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The dengue fever epidemic in Guangzhou may have been affected by the Coronavirus Disease 2019 (COVID-19) pandemic. The number of dengue cases dropped drastically in 2020, and there have been only 2 local cases, suggesting that dengue has not become endemic in Guangzhou.

Guangzhou is located on the southeast coast of China and is the country’s third largest city. Since 1978, outbreaks of dengue fever have occurred intermittently in this city. In the past decade, the number of reported dengue cases reached more than 1,000 in 2013, 2014, 2018, and 2019, with 37,385 cases reported in 2014 alone. Therefore, dengue fever is a major public health concern in Guangzhou, and there is a continuing argument that it is endemic in Guangzhou [13].The numbers of dengue cases from 2017 to 2020 are shown in Table 1. In 2020, the total and local case numbers dropped dramatically compared to the previous years. With a high proportion of imported cases (n = 32, 94.12%), the proportion of local cases (n = 2, 5.88%) was considerably low in 2020. All the prevention and control strategies for dengue, including issuing public education messages, preventing further mosquito bites in patients, cleaning vector breeding sites, and using pesticides, were similar during these years. Additionally, dengue, as a mosquito-borne viral infectious disease, is closely related to mosquito density. The mosquito ovitrap index (MOI), which is the proportion of positive mosquito ovitraps, is usually used to indicate mosquito density. The MOI in 2017, 2018, and 2019 was 7.073 ± 1.016, 9.657 ± 1.307, and 8.464 ± 0.961, respectively. The average MOI was 8.398 ± 0.648 from 2017 to 2019 in Guangzhou. The MOI in 2020 was 7.135 ± 0.786, which remained at the median risk level. Therefore, the abnormal decline in dengue cases could not be attributed to the change in mosquito density in 2020.Table 1Numbers and percentages of dengue cases from 2017 to 2019.
Year2017201820192020
Total cases9441,2951,65534
Imported cases(percentage)69 (7.31%)96 (7.41%)270 (16.31%)32 (94.12%)
Local cases (percentage)875 (92.69%)1,199 (92.59%)1,385 (83.69%)2 (5.88%)
Open in a separate windowIn 2020, the 14-day quarantine in a designated hotel for international travelers to curb the spread of Coronavirus Disease 2019 (COVID-19) was an important public health intervention. People had to remain indoors except for medical care needs. All imported dengue cases were identified during their quarantine periods. No secondary case related to the imported cases was reported. This may be because Aedes albopictus, which is the major vector of dengue in Guangzhou, bites aggressively during the day outdoors. The chance of being bitten by A. albopictus was reduced by staying all day indoors. Moreover, some research revealed that viremia occurred 6 to 18 hours before symptoms appeared and lasted as long as 12 days [4]. After the 14-day quarantine, viremia had almost subsided. Therefore, imported dengue cases were unlikely to be transmitted. The impact of imported dengue cases was limited by the quarantine, which provided a rare opportunity to identify the local epidemic.The epidemiology investigation showed that the 2 local cases, who were living in the same building, had no travel history outside Guangzhou in 2020 and had symptoms successively. Two dengue virus serotype 2 (DENV-2) strains were isolated from them. The envelope gene sequences were obtained and deposited in GenBank under accession numbers MW295818 and MW345921. Reference sequences, which were downloaded from GenBank, and sequences of Guangzhou strains identified in the previous years, were used to construct a phylogenetic tree. The 2 isolated strains in 2020 were identical. The tree (Fig 1) shows that the 2 strains belonged to the Malaysia/Indian subcontinent genotype, which was the prevailing genotype in Guangzhou [5]. However, they were neither identical with nor derived from the Guangzhou strains obtained from the previous years. Using the Basic Local Alignment Search Tool in GenBank, the 2 strains were found to be highly similar to those identified in Zhejiang (China), Singapore, and Guangdong (China) in 2017. These results imply that the local cases may be secondary to some undiscovered cases imported from other cities in China, as no restriction and quarantine was imposed for domestic travels.Open in a separate windowFig 1Maximum-likelihood phylogenetic tree shows the evolutionary relationships of DENV-2 detected in the sera of 2 local cases along with 45 other sequences.The reference sequences are named using the GenBank accession number, country, and year. The sequences of strains isolated in Guangzhou are named using the GenBank accession number, year, and our lab number. Bootstrap support values are shown in the notes. Strains isolated in 2020 are indicated with a black triangle.When the impact of imported dengue cases was limited by quarantine, dengue did not spread in Guangzhou during 2020, with the MOI still at median risk level and without any changes in the prevention and control strategies. Moreover, serotype 1 had been prevalent in Guangzhou since 2011 [6,7]. However, there was no local infection of serotype 1 detected in 2020. These observations may provide further evidence that dengue fever is not endemic in Guangzhou.In conclusion, the number of dengue cases decreased during the COVID-19 epidemic in Guangzhou in 2020. Thus, we believe that dengue fever is not endemic in Guangzhou.  相似文献   
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We have developed a personal-computer-based water quality analysis system for river basins. The system estimates potential N outflow by model and calculates actual N outflow from monitoring data. For the former it uses the potential load factor method to estimate annual nitrogen load from various sources and runoff potential from each area of land in a basin. For the latter it analyzes water quality monitoring data in relation to meteorological data. We used the system to analyze N outflow in basins around Lake Kasumigaura and the Yahagi River in central Honshu, Japan. The land around Lake Kasumigaura is rather flat, and about 25% is periodically flooded for rice and lotus cultivation. The land around the Yahagi River is mountainous, and much less land is flooded. In the Yahagi River basin the actual N outflow agreed closely with the potential. However, the actual N outflow in the basin around Lake Kasumigaura was much less than the potential, suggesting that a large part of the N load is denitrified in flooded soils. This further indicates that a sequence of different land uses including flooded rice fields is an important factor determining N outflow in basins in Japan. On the basis of the above analyses, we incorporated a denitrification model into the system that enables us to estimate N balance in a designated basin; this system may be helpful in the formulation of scenarios of land use and soil management for improving water quality.  相似文献   
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The generation of long-lived microplasmoids is observed during the irradiation of a metal-dielectric surface with a high-power microwave beam in a chemically active gas mixture (H2 + O2; CH4 + O2). The lifetime of these plasmoids substantially exceeds the characteristic recombination and cooling times of plasmoids arising at the target surface in a chemically inactive medium.  相似文献   
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Eradication of alien species is a key conservation tool to mitigate the impacts caused by biologic invasions. The aim of the present paper is to review the eradications successfully completed in Europe and to discuss the main limits to a wider application of this management option in the region. On the basis of the available literature – including conference proceedings, national reports to the Bern Convention, etc. – a total of 37 eradication programmes have been recorded. Thirty-three eradications were carried out on islands and four on the mainland. The rat (Rattus spp.) has been the most common target (n = 25, 67%), followed by the rabbit (n = 4). In many cases, these eradications determined a significant recovery of native biodiversity. Differently to other regions of the world, no eradications of alien invertebrates and marine organisms have been recorded; regarding invasive alien plants, it appears that only some very localized removals have been completed so far in Europe. The limited number of eradications carried out in Europe so far is probably due to the limited awareness of the public and the decision makers, the inadequacy of the legal framework, and the scarcity of resources. Synthetic guidelines for improving the ability of European states to respond to aliens incursions are presented. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
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Partial caching of large media objects such as video files has been proposed recently as the caching of entire objects can easily exhaust the storage resources of a proxy server. In this paper the idea of segmenting video files into chunks and applying replacement decisions at the chunk level rather than on entire videos is examined. It is shown that a higher byte hit ratio (BHR) can be achieved by appropriately adjusting the replacement granularity. The price paid for the improved BHR performance is that the replacement algorithm takes a longer time to converge to the steady state BHR. For the segmentation of video into chunks two methods are presented. The Fixed Chunk Size segmentation scheme that is rather simple and reveals the basic trade-off between byte hit ratio (BHR) and responsiveness to changes of popularity; the Variable Chunk Size segmentation scheme that uses the request frequencies to dynamically adjust the size of the chunk and is shown to be capable of combining a small response time with high BHR. Moreover, a variation of the fixed chunk size segmentation scheme is presented, which is shown to improve its performance by switching between different chunk sizes. Video segmentation is also considered as a mechanism to provide for caching differentiation based on access costs. By employing access cost dependent chunk sizes an overall access cost reduction is demonstrated.  相似文献   
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The genus Leptocorticium is redescribed, and a key to the species is provided. A new taxon, Leptocorticium tenellum, is described, and two new combinations, L. sasae and L. utribasidiatum, are proposed. Dentocorticium nephrolepidis is determined to be conspecific with L. cyatheae. All four species are described and illustrated.  相似文献   
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Sphaerophragmium pulchrum is proposed as a new microcyclic rust species on Albizia adinocephala from Panama. Telia and spermogonia are described, illustrated, and compared to those of known species of Sphaerophragmium. Spermogonia are described for the first time for a species of Sphaerophragmium. This is the first record of this genus for the southern part of the Central American isthmus.  相似文献   
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