chapter 8 Flashcards
Emergence
The process of coming into being
Epidemic
A widespread occurrence of an infectious disease in a community at a particular time
Pandemic
An outbreak of a disease that affects a whole country or the world
Emerging disease
A disease of infectious origin with an incidence that has increased within the last two decades or threatens to increase in the near future
-Virus can be new, well-established in the human population
what are the 9 types of Types of Emergence we only focus on 5
Zoonosis Geographical contact Mutation Deliberate Release Accidental Release
- Zoonosis
- Usually asymptomatic in animal reservoir
- Jump to humans causes severe symptoms
what are the three types of zoonosis
Direct zoonosis, cyclo and meta
Direct zoonosis
transmitted from an infected vertebrate host to another host by direct contact, fomite or mechanical vector.
One example is rabies.
dog to humans
Cyclozoonosis
requires more than one vertebrate host but no invertebrate host is needed.
Metazoonosis
require an invertebrate host where the pathogen multiples or develops before it can infect a vertebrate host.
One example is yellow fever.
Mosquitoes to humans
Zoonotic Examples
Ebola and HIV
- Geographical Contact
Increased travel causes emergence of virus pathogens in unprotected populations.
HIV thought to be present for ~ 50 yrs in isolated areas of central Africa
- Mutation Influencing Emergence
Mutation of an existing virus to create a new one
Most commonly be RNA viruses because of their low fidelity polymerase
- Deliberate Release
-Release of a pathogenic virus to control an animal (or human) population
international treaty to prevent stockpiling of biological weapons
Eg. rabbit hemorrhagic disease and Smallpox
- Accidental Release
- Release of the rabbit hemorrhagic virus from the testing grounds on Wardang Island (Australia)
- leakage of smallpox into the ventilation system at the University of Birmingham, England
Arboviruses
Virus transmission via biting insects and ticks
Insects as vectors to transmit disease
Mosquitoes most common
Eg. West Nile virus
-Virus can be passed to subsequent generations in vector species’ eggs
-Can overwinter in the arthropod host
-Arthropod can sometimes act as a reservoir (ex. –Crimean-Congo hemorrhagic fever)
Arthropods can also be vectors for bacterial and protozoan infections [eg. bubonic plague (fleas) and malaria (mosquitoes)]
Control of arboviruses
- Mosquito nets impregnated with insecticide permiethrin
- Removal of breeding habitats (stagnant water)
- Chemical insecticides (temephos, DDT)
- Larval growth inhibitors (methoprene)
- Biological control agents (bacteria, predator fish, crustaceans)
Extinction
The disappearance of a virus from the earth
99.9% of all species that ever existed are now extinct
High mutation rates in virus
eg, ebola or measles
