Video 5.4: The Host: Overview

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Do curso por The University of Hong Kong

Epidemics

23 ratings

The University of Hong Kong

Epidemics

23 ratings

“If history is our guide, we can assume that the battle between the intellect and will of the human species and the extraordinary adaptability of microbes will be never-ending.” (1) Despite all the remarkable technological breakthroughs that we have made over the past few decades, the threat from infectious diseases has significantly accelerated. In this course, we will learn why this is the case by looking at the fundamental scientific principles underlying epidemics and the public health actions behind their prevention and control in the 21st century. This course covers the following four topics: 1. Origins of novel pathogens; 2. Analysis of the spread of infectious diseases; 3. Medical and public health countermeasures to prevent and control epidemics; 4. Panel discussions involving leading public health experts with deep frontline experiences to share their views on risk communication, crisis management, ethics and public trust in the context of infectious disease control. In addition to the original introductory sessions on epidemics, we revamped the course by adding: - new panel discussions with world-leading experts; and - supplementary modules on next generation informatics for combating epidemics. -------------------------------------------------------- (1) Fauci AS, Touchette NA, Folkers GK. Emerging Infectious Diseases: a 10-Year Perspective from the National Institute of Allergy and Infectious Diseases. Emerg Infect Dis 2005 Apr; 11(4):519-25. What you'll learn - Demonstrate knowledge of the origins, spread and control of infectious disease epidemics - Demonstrate understanding of the importance of effective communication about epidemics - Demonstrate understanding of key contemporary issues relating to epidemics from a global perspective

Na lição

Theme Two: Spread (Epidemiological triangle)

Theme One descriptions

Week 5 Introduction0:51

Video 5.1: Epidemiologic Triangle1:08

Video 5.2: The Pathogen: The effects of dose and pathogen genetics5:13

Video 5.3: The Pathogen: Evolution9:29

Video 5.4: The Host: Overview5:00

Video 5.5: The Host: Age7:33

Video 5.6: The Host: Sexual mixing4:45

Video 5.7: The Environment7:54

Conheça os instrutores

Gabriel M. Leung (HKU)
Dean
Li Ka Shing Faculty of Medicine
Joseph T. Wu (HKU)
Associate Professor
Li Ka Shing Faculty of Medicine
Kwok-Yung Yuen (HKU)
Professor
Li Ka Shing Faculty of Medicine
Tommy Lam (HKU)
Assistant Professor
Li Ka Shing Faculty of Medicine
Maria Huachen Zhu (HKU)
Associate Professor
Li Ka Shing Faculty of Medicine
Guan Yi (HKU)
Chair Professor
Li Ka Shing Faculty of Medicine
Benjamin Cowling (HKU)
Professor
Li Ka Shing Faculty of Medicine
Thomas Abraham (HKU)
Associate Professor
Journalism and Media Studies Centre
Mark Jit (LSHTM)
Professor
Department of Infectious Disease Epidemiology
Malik Peiris (HKU)
Chair Professor
Li Ka Shing Faculty of Medicine
Marc Lipsitch (Harvard)
Professor
Department of Epidemiology

The host is the second component

of the epidemiologic triangle.

For disease transmission,

perhaps the most important attribute

of a host is their age.

Age affects almost every aspect of infection:

the likelihood of becoming infected,

the severity of disease if infected,

and the likelihood of transmitting it to others.

An individual's age affects the types

and frequencies of social interactions,

such as attendance at group child care, school, and work.

It also affects the tendency to engage in activities

that can transmit specific types of infection,

such as sexually transmitted infections.

The frequency and intensity

of these interactions affect the risk

of being exposed to an infectious person

and the rate of passing on infections

to other susceptible persons.

For many infectious diseases, infection leads to immunity.

This immunity may protect the individual against re-infection

for many years, or even for life.

Typically, for such diseases, children are at greatest risk

of contracting the infection because they are less likely

to have had it before.

However, in the first half year of life there may be some protection

against infection from antibodies the child receives

from the mother transplacentally before birth and in breast milk.

For some infections, such as influenza, pertussis, and tetanus,

we use this fact as a public health strategy and offer vaccines

to pregnant women to protect their children after birth.

In many diseases the immune response begins to decline

with advancing age, resulting in a distribution of disease incidence

that has two peaks: one after the decline of maternal antibodies

and another in old age.

More generally, the health of an individual's immune system

can affect their susceptibility to infection and disease.

Diabetics, people undergoing certain types of cancer treatments,

and other immuno-compromised people

are at elevated risk of contracting certain infections.

Some infections predispose a host to acquire other infections.

Perhaps the best known example is HIV.

HIV increases a person's risk of many diseases:

including bacterial pneumonia, tuberculosis,

and some other infections.

Some so-called “opportunistic infections” are common

in HIV patients but are almost never observed

in people with healthy immune systems.

In fact, the discovery of the HIV virus began with an observation

of unusual fungal pneumonia and an unusual, infectious form

of cancer, known as Kaposi's sarcoma,

which were seen in men who have sex with men.

Epidemiologists were able to work out that these men

had compromised immune systems,

which make them susceptible to the unusual infections

that first brought them to medical attention.

HIV was discovered as the cause

of this immuno-compromised state.

Other examples in which one infection increases the risk

of another infection include influenza,

a viral disease which can lead to secondary bacterial

pneumonia, and schistosomiasis, a helminth or worm disease

that can increase one's risk of acquiring HIV.

A person’s behavior affects their risks of becoming infected

and passing on infection to others.

One type of behavior that is extremely variable

across different hosts is the level of sexual activity,

which may range from abstinence

or long-term monogamy for many individuals,

to extremely high rates of new partner acquisition for others.

This variation has important consequences

both for the maintenance of sexually-transmitted diseases

in populations and for their control.

Sometimes particular hosts are unusually infectious

to others because of the site at which they are infected.

Tuberculosis infection in the larynx or throat is especially likely

to transmit to others, while extrapulmonary TB

or infections outside the respiratory tract

are much less likely to be transmitted.

Finally, sometimes people vary in the number of secondary

cases they infect, and we don't know the reason.

During the SARS epidemics in 2003,

there were a number of super spreading events.

Whereas a typical SARS case infected about three other people

in the period before control measures were introduced,

there were a few instances in which so called “super spreaders”

infected upwards of 20 other individuals.

In this session we have had an overview

of the major host factors

that affect transmission and severity of disease.

In the upcoming sessions we will focus

on two of these in more detail.

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