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Lecture 5

5 Pages

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Ingrid L.Stefanovic

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ANTC68 Lecture 5: Deconstructing Cholera Cholera Acute intestinal bacterial disease of Vibrio cholerae 01 (classical and El Tor biotypes) & 0139 Bacteria sensitive to high temperatures, acidity, dry conditions Incubation period of 1-2 days; transmission through contaminated food, water, utensils; importance of seasonality Cholera bacteria adheres to small bowel and produces a toxin that inhibits the absorption of liquids by the body (stimulates over- secretion of water and electrolytes) - kills via dehydration Note: most strains of Vibrio do not carry the genes to make toxin Pathogen multiplies in the gut of the carrier and are excreted Majority of cases - mild (90%); many infected have no symptoms (carriers); 5-8% get mild to moderate diarrhea; 2-5% get severe cholera gravis: severe diarrhea, vomiting, and dehydration Malnourished people and those who are carrying many intestinal parasites may be more susceptible than healthy people: it takes 100 billion vibrios in the gut of a healthy person to cause disease, because large numbers are immobilized by acids in the stomach, but in someone whose gut is less acidic, because of heavy parasite burden, it takes only 1 million organisms Risk Factors: hygiene, sanitation, health care resources, SES ORIGINS? Interaction with humans probably began with agriculture, as populations grew and polluted their water sources with human and domesticated animal waste which created nutrient- rich ecosystems that allowed pathogens to thrive First recorded historical outbreak: 1817, India Innumerable epidemics around the world; end of 20 century some of most extensive epidemics in recent times, esp. during refugee crisis in Central Africa (Rwanda, Burundi, DR Congo) in 19945: 40,000 cases, case fatality rates exceeding 30% in some areas (limited med facilities); also South Africa, 2001, 86,000 cases 7 successive pandemics; 7 one in 1960s, El Tor strain (which later led to 1991 epidemic in Peru) th May be 8 pandemic in future, with new strain 0139 Bengal causing high mortality in South Asia in 1992 ORT and RIT Mortality resulting from severe dehydration may be >50% if left untreated (< 2% with ORT) Oral rehydration treatment (ORT) and rapid intravenous rehydration therapy (RIT)-effective Chemoprofilaxis and vaccination are not recommended: mass treatment with antibiotics may lead to emergence of drug resistance and vaccination has been effective in only 50% of cases Being vaccinated may also give a false sense of protection The key to effective control is environmental sanitation Cholera in Peru, 1991 POSSIBLE CAUSES OF THE 1991-2 EPIDEMIC: Dumped bilge water from an Asian freighter Sea current El Nio : is a hot current coming from the north to the south along the South American coast in Pacific Ocean (usually takes place at the end of December and beginning of January) 1991: this current produced higher temp . than usual in that part of Pacific Zooplankton that inhabit cold waters can carry large number of cholera vibrio on their bodies (zooplankton feed by grazing on phytoplankton which bloom with sunshine and warm conditions; thus, a phytoplankton bloom leads to increase in pop. of zooplankton which carry the vibrio) A warmer than usual El Niomay have created ideal conditions along the Peruvian coast for humans to become infected with cholera
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