for parasite detection help in differentiation of various species of parasite with the help of PCR.