Vibrionaceae - Study Handouts

University:
Franklin University
Course:
BIO-201 | Introductory Biology I
Academic year:

2020
Views:

368

Pages:

29
Author:

LunarLuminary

Vibrionaceae Cholera A life‐threatening secretory diarrhea induced by enterotoxin secreted by V. cholerae Water‐borne illness caused by ingesting water/food contaminated by V. cholerae An enterotoxic enteropathy (a non‐invasive diarrheal disease) A major epidemic disease V. cholerae Grows in salt and fresh water Can survive and multiply in brackish water Has over 150 identified serotypes based on O‐ antigen Only O1 and O139 are toxigenic and cause Cholera disease 2 categories of O1 serotypes – Classical and El Tor V. cholerae Transmitted by fecal‐oral route Endemic in areas of poor sanitation (India and Bangladesh ) May persist in shellfish or plankton 7 pandemics since 1817 – first 6 from Classical strains, 7th from El Tor 1993: Cholera in Bengal caused by O139 – may be cause of 8th pandemic Discoveries 1959: cholera enterotoxin by S.N. De in Calcutta Cholera bacillus is not harmful – toxin is what induces outpouring of fluid and inhibits sodium transport Treatment by rehydration (oral or intravenously) of fluid and electrolytes How to measure rapid fluid loss 1854: identified comma‐shaped bacterium Named it Vibrio cholerae People Most at Risk People with low gastric acid levels Children: 10x more susceptible than adults Elderly Period of Communicability During acute stage A few days after recovery By end of week, 70% of patients non‐infectious By end of third week, 98% non‐infectious Incubation Ranges from a few hours to 5 days Average is 1‐3 days Shorter incubation period: High gastric pH (from use of antacids) Consumption of high dosage of cholera How Does Cholera Toxin Work? Inactivates GTPase function of G‐protein coupled receptors in intestinal cells G proteins stuck in “On” position 100 fold increase in cAMP Activation of ion channels Ions flow out and water follows Infectious Dose 106‐1011 colony‐forming units Why such a high dosage? Series of changes as moves from aquatic environment to intestine Temperature, acidity Acidic environment of stomach Intestinal environment Bile salts, organic acids, complement inhibit bacteria growth Must penetrate mucous lining of intestinal epithelial cells Symptoms Occur 2‐3 days after consumption of contaminated food/water Usually mild, or no symptoms at all 75% asymptomatic 20% mild disease 2‐5% severe Vomiting Cramps Watery diarrhea (1L/hour) Without treatment, death in 18 hours‐several days Cholera More severe symptoms Rapid loss of body fluids 6 liters/hour 107 vibrios/mL Rapidly lose more than 10% of bodyweight Dehydration and shock Death within 12 hours or less Death can occur within 2‐3 hours Consequences of Severe Dehydration Intravascular volume depletion Severe metabolic acidosis Hypokalemia Cardiac and renal failure Sunken eyes, decreased skin turgor Almost no urine production Mortality Rate With prompt rehydration: <1% Without treatment: 50%‐60% Vibrio cholerae DiagnosisTr eatmentsPre vention Diagnosis Cholera should be suspected when patients present with watery diarrhea, severe dehydration Based on clinical presentation and confirmed by isolation of vibrio cholera from stool Diagnosis No clinical manifestations help distinguish cholera from other causes of severe diarrhea: Enterotoxigenic e. coli Viral gastroenteritis Bacterial food poisoning Diagnosis: Visible Symptoms Decreased skin turgor Sunken eyes, cheeks Almost no urine production Dry mucous membranes Watery diarrhea consists of: fluid without RBC, proteins electrolytes enormous numbers of vibrio cholera (107 vibrios/mL) Laboratory Diagnosis Visualization by dark field or phase microscopy Look like “shooting stars” Gram Stain Red, curved rods of bacteria Isolate V. cholerae from patient’s stool Plate on sucrose agar Yellow colonies form Vibrio dark fild microscope Treatment *Even before identifying cause of disease, rehydration therapy must begin Immediately because death can occur within hours* Oral rehydration Intravenous rehydration Antimicrobial therapy Treatment: Oral Rehydration Reduces mortality rate from over 50% to less than 1% Recover within 3‐6 days Use when less than 10% of bodyweight lost in dehydration Treatment: Oral Rehydration Salts (ORS) Reduces mortality from over 50% to less than 1% Packets of Oral Rehydration Salts Distributed by WHO, UNICEF Dissolve in 1 L water NaCl, KCl, NaHCO3, glucose Treatment: How ORS Works Na+ transport coupled to glucose transport in small intestine Glucose enables more efficient absorption of fluids and salts Potassium passively absorbed Treatment: Intravenous Rehydration Used when patients have lost more than 10% bodyweight from dehydration Unable to drink due to vomiting Only treatment for severe dehydration Treatment: Intravenous Rehydration Ringer’s Lactate Commercial product Has necessary concentrations of electrolytes Alternative options Saline Sugar and water Treatment: Antibiotics Adjunct to oral rehydration Reduce fluid loss by half Reduce recovery time by half 2‐3 days instead of 4‐6 Tetracycline, Doxycycline Not recommended Short duration of illness Antibiotic resistance Limited gain from usage Traveling Precautions Boil or treat water with chlorine or iodine No ice Cook everything Rule of thumb: “Boil it, cook it, peel it, or forget it.” Wash hands frequently