Lec 9: Zoonosis Flashcards
Describe Walkerton - May 2000
- E coli and campylobacter caused the death of 7 people and resulted in 2300 additional infections
- well water serving the community of Walkerton Ontario was contaminated by surface water carrying livestock waste from neighbouring farms during spring run off and heavy rains
- outcomes of this outbreak drove an overhaul to Ontario’s water safety policy and generated ripples that continue to be felt across the Canadian cattle industry
- estimated direct and indirect costs to Canadian economy $155 million
Describe SARS - March 2003.
Feb 15 - China reports 305 cases of atypical pneumonia
March 12 - WHO issues global SARS alert
March 17 - 11 suspected cases in Canada
May 8 - 15% of people who get SARS will die
- estimated cost to Canadian economy 2 billion
Describe BSE May 2003.
- May 8: first case confirmed in Canada
- May 21: Mexico, Japan and South Korea temporarily ban Canadian beef
- Canadian loss 5.5 billion
- 10 years later, decreased beef producers, beef exports and beef consumption
What is an emerging infectious disease?
- a new agent appears in a new geographic area
- a known agent or its close relative affects a new host species
- a previously unknown agent is detected for the first time
- more loosely, term also relates to a pathogen that has been present historically but which has recently increased in incidence
Define zoonoses.
any disease or infection that is naturally transmissible from animals to humans or vice versa
Define zooanthroponosis.
A zoonosis normally maintained by humans but that can be transmitted to other vertebrates
Define anthropozoonosis.
A zoonosis maintained in nature by animals and transmissible to humans
3 methods of transmission
- direct contact
- environmental transmission
- vectors
Define outbreak
occurrence of cases of disease in excess of what normally would be expected in a defined community, geographical location or season
Define epidemic
a widespread outbreak of an infectious disease; many people infected at the same time
Define pandemic.
A large epidemic with:
- wide geographic extension
- significant transmission that leads to disease movement and extension of geographic range
- highly contagious and short incubation times
- minimal population herd immunity contributes to disease spread
- generally associated with infectious disease
- often severe (fatal)
What is herd immunity?
- protection of a proportion of the population or herd provides vaccination to other individuals
- affects rates/efficiency of disease transmission
- in diseases passed from person to person, it is more difficult to maintain a chain of infection when large numbers of a population are immune
- the more immune individuals present in a population, the lower the likelihood that a susceptible person will come into contact with an infected individual
What is a species barrier?
- natural mechanisms that prevent a pathogen from spreading from one species to another
Pathogenicity
- qualitative (not quantitative) trait, referring to the inherent, genetic capacity of a microorganism to cause disease
- mediated by specific virulence factors
Virulence
- degree of pathogen’s infectivity or disease severity an organism has the potential to cause
- ie a highly virulent pathogen is likely to cause significant disease whereas an avirulent microorganism is likely to cause little or no disease
Virulence factor
- pathogen product or strategy that contributes to its ability to cause infection
- some examples include microorganism production of toxins that kill the host cell, enzymes that act on the host cell walls, or substances that alter the normal cell growth
Prevalance
- the proportion of a population that is infected, or diseased, at any one time
- the actual number of cases alive, with the disease either during a period of time (period prevalence) or at a particular date in time (point prevalence)
Incidence
- the rate of new (or newly diagnosed) cases of the disease
- it is generally reported as the number of new cases occurring within a period of time (e.g. per month, per year)
Infectivity
- refers to the ability of a microorganism to invade and replicate in a host cell or tissue
Transmissibility
- refers to the efficiency with which a pathogen is transmitted to naive hosts
- there are valid arguments that at epidemiological level, transmissibility could be considered a component of virulence
Describe global trends in emerging infectious diseases.
- have risen over time
- 335 infectious diseases have emerged between 1940 and 2004
- dominated by zoonoses (60% of EID)
- majority of these originate in wildlife
What are 3 common misconceptions about emerging diseases?
- Medicine and technology will progressively lead to a decrease in infectious disease emergence
- The majority of emerging infectious disease events occur in geographic areas near the equator
- Viral pathogens (particularly RNA viruses) represent a major threat and most likely to result in EIDs
How have the leading causes of death in the US changed from 1900 to 1997?
- infectious diseases have been replaced by chronic diseases as most important causes of death
What are some factors that influence the decrease in infectious diseases in the 20th century?
- better nutrition, antibiotics, improved hygiene and sanitation, immunizations, safer food and water, better housing
- have lead to decrease in host susceptibility and disease transmission
- which has lead to decrease in infectious diseases
