Diarrhoea is defined as an increase in the frequency fluidity or volume of bowel movements relative to the usual habits of an individual Passage of three or more loose or liquid stools a day can be taken as ID: 1045239
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1. DIARRHOEA AND DYSENTERY
2. DIARRHOEADiarrhoea is defined as an increase in the frequency, fluidity or volume of bowel movements, relative to the usual habits of an individual.Passage of three or more loose or liquid stools a day can be taken as diarrhoea.It is usually caused by bacterial, viral and parasitic infections through contaminated food, water.However some gastrointestinal inflammatory disorders may result in diarrhoea.
3. CAUSATIVE AGENTS OF DIARRHOEABACTERIAVibrio choleraeEscherichia coli (ETEC, EPEC, EIEC)Non-typhoidal salmonellae (Salmonella enteritidis, S. Typhimurium etc.)Clostridium perfringensClostridivides difficileBacillus cereusStaphylococcus aureusYersinia enterocolitica
4. VIRUSESRotavirusNorwalk virusCalicivirusAstrovirusCoronavirusAdenovirus types 40 and 41PARASITESGiardia lambliaCryptosporidium parvumCystoisospora belliCyclospora spp.
5. TYPES OF DIARRHOEAACUTE DIARRHOEAIt usually lasts for less than 14 days and most often caused by viruses (e.g. rotavirus or norwalk virus) followed by bacterial (e.g. Salmonella spp.) and parasitic (e.g. Giardia lamblia) causes.PERSISTENT DIARRHOEAWhen diarrhoea lasts for more than 14 days (usually 2-4 weeks), it is called persistent diarrhoea.CHRONIC DIARRHOEAIt lasts for more than 4 weeks. Parasitic causes (e.g. cryptosporidium parvum, cyclospora, entamoeba histolytica, giardia lamblia) are responsible for majority cases of chronic diarrhoea.Chronic diarrhoea may also occur due to non-infectious causes e.g. Crohn’s disease, ulcerative colitis.
6. TRAVELLER’S DIARRHOEAIt is an acute diarrhoeal illness that occurs in persons travelling from temperate countries to tropical countries.It occurs within a week or two of arrival.The most common infectious agents of traveller’s diarrhoea include enterotoxigenic Escherichia coli (ETEC) followed by rotavirus, norwalk virus.DYSENTERYDysentery means passage of blood and mucous with motion, often associated with tenesmus (sensation of a desire to pass stools despite an empty colon).Dysentery is most often caused by Shigella (bacteria) or Entamoeba histolytica (parasite). It occurs through contaminated food or water.
7. GASTROENTERITISIt is often used as synonym for acute diarrhoea, especially when associated with vomiting.Gastroenteritis may be defined as inflammation of the mucous membrane of stomach and intestine resulting in frequent loose motions and abdominal cramps, vomiting, with or without mucous or blood in stool.For all practical purposes, the terms diarrhoea, gastroenteritis and dysentery are collectively included as diarrhoeal diseases.
8. ETIOLOGYCausative agents of diarrhoea and dysentery are as following:BACTERIAShigella spp.Escherichia coliCampylobacter jejuniVibrio parahaemolyticusPARASITESEntamoeba histolyticaBalantidium coli
9. PATHOGENESISThe infection occurs by ingestion of contaminated water or food.A. INFECTIVE DOSEInfective dose (minimum dose required to start infection ) differ in different causative agents.High infective dose required in vibrio cholerae and salmonella in contrast to low infective dose in shigella spp. And entamoeba histolytica.B. PATHOGENIC MECHANISMSPathogenic mechanisms include:Toxin productionInvasionAdhesionMultiplication within intestinal cells.
10. 1. TOXIN PRODUCTIONEnteric pathogens can produce a number of toxins which are involved in pathogenesis of diarrhoea.These toxins include:(1). EnterotoxinsThey act directly on secretory mechanisms in the intestinal mucosa and results in outpouring of electrolytes and fluids into the intestinal lumen.This occurs mainly due to activation of adenyl cyclase which converts adenosine triphosphate (ATP) to adenosine 5-monophosphate (cAMP).The marked increase of cAMP results in intense and prolonged hypersecretion of water and chlorides and inhibits the reabsorption of sodium.
11. The intestinal lumen is distended with fluid and hypermotility leads to profuse watery diarrhoea.Examples: Vibrio cholerae and Enterotoxigenic Esch. Coli.(2). CYTOTOXINSThey destroy intestinal mucosal cells and initiate inflammatory response. The secretary or absorptive functions of cells are affected, leading to diarrhoea.The important example of cytotoxin producing bacteria include Shigella dysentriae, enterohaemorrhagic Esch. Coli and Clostridioides difficile (toxin B).(3). NEUROTOXINSThey act on the central nervous system (CNS) and produce vomiting. The important example of neurotoxin producing bacteria is Clostridium botulinum.
12. 2. INVASIONThese microorganisms invade the intestinal mucosal cells and destroy them, leading to dysentry.The important invasive microorganisms include Shigella species, Enteroinvasive Esch. Coli, Campylobactor jejuni, Yersinia enterocolitica and parasites such as Entamoeba histolytica.3.ADHESIONAdherence to intestinal mucosa helps these organisms to compete with normal flora and thus to colonise the intestinal mucosa.
13. They destroy the ability of intestinal mucosal cells to participate in normal function of secretion and absorption, leading to diarrhoea. The important examples include Enteropathogenic Esch. Coli, Enterohaemorrhagic Esch. Coli and Cryptosporidium parvum.4. MULTIPLICATION WITHIN INTESTINAL CELLSMultiplication within cells of mucosa cause destruction of cell function leading to diarrhoea. The important examples are Rotavirus, Hepatitis A virus and adenoviruses.
14. CLINICAL FEATURES1. NON-INVASIVE DIARRHOEA (WATERY DIARRHOEA)Loose, watery stool without blood or mucusNausea and vomitingLow grade fever or no fever2. INVASIVE DIARRHOEA (DYSENTERY TYPE)Loose stool with blood or mucusAbdominal pain/crampsMild feverVomiting
15. LABORATORY DIAGNOSISA.SPECIMENSFaecesRectal swabs: If faeces are not readily available.Vomit: Less useful.Blood and serology: Useful in viral causative agents.B. COLLECTIONFaeces, specimen is collected in dry, clean, sterile, screw capped, wide mouthed, leak proof container. Make sure that no urine, water or other material gets in the container.Sterile swab should be used for rectal swab.Vomit or any other specimen should be collected in a sterile container.Blood is collected in a plain vial for serology.
16. C. TRANSPORTThe specimen should be transported and processed immediately.In case of faeces specimen for bacterial culture, if a delay of more than two hours is anticipated, the specimen should be collected in a suitable transport medium. The following transport media can be used:Cary-Blair transport mediumStuart’s transport mediumAmies transport mediumAlkaline peptone water (if clinically cholera is suspected).FOR VIRAL DIARRHOEAFaeces can be refrigerated at 2-8°C, if viral antigen is to be detected. If delay more than 24 hours then store at -20°C.
17. D. MACROSCOPIC EXAMINATIONThe faeces specimen is examined by naked eye for the following:ColourConsistency : Formed, semiformed or liquid e.g. watery stool in cholera.Blood : Suggestive of dysentery.Mucus : Suggestive of inflammatory diarrhoea.Presence of parasites e.g. Ascaris lumbricoides or Taenia segments.
18. E. DIRECT MICROSCOPY1.WET MOUNT PREPARATIONSaline and iodine preparation is done for detection of pus cells and erythrocytes which indicate invasive disease.It is also used for detection of trophozoites, cysts, ova, and larvae of parasites.2. HANGING DROP PREPARATIONIt is done to demonstrate the darting motility of Vibrio cholerae, which can be confirmed by inhibition of motility by adding vibrio antisera. 3. MODIFIED ACID-FAST STAINING (USING 0.5-1% SULPHURIC ACID)It is done for detection of acid-fast oocysts of Cryptosporidium parvum, Cyclospora species, Cystoisospora belli.
19. 3. GRAM STAININGIt is routinely not done due to presence of normal flora in faeces. However, it can be done in the following conditions:Suspected cholera case: Presence of comma shaped Vibrio cholerae.Suspected fungal cause: Presence of Gram positive budding yeasts cells-Candida albicans.5.ELECTRON MICROSCOPYElectron microscopy is done to detect typical morphology of certain viruses causing diarrhoea.Rotaviruses: Wheel shaped with short spokes radiating from a wide hub.Astroviruses: Star-like.
20. F. CULTURE1. BACTERIAL CULTUREFor identification of bacterial pathogens (except anerobic bacteria), the faeces specimen is inoculated on the following culture media.SOLID MEDIAMacConkey agarDeoxycholate citrate agar (DCA)Xylose lysine deoxycholate (XLD)Thiosulfate citrate bile salt sucrose (TCBS) agarThese are highly selective media.TCBS agar is a selective medium for vibrio cholerae.Another selective medium Bile salt agar (BSA) may also be used as an alternative to TCBS agar.All solid culture media are incubated at 37°C for 18-20 hours.
21. LIQUID MEDIAEnrichment broth Selenite F broth (for gram negative bacteria)Alkaline peptone water (APW) (for vibrio cholerae)Liquid culture media are incubated at 37°C for 6 hours and then subcultured onto solid culture media.IDENTIFICATION:The bacteria grown on culture media and identified by study of:Colony morphology Gram staining of colonyHanging drop for motilityBiochemical testsThe presumptive diagnosis of bacterium can be made by above tests. However, confirmatory diagnosis is done by slide agglutination using specific group or type specific antisera.Automated methods such as VITEK may also be used for identification.
22. ANTIBIOTIC SENSITIVITY TESTINGIt is done by disc diffusion method for choosing the appropriate antibiotics for treatment.Automated method VITEK can also be used for antibiotic sensitivity testing.2. Anaerobic Bacterial CultureCooked meat broth (CMB) is inoculated for growing Clostridia.Subculture from CMB is made on solid media such as freshly prepared blood agar and incubated at 37°C for 48 hours in anaerobic environment using anaerobic jar.Growth is identified by colony morphology, gram staining, hanging drop and biochemical tests.
23. 3. VIRAL CULTURETissue cell lines are used for detection of enteric viruses.Hela and Hep-2 cell lines can also be used for identification of Enterotoxigenic Escherichia coli (EHEC) can produce cytotoxic changes on vero cell line.G. ANTIGEN DETECTIONVarious serological tests are used for detection of antigen in faeces. These include:ELISA:ELISA Kits are available for antigen detection of rotavirus, Cryptosporidium spp. In faeces.DIRECT IMMUNOFLUORESCENCE TEST: For detection of Cryptosporidium spp. And giardia using monoclonal antibody tagged with fluorescent dye.
24. IMMUNOCHROMATOGRAPHIC TEST: It is available for simultaneous detection of Cryptosporidium parvum, Entamoeba histolytica, Giardia lamblia in faeces.Rapid test is available for detection of C. difficile toxin in faeces.H. MOLECULAR METHODSPolymerase chain reaction (PCR) can be used for amplification of specific genes of various enteric pathogens.BIOFIRE ARRAY: It is automated multiplex PCR to detect common bacterial, viral parasitic agents causing diarrhoea. It is commercially available.
25. I. TOXIN DEMONSTRATIONELISA for demonstration of cholera toxin (CT) and Esch. Coli toxin (LT and ST).PCR for detection of genes coding for different enterotoxins.J. MANAGEMENT1. ORAL REHYDRATION THERAPYThe most important is prompt water and electrolyte replacement to correct the severe dehydration and salt deplition.This can be achieved by oral rehydration therapy either alone or supplemented by intravenous fluids.2. ANTIBIOTICS: Antibiotics are of secondary importance. These are indicated in complicated cases or for severe diarrhoea.
26. K. PROPHYLAXISPURIFICATION OF WATER SUPPLIES.BETTER PROVISION FOR SEWAGE DISPOSAL.PERSONAL HYGINE.DETECTION AND ISOLATION OF CARRIERS.VACCINATION: IF VACCINE AVAILABLE THEN IT IS A SPECIFIC PROPHYLACTIC MEASURE FOR EXAMPLE ROTAVIRUS VACCINE.
27. REFERENCE BOOKSTextbook of microbiology by Ananthanarayan and Paniker’s.Textbook of microbiology by D. R. Arora and Brij Bala Arora.Textbook of microbiology by Dr. C. P. Baveja.