High habitat richness limits the risk of tick-borne encephalitis in Europe: a multi-scale study
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| Number of Parts | 45 | |
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| License | CC Attribution 3.0 Germany: You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
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| Production Year | 2023 | |
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MOOD Science Webinars34 / 45
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Transcript: English(auto-generated)
00:08
So today I will talk about this study, performed first of all by Francesca D'Agustin and by the others, co-authors and my colleagues, in order to evaluate what is the role of
00:21
habitat richness in moderating the risk of fatigue-borne encephalitis in Europe. And this study has been funded by the MUD Project and essentially I will go through a small overview on the tick-borne encephalitis disease. It is a viral infection disease which involved
00:44
the central nervous system and of course in Europe and in Asia, as you can see from the right side map, and is caused by the TB virus of the family flavivirus. It is endemic in 25 European countries and causes more than 3,000 cases each year.
01:04
And if we account for example the last 10-15 years, we were able to see an increase of the human cases across Europe, spanning especially from 2016 and 2020. However, the circulation of
01:23
the virus in Europe is spatially and temporally limited to natural foci and sod endemic areas, which are highly variable in time and space and usually unstable in both terms of impact and location. However, the tick-borne encephalitis is also a seasonal
01:43
disease, so has been affected and is affected by abiotic and climatic factors, for example precipitation, dial temperature, autumnal cooling. Not only it has been governed also by biotic factors, so variable, for example the percentage of arrested area and the presence of
02:05
competent hostels, for example rodents, but also those hosts that maintain the tick population in the environment. And this is a recent work performed by the colleagues and Francesca, which has been published last year on Euro surveillance. And if you are interested in this topic, you can
02:25
see the recording of her presentation during a MOOD webinar, which occurred last year, and you can find it on the MOOD project website. However, we can dig more on the transmission mode of the TB virus. First of all, the major transmission which enhances the circulation
02:45
of the virus is the co-feeding, which is defined by the simultaneous presence of one or more larvae or one or more nymphs feeding at the same host, competent host, with a maximum distance of five millimeters from one to the other. And from a work published and evaluated from a colleague
03:08
of ours at the Foundation Edmond Mach, they saw that the TB prevalence in rodents has a positive influences of the co-feeding groups recorded in the previous years, as you can see from the plot
03:22
on the left side. And also they found that there is a parabolic effect performed by the rodent density on the TB prevalence, probably due to the discrete nature of the tick demography in the environment. But if we go more deeply on the transmission cycle of the virus in nature,
03:43
and which are the components that influence its circulation, we can see that the virus circulation relied especially on the Xodes sericinus complex, while the host which enhance and govern the transmission of the virus are, for instance, and first of all,
04:03
the competent reservoir rodents, for instance, woodland mice and the bank bull. Not only there are other hosts, domestic animals, wild ungulates, livestock, and also carnivores, which are non-competent hosts for the transmission of the virus, but they can maintain and sustain the reproductive stages of ticks in an environment.
04:27
So ticks are both a vector and a reservoir for TB virus, and they can remain infected throughout the life cycle through trans-tadial transmissions or trans-viral vertical transmissions.
04:43
Moreover, the virus can be transmitted also by relying on host through horizontal voramic transmission. So, for example, non-infected ticks became infected by feeding on infected host, but also through the horizontal non-viramic transmission, for example,
05:03
the co-feeding mechanism that we already seen before. For the rest of the host, including also human, they can acquire the virus through tick bite, for example, domestic or wild ungulates, but also for carnivores, for the consumption of infected
05:23
prey such as rodents. And finally, humans can become infected and acquire the virus also by eating unpasteurized milk and milk products, which are produced by infected livestock.
05:40
And given the variety of hosts that we already seen and a different role that they can maintain and sustain within the TB transmission cycle, there is the need to evaluate how the biodiversity of hosting wild and domestic environments favor and govern the
06:02
circulation of these tick-borne diseases. Currently, there is little research that has been done at the European level, and mainly because it is essentially difficult to retrieve abundance and the community data on a host covering the whole European continent.
06:22
For this reason, our aim is to assess the role of habitat richness on the geographical distribution on TB by using a novel index that is called the habitat richness to evaluate the effect of habitat diversity on the TB presence. And this index is a proxy of
06:41
species biodiversity that I will cover more deeply afterwards. So, first of all, we divided the study in two scales, the European scale and the local one, performed in Northern Italy. And by starting with the European scale, we obtained the data provided by ACDC at the European level, considering the NATS region, so it is the
07:11
to standardize the spatial resolution across Europe. And we have the data on TB in humans from 2017 to 2021. And so we will treat the data from 80-72 regions on presence or absence
07:27
of the virus. Then we have the data on the habitat richness index, which instead was developed by the University of Bologna in Italy. And they provided this index, which is essentially the number of terrestrial habitat of community interest in a cell grid of 10
07:46
kilometers. And as I said before, it is an index of species biodiversity because it is correlated with the richness of species within the annex of species of birds and the habitat directives. And moreover, we are counting also for the probability of presence of some key
08:06
host that contributed to the circulation of TB, especially the yellow-necked mouse, the banked bull and the cherubits. Those data were provided by the ERG group and are data on the abundance of the host across Europe, depending on the habitat suitability
08:25
in one kilometer grids. And to assess the association between the TB data across Europe and the habitat richness index, we applied a binomial linear regression model with linear
08:41
and quadratic habitat richness covariate. And also we accounted for this value, which is the autocovariate, to account to the closest regions, essentially. And performing the model selection through IC, we found that the quadratic covariate of habitat
09:04
richness explored better the TB data. And afterwards, we also evaluated the effect of habitat richness on the probability of presence of host performing Pearson correlation coefficient. So the map on the sides showed the habitat richness across Europe. And you
09:26
can see that it's spanning from low to high values. Essentially, high value of habitat richness we can find it in mountainous regions, for example, the Pyrenees, the Alpine chain, and the Balkanian countries, while the low value of habitat richness are in the central
09:45
part of France or in Far East countries. With respect to the TB data, instead, we have endemic areas in the central eastern part of Europe, also in Sweden and Finland, while Spain and Ireland are absent, and there is no presence of the virus.
10:06
So the result of the model that we perform at the European level, we see this parabolic effect. And specifically, the TB presence was higher in the intermediate value of habitat
10:22
richness, while at the edge of the low value of habitat rich and very high value, we have very low presence of TB. This depends also on the fact, I mean, at the left side of the plot, because at the European scale, we can find also habitat which are not suitable
10:42
for the presence of vectors and host. And for this reason, we found low presence of TB, while in on the right side of the plot, we have this decrease of TB presence where the diversity was very high. And regarding the results on the effect of habitat richness
11:04
on the presence of host, we found a negative significant relationship between habitat richness and yellow neck mouse. Essentially, this means that the species was present in habitat with very low habitat diversity. And this also explains the result found on the TB cases.
11:27
Instead, for the bank vole and the three species considered of ungulates, we didn't find any significant effect but still negative. And then we move on the more local scale,
11:41
we try to validate the same models, accounting for TB data provided by public health agency of two Italian provinces in the northeastern Alps, province of Trento and province of Belluno. And here you can see the map showing the absence and presence of TB across several
12:04
municipalities. And then we retrieve the habitat richness for the same areas. And you can see instead in this map that the habitat richness was a bit restricted, respect to the European ones. And especially it was very interesting to note that the habitat richness and habitat
12:23
diversity was higher in natural parks and natural areas, which are those areas with the white border. And when we combine those two types of data, we found a similar
12:40
relationship between TB and habitat richness also at local scale. And in particular, we see high value of TB where the habitat richness or habitat diversity was very low. And instead, the decrease and the TB presence decrease as far as the habitat
13:01
richness index increases. To wrap up a bit what we found in the study, it is a study and studying the relationship between biodiversity and the disease was very challenging as the data available are very limited across European scale. And therefore, we try to test this relationship
13:28
with a new index, the habitat richness. Also, the habitat richness is related with the exposure of humans in different environment, especially due to touristic or occupational
13:43
activity were performed in area where the habitat richness are low or intermediate. And are the areas where we found a high TB presence or a higher risk for humans due to the TB.
14:00
However, there are other crucial aspects that need to be uncovered. And especially we didn't consider in the study the vector of preference, the host competence, the different role of host, low quality host, and how they interact to each other to enhance or limit the
14:21
circulation of the disease. And especially is necessary to not only account in the amplifying host, for example, the rodents, but also those hosts that maintain the tick population and environment, such as large ungulates, the host that they said that they dilute the disease
14:43
so they can divert the infected ticks to the competent host. And therefore, they can decrease the occurrence or the prevalence in the environment. And finally, giving the focus or more importance to also the host that are not competent, but they can control and for decrease
15:04
the population of the competent host. To our knowledge, this is the first attempt to relate the TB with the diversity of habitats across Europe. And this is needed not only to prevent the future disease outbreaks, but also to inform the public agency, public health agency,
15:26
or the community, in order to perform control and prevention strategies, and also to try to conserve and species or try to perform strategies to conserve species and ecosystems, which are
15:44
needed to decrease the disease at the European level. So finally, I wanted to thank all my colleagues and the co-authors of this work, and especially the MOOD project, which I said
16:00
before funding the work and also provided the data, for example, for the host. And I want to acknowledge the different research institutes or agencies that contributed to this work, especially beyond the Foundation and MUMAC and National Biodiversity Future Center in Italy,
16:20
but the public health agency in Veneto and Trentino, the University of Bologna that provided the index of habitats, the environmental research group in Oxford that instead provided the data for the host, and the public agency of Finland that also contributed within this work.