ANTC67H3 Chapter Notes - Chapter 7: Infection, Human Security, Yellow Fever
ANTC67
Foundations in Epidemiology
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CHAPTER 7 — COMMUNICABLE DISEASES: EPIDEMIOLOGY SURVEILLANCE
AND RESPONSE
INTRODUCTION
Definitions
-communicable (infectious) disease - caused by transmission of a specific pathogenic agent to
a susceptible host (transmitted directly or indirectly through vectors)
-vectors - insects or other animals that carry infectious agent from person to person
-vehicles - contaminated objects or elements of the environment (ex, clothes, food, plasma)
-contagious diseases - can spread between humans without an intervening vector or vehicle
-ex. malaria is communicable but not contagious, syphilis and measles are both communicable
and contagious
-can cause disease through toxic effect of chemicals that infection produces
Role of Epidemiology
-epidemiology - study of outbreaks of communicable disease and interaction between agents,
hosts, vectors and reservoirs
-describe circumstances that spark epidemics in human populations
-increases human ability to control spread of communicable disease
-surveillance, prevention, quarantine, treatment
The Burden of Communicable Disease
-dominated by HIV/AIDS, tuberculosis and malaria
-emerging disease put a large unpredictable burden on health systems
-emerging diseases: diphtheria, yellow fever, anthrax, plague, SARS etc.
Threats to Human Security and Health Systems
-communicable diseases pose an acute threat to individual health and collective human security
-communicable diseases common in low income countries
-rising chronic diseases in urban settings
-investigation must be done quickly and with limited resources
-failure to act effectively can be damaging
EPIDEMIC AND ENDEMIC DISEASE
Epidemics
-epidemics - occurrence of cases in excess of what is normally expected in a community/
region with specified time period, geographical region and particulars of population
-number of cases needed to define an epidemic depends on: agent, size, type and susceptibility
of population exposed, time and place of occurrence
-dynamic of epidemic determined by: characteristics of its agent, patterns of transmission,
susceptibility of its human hosts
-three main groups of pathogenic agents: bacteria, viruses and parasites
-vaccines are the most effective means of preventing infectious diseases (viral and bacterial)
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ANTC67
Foundations in Epidemiology
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-vaccines provide individual prevention/attenuation clinical disease in an exposed person and
providing herd community (population)
-point source epidemic - susceptible individuals are exposed simultaneously to one source of
infection resulting in very rapid increase in number of cases in short amount of time (ex.
cholera epidemic)
-contagious/propagated epidemic - disease is passed from person to person and the initial rise
in number of cases is slower
-determining spread of disease: number of susceptible individuals, potential sources of
infection
Endemic Diseases
-endemic disease - relatively stable pattern of occurrence in a given geographical area or
population group at relatively high prevalence and incidence
-ex. malaria in low income tropical countries
-changes in the host, agent, environment may cause disease to become epidemic
-ex. HIV infectious disease has gone from endemic in many areas to epidemic
-climate can affect whether disease becomes endemic
Emerging and Re-Emerging Infections
-last decades of the 20th century, newly emerging and re-emerging diseases
-ex. HIV aids
-ex. vora; haemorrhagic fevers: ebola, yellow fever, west nile, dengue
-ex. poliomyelitis, SARS, influenza A
-ex. bacterial diseases: anthrax, cholera, typhoid, plague
-some diseases may have existed previously but were only recognized recently because
etiological or environmental changes have increased the risk of human infection or ability to
detect infections has improved (ascertainment bias)
-also changes in hosts, agents and environmental conditions
CHAIN OF INFECTION
-communicable diseases occur as a result of the interaction between: infectious agent,
transmission process, host and environment
-controlling disease involves changing one or more of these components
-clarify the processes of infection to develop
-implement and evaluate appropriate control measures
-knowledge of each factor in the chain of infection
-also possible to control disease with only limited knowledge of its specific chain of infection
The Infectious Agent
-infection - entry and development or multiplication of an infectious agent in the host
-some infections do not produce clinical disease
-determining the nature of infection: pathogenicity, virulence, infective dose, reservoir of
agent, source of infection
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Document Summary
Communicable (infectious) disease - caused by transmission of a specific pathogenic agent to a susceptible host (transmitted directly or indirectly through vectors) Vectors - insects or other animals that carry infectious agent from person to person. Vehicles - contaminated objects or elements of the environment (ex, clothes, food, plasma) Contagious diseases - can spread between humans without an intervening vector or vehicle. Ex. malaria is communicable but not contagious, syphilis and measles are both communicable and contagious. Can cause disease through toxic effect of chemicals that infection produces. Epidemiology - study of outbreaks of communicable disease and interaction between agents, hosts, vectors and reservoirs. Describe circumstances that spark epidemics in human populations. Increases human ability to control spread of communicable disease. Emerging disease put a large unpredictable burden on health systems. Emerging diseases: diphtheria, yellow fever, anthrax, plague, sars etc. Communicable diseases pose an acute threat to individual health and collective human security. Communicable diseases common in low income countries.
