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Imported infections’ importance: global change driving Dengue dynamics
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Epidemiology and Global Health.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Vikten av importerade infektioner : kan globala förändringar förklara Dengue utbrott? (Swedish)
Abstract [en]

Background Dengue is a significant problem of international health concern. According to the World Health Organization in 2012, globally, dengue is “the most important mosquito borne viral disease” with incidence 30 higher than it had been 50 years ago. While most of the burden of disease associated with dengue is located in areas with a tropical and sub-tropical climate, increasing evidence suggests temperate areas are also at risk. Considering the recent introduction of relevant mosquito vectors into Southern Europe, and increasing numbers of imported dengue via travelers, Europe and other temperate areas may be increasingly at risk for dengue emergence, establishment and local transmission in the foreseeable future.

Methods Recent dengue emergence in Madeira and reemergence in Tokyo underline the hypothesis that passenger air-travel can be an important conduit for the importation of vector-borne disease leading to emergence in naïve areas climatically suitable for dengue transmission, including parts of Europe. Combining information on travel with virus genetic similarity was useful in discerning likely pathways of for the importation of infections. Generalizing information learned from outbreaks in Tokyo and Madeira with global epidemic intelligence, global travel networks, and climate change projections, leads to more refined understanding of the magnitude of dengue infectious imported into temperate areas and these virus introduction events’ potential implications for seeding epidemics in the 21st century.

Results While compared to total travel, imported dengue events and epidemics of dengue outside the tropics are rare, our combined evidence and modeled estimations suggest strongly that epidemic dengue emergence in temperate areas is possible and will continue to increase. We found that global change dynamics including warming temperatures in the much of the northern hemisphere and increasing passenger interconnectivity between areas endemic for dengue and dengue free areas are key mechanisms partly explaining these unprecedented epidemiological transitions.

Conclusion While we calibrated our models on information known about dengue, many elements of the methods and conclusions may increase understanding of the potentially global implications for imported infections of other climate-sensitive infectious diseases’ that may have similar parameters. During 2016 and the years to come, techniques developed in this doctoral research will contribute to models used in risk analysis for vector-borne diseases of interest, including the increasing important potential for imported Chikungunya and Zika viruses into a variety of unexposed areas. 

Place, publisher, year, edition, pages
Umeå: Umeå University , 2016. , 99 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1793
Keyword [en]
Dengue, Zika, Vector-borne Disease, Aedes, Global Change, Climate Change, Viral Evolution, Phylogenetics, Travel, Interconnectivity, Disease Modeling, Madeira, Italy, Japan, Europe
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Identifiers
URN: urn:nbn:se:umu:diva-118645ISBN: 978-91-7601-443-1 (print)OAI: oai:DiVA.org:umu-118645DiVA: diva2:914952
Public defence
2016-04-22, Room 135, Building 9A, Northlands University Hospital (sal 135, byggnad 9A, Norrlands Universitetssjukhus), Umeå, Sweden, 13:00 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework Programme, 282589
Available from: 2016-03-31 Created: 2016-03-28 Last updated: 2016-04-20Bibliographically approved
List of papers
1. The 2012 dengue outbreak in Madeira: exploring the origins
Open this publication in new window or tab >>The 2012 dengue outbreak in Madeira: exploring the origins
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2014 (English)In: Eurosurveillance, ISSN 1025-496X, E-ISSN 1560-7917, Vol. 19, no 8, 20718- p.Article in journal (Refereed) Published
Abstract [en]

In 2012, Madeira reported its first major outbreak of dengue. To identify the origin of the imported dengue virus, we investigated the interconnectivity via air travel between dengue-endemic countries and Madeira, and compared available sequences against GenBank. There were 22,948 air travellers to Madeira in 2012, originating from twenty-nine dengue-endemic countries; 89.6% of these international travellers originated from Venezuela and Brazil. We developed an importation index that takes into account both travel volume and the extent of dengue incidence in the country of origin. Venezuela and Brazil had by far the highest importation indices compared with all other dengue-endemic countries. The importation index for Venezuela was twice as high as that for Brazil. When taking into account seasonality in the months preceding the onset of the Madeira outbreak, this index was even seven times higher for Venezuela than for Brazil during this time. Dengue sequencing shows that the virus responsible for the Madeira outbreak was most closely related to viruses circulating in Venezuela, Brazil and Columbia. Applying the importation index, Venezuela was identified as the most likely origin of importation of dengue virus via travellers to Madeira. We propose that the importation index is a new additional tool that can help to identify and anticipate the most probable country of origin for importation of dengue into currently non-endemic countries.

National Category
Infectious Medicine
Identifiers
urn:nbn:se:umu:diva-87645 (URN)000332376900002 ()
Available from: 2014-04-09 Created: 2014-04-07 Last updated: 2017-12-05Bibliographically approved
2. Estimating Air Travel-Associated Importations of Dengue Virus Into Italy
Open this publication in new window or tab >>Estimating Air Travel-Associated Importations of Dengue Virus Into Italy
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2015 (English)In: Journal of Travel Medicine, ISSN 1195-1982, E-ISSN 1708-8305, Vol. 22, no 3, 186-193 p.Article in journal (Refereed) Published
Abstract [en]

Background: Southern Europe is increasingly at risk for dengue emergence, given the seasonal presence of relevant mosquito vectors and suitable climatic conditions. For example, Aedes mosquitoes, the main vector for both dengue and chikungunya, are abundant in Italy, and Italy experienced the first ever outbreak of chikungunya in Europe in 2007. We set out to estimate the extent of dengue virus importations into Italy via air travelers.

Methods: We attempted to quantify the number of dengue virus importations based on modeling of published estimates on dengue incidence in the countries of disembarkation and analysis of data on comprehensive air travel from these countries into Italy's largest international airport in Rome.

Results: From 2005 to 2012, more than 7.3 million air passengers departing from 100 dengue-endemic countries arrived in Rome. Our Importation Model, which included air traveler volume, estimated the incidence of dengue infections in the countries of disembarkation, and the probability of infection coinciding with travel accounted for an average of 2,320 (1,621–3,255) imported dengue virus infections per year, of which 572 (381–858) were “apparent” dengue infections and 1,747 (1,240–2,397) “inapparent.”

Conclusions: Between 2005 and 2012, we found an increasing trend of dengue virus infections imported into Rome via air travel, which may pose a potential threat for future emergence of dengue in Italy, given that the reoccurring pattern of peak importations corresponds seasonally with periods of relevant mosquito vector activity. The observed increasing annual trends of dengue importation and the consistent peaks in late summer underpin the urgency in determining the threshold levels for the vector and infected human populations that could facilitate novel autochthonous transmission of dengue in Europe.

National Category
Public Health, Global Health, Social Medicine and Epidemiology
Identifiers
urn:nbn:se:umu:diva-103205 (URN)10.1111/jtm.12192 (DOI)000353382800008 ()25756472 (PubMedID)
Available from: 2015-05-26 Created: 2015-05-18 Last updated: 2017-12-04Bibliographically approved
3. Dissecting Japan's Dengue Outbreak in 2014
Open this publication in new window or tab >>Dissecting Japan's Dengue Outbreak in 2014
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2016 (English)In: American Journal of Tropical Medicine and Hygiene, ISSN 0002-9637, E-ISSN 1476-1645, Vol. 94, no 2, 409-412 p.Article in journal (Refereed) Published
Abstract [en]

Despite Japan's temperate climate, a dengue outbreak occurred in Tokyo for the first time in over 70 years in 2014. We dissected this dengue outbreak based on phylogenetic analysis, travel interconnectivity, and environmental drivers for dengue epidemics. Comparing the available dengue virus 1 (DENV1) E gene sequence from this outbreak with 3,282 unique DENV1 sequences in National Center for Biotechnology Information suggested that the DENV might have been imported from China, Indonesia, Singapore, or Vietnam. With travelers arriving into Japan, Guangzhou (China) may have been the source of DENV introduction, given that Guangzhou also reported a large-scale dengue outbreak in 2014. Coinciding with the 2014 outbreak, Tokyo's climate conditions permitted the amplification of Aedes vectors and the annual peak of vectorial capacity. Given suitable vectors and climate conditions in addition to increasing interconnectivity with endemic areas of Asia, Tokyo's 2014 outbreak did not come as a surprise and may foretell more to come.

National Category
Public Health, Global Health, Social Medicine and Epidemiology
Identifiers
urn:nbn:se:umu:diva-115790 (URN)10.4269/ajtmh.15-0468 (DOI)000369465500028 ()26711518 (PubMedID)
Funder
EU, FP7, Seventh Framework Programme, 282589
Available from: 2016-02-04 Created: 2016-02-04 Last updated: 2017-11-30Bibliographically approved
4. Climate Change and Aedes Vectors: 21st Century Projections for Dengue Transmission in Europe
Open this publication in new window or tab >>Climate Change and Aedes Vectors: 21st Century Projections for Dengue Transmission in Europe
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(English)Article in journal (Refereed) Submitted
Abstract [en]

Warming temperatures may increase the geographic spread of vector-borne diseases into temperate areas. Although a tropical mosquito-borne viral disease, a dengue outbreak occurred in Madeira, Portugal, in 2012; the first in Europe since 1920s. This outbreak emphasizes the potential for dengue re-emergence in Europe given changing climates. We present estimates of dengue epidemic potential using vectorial capacity (VC) based on historic and projected temperature (1901 - 2099). VC indicates the vectors’ ability to spread disease among humans. We calculated temperature-dependent VC for Europe, highlighting 10 European cities and three non-European reference cities. Compared with the tropics, Europe shows pronounced seasonality and geographical heterogeneity. Although low, VC during summer is currently sufficient for dengue outbreaks in Southern Europe to commence–if sufficient vector populations (either Ae. aegypti and Ae. albopictus) were active and virus were introduced. Under various climate change scenarios, the seasonal peak and time window for dengue epidemic potential increases during the 21st century. Our study maps dengue epidemic potential in Europe and identifies seasonal time windows when major cities are most conducive for dengue transmission from 1901-2099. Our findings illustrate, that besides vector control, mitigating greenhouse gas emissions crucially reduces the future epidemic potential of dengue in Europe.

Keyword
Vectorial Capacity Aedes aegyptus Aedes albopictus Temperature Climate Change
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Identifiers
urn:nbn:se:umu:diva-118643 (URN)
Funder
EU, FP7, Seventh Framework Programme, 282589
Note

This study is part of the DengueTools project funded by the European Union Seventh Framework Programme FP7/2007-2013 under grant agreement no. 282589.

Available from: 2016-03-28 Created: 2016-03-28 Last updated: 2016-04-04Bibliographically approved

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