Global patterns of disease - infectious Flashcards
Why is human evolution slower than viruses and bacteria?
Human generation time (approx 25 yrs) is long, for influenza this is 2-3 days
What is the average time taken to develop a new drug?
15 years
How long does it take to produce and release a vaccine?
3 months to make but 8 years to trial
What are the 3 origins of human infections?
Ancestors
wildlife
livestock
What is the percentage of infections spread by zoonosis?
60-70
What changes in the world are leading to greater rates of transmission?
Increasing population
Transport- e.g. planes
What is epidemiology?
Quantifying the occurrence of disease in population
What does case mean in epidemiology?
Person with a disease or health problem
What is prevalence?
It is the frequency of disease in a population at a given point in time.
How is prevalence calculated?
Number of cases in a population/number of people in a population (at given time)
What does prevalence tell us?
The burden of disease in a population
What is incidence?
Number of new cases arising over a given time
What can prevalence tell us about the risk of developing disease?
How likely you are to develop a disease during a given time period
Which measures and tools are needed to estimate incidence?
Define time, total risk population and an accurate test to determine if the person has the disease
Why might it be difficult to measure whether a case is new or old?
Chronic conditions - can’t tell whether it is new or old
How does incidence influence the development of policies?
One incidence has reached 0, outbreak is over and places can reopen
Why might prevalence increase even if incidence stays the same?
If people with the condition are surviving- e.g. use of medication
What is mortality?
Number of deaths from a particular disease in a given time
If mortality and incidence are equal, what does that mean about the epidemic?
The epidemic is stable
How is mortality calculated?
deaths from a disease in a given time/ population at start of time period
What is the negative aspect of people with disease living longer?
The transmission increases and incidence increases
Prevalence also increases
What is morbidity?
Number of cases of ill health, complications and side effects related to a specific condition over a particular time period.
What is the unit for mortality?
number of deaths per 1000 per year
What are the leading causes of death?
heart disease cerebro-vascular disease respiratory infection HIV/AIDS COPD
Which country has the highest mortality rate?
Swaziland (30.83)
Sierra Leone, Zambia, Angola, Lesotho also high
What causes the majority of deaths in third world countries?
malnutrition
Which systems can be used to give scores of morbidity?
APACHE II, SAPS II/III, Glasgow Coma Scale, PIM2, SOFA
How can morbidity scores be useful?
Help to decide the type of treatment
What are the main types of infectious disease?
Lower respiratory infection HIV/AIDS Diarrhoeal disease TB Malaria Measles
What is the leading cause of death in Sub Saharan Africa?
Infectious disease
Why are death rates important?
Important to assess how good the health system is in a country
Allows specific public health sectors to be targeted
Where did SARS virus originate from, which animal from, and which year was the outbreak?
Origin was the bat is central Asia
2003
What was the origin of the West Nile Virus, which year was the outbreak?
Birds (crow/rooks)
1999
Does the West Nile Virus have a high or low infectious rate?
How close is the vaccine to being produced?
High infection rate
Vaccine is near clinical trial end
Where did MERS virus originate from and where is its incidence high?
Camels
Middle East
How does malaria increase its genetic variability?
Mutations and recombination of gametes, plasmid transfer
Why is hard to target a vaccine for Plasmodium (causes malaria)?
It has lots of antigens and each one is different
Does ebola transmit fast or slow?
slow
Why can transmission of ebola be prevented even though it is very contagious?
Symptoms develop before you become infectious so person can be isolated
How is ebola transmitted?
Blood, saliva, urine, semen (body fluids) and through contact with contaminated surfaces e.g. soiled cloth
What are the public health measures taken in regards to ebola?
- Identify, isolate and follow up contacts of an infected person
- Isolation of contacts for 21 days
- Border controls are ineffective
- House control not used
Which animal did Zika virus originate from?
Where did it emerge?
Rhesus monkey
South America
What is the risk of infection of Zika virus in pregnant women?
1 in 100 in 1st trimester
1 in 1000 in whole pregnancy
What type of virus is Zika and which animal transmits it?
flavivirus
mosquitoes
What other viruses is Zika related to?
Yellow virus
Dengue virus
West Nile virus
(They are all arboviruses)
How can Zika Virus be transmitted between people?
Sexually
What steps are taken when a new epidemic emerges?
- To indicate emergence of infectious disease - look morbidity/mortality in space and time
- Look through databases to find similarities in cases to identify aetiology
- Diagnostic tests development
- Follow the routes of infection
- Ensure the public are aware of new information - avoidance/precaution
- Identify ways to reduce mortality/morbidity
What is the basic reproductive number (R0)?
average number of secondary cases emerging from a primary one
What does it mean if R0 is less than 1 or above 1?
The disease will become extinct if less than 1
If greater than 1 than means transmission occurs and could lead to an epidemic
What factors affect R0?
- incubation period
- infectiousness
- How long infectiousness lasts
- is acquired immunity important
What are the prevention and control policies for Influenza?
- Minimise morbidity/mortality
- Buy time to wait for vaccine
- Minimise duration
- Minimise impact on economy
Minimise prevalence to stop healthcare collapsing
What are some neglected tropical diseases?
Leishmaniasis and African Trypanosomiasis
(Protozoan)
Schistosomiasis, Lymphatic Filariasis, Onchocerciasis, Dracunculiasis, Ascariasis-Trichuriasis- Hookworm (Helminth)
Leprosy, Trachoma, Buruli Ulcer (Bacterial)
What does the graph for infection growth look like over time?
increases slowly, then exponential growth. Eventually levels off as the number of people susceptible is very low. Eventually rise due to mutation.
Why is it hard to find vaccines against RNA viruses?
No proofreading mechanisms so high mutation rate
