Cholera Flashcards
What is vibrio cholerae?
the causative agent of cholera
Describe vibrio cholerae?
- it is a gram negative shaped bacteria with polar flagella - share the same flagellar (H) antigen
- stain pink or red
- survive in alkaline conditions
- facultatively anaerobic
- produce the enzyme oxidase
- give a positive indole reaction (test to differentiate gram negative and gram positive)
Describe the doubling time of cholera?
13 minutes
How does vibrio cholerae spread?
- Water supplies 2. food from fecal contamination of an infected person - Can also live in brackish / salty water
What is the mortality of cholera?
can kill within 12 hours
What are the most important pathogens of man?
- vibrio cholerae 2. v. parahaemolyticus 3. v. vulnificus
The genus vibrio can be divided into?
- non-halophilic 2. halophilic
What are halophilic species?
require salt for growth - V. parahaemolyticus and V. vulnificus
What are non-halophilic species?
do not require salt - v. cholerae
Describe the growth conditions of vibrio?
- grow best at 30C and some grow poorly at 37C - V. cholerae, V. parahaemolyticus and V. alginolyticus grow at 42C 2. low tolerance to acid and prefer alkaline conditions (growth range pH 6.8 – 10.2, optimum pH 7.4 – 9.6)
What are the 2 major serogroups of vibrio cholerae?
- O1 2. O139
Serogroup O1 is further classified into which 2 biotypes?
- classical 2. El Tor - biotype expresses a haemolysin and is resistant to polymixin B
Serogroup O1 is further classified into which 3 serotypes?
- Inaba 2. Ogawa 3. Hikojima - transitional serotype that has characteristics of both Ogawa and Inaba
Describe the structure of vibrio cholerae?
has an outer membrane that has a liposacchiride
The liposacchiride is divided into?
- lipid A (endotoxin) 2. core polysacchiride 3. O-polysacchiride
What is the funtion of O-polysacchiride?
can subdivide vibrio into many serogroups
How do you differentiate the different cell types?
agglutination through antiserum
What is the difference between O1 and O139?
- O1 has long O-polysaccharide chains and O139 has short O-polysacchiride chains 2. They also differ in susceptibility to phage 3. V. cholerae O139 has a modified LPS structure
What are the symptoms of cholera?
- Sudden onset of effortless vomiting and profuse watery diarrhea
- Rapid dehydrationa and hypovolaemic shock which may cause death in 12 – 24h are related mainly to the profuse, watery, colourless stools with flecks of mucus and a distinctive fishy odour
- Rice water stools contain little protein and are very different from the mucopurulent blood-stained stools of bacillary dysentery
- Anuria develops, muscle cramps occur
- Patient is weak and lethargic with loss of skin turgor, low blood pressure and an absent or thready pulse
Describe the pathogenic mechanisms of vibrio cholerae?
- Production of cholera toxin
- Expression of co-regulated pili
- V. cholerae are confined to the gut
- Multiply in the alkaline environment of the small intestine
- Migrates towards epithelial cells facilitated by active motility and production of mucinase and other proteolytic enzymes
- Adheres to enterocyte surface
Describe the affect of the cholera toxin on the cells in the intestines?
- Cholera toxin, co-regulated pili, haemagglutinins and lipopolysaccharide contribute to adhesion
- Cholera toxin causes transfer of adenosine diphosphoribose (ADP ribose) from nicotinamide adenine dinucleotide (NAD) to a regulatory protein, part of adenylate cyclase enzyme
- Adenylate cyclase enzyme is responsible for the generation of intracellular cyclic adenosine monophosphate (cAMP)
- Adenylate cyclase enzyme is activated irreversibly resulting in overproduction of cAMP
- Results are inhibition of Na and Cl ions uptake by cells lining the villi, together with hypersecretion of Cl and HCO3
- Water uptake is blocked because it normally accompanies Na and Cl absorption
- There is a passive net outflow of water across mucosal cells, leading to serious loss of water and electrolytes
Describe the laboratory diagnosis?
- Stool specimens are inoculated into alkaline peptone water, in which grow rapidly and accumulate on the surface 2. After incubation for 3-6h a loopful from the surface is inoculated on to a suitable solid medium such as thiosulphate-citrate-bile-sucrose (TCBS) agar 3. V. cholerae forms yellow colonies 4. Colonies are tested for the enzyme oxidase 5. Agglutination test with rabbit antibodies specific for the O1 LPS antigens is done 6. Cholera toxin is detected by tissue culture assays and immunological techniques 7. PCR for haemolysins has been developed
Describe the epidemiology of cholera?
- Vast majority of cases occur in Africa and Asia 2. Infection is spread by contaminated water or foods such as uncooked seafood or vegetables 3. Source of contamination is usually faeces of carriers or patients with cholera 4. It is an infection of crowded communities with poor standards of hygiene and shared communal water supplies such as ponds, rivers for washing and household use 5. Outbreaks occur as either explosive epidemic waves in non-endemic regions or as protracted waves in endemic areas 6. Spread of infection is facilitated by the high ratio of symptomless carriers to clinical cases which varies from 10:1 to 100:1 depending on living conditions and biotype 7. Symptomless carriers occur more frequently in El Tor than in classical infections
What is the treatment?
- Replacement of fluid and electrolytes is necessary - Oral rehydration is sufficient but severe cases may require intravenous rehydration 2. Tetracyclines, chloramphenicol, and cotrimoxazole reduce the period of V. cholerae in the stools of patients with cholera - multidrug resistant strains have already been identified
Describe the control of the spread of cholera?
- Provision of safe drinking water supplies and the proper disposal of human faeces 2. health education campaigns - Community engagement is key to long term changes in behaviour and to the control of cholera
Describe the vaccines of cholera?
- Immune response is towards bacterium rather than toxin 2. It is serotype specific 3. Infection with the classical biotype is followed by immunity for several years 4. Infection with the El Tor biotype confers little or no immunity 5. Development of effective vaccines has proved difficult 6. Oral vaccines combining B subunit and killed whole cells are widely available and appear to be safe and protective
Describe the growth conditions for halophilic vibrio?
doesn’t grow in absence of sodium chloride
Describe the test results for V. haemolyticus?
form green, non-sucrose fermenting colonies on TCBS
What are the symptoms of V. parahaemolyticus?
- Cause explosive diarrhoea but symptoms abate after 3 days 2. include abdominal pain 3. nausea 4. vomiting 5. there may be blood in stools
How do you test seafood and sea/esturine waters for halophilic species?
enrichment culture in alkaline peptone water containing 1% sodium chloride is used
Describe the laboratory diagnosis of V. parahaemolyticus?
- Stool specimens are inoculated into alkaline peptone water, in which grow rapidly and accumulate on the surface 2. After incubation for 3-6h a loopful from the surface is inoculated on to a suitable solid medium such as thiosulphate-citrate-bile-sucrose (TCBS) agar 3. V. cholerae forms yellow colonies 4. Colonies are tested for the enzyme oxidase 5. Agglutination test with rabbit antibodies specific for the O1 LPS antigens is done 6. Cholera toxin is detected by tissue culture assays and immunological techniques 7. PCR for haemolysins has been developed
Describe the epidemiology of V. parahaemolyticus?
- It is a common cause of diarrhoea in Japan and South-East Asia 2. Also causes illnesses associated with sea food in UK and USA 3. Organisms are common in fish and shellfish and in the waters they are harvested 4. Infections occur more frequently in the warmer months
Describe the treatment and control?
- Fluid replacement therapy is needed 2. Organism is susceptible to antibiotics used for enteric pathogens 3. Infection can be avoided by normal food hygiene procedures and by refrigeration of seafood to reduce possible bacterial multiplication 4. For wound infections and septicaemia, the most effective antimicrobial agents include tetracyclines, ciprofloxacin, ceftazidime and gentamicin
