Introduction to Microbiology Clinical Presentation

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Из курса от партнера Stanford University

Stories of Infection

671 оценки

Stanford University

Stories of Infection

671 оценки

This course introduces learners to a variety of infectious diseases using a patient-centered, story-based approach. Through illustrated, short videos, learners will follow the course of each patient’s illness, from initial presentation to resolution. Integrating the relevant microbiology, pathophysiology and immunology, this course aims to engage and entice the learner towards future studies in microbiology, immunology and infectious diseases. The patient-centered videos included in this course were created as part of the Re-imagining Medical Education initiative, led by Charles Prober MD, Senior Associate Dean of Medical Education at the Stanford School of Medicine. This initiative was the first of its kind to explore the collaborative creation of foundational medical education online content by inter-institutional teams of faculty. The content presented in this course was created by faculty from Stanford University School of Medicine, in collaboration with The University of Washington School of Medicine, Duke University School of Medicine, UCSF School of Medicine, and The University of Michigan Medical School. Support for this initiative was provided by the Robert Wood Johnson Foundation and the Burke Family Foundation. PLEASE NOTE: Information provided in this course is for educational purposes only and is not intended to be used for diagnostic and/or treatment purposes.

Из урока

Introductory Module

In Module One, we will begin to hear how some microbes cause disease in humans. We will familiarize ourselves with the human immune system, including the cells that make up the innate and adaptive immune responses. We will also examine the relationship between socioeconomic conditions and infectious disease as we explore the story of one person’s experience with cholera. By the end of this module, learners will be more familiar with how the host immune defenses actively defend the body against disease-causing microbes. After each lecture, there is a glossary of terms pertaining to that lecture, which will assist learners in answering the quiz questions. Learners can also find a glossary of all terms from the course, listed alphabetically, under the "Resources" tab.

Introduction to Microbiology Clinical Presentation9:04

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Maya Adam, MD
Lecturer
Stanford School of Medicine

Microbiology is the study of microscopic organisms.

Some of which can cause the most serious diseases encountered by humans.

When a micro causes disease physicians around the world

are the one's called on to intervene.

In many developing parts of the world,

access to resources like clean water and basic sanitation is limited.

And in those same areas, higher rates of malnutrition, especially among children,

often lead to immune suppression, meaning that the microbes in, for

example, contaminated water, can more easily infect their human hosts.

Today we're going be talking about a bacterium

that measure only about two microns in length.

But, if it's brought into an area where it can easily spread.

This microbe can sweep through a community,

causing potentially deadly infectious disease.

The most powerful protection we have against infectious diseases like

this one is our knowledge of how microbes cause disease.

Both at the level of the community and at the level of the microbe.

In order to effectively prevent and treat infectious diseases,

we need to understand the environments in which they're more likely to spread,

and how the actions of microbes result in the clinical disease.

This knowledge can lead to interventions that protect the health of the individual

and the society in which they live, as we'll see in this case.

Filipe is an eight year old boy living in Chapoteau,

a village located on an isolated spit of land in Haiti.

Since the earthquake that shook the region in 2010 clean drinking water and

sanitation remain scarce in Haiti.

There are no sewers here and even latrines are rare.

Because of this, Filipe and his brother have already seen first-hand the health

consequences of living without access to basic resources.

Their father passed away from dehydration due to diarrheal disease three years ago.

And determine to protect the health of his family in the future,

Filipe's older brother Yan had left home a year ago

to study medicine at the University of Haiti in Port-au-Prince.

He was the first boy in his village to attend medical school.

On a visit home last April just after the spring rains had began in Haiti the two

brother were playing soccer when Fillipe took a drink from a nearby communal tap.

That night Filipe started having stomach cramps and

began having terrible watery diarrhea.

Yan was alarmed when he helped his brother to the makeshift latrine

that hung over the water near their home at about two in the morning.

And he saw his brother passing what seemed like liters of stool and

the stool reminded him of cloudy white rice water.

Yan immediately suspected that his younger brother was suffering from cholera after

contracting vibrio cholerae, the tiny bacterium that infects the small

intestine, causing a sudden onset of violent gastrointestinal symptoms.

He remembered hearing from his mother that several homes in the area had

recently reported family members suffering from a terrible form of diarrhea.

Yan thought back to his first year of medical school and

remembered learning about the father of epidemiology.

A physician by the name of Jon Snow who

had noticed the similar clustering of cholera in a London neighborhood and

had linked the disease back to a contaminated water supply.

Remembering his younger brother's choice of water supply that morning,

Yan began mentally mapping the families who had been reported ill,

they all collected water from that communal source.

Yan knew that his next steps would be critical to his brother's survival.

Several cholera treatment centers had been opened in Haiti since the disease

was first introduced into the area likely

by UN peacekeepers who came to Haiti from Nepal.

But the nearest cholera treatment center would have required a two hour trek

including a river crossing and Yan knew that infection with vibrio cholerae

could cause rapid dehydration and death in a matter of 12 hours if left untreated.

In order to result in disease, a relatively large number of

the chomashate vibrio cholerae bacteria need to be ingested

because most of them are killed in the acidic environment of the stomach.

Vibrio cholerae that have recently been shed by another human

are hyper-infectious,

meaning that they're better able to survive passage through the stomach.

Once inside the small intestine, the bacterium uses its flagellum

as a propeller and, guided by chemotaxis, it swims towards

the surface of the intestine and avoids being cleared by peristalsis.

When the bacteria reach the surface, they need to overcome another protective

mechanism, the thick mucous net, that's made by goblet cells, to keep bacteria

away from the surface of the epithelial cells lining the intestinal tract.

Vibrio cholerae makes enzymes that digest the mucous and

allow the bacteria to penetrate the mucous.

Next, the bacteria need to attach to the epithelial cells and

this is mediated by thread like appendages

that grow out of the bacterial surface called pillai, or febriae.

Once the bacterium attaches itself to the cell,

it begins producing a toxin that's engulfed by the epithelial cells.

Inside the cells, the cholera toxin disrupts the functioning of chloride

channels in the cell, allowing large amounts of chloride ion to leave the cell,

followed by large amounts of sodium ion.

Water in the lumen of the small intestine is no longer able to be absorbed and

patients shed liter volumes of stool.

With this stool, the colon loses bicarbonate base and

infected patients become dehydrated and acidotic.

The copious amounts of diarrhea seen in cholera patients

is actually beneficial to the organism that causes the disease.

Vibrio cholerae replicates rapidly inside the small intestine.

And the watery stools allow the newly minted bacteria to exit the host and

be transmitted to another usually via fecal-oral contamination.

This is why in parts of the world where running water and

sanitation aren't available, cholera can spread quickly and easily.

Back at home, Yan sees Filipe deteriorating rapidly.

His eyes are sunken, his skin torque is low and he's too weak to walk.

The young medical student fashions a cholera cot out of a rusted deck chair and

asks his mother to begin sterilizing water by boiling it over the kerosene stove.

When the water has cooled Yan mixes six teaspoons of sugar and

half a teaspoon of salt into one liter of sterile water,

trying to stay calm as he remembers the correct proportions of salt, sugar and

water for a homemade version of oral re-hydration solution, or ORS.

ORS is considered first line therapy for cholera, and it's sometimes

all that's necessary to set an infected patient on the road to recovery.

The sodium and glucose in ORS

make use of a different transporter to replenish electrolytes in the host.

This allows for rehydration and recovery to occur.

In Filipe's case, the ORS saved his life, and

allowed his family to transport him to a satellite clinic

operated by a non-profit organization about an hour from their home.

At the clinic, Filipe received rehydration therapy and the family was given chlorine

bleach and advice to sanitize the home and safely dispose of all fecal waste.

Yan contacted local government officials and

warnings were posted around the contaminated water source with directions

on how to decontaminate the water used by Yan and Felipe's neighbors.

Oral rehydration therapy can reduce the risk of dying from cholera

from 20% to 1% in many parts of the world.

By understanding the interactions between socioeconomics and

the pathogenesis of infectious disease, medical teams can develop strategies for

treating and preventing infectious disease around the world.

And health outcomes,

like Filipe's complete recovery can become the norm instead of the exception.

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