Whether that will increase the intensity in, in areas where there is
already transmission, or will it lead to subsequent spread and
reestablishment or changes in range, possibly into new areas, or
to reestablishing areas where it's already gone extinct.
and, so I think there are a number of it, sort of interesting elements to that.
First of all, that, that diseases like vector-borne diseases are strongly
influenced by environmental factors, and that's because they're linked very
critically to the ecology and the biology of the mosquito, and these are small
cold blooded organisms, whose biology, physiology, lifespan, what they feed on,
how regularly they feed, is strongly influenced by environmental factors.
So when you have small changes in the temperature,
that can influence where the young mosquito lives for
2 weeks or 3 weeks, how many eggs it lays, how quick do the larvae develop and so on,
and how well it's, and how well the disease incubates inside it.
Very strongly temperature dependant, does it take just one week to get through,
two weeks to get through, three weeks to get through, and so on.
So clearly environments is a very strong driver.
One of the challenges however,
is that there are many other factors that are also drivers of the disease itself.
>> Mm-hm. >> Not just a transmission but
whether we have it or not, and if you look at climate suitability,
if you look at climate maps, You can go down to Florida, or
if you can go to the top end of Australia in Queensland, and
you can see the perfect environment for Malaria transmission.
But there is none, there used to be, but there isn't any anymore, and
that's because there's now, in some places this disconnect between environment and
transmission through economic development access to
good public health infrastructure, new houses, air conditioning, screening,
people sitting indoors watching TV rather than sitting outside on the veranda.
So all of these factors contribute to massive change in disease,
risk disease transmission.
In some places however, you don't have those changes and
so environments are still already key driver.
And so I, that's not a very satisfactory answer but
unfortunately it's really rather complicated.
There are places where you might expect small changes in climate to have
a big impact on disease, particularly areas which are at the sort of
the edges of range now, where perhaps climate isn't quite suitable enough but,
just a small change in temperature can lead to the establishment of the disease.
Or it can change it from where maybe, transmission is suitable for
one month a year and suddenly it can become three months a year, and
those sort of areas you might expect to see emergence and
reestablishment of disease, but then even there that's subject to where they are,
if that's in Florida, it doesn't matter.
>> Well oh, and we often times shorthand, climate change as global warming.
And that, and that sort of simplifies the, the range of
possible environmental changes that might occur at any given place, so
we might have some places will warm, some places will get colder,
some places will get drier, some places will get wetter.
And so the ecological niche that, that, that, creates suitability for
some of these vectors and some of these transmission mechanisms,
is simpler than just a, than a si, than just a single dimension, right?
It's just, just being warmer doesn't necessarily mean more, more mosquitos,
you also have to have enough water that you have aquatic breeding sites, right?
Because they're, they're, they may be limited by the, the, the availability of-
>> Yep. >> of larval [CROSSTALK].
>> And Meg's done some very nice work showing that in fact even changes in
the diurnal temperature variation during the day,
no change in the actual average temperature in the day, but
the extremes during the day is enough to radically change disease risks.
So very subtle variables can make a big difference.
>> And you can achieve, and so we tend to think about global change, and
we talk about climate change, and what's going to happen you know, with the two to,
to four degree changes in mean temperature for the next 20 to 50 years,
as Andrew said, but that's only going to tell you part of the story.
Because, perhaps, patterns of the, the extreme events and
the patterns of the fluctuation aren't as important as the shift in the mean.
But also, you can get changes, very local habitat changes, overnight.
I mean, if you have your household environment, and
you go to sort of traditional mud thatch house in an African village,
and you put a tin roof on it you've changed the indoor environment overnight.
You didn't have to wait for 50 years for
climate change, to alter the environment in which that mosquito is resting.
So we have and you can, and you were saying,
I mean absolutely right that, availability of breeding sites, water for instance.
You can change the availability of water by putting in an irrigation scheme or
draining a swamp, that can happen overnight.
So, some of these really important drivers of environmental change aren't on sort of
decadal time scales, but they're happening now and
having potentially really big impact.
[CROSSTALK] Right. >> Or air conditioning.
>> Right, and in fact, so, there is, there are cultural practices that humans,
you know the style of, of housing, whether or not there was air conditioning,
et cetera, that actually sets the micro climate for some of these vectors, right?
So, the quest, one question is, are they broadly experiencing you know,
global climate or
are they experiencing the microclimate that's probably changing very rapidly
as a consequence of economic development in just, and broad scale cultural change?
>> Yep, trans, I mean transmission is very local, so, what you do at a local level,
at the household level, at the village level, changes in microclimate,
changes in environment, changes in cultural practices, access to bed nets,
all of those things have a very big impact.
Oh, and over, you sort of overlay on top of that these long term
environmental changes that can, sometimes act in synergy and make things worse.
Sometimes they can sort of cancel each other out in that's kind of
an interesting challenge, because we're doing interventions, we're having change
short term in a, in a context of longer term environmental change.
And there's been some rather nice work trying to evaluate, for
instance, the impact of bed nets.
And, in some environments, you can see a bed net, so
you, people have put out bed nets and you've seen a decline in transmission.
And actually when you start to tease apart, well what's been the driver of
that, in some cases you can attribute it almost solely to the bed nets.
In other places you can see well, it's been the bed nets, but
actually something else has changed as well, the environment's changed too, and
there are areas that have paralleled it where you've had the equivalent decline,
and they haven't even but out bed nets.
>> Mm-hm.
>> Other places where control hasn't been as good as one might have imagined,
having given out that many bed nets and
it turns out that in fact the long term environment has been or, or the, the sort
of more regional scale environment has more conducive to transmission.
So we've had an effect, but it's not been as good because in the background,
transmission and suitability has been going up.
So if we don't understand these things even on our short term interventions,
we don't really understand how they work.
When they're not working as well as they might be,
or, in fact, we're attributing great success to something which is,
in fact, partly attributable to something else.
>> Yeah, and again I think, the refrain for
lots of this course is that it's, to understand and
to predict some of these very complex processes, we need, biologists.
We need an under, you know, an understanding of social and
cultural practices, ec, economics and development and global change, written
large I think, to really grapple with the complexity of some of these problems.
>> Yeah.
Dr. Ottar N. BjornstadProfessor of Entomology and Biology
Dr. Rachel A. SmithAssociate Professor
Dr. Mary L. PossProfessor of Biology
Dr. David P. HughesAssistant Professor of Entomology and Biology
Dr. Peter HudsonWillaman Professor of Biology
Dr. Matthew FerrariAssistant Professor of Biology
Dr. Andrew ReadAlumni Professor in the Biological Sciences, and Professor of Entomology
Dr. Marcel SalathéAssistant Professor of Biology
