UNIVERSITY OF GONDARCOLLEGE OF MEDICINE AND HEALTH SCIENCES SCHOOL OF BIOMEDICAL AND LABORATORY SCIENCES DEPARTMENT OF MEDICAL MICROBIOLOGY Global Burden of Salmonellosis and Shigellosis in diarrheic Pediatric Population By: - Amare Alemu (Bsc) Advisors: - Setegn Eshetie (Bsc, Msc) Tigist Engida (BSc, MSc) December, 2017 Gondar, Ethiopia ACKNOWLEDGEMENT I would like to thank SetegnEshetie and TigistEngida to let me come up with this valuable seminar topic and offering for their tremendous technical support. I would like to extend my gratitude to School of Biomedical and Laboratory Sciences and Department of Medical Microbiology for their technical support and enrolling me as MSc student. I Contents ACKNOWLEDGEMENT .............................................................................................................................. I Abbreviations ......................................................................................................................................... III Summary ................................................................................................................................................ IV 1. Introduction ........................................................................................................................................ 1 1.1. Background................................................................................................................................... 1 2. Literature review ................................................................................................................................. 3 2.1. General Characteristics of Salmonella and shigella species............................................................ 3 2.2. Classification and nomenclature ................................................................................................... 4 2.3. Epidemiology ................................................................................................................................ 4 2.4. Transmission ................................................................................................................................. 7 2.5. Pathogenesis .............................................................................................................................. 78 2.6. Virulence factors ........................................................................................................................... 9 2.7. Clinical manifestations ................................................................................................................ 10 2.8. Diagnosis .................................................................................................................................... 11 2.9. Treatment, prevention and control ......................................................................................... 1112 3. Significance of the review .............................................................................................................. 1213 4. Methods ........................................................................................................................................ 1213 4.1. Search strategies..................................................................................................................... 1213 4.2. Study selection ........................................................................................................................... 13 5. Conclusion ..................................................................................................................................... 1314 6. Reference ...................................................................................................................................... 1415 II Abbreviations AIDS--------------------------------------Acquired Immuno Deficiency Syndrome CDC---------------------------------------Centers of Disease Control EIEC--------------------------------------EnteroinvasiveEscherichia coli GALT------------------------------------- Gastrointestinal Associated Lymphoid Tissue HCL----------------------------------------Hydrochloric Acid HIV-----------------------------------------Human Immuno Virus IpaB--------------------------------------- Invasion of plasmid antigen B LPS-----------------------------------------Lipopolysaccharide MLST---------------------------------------Multiple Loci Sequencing typing NTS----------------------------------------- Non-Typhoidal Salmonella PFGE -------------------------------------- Pulse-field Gel Electrophoresis PMNs---------------------------------------Polymorphonuclear cells RES----------------------------------------Reticuloendothelial System T3SS---------------------------------------Type III-Secretion-System WHO---------------------------------------World Health Organization USA----------------------------------------United States of America III Commented [D1]: Not looks like a summary, please consider Summary the following formats Background: - Salmonella and Shigella are members of the Enterobacteriaceae characterized by Background: Aim of the review non-lactose fermenters, gram-negative rods, non-spore formers and facultative anaerobes. The Methods Literature review Conclusion Shigella species are non-motile, and non-gas producers. and Salmonella species are motile, Keywords: produces acid and gas from glucose, normally inhabit the intestines of animals and humans. Formatted: Font: Bold, Not Italic Aim of the review:- Members of the genus Salmonella are ubiquitous pathogens found in Formatted: Font: Bold Formatted: Font: Not Italic humans and livestock, wild animals, reptiles, birds, insects.The genus Shigella encompasses four Formatted: Font: Not Italic subgroups historically treated as species. Shigella species are found only in the human intestinal Formatted: Font: Not Italic tract. Formatted: Font: Not Bold Primarily Salmonella and Shigella transmitted through ingestion of contaminated food and water. Children living in areas with poor sanitation are at higher risk for fecal-oral transmission. Food and water contamination will result in a higher risk of acquiring infection caused by Salmonella and Shigella. When the bacteria enter the digestive tract via contaminated water or food, they tend to penetrate the epithelial cells lining the intestinal wall. SPIs encode for type III secretion systems, multi- channel proteins that allow Salmonella to inject its effectors across the intestinal epithelial cell membrane into the cytoplasm. Strains of Shigella spp. are non-motile and it is not known how the bacteria reach and adhere to M cells.The capacity of the bacteria to cross the colonic mucosa via M cells associated with Gastrointestinal Associated Lymphoid Tissue (GALT) and reprogram epithelial cells to produce pro-inflammatory mediators, such as interleukin 8, which play a major role in the strong inflammatory response facilitating further bacterial invasion. This triggers an intense acute inflammatory reaction with infiltration by polymorph nuclear leukocytes. The shigella species cause bacillary dysentery leading to watery or bloody diarrhea. Shigella virulence is based on the presence of a large virulence invplasmid, carrying an operon that encodes the type III-secretion-system (T3SS) responsible for bacterial entry. The T3SS is composed of several proteins which connects the inner and outer bacterial membranes. Commented [D2]: This story indicates background information, so please make it concise and short not more than one small paragraph. Formatted: Space After: 0 pt, Line spacing: 1.5 lines IV 1. Introduction 1.1. Background Human diarrheal diseases have been recognized from the beginning of civilization and remain one of the most prevalent public health problems of today. Gastrointestinal infections due to pathogenic Enterobacteriaceae in particular Shigella and Salmonella species are significant causes of morbidity and mortality worldwide; mainly children under the age of 5 years are at high risk (1, 2). Recently, the World Health Organization (WHO) estimated that 1.1 million deaths per year are attributed to shigellosis (3). Salmonella and Shigella are members of the Enterobacteriaceae characterized by non-lactose fermenters, gram-negative rods, non-spore formers and facultative anaerobes (4). The Shigella species are non-motile, and non-gas producers’(4, 5) andSalmonella species are motile, produces acid and gas from glucose, normally inhabit the intestines of animals and humans(4, 6). The pathogenesis of Salmonella species is characterized by the invasion of non-phagocytic cells.Salmonella will penetrate into the intestinal epithelial cells by inducing their own uptake, in a complex and active process that morphologically resembles phagocytosis(4, 5).They invade the mucosa of the small and large intestines and produce inflammation. Invasion of intestinal epithelial cells induces an inflammatory reaction which causes diarrhea due to Salmonella infections(4, 7). The virulence factors associated with Salmonella species such as adhesion, invasion, and toxin genes are clustered in certain areas of the chromosome known as “Salmonella pathogenicity islands (4, 8) Commented [D3]: Merge these two paragraphs Most of the current knowledge on mechanisms of Shigella pathogenesis is derived from studies of S. flexneri.The Shigella species enters and invade the intestinal mucosa by using M cells of the intestinal epithelial cells as the portal of entry(8). The bacteria are highly infectious, since as few as 10 to 100 microorganisms are sufficient to cause disease(8-10). Because of delay in humoral responses, complication and mortality rate due to shigellosis in children is higher than in other age groups (5, 9). The highest susceptibility of this age group may be due to the fact that children less than 2 months old produce little hydrochloric acid (gastric HCl), a natural barrier to many microorganisms (4, 7).The severe tissue destruction caused by Shigella species results in an impaired adsorption of water, nutrients, and solutes, which might cause the watery diarrhea as well as the blood and mucus in stools characteristic of shigellosis A disturbance of electrolyte homeostasis and 1 changes in membrane transport processes, such as uncontrolled ion and fluid secretion, are typical ofdiarrheal disease. Shigella enterotoxins which are produced by several Shigella strains, were found to induce fluid secretion into the intestine, thus accounting for the watery phase of diarrhea (8). The virulence plasmid is an essential virulence determinant of all Shigella species and encodes the molecular machinery necessary for tissue invasion and the intracellular lifestyle. The Shigella species have a lot of virulence factors that allow it to adhere to the epithelium of the intestine, survive stomach acid, invade host cells, evade immune responses, and introduce toxins into the body. Invasion of plasmid antigen B (IpaB) initiates binding to the host cell and initiating pathways that kill macrophages upon infection, IpaC activates proteins to form the actin-polymerizing complex that allows Shigella to move and spread within host cells (4, 10).Shigella virulence is based on the presence of a large virulence invplasmid, carrying an operon that encodes the type III-secretion- system (T3SS) responsible for bacterial entry (11). The Salmonella and Shigella are transmitted from person to person usually by asymptomatic carriers and via contaminated food, flies, feces, fingers, and water (4, 5, 11, 12). A severe infection of diarrhea in children is highly associated with risk factors such as poor environmental sanitation and hygiene, poverty and malnutrition (11, 13). Salmonellosis and shigellosis can be diagnosed by using culture and molecular techniques (4). Prevention and control of salmonella rely on the strategies that prevent spread of the organism within the community and from person to person. These include: hand-washing with soap, ensuring the availability of safe drinking water, safely disposing of human waste, breastfeeding of infants and young children, safe handling and processing of food, and control of flies and health education (5). 2 Commented [D4]: Move this section after methodology of the 2. Literature review review, Besides, this part needs complete revision. Since the aim of this 2.1. General Characteristics of Salmonella and shigella species study is to explore the global burden, therefore please specific to Salmonella and Shigella are members of the Enterobacteriaceae and characterized by non-lactose like e.g. prevalence, morbidity, and mortality, etc. fermenters, gram-negative rods, non-spore formers and facultative anaerobes (4). Shigella species are non-motile, and non-gas producers(4, 5) and Salmonella species are motile, produces acid and gas from glucose (4). Members of the genus Salmonella are ubiquitous pathogens found in humans and livestock, wild animals, reptiles, birds, insects(14). Salmonella is an important pathogen both for humans and animals and causes severe infections (15). It causes infections in human and other vertebrates. It is believed that it is an important cause of typhoid fever (enteric fever), gastrointestinal enteritis, septicemia, and carrier states in human (4). It is a very complex group and contains more than 2000 species and typed on the basis of serotyping and species typing (6, 15). The genusShigella encompasses four subgroups historically treated as species. Shigella species are found only in the human intestinal tract (6) and are killed by drying (4). The natural habitat of Shigella is limited to the intestinal tracts of humans and other primates, where they produce bacillary dysentery. Shigellosis is an acute intestinal infection, the symptomsof which can range from mild watery diarrhea to severeinflammatory bacillary dysentery (16).Shigella is similar to enteroinvasiveEscherichia coli(EIEC) in that they both invade intestinal epithelial cells and release Shiga toxin, which causes cell destruction(17). Microscopically and culturally Shigella are indistinguishable from other enteric Gram-negative bacilli (2 old,4).They are non-motile, non-capsulate and appear notto express fmbriae. Strains of Shigella spp. Sharelipopolysaccharide (LPS) antigens with strains of E. coli but the LPS structures are distinct and merelyshare common epitopes.The distinction between strains of Shigella spp. AndE. coli depends on a limited number of diagnostic testsincluding motility, production of lysine decarboxylaseand the utilization of citrate(4, 18). 3 2.2. Classification and nomenclature Salmonella was first discovered and isolated from theintestines of pigs by Theobald Smith in 1855 and Dr Daniel Elmer Salmon take the discovery credit (15).The nomenclature of Salmonellais controversial and still evolving. Currently, the CDC and WHO collaborating centers classifies Salmonella species into two broad groups; Salmonellaenterica (type species) and Salmonellabongori, based ondifferences in their 16S rRNA sequence analysis(14) On the other hand, Kauffman and White developed a schemeto further classify Salmonella by serotype based on threemajor antigenic determinants: somatic (O), capsular (K)and flagella.Virulence (Vi)antigens, a special subtype of K antigen, are found only inthree pathogenic serotypes: Paratyphi C, Dublin and Typhi.Salmonella(19).The genus Shigella is subdivided on biochemical andserological grounds into four species.All strains express LPS somatic antigens whichform the basis for the Shigella serotyping scheme.There are 13 serotypes of which 4 of them are pathogenic (4). 2.3. Epidemiology Shigellosis is one of the most common diarrheal diseases in humans worldwide. Shigellosis is endemic throughout the world where it is held responsible for some 165 million cases of severe dysentery (4).In the early 1980s, diarrheal disorders were the biggest child killers, responsible for an estimated 4·6 million deaths worldwide every year(20). The incidences of Salmonella infections in humans have dramatically increasedthroughout the world over the past few years leading to its emergence as an important publichealth concern. S. enterica has become the second most common bacterial cause of foodbornegastroenteritis cases worldwide(14). According to the Centers for Disease Control and Prevention (CDC), approximately 42,000 salmonellosis cases are reported every year in theUnited States.Thus, every year, Salmonella infection is estimatedto cause about 1.4 million human cases in the United States and to be the leading cause of23,000 hospitalizations and 450 deaths from foodborne disease.The global healthimpact is as high as an estimated 93.8 million illnesses and 155,000 deaths each year(21) The devastating majority of these cases occur in the developing countries.Diarrhea was a common cause of death among children under 5 years old (22).There are approximately 1.4 million cases of salmonellosis per year resulting in about 15,000 hospitalizations and 400 deaths per year in the United States of America(23).2·5 million children still die from these illnesses 4 every year, almost all of them in developing countries(20).Diarrhea, however, remains a prolific killer of children. Some data suggest that in children younger than 5 years it accounts for 15% of cause-specific proportional mortality. The burden of diarrheal illness sits firmly in the developing world, both for morbidity and mortality. Malnutrition andinadequate provision of safe water, sanitation, and hygiene highlight the stark inequalities that exist within our world. A quarter of children in developing countries are still malnourished1·1 billion people do not have access to safe drinking water, and 2·4 billion are without adequate sanitation (4). The epidemiology of salmonella and Shigella species depends on the country: S. flexneri is predominant in developing countries, whilst S. sonnei is most reported in developed countries (14). S. sonnei has become dominant in some Asian countries. Due to international travel and trade of animals and food products, there is a shift in the prevalence of specific Shigella strain types and serovars in different places (2, 7, 14). Shigella species, continue to have an important global impact, causing an estimated 1 million deaths and 163 million cases of dysentery annually.Shigellaspeciesare the most important causes of acute bloody diarrhea (dysentery) and account for about 15% of all deathsattributable to diarrhea in children younger than 5 years (20).Based on a research conducted for 3-year period, in a web-based surveillance, Salmonella enterica serovarEnteritidis was by far the most common serotype reported from human isolates globally. In 2002, it accounted for 65% of all isolates, followed by S. Typhimurium at 12% and S. Newport at 4% (24). S. Enteritidis represented 85% of isolates in Europe but only 9% in Oceania. In Latin America and the Caribbean, S. Typhi accounted for the greatest proportion of salmonellae (13%) (9, 25). In Asia, from 2000 through 2002, Japan, Korea, and Thailand together reported S. Enteritidis as the most common human serotype(26). In China, shigellosis is one of the top four notifiable infectious diseases, with 1.7 million episodes of bacillary dysentery, and 200,000 patients admitted to hospitals each year (27). Salmonella which has 2500 different serotypes is a leading cause of food borne infections worldwide(28). 1.4 million Cases of food-borne salmonella disease have been reported in USA alone (9). There is a slight increase (4.2%) compared with 1996 and a large increase compared with 2005 (12.3%); this could be attributed to increased reports from several states, including Texas and California (9, 24). In the same time in USA, the national incidence of laboratory 5 confirmed Shigella was 3.5 per 100,000 populations. This was isolated frequently from children < 5 years of age, who accounted for 31.1% of all isolates (24). In endemic regions of developing countries, salmonellosis and shigellosis are predominantly a pediatric disease (24, 29). These diseases are important cause of morbidity and mortality especially in children(30).More than one million deaths occur in the developing world yearly due to Shigella infection (31).Estimates suggest that during the 1990s, nearly 1.4 billion diarrhea episodes occurred every year among children younger than 5 years of age in socioeconomically developing countries (32). In developing countries, a number of studies report the high prevalence of salmonellosis and shigellosis, especially in under 5- children. Higher infection rates of Salmonella have been estimated in African countries annually (15). In a recent study carried out in a pediatric hospital in the Democratic Republic of Congo, among the 1,528 children included in the study, 26.8% were bacteremia and Salmonella accounted for 59% of all bloodstream infections. In 1994, an explosive outbreak among Rwandan refugees in Zaïre caused approximately 20,000 deaths during the first month alone. Between 1999 and 2003, outbreaks were reported in Sierra Leone, Liberia, Guinea, Senegal, Angola, the Central African Republic and the Democratic Republic of Congo (5). A study of the etiological agents of childhood diarrhea in Lagos, Nigeria, reports a prevalence of Shigellaand Salmonella was5.1% and 3.3% respectively(33) The etiology and epidemiology of acute diarrheal disease on children in East Africa remain largely undefined. As indicated in a research conducted in Dares Salaam,Tanzania, the prevalence of Shigellaand Salmonellain under five children was 5.4% and 2.5% respectively(34).A research from southern Libya points out a higher percentage of infection (36%) by Salmonella species below 15 years of child age (35). In Ethiopia, like other developing countries, salmonellosis and shigellosis are the common cause of morbidity and mortality, particularly in children. According to a study conducted among diarrheal patients at some selected health facilities in Addis Ababa, Ethiopia, the prevalence of Shigella in stool samples was found to be 9.1%, and (3.9%) of children were found to be infected with Salmonella species (13). According to a study conducted in the isolation rate of Shigella 6 species among diarrheal patients attending at HiwotFana Hospital, Harar, Ethiopia, the prevalence of Shigella within 0-5 years of age was 17.7% (26). A research conducted in Jimma, Ethiopia, from pediatric diarrheic outpatients, the prevalence of Salmonella species was 15.4% (36). In a research conducted on the prevalence of Shigella among diarrheic children under-5 years of age attending at Mekelle health center, northern Ethiopia, showed a prevalence of 13.3 % (37). According to a research conducted on biodiversity of Shigella isolates at Gondar university hospital, northwest Ethiopia, reported that 58.5% of patients were 0-5 years old (38). In another research from a five-year antimicrobial resistance pattern observed in shigella species isolated from stool samples in Gondar University Hospital,northwest Ethiopia, report that children accounted for more than a third (36.4%) of all Shigella positive patients(39). 2.4. Transmission Typhoid (enteric fever) and Non-typhoidal Salmonella (NTS, e.g. food poisoning) is an important public health problem worldwide. Shigellosis (bacillary dysentery), the result of infection with Shigella, is one of the most common diarrhea-related causes of morbidity and mortality in children under 5 years in developing countries (34). Around 95% of these cases are caused by consumption of contaminated food products, and S. Enteritidis is responsible for at least 15% of these cases (23). Primarily salmonella and shigella transmitted through ingestion of contaminated food and water(40) . Direct or indirect contact with infected animals and/or persons or from contact with pets such as cats, dogs, rodents, reptiles, or amphibians can transmit the disease. Several recent outbreaks have also been associated with consumption of contaminated plant products such as sprouts, tomatoes, fruits, peanuts, and spinach(41) . Children living in areas with poor sanitation are at higher risk for fecal-oral transmission. Food and water contamination will result in a higher risk of acquiring infection caused by Salmonella and Shigella(32). 2.5. Pathogenesis Diarrhea poses a very serious problem in developing countries where it is the leading cause of morbidity and mortality. As of other enteric bacteria salmonella and shigella species require a mechanism to survive through the digestive tract and colonize a host and cause disease. 7 Salmonella species can infect both warm and cold-blooded hosts (4). By its ability of the organism to avoid fusion of Salmonella containing vacuoles with dendritic cell lysosomes in the intestine is the mechanism by which it can escape of killing. By surviving within macrophages, Salmonella species will be carried to the spleen, lymph nodes and throughout the reticuloendothelial system (6). The severity of Salmonella infections in humans variesdepending on the serotype involved and the health status ofthe human host. The number of bacteria that must be ingested to causesymptomatic disease in healthy adults is 106-108nontyphoidSalmonella Organisms(42). Children below the age of 5 years, elderlypeople and patients with immunosuppression are more susceptible to Salmonella infection than healthy individuals(19). When the bacteria enter thedigestive tract via contaminated water or food, they tendto penetrate the epithelial cells lining the intestinal wall.SPIs encode for type III secretion systems, multi- channelproteins that allow Salmonella to inject its effectors acrossthe intestinal epithelial cell membrane into the cytoplasm.The bacterial effectors then activate the signal transductionpathway and trigger reconstruction of the actin cytoskeleton of the host cell, resulting in the outward extension orruffle of the epithelial cell membrane to engulf the bacteria. The morphology of the membrane ruffle resembles theprocess of phagocytosis(19, 23). Following theengulfment of Salmonella into the host cell, the bacteriumis encased in a membrane compartment called a vacuole,which is composed of the host cell membrane. Under normal circumstances, the presence of the bacterial foreignbody would activate the host cell immune response, resulting in the fusion of the lysosomes and the secretion ofdigesting enzymes to degrade the intracellular bacteria.However, Salmonella uses the type III secretion systemto inject other effector proteins into the vacuole, causingthe alteration of the compartment structure. The remodeled vacuole blocks the fusion of the lysosomes and thispermits the intracellular survival and replication of the bacteria within the host cells. The capability of the bacteria tosurvive within macrophages allows them to be carried in the reticuloendothelial system (RES)(19). Shigella is the leading cause of infant diarrhea and mortality (death) in developing countries. In shigella the infective dose is small and causes bacillary dysentery (4, 11). It infects the M cells in the Peyer’s patches of the large intestine. Strains ofShigella spp. are non-motile and it is not 8 known howthe bacteria reach and adhere to M cells. (4,5).The capacity of the bacteria to cross the colonic mucosa via M cells associated with Gastrointestinal Associated Lymphoid Tissue (GALT) and reprogram epithelial cells to produce pro-inflammatory mediators, such as interleukin 8, which play a major role in the strong inflammatory response facilitating further bacterial invasion. This triggers an intense acute inflammatory reaction with infiltration by polymorph nuclear leukocytes. The shigella species cause bacillary dysentery leading to watery or bloody diarrhea(40).Patients develop diarrhea because the inflamed colon, damaged by the Shiga toxin, is unable to reabsorb fluids and electrolyte(17). 2.6. Virulence factors The virulence factors of a pathogen are a multifactorial process that requires different general class of determinants. Some of these are virulence genes that are required for physiological process for survival in host and non-host environment (23). The second class of virulence genes are unique to pathogenic organisms and these genes are rarely detected in non-pathogenic organisms.Incorporation of a pathogenicity island can, in a singlestep, transform a normally benign organism into a pathogen(19). Two pathogenicity islands have been identified in Salmonella; the island at 63’ designated as SPI-1 which governs the ability of Salmonella to invade epithelial cells and the second island at 31’designated SPI-2, mediates survival withinmacrophages(43).The nucleotide sequence of the SPI-1 island iscompleteand includes at least 25 genes, themajority of which encode components of a Type III secretion system and its effector proteins. The SPI-2 island of Salmonella harbors at least 15 genesthat code for a distinct Type III secretion systemand fora two-component regulatory system(23). Shigella virulence is based on the presence of a large virulence invplasmid, carrying an operon that encodes the type III-secretion-system (T3SS) responsible for bacterial entry. The T3SS is composed of several proteins which connects the inner and outer bacterial membranes. As indicated in a research in on Virulence Factors Associated with Pediatric Shigellosis in BrazilianAmazon, all the isolates were positive for the ipaBCDgene, as expected, whereas IpaB,IpaC, and IpaDare key factors of virulentShigella (16).Long-chain lipopolysaccharide andthelipid A component playarole invirulence by preventing the effects of serum complement and by causing localized cytokine release (4). 9 2.7. Clinical manifestations Based on the clinical patterns in human salmonellosis,Salmonella strains can be grouped into typhoid Salmonellaand non-typhoid Salmonella (NTS). In human infections, the four different clinical manifestations are entericfever, gastroenteritis, bacteremia and other extra intestinal complications, and chronic carrier state(19). Human salmonellosis and shigellosis is usually characterized by acute onset of fever, abdominal pain, diarrhea,nausea and sometimes vomiting(44). Typically, symptoms of gastroenteritis developwithin 6 to 72 hours after ingestion of the bacteria. The symptoms are usually self- limiting andtypically resolve within 2 to 7 days. In a small percentage of cases, septicemia and invasiveinfections of organs and tissues can occur, leading to diseases such as osteomyelitis, pneumonia,and meningitis(21). In some cases, particularly in the very young and in the elderly, theassociated dehydration can become severe and life threatening. In such cases, as well as in caseswhere Salmonella causes bloodstream infection, effective antimicrobials are essential drugs fortreatment. Serious complications occur in a small proportion of cases (44). Althoughmost cases are self-limiting, the degree to which a person becomes sick depends on his or herhealth status and the number and virulence of Salmonella species ingested. In general, the poorerthe individuals’ health and the more Salmonella ingested, the greater the probability for seriousillness and death (14). Of these Salmonella pathogens, most cause acute gastroenteritis, which is the mostcommon form of salmonellosis. Also known as food poisoning, gastroenteritis ischaracterized by a short incubation period and a predominance of an initial presentation ofsymptoms such as nausea, vomiting, diarrhea, fever, headache, abdominal cramps, andmyalgias(4, 45) Shigellosis clinical manifestations may vary fromasymptomatic to severe dysentery with several complications.Infants were morecommon to have a history of non-bloody diarrhea,moderate to severe dehydration, or bacteremia, butless common to have fever(46). Shigellosis is an acute intestinal infection, the symptoms of which can range from mild watery diarrhea to severe inflammatory bacillary dysentery (16). The most common symptom of shigellosis is diarrhea, which often contains blood and mucusfrom the intestinal walls. Other symptoms may include fever, nausea, vomiting, stomach cramps,tenesmus, dehydration and loss of appetite. For young children, a fever and infection may lead toconvulsions. Some people may 10 remain asymptomatic (not develop symptoms) while infected.Symptoms usually appear 12 to 96 hours after infection (shigella).Aboutthree percent of people who are infected with S. flexneri will develop Reiter’s Syndrome, which ischaracterized by joint pain, eye irritation and painful urination. Reiter’s Syndrome can lastseveral months or years, and can lead to chronic arthritis, but Reiter’s Syndrome only occurs when the person has a genetic predisposition to it(18, 47). 2.8. Diagnosis Salmonellosis and shigellosis cannot be distinguished reliably from other causes of bloody diarrhea on the basis of clinical features alone. Routine microscopy must be performed and the presence of PMNs suggests a bacterial etiology but does not necessarily indicate salmonellosis or shigellosis; it may be C. jejuni or diarrheagenic E. coli. To identify accurately culture and biochemical tests must be performed. Blood culture and bone marrow aspirate may be used if the source and trained personnel are available (17). The higher sensitivityof bone marrow cultures compared to blood in part relates to the higherconcentration of organisms in bone marrow (48)Molecular techniques are also more necessary to identify them correctly. The most common methods currently in use are the pulse-field gel electrophoresis (PFGE) and multiple loci sequencing typing (MLST) (4, 5, 17). The thirty isolates of Shigella species were confirmed by conventional and 16S rRNA sequencing methods (16). 2.9. Treatment, prevention and control Prevention of salmonellosis and shigellosis can be primarily on measures to control the spread of the organism within the community. 1. Health education: - Teaching the child bearing mothers and school children about these diseases and spreading the information in the local communities via health and religious institutions, mass media, schools, and markets by using posters, drama etc. 2. Hand washing: - Hand-washing using soap is important after defecation, after cleaning a child who has defecated, after disposing of a child’s stool, before preparing or handling food, and before eating. 3. pure water supply: - The use of surface water for drinking, like water from a river, pond, or open well, should be discouraged. To be used for drinking, it must be disinfected with chlorine or it must be boiled. 11 4. breastfeeding: - breast feeding until 6 months must be promoted and continue breast feeding with other nutrients for about 3 years are advisable. 5.Other prevention methods: -Other prevention methods should be promoted in the general communities. In this regard health education must stress on the preparation and consumption of safe food supply and on the disposal of environmental wastes. Vaccine trials should be carried out to prevent it. But still there is no WHO recommended vaccine that is effective in preventing shigella infections. Currently there is a trial against S. flexneri but still it is under development (5). In other countries, heat-killed, phenol preserved whole cell salmonella vaccines containing a mixture of culture of S. typhi and S.paratyphi have been used. But these were not effective. Capsular (vi) polysaccharide replaces the existing vaccine. Now oral live-attenuated salmonella vaccine is used (4, 17). Antibiotics and use of oral rehydration therapy in developing countries has contributed significantly to reduce mortality from diarrheal dehydration (4). 3. Significance of the review Salmonellosis and Shigellosis are endemic in most developing countries and is the most important cause of bloody diarrhea worldwide. There is a need to estimate the magnitude of the global burden of disease and death caused by Shigella and Salmonella in children specially in under 5- children (4). Several recent efforts are carried out in modern medical and public health in controlling this global threat; the consequences of which are most devastating in the developing world. Understanding the global burden of infections caused by entero-pathogens particularly due to Salmonella and Shigella is essential to design effective control and preventive strategies(5, 14). 4. Methods 4.1. Search strategies Through computerized search using databases such as PubMed, goggle scholar, sci-hub and different journal sites are assessed to download scientific papers around the world. Combination of key words such as global burden of Shigella and Salmonella, diarrheal pediatric patients etc are used to search journal articles. 12 4.2. Study selection Estimates suggest that during the 1990s, nearly 1.4 billion diarrhea episodes occurred every year among children younger than 5 years of age in socio-economically developing countries, of which 123.6 million episodes required outpatient medical care and 9 million episodes required hospitalization. Children living in socioeconomically underdeveloped areas will have more overall diarrhea episodes which are caused by enteric pathogens mainly by Salmonella and Shigella. Severe episodes with dehydration and a higher death rate occur in children living in more economically underdeveloped areas(32). Therefore, studying these deadly pathogens in diarrheic pediatric population in Gondar, Ethiopia is crucial to have information for designing strategies for preventing and controlling shigellosis and salmonellosis in diarrheic pediatric patients in the area. 5. Conclusion Globally, Salmonellae and Shigella infections remain a major public health threat and the significant cause of morbidity and mortality especially in the pediatric population. Diarrhea- causing pathogens are the second leading cause of morbidity and mortality worldwide; mainly children under the age of 5 years are at high risk. The highest susceptibility of this age group may be due to the fact that children less than 2 months old produce little hydrochloric acid (gastric HCl), a natural barrier to many microorganisms. 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