Lecture 15 - Emerging Viruses Flashcards
What challenges do emerging infectious diseases pose?
- Identification: of the pathogen, reservoir, and transmission
- Therapy: lack of specific antivirals
- Prevention, control: lack of vaccines, identify index case, quarantine
- Effects on health care system: nosocomial infection, infectious material can require biosafety level 4
- Bioterror considerations
Where do emerging viruses come from?
Usually adapted to a specific host species from animals (zoonotic infections) (so humans are not the natural host)
Why are viruses usually adapted to a specific host species?
- Cell surface proteins for virus adhesion vary between species
- Intracellular replication dependent upon the presence of many species specific molecules
- Virus’ ability to block host immune system, which is species specific
How does human infection by zoonotic viruses occur? What to note?
Occurs via contact with animal/insect reservoir:
- Direct contact with carrier animal
- Contact with secretions
- Bite from an insect vector
NOTES:
- Typically geographically restricted
- Usually dead-end because human-human transmission not typical (often nosocomial)
How to prepare an attenuated vaccine?
Grow it in another species’ cell so it adapts to that other species => will cause an immune response in humans but not enough to cause disease
What 3 emerging viruses include human-human transmission?
- Ebola
- Lassa
- SARS
What 2 factors govern human infection by emerging viruses?
Ecological systems are DYNAMIC:
- Environmental variables affecting how much contact there is between humans and the reservoir
- Potential for person-to-person transmission
What is the size of the reservoir of zoonotic viruses depend on?
Climate
What does person-to-person transmission depend on?
- Amount of virus produced
2. Tissues in which virus replicates
What can allow human-to-human transmission of an emerging virus to be more efficient? Examples?
Mutations
Examples: SARS coronavirus and HIV
What does human-to-human transmission of an emerging virus often involve? Implication?
Close contact => health care workers at risk
Host of Ebola?
Bats
Environmental change causing human infection with Ebola?
Sporadic and unknown
Host of Hanta (N. Amer)?
Rodents
Environmental change causing human infection with Hanta (N. Amer)?
Rain
Host of West Nile?
Mosquitoes
Environmental change causing human infection with West Nile?
Transportation and climate
Host of SARS?
Bats and palm civets
Environmental change causing human infection with SARS?
Human behavior
Host of Dengue?
Mosquitoes
Environmental change causing human infection with Dengue?
Transportation and climate
Host of Zika?
Mosquitoes
Environmental change causing human infection with Zika?
Transportation
Symptoms of Ebola virus? What are these symptoms called? What to note?
- Fever (rapid onset)
- Severe headache
- Muscle pain
- Weakness
- Fatigue
- Diarrhea
- Vomiting
- Abdominal (stomach) pain
- Unexplained hemorrhage (bleeding or bruising)
= Viral hemorrhagic fever
NOTE: these symptoms are non-specific so difficult to distinguish from endemic diseases
When do Ebola symptoms appear?
8-10 days after exposure (2-21 day range)
If no symptoms have been seen in a population with an Ebola outbreak have been seen in 21 days, is the outbreak necessarily over?
Probably, but virus can remain in semen and could still be sexually transmitted
What causes death in Ebola patients?
Low BP due to the hemorrhage => shock => death
Fatality rate of Ebola virus disease?
50-90%
What does the recovery of Ebola virus disease depend on?
Antibody response
What are poor outcomes associated with in Ebola virus disease?
High viremia and weak/non-existent antibody response
What Ebola patients can transmit the virus?
Patients with very severe symptoms + men with virus in semen
Ebola virus pathogenesis?
Impairs the host immune response through many different mechanisms
Do most Ebola virus infection occur when humans are exposed to bats?
NOPE, bats first transmit the virus to primates, which then transmit it to humans
Describe the West Africa Ebola outbreak. What caused the outbreak? 4 things.
Initiated by infection from a single source (bat) followed entirely by human-to-human transmission with patient care and burial practices being the highest risk activities
- Failure to diagnose correctly due to Lassa and other diseases present in region and an incomplete understanding of Ebola natural history
- Inadequate health systems
(e. g. Guinea: 1 doctor per 10,000 people) - Delayed international response
- Lack of fully effective treatment options (not high priority)
How does transmission of the Ebola virus occur?
Via contact with body fluids
How to treat Ebola?
Simple supportive care
How to confirm infection status?
Molecular detection
What are 5 viruses that have successfully adapted to humans and their sources?
- Measles from cattle
- Smallpox (not sure from where)
- HIV from primates
- SARS from bats
- Influenza from birds
What does the SARS coronavirus infects?
- Upper and lower respiratory tract => pneumonia
2. GIT (important for transmission th
What does SARS stand for?
Sudden Acute Respiratory Syndrome
Fatality rate of SARS coronavirus outbreak in 2003? Total number of cases?
10%
8,000 cases
Where did the 2003 SARS outbreak start? Why?
South East China
People were eating more and more exotic animals like palm civets (not the original source of the disease though)
What allowed the SARS virus to cause disease in humans?
Genetic changes in the civet SARS spike protein (2 AAs) allowed better binding to the human cell receptor (ACE2)
What people were at an elevated risk of acquiring the SARS infection?
Health care workers
Were vaccines and therapeutics useful against SARS?
NOPE
What did we learn during the 2003 SARS outbreak?
- Old fashioned preventive measures worked
2. Expect the unexpected as coronaviruses were previously viewed as relatively harmless
What 3 factors determine the emergence of new viral diseases?
- Proximity of host to human habitats
- Climate
- Virus genetic changes
What are most emerging viruses constrained by?
Constrained geographically by the range of reservoir animal
