Emergence and spillover

Question 1

What is a reservoir?

Answer 1

reservoir - animal population that can maintain a virus in circulation and which transmit to a target species such as humans; the reservoir organisms can not have any signs of diseases but when it goes to humans it ccan cause epidemics and even pandemics

Question 2

What is a spillover?

Answer 2

spillover - the process of the pathogen moving from the reservoir population into the focal host

Question 3

What is spillover dependant on?

Answer 3

spillover is heavily dependant on the contact rate between the reservoir population and the focal host population

Question 4

What is the difference between spillover and emergence?

Answer 4

• spillover is when the pathogen gets into the humans host
• emergence is when that pathogen is able to be passed from human to human at a high enough rate that it can cause a disease outbreak

Question 5

What do ecologists studying spillover focus on?

Answer 5

• describing the process of spillover and the interactions and state changes that lead to emergence
• developing models to explain spillover patterns and forecast emergence, epidemic behaviour and how we can intervene
• develop interventions that mitigate, control, or even prevent epidemics and pandemics

Question 6

What are indirect and direct spillover?

Answer 6

• indirect spillover - from reservoir to intermediary or vector to focal host
• direct spillover - from reservoir to focal host

Question 7

What happens to emergence when R0=0

Answer 7

we get spillover from the reservoir, R0=0 → no human to human transmission → no outbreak it hits a dead end - it’s spilling over but it is not emerging (eg avian flu - you can get it from a chicken but human to human transmission is very rare)

Question 8

What happens to emergence when R0<=1

Answer 8

R0 ≤ 1 - you get sputtering epidemics, you get some cases but they inevitably fade out - spreading due to stochastic events

Question 9

What happens to emergence when you have R0>1

Answer 9

R0>1 in the FHC transmission takes off with the probability 1/R0; it doesn’t rely on chance that much anymore, for the disease to go into emergence it requires that the pathogen adapts to the host

Question 10

What is a spillover epidemic?

Answer 10

spillover epidemic - spillover transmission occurs and FHCC is dead-end

Question 11

What is a mixed epidemic?

Answer 11

mixed epidemic- spillover may be persistent but is accompanied by limited secondary human to human or animal to animal transmission in the host endemic space

Question 12

What is a human host epidemic of zoonotic origin?

Answer 12

human host epidemic of zoonotic origin - a zoonotic pathogen makes a species jump from zoonotic host departs from spillover epidemic space and gets sustained human-to-human transmission

Question 13

What is a human host epidemic with zoonotic genetic source contribution?

Answer 13

human host epidemic with zoonotic genetic source contribution- human flu has chunks of swine or avian viruses

Question 14

What is animal host epidemic with human origin?

Answer 14

animal host epidemic with human origin - a human source pathogen jumps into another species and gets sustained transmission

Question 15

animal host epidemic with human genetic source contributions

Answer 15

Animal virus with human virus genetic chunks

Question 16

What has to happen for a succesfull spillover

Answer 16

• has to get into the focal host population - contact rates between host population and focal population create the potential for spillover
• once it is in, it must be biologically capable to FHC to FHC transmission
• have high enough R0 to sustain in transmission

Question 17

How many types of human influenza do we have?

Answer 17

• human seasonal influenza has two main types: A and B
• within those types you have many different subtypes which are named based on the different version of the H and N proteins on the surface of the virus

Question 18

Why is the flu so good at spilling over?

Answer 18

the reason the flu is so good at spilling over is because the virus can go through recombination be reassortment - if an influenza virus connects a cell with another influenza virus they can swap whole genes between each other and when they do that it causes something called antigenic shift which has a huge effect on which kinds of cells they can infect

Question 19

How do we get random mutations in flu?

Answer 19

in flu we have rapid generation of mutations by the error-prone viral RNA -dependent RNA polymerase

Question 20

HIV M group

Answer 20

• we now that chimpanzees in southern Cameroon harbour simian immune deficiency virus that is the most similar to HIV-1 group M
• M group is important. It is the only group to establish pandemic spread . Within there are several distinc subtypes A, B, C and so on

Question 21

What were the public health interventions in 1960s in the context of HIV?

Answer 21

• unsterilised injections at STD clinics and or subsequent changes to sex work in Kinasha in 1960s which lead to increase in client numbers
• latrogenic - relating to illness caused by medical examination or treatment
• other blood borne pathogens that are not STIs exhibit similar increases during the period

Question 21

What were the public health interventions in 1960s in the context of HIV?

Answer 21

• unsterilised injections at STD clinics and or subsequent changes to sex work in Kinasha in 1960s which lead to increase in client numbers
• latrogenic - relating to illness caused by medical examination or treatment
• other blood borne pathogens that are not STIs exhibit similar increases during the period

Question 22

what is equally as important as genetic mutations for pathogen emergance?

Answer 22

host demographics and behaviours can be as important as genetic mutation rates in determining whether emergence occurs

Question 23

When was the largest outbreak of Ebola so far?

Answer 23

• the largest Ebola outbreak in history was first reported in March 2014 and declared over by the WHO on June 10, 2016. While the epidemic spread to other parts of Africa, Europe and the US the largest impact was in Guinea, Sierra LEone and Liberia, the epicentre of the outbreak
• using molecular methods we can trace what those different outbreak lineages did ; you can see how freaquenstly the changes resulted in an epidemic outbreak

Question 24

What were the factors affecting the dispersal of the ebola virus?

Answer 24

• both distance and size of populations at origin and destination were important - the closer the populattions and the larger they are then the outbreak is more likely
• for a given lineage of the virus, dispersal events were intense in administrative regions sharing an international border
• urbanisation, large population sizes and short travel time t nearest settlement with > 50k inhabitantts were significant factors implementing whether or not the outbreak was going to occur