Objective To investigate the species composition and distribution of ectoparasitic chigger mites on the rodents in some areas of Heihe, Heilongjiang province, China. Methods Rodents were captured using rat snap traps in Aihui district, Xunke county, and Wudalianchi of Heihe in mid-September, 2015. Chigger mites were collected from the body surface of rodents. The species of chigger mites was identified according to their morphologic characteristics, and the species of rodents and pikas were identified by morphology and DNA barcoding technique. The species composition, chigger infestation rate, chigger index in each area and habitat were calculated and analyzed. The nucleic acid of Orientia tsutsugamushi was detected by nested PCR. Results A total of 170 rodents were captured, involving 8 species of 6 genera from 3 families under 2 orders. Myodes rutilus (38.26%), Ochotona mantchurica (34.78%), and M. rufocanus (14.78%) were the dominant species in the volcanic geopark of Xunke county. Apodemus agrarius was the dominant species in the farmland of Wudalianchi (76.67%) and Aihui district (64.00%). Or. tsutsugamushi was negative in all rodents captured. No chigger mite was found on the bodies of rodents from Wudalianchi and Aihui district, while 11 256 chigger mites were found on rodents from Xunke county, belonging to 5 species of 2 genera, with the dominant mite species Neotrombicula gardellai (87.50%). The main hosts of chigger mites were O. mantchurica, M. rutilus, and M. rufocanus. Conclusion The different areas of Heihe have distinct species compositions of rodents, and different species of rodents carry distinct numbers of chigger mite.

Objective To investigate the difference in the positive rate of Orientia tsutsugamushi between different organs of small mammals, and to provide a reference for the pathogen monitoring of scrub typhus. Methods Liver, spleen, lung, kidney, and ear samples were collected from 105 small mammals collected in Yongcheng city of Henan province, China in October 2017, and liver, spleen, and ear samples were collected from 324 small mammals collected in Pinggu district of Beijing, China from September to November 2018. DNA was extracted, and nested PCR amplification was used to detect the nucleic acid fragment of the 56 kDa protein gene of O. tsutsugamushi. The specimens with specific bands were genotyped by comparison of nucleotide sequence, and the positive rate was calculated. Results The positive rate of O. tsutsugamushi in small mammals was 10.48% in Yongcheng city and 12.96% in Pinggu district, with no significant difference ( χ ²=0.494, P=0.504). The positive rate of O. tsutsugamushi in different organs within the same site was 0.98%-14.81%; pairwise comparison showed that the positive rate of O. tsutsugamushi in the ear of the small mammals in Yongcheng city was higher than that in the other four organs, and the positive rate of O. tsutsugamushi in the liver of the small animals in Pinggu district was significantly higher than that in the spleen ( χ ²=5.818, P=0.022). The comparison of the two places showed that the positive rate of O. tsutsugamushi in the ear of the small mammals in Yongcheng city was significantly higher than that in Pinggu district ( χ ²=6.525, P=0.011). For the small mammals in Pinggu district, the positive rate of Shimokoshi-type O. tsutsugamushi in the spleen was lower than that in liver and the ear, while there was no significant difference in the positive rate of Kawasaki-type O. tsutsugamushi between the different organs ( χ ²=1.560, P=0.455). The pooled analysis of the detection results of the liver and the spleen in Yongcheng city and Pinggu district showed that the positive rate of O. tsutsugamushi in the liver was higher than that in the spleen. The results of consistency test showed no significant difference (Kappa=0.015, P=0.744), with poor consistency of positive infection in the liver and the spleen. Conclusion There are no significant differences in the positive rates of Kawasaki-type O. tsutsugamushi in the liver, spleen, lung, and kidney of small mammals between Yongcheng city and Pinggu district, while the positive rate of Shimokoshi-type O. tsutsugamushi in the liver and the ear is higher than that in the spleen. Detection of O. tsutsugamushi in the organ of various small mammals or in multiple organs can improve the detection rate of O. tsutsugamushi, and rodent ears can also be used as samples for the pathogen monitoring of scrub typhus.

Objective To analyze the epidemiological characteristics and changing trend of scrub typhus cases in Guangdong province, China from 2012 to 2018, to predict the incidence trend, and to provide a scientific basis for evaluating the prevention and control measures of scrub typhus. Methods The data of scrub typhus cases in Guangdong province from 2012 to 2018 were collected. A descriptive epidemiological analysis was conducted. A seasonal autoregressive integrated moving average (ARIMA) time series model was used to establish a forecasting model, which was evaluated by comparing the observed and predicted values in 2019, and the incidence of scrub typhus in Guangdong province in 2020 was predicted using the model. Results A total of 33 490 scrub typhus cases were reported in Guangdong province from 2012 to 2018, with the incidence increasing year by year, and the cases mainly occurred in June to October. The incidence was highest in the 50-60 years group; there were more cases in females than in males, and farmers (65.49%) were the dominant occupation. The ARIMA (1,1,1)(0,1,1)₁₂ model was fitted with the monthly case data; the Bayesian information criterion was 879.36; the residual sequence was white noise sequence according to the Ljung-Box test, and the adjusted R² value was 0.377. The fitting effect of the model was good. The actual value in 2019 was basically consistent with the predicted value with 95% confidence interval; the model had a good predictive effect. Conclusion The scrub typhus incidence shows an increasing trend year by year in Guangdong province. The main susceptible populations were people aged 50-60 years, females, and farmers. The ARIMA model can be used to predict the changes in scrub typhus cases in Guangdong province well, suggesting that the relevant departments should strengthen the publicity and education of key population and the epidemic prevention and control in the season with high incidence of scrub typhus.

Objective To investigate the species of hosts and vectors, seasonal variation, and pathogen genotypes in the natural focus of scrub typhus in Pinggu district of Beijing, China through field investigation and laboratory study, and to provide a basis for the prevention and control of scrub typhus. Methods Rat traps were placed in field every month for one year, and small mammals were captured to collect chigger mites on body surface and analyze the number, species composition, seasonal variation, and spatial distribution of chigger mites. The small mammals were dissected to collect the liver and the spleen and extract DNA from the tissue, and nested PCR amplification was used to detect the 56 kDa protein gene of Orientia tsutsugamushi (Ot). The genotype of Ot was determined by nucleic acid sequence alignment and the positive rate in small mammals was calculated. Results A total of 734 small mammals belonging to 7 species were captured from September 2018 to August 2019, among which Apodemus agrarius and Mus musculus accounted for 65.26% and 30.52%, respectively, and were the dominant species in Pinggu district. Three genotypes of Ot, i.e., Shimokoshi, Kawasaki, and Japan Gilliam, were detected in the liver and spleen of small mammals, among which Shimokoshi and Kawasaki were more common. The positive rate of Ot was 10.90% in small mammals. The positive rate of Ot was 14.86% in M. musculus and 9.30% in A. agrarius, and thus they were the main hosts in Pinggu district. A total of 31 321 chigger mites belonging to 10 species were collected on the body surface of the small mammals, and Leptotrombidium subpalpale, L. linhuaikongense, and L. scutellare accounted for 84.79%, 6.49%, and 3.63%, respectively. The seasonal variation of L. scutellare was generally consistent with that of scrub typhus cases, and thus L. scutellare might be the main vector in this epidemic focus. L. scutellare was only distributed in the mountainous area and the piedmont transitional zone of Pinggu district. Conclusion A. agrarius and M. musculus are the main hosts and L. scutellare is the main vector in the natural focus of scrub typhus in Pinggu district, and there are at least three genotypes of scrub typhus pathogens. This investigation clarifies the basic elements in the natural focus of scrub typhus in Pinggu district and provides a basis for the prevention and control of scrub typhus, but further studies are needed to investigate the vector effect of other species of chigger mites.

Scrub typhus is an acute febrile vector-borne infectious disease caused by Orientia tsutsugamushi. It is transmitted by the bite of chigger mite larvae. Now scrub typhus is a relatively serious public health issue in the Asia-Pacific region, threatening the health of more than one billion people worldwide. China is one of the countries with relatively serious burden of scrub typhus. In recent years, there has been an increasing trend in the epidemic areas of scrub typhus and the number of infected cases. With the development of "3S" spatial information technologies represented by geographic information system (GIS), remote sensing (RS), and global positioning system (GPS), many scholars have applied these technologies to studies on the spatial epidemic pattern of scrub typhus. This article mainly introduces the epidemiological characteristics and spatiotemporal dynamic trends of scrub typhus domestic and overseas, as well as the natural environmental factors and socioeconomic factors affecting the epidemic of scrub typhus, and focuses on the roles of spatial statistics and GIS technology in the epidemiological study of scrub typhus, so as to provide a reference for the future epidemiological study and the prevention and control of scrub typhus.

Vectors can transmit viruses by mechanical transmission, and some species can transmit viruses by biological means. As for whether vectors can transmit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), this article assess the risk of several categories of vectors closely related to humans in transmitting SARS-CoV-2, so as to provide a basis for developing more precise SARS-CoV-2 prevention and control measures. Based on the collected literature, the risk matrix method was used to evaluate the probability of vectors transmitting SARS-CoV-2 and determine the level of exposure to SARS-CoV-2 and the risk level of SARS-CoV-2 transmission for different vectors in different places. The preliminary results showed that the risk of mosquitoes in transmitting SARS-CoV-2 was very low; rodents, cockroaches, and flies had a potential risk of mechanical transmission of SARS-CoV-2, and rodents also had a potential risk of biological transmission of SARS-CoV-2; the three categories of vectors had different risks of the transmission of SARS-CoV-2 in different places, and the risk level of transmission was associated with the risk level of exposure to SARS-CoV-2, as well as the distribution, density, and activity of vectors. In general, the risk of mosquitoes in transmitting SARS-CoV-2 could be excluded; the vectors including rodents, cockroaches, and flies have a potential but low risk of transmitting SARS-CoV-2 in specific places and surroundings exposed to SARS-CoV-2.

Objective To investigate the density and seasonal fluctuation of ticks captured from human habitats and body surfaces of domestic animals in China, and to provide a basis for the risk assessment and scientific prevention and control of ticks and tick-borne diseases. Methods The surveillance data of ticks were collected from 45 surveillance sites in the national vector surveillance system in China, 2019. The dominant tick species was analyzed, and the density and seasonal fluctuation of ticks were compared between different habitats, hosts, and provinces. Results Among the ticks captured in 2019, Haemaphysalis was the most frequently captured genus; the number of times that parasitic and questing Haemaphysalis were captured accounted for 57.31% and 95.56% of the total catch, respectively. Among various host animals, sheep and cattle had higher tick indices (3.06 and 2.72, respectively), and ticks were also captured from dogs in rural and urban areas. The tick density in surroundings of villages (0.83 ticks/flag·100 m) was higher than that in scenic areas (0.32 ticks/flag·100 m). Among different months of surveillance, the seasonal fluctuation curves of parasitic tick index and questing tick density both showed two peaks; the index of parasitic ticks was high throughout the first half of the year and decreased after July, while the density of questing ticks peaked in June. Conclusion The tick surveillance results in 2019 show that Haemaphysalis is the most frequently captured genus. Sheep and cattle are dominant host animals of those captured ticks, while dogs, as domestic animals in close contact with human beings, should be paid attention to their tick infection. Surroundings of villages are the dominant habitat of ticks. The peak period of tick infestation is found in the first half of the year. Tick prevention and control should be carried out according to the above-mentioned key species, hosts, habitats, and time periods.

Objective To investigate the species, density, and spatio-temporal characteristics of cockroaches in human habitats and surroundings in China and the cockroach surveillance results based on the sticky trap method and visual observation, and to provide a scientific basis for cockroach prevention and control. Methods The cockroach surveillance data were collected from the national surveillance sites for vectors in China, 2019. Excel 2013 software was used to analyze the cockroach distribution characteristics of different species in different habitats, in different provinces, and at different times. Results In 2019, the surveillance results according to the sticky trap method showed that the sticky trapping rate was 5.45% and the infestation rate was 5.25%. Blattella germanica was the dominant species, accounting for 95.65% of the total catch, Periplaneta americana accounted for 2.42%, and the rest accounted for 1.93%. The surveillance results according to visual observation showed that the infestation rate of adult and nymph cockroaches was 3.63%, with 3.07% for B. germanica and 1.28% for P. americana. Farmers' markets and restaurants had high cockroach infestation rates. The cockroach infestation rate was high in South China and low in North China. The cockroach infestation rate measured by the sticky trap method was 1.45 times that by visual observation. Conclusion The national cockroach surveillance results in 2019 are conducive to the targeted cockroach control of key species in key habitats and areas, and at key times.

Objective To analyze the Aedes surveillance data of 23 project provinces (autonomous regions and municipalities directly under the central government) in China, 2019, and to provide scientific evidence for the prevention and control of Aedes-borne diseases such as dengue. Methods The surveillance data of larval and adult Aedes mosquitoes from the surveillance sites of the 23 regions were analyzed using SPSS 18.0 software for a preliminary assessment of the risk of dengue transmission. Results In China, 2019, the mean Breteau index (BI) of Aedes mosquitoes was 3.56, and the mean mosquito ovitrap index (MOI) was 4.89. During the key months of the surveillance periods, the mean BI exceeded 10 in Zhejiang, Hainan, and Fujian provinces, and exceeded 5 in some surveillance points of Yunnan province. MOI was over 5 in Guangdong province and Guangxi Zhuang autonomous region during the key months of the surveillance periods. In Jiangxi, Anhui, Hunan, Henan, Sichuan, and Hubei provinces and Chongqing municipality, BI exceeded 5 in most months of the surveillance periods; MOI exceeded 5 in Hunan province from June to August and in Guizhou province from July to September, reaching the spreading risk of dengue. During the surveillance periods, BI exceeded 10 in Hebei province, and exceeded 5 in Shaanxi province from July to August and in Shandong province from August to September. The density of adult mosquitoes (net trap index) was more than 2 mosquitoes/net·hour in Fujian and Jiangsu provinces and Guangxi autonomous region during most months of the surveillance periods, in Hubei province from June to July, and in Shaanxi and Sichuan provinces during September. Conclusion In 2019, the densities of Aedes mosquitoes in most project provinces (autonomous regions and municipalities directly under the central government) of China exceed the transmission or outbreak threshold of dengue, indicating a high risk of local transmission and outbreak of dengue. Aedes surveillance and risk assessment should be strengthened continuously to ensure sustainable and precise control of Aedes mosquitoes and Aedes-borne diseases.

Objective To investigate the species, composition, density, distribution, and seasonal fluctuation of mosquitoes in China, 2019, and to provide a scientific basis for the prevention and control of mosquito-borne diseases. Methods The mosquito vector surveillance data of 88 surveillance sites in 30 provinces (autonomous regions and municipalities directly under the central government) of China in 2019 were collected. The light trapping and human-baited double net trapping methods were employed to monitor adult mosquitoes, and the Breteau index (BI), scoop capture, and route methods were adopted to monitor mosquito larvae. Adult mosquitoes were monitored twice a month, and mosquito larvae were monitored once a month. Excel 2013 software was used to analyze the mosquito vector surveillance data. Results The mean density of mosquitoes was 9.81 mosquitoes/lamp·night in China in 2019. Culex pipiens pallens/Cx. pipiens quinquefasciatus accounted for 57.73% of all captured mosquitoes, followed by Anopheles sinensis, Cx. tritaeniorhynchus, Aedes albopictus, and Ae. aegypti, which accounted for 20.27%, 12.22%, 2.29%, and 0.02%, respectively. The mosquito densities in Inner Mongolia, Hubei, Qinghai, Yunnan, and Hunan provinces were relatively high, being 22.60, 21.72, 17.14, 12.71, and 10.18 mosquitoes/lamp·night, respectively. The results of seasonal fluctuation by light trapping, human-baited double net trapping, scoop capture, and route methods all indicated that the peak period of mosquito activity was from June to September, and the highest peak was in July or August. The results of the Breteau index method indicated that the peak period of Aedes larvae was from April to September. The highest density of adult mosquitoes was in livestock sheds, being 36.29 mosquitoes/lamp·night, while the highest Breteau index of mosquito larvae was in waste tyre recycling factories, being 19.25 mosquitoes/lamp·night. Conclusion The dominant mosquito specie is Cx. pipiens/Cx. pipiens quinquefasciatus in China. It is recommended to implement prevention and control measures such as overwintering mosquito elimination and environment management from April each year in all provinces (autonomous regions and municipalities directly under the Central Government). In 2020, the main prevention and control measure is to pay more attention to timely cleaning of the mosquito breeding sites in residential areas, waste tyre recycling factories, and waste collection areas, so as to prevent and control mosquito-borne diseases from the origins.

Objective To analyze the national surveillance data of rodents in China, 2019, and to provide a basis for improving the quality of national rodent surveillance and formulating scientific control measures. Methods Eighty-nine prefecture-level cities were set up as surveillance sites in 30 provinces (autonomous regions and municipalities) and Xinjiang Production and Construction Corps. Rodents were captured once every two months in three habitats by night-trapping, night-cage and sticky board methods. The surveillance data of rodents were collected and sorted to analyze the species composition, distribution, and seasonal density fluctuation of rodents. Results A total of 4 317 rodents were captured in 2019, with a total density of 0.78 rodents/100 traps. Cage trapping had the highest density of captured rodents, followed by sticky trapping. Rattus norvegicus, Mus musculus, and R. tanezumi accounted for 47.30%, 27.89%, and 12.55% of the total rodents captured, respectively. The highest density of rodents was in rural residential areas among three habitats. The density of rodents first increased and then decreased all year round, and peaked in May. Conclusion The density, species composition, and seasonal fluctuation of rodents at national surveillance sites across China in 2019 show no significant differences from the results in 2005-2016. Local authorities should assess risks and formulate control strategies based on their surveillance results of previous years.

Objective To establish the mosquito vector surveillance capacity in Freetown, Sierra Leone, and to investigate local mosquito density, geographical distribution, population characteristics, and seasonal fluctuations. Methods A total of nine zones were selected as mosquito surveillance sites in the western urban and rural areas of Freetown, Sierra Leone, with at least one site in each of residential areas, general working institutions, hospitals, and livestock sheds, and mosquito trap lamps were used for surveillance. Each surveillance site had 2-4 mosquito trap lamps, which were fixed in an outdoor place protected from wind, rain, and light at about 1.5 meters above the ground. The mosquito trap lamps were placed at 1 hour before sunset and the net was collected at 1 hour after sunrise in the next morning. Then the collected mosquitoes were classified by morphological characteristics in the laboratory. Mosquito surveillance was conducted once a week from June 26, 2019 to December 31, 2019. Excel 2007 software was used for the statistical analysis of mosquito vector surveillance data. Results A total of 3 012 mosquitoes were collected, among which Culex mosquitoes accounted for 84.86% and was the dominant mosquito genus in Freetown. Compared with the western urban areas, the western rural areas had significantly higher mean total mosquito density (5.01 mosquitoes/trap·night vs 3.87 mosquitoes/trap·night), mean Anopheles density (1.28 mosquitoes/trap·night vs 0.12 mosquitoes/trap·night), and composition ratio of Anopheles (1.14%-44.53% vs 0.72%-11.90%). Seasonal fluctuations of mosquito density showed that in Freetown, high mosquito density was observed during the alternate period of dry and rainy seasons in late June and early July and during the alternate period of rainy and dry seasons in late October and early November, and the lowest mosquito density was observed in late August. In addition, the seasonal fluctuation trend of Anopheles density was consistent with that of total mosquito density. A comparative analysis of different habitats showed that the livestock sheds with poor environmental sanitation and more mosquito breeding sites had a higher mosquito density (10.40 mosquitoes/trap·night), followed by residential areas (4.45 mosquitoes/trap·night) and general working institutions (2.80 mosquitoes/trap·night), and the hospitals with better environmental sanitation and fewer breeding sites had the lowest mosquito density (1.21 mosquitoes/trap·night). Conclusion The risk of mosquito bite and malaria infection in the western rural area is higher than that in the western urban area. The alternate periods from the dry season to the rainy season and from the rainy season to the dry season are important periods for the prevention and control of mosquito vectors and their infectious diseases (including malaria). Sierra Leone needs to further strengthen the management of mosquito breeding sites.

Objective To investigate the genotypes and distribution characteristics of the ace gene of the dengue vector Aedes albopictus (field population) in different regions of China, and to preliminarily explore their resistance mechanism to organophosphorus and carbamate insecticides. Methods A total of 422 larvae, pupae, or adults of Ae. albopictus were collected at 14 sampling sites (14 geographical populations) in Haikou of Hainan province, Guangzhou of Guangdong province, Jinghong of Yunnan province, and Xingyi of Guizhou province from June to September 2018, and they were identified by morphology or molecular biology, soaked in anhydrous ethanol, and stored at -20℃. DNA was extracted from individual mosquito, and the partial fragment of the ace gene was amplified by PCR, sequenced, and analyzed for mutation at G119. Results There were only a few base mutations but no amino acid mutations at G119 of the ace gene. Two alleles were detected, namely wild-type GGA/G (832/98.58%) and mutant-type GGG/G (12/1.42%), and one genotype was detected, namely wild-type homozygote G/G (422/100%). Conclusion Only a few individuals of Ae. albopictus showed a base mutation at G119 of the ace gene, but the base substitution did not cause the corresponding amino acid mutation. Therefore, the resistance mechanism of Ae. albopictus to organophosphorus and carbamate insecticides needs to be further explored.

Objective To observe the effect of clarified lime water on Aedes albopictus at different stages of larval development in the laboratory and determine the effect of quicklime in the prevention and control of Ae. albopictus, and to provide basic data for the application of quicklime in the prevention and control of Ae. albopictus. Methods A certain number of Ae. albopictus at different developmental stages (eggs, 1 st to 4 th instar larvae, and pupae) were separately reared in clarified lime water, and the hatching rate, mortality rate, eclosion rate, and development time for each stage were recorded. Meanwhile, the development of Ae. albopictus in different feeding environments and different stages was analyzed and compared by taking the mosquitoes reared in overnight tap water as a control. Results The hatching rate of Ae. albopictus eggs in the experimental group was 82.22%, and that in the control group was 94.44%; the hatching rate of Ae. albopictus eggs was significantly lower in the experimental group than in the control group ( χ ²=6.523, P=0.011). According to the t-test, the hatching time of eggs was significantly longer in the experimental group than in the control group. The mortality rate of the 1st to 4th instar larvae was significantly higher in the experimental group than in the control group ( χ ²=4.624, 234.994, and 284.312, P=0.032, <0.003, and <0.003); particularly, the mortality rate of the 3rd and 4th instar larvae was significantly increased in the experimental group. There was no significant difference in eclosion rate between the experimental group and the control group ( χ ²=0.593, P=0.441). Conclusion Clarified lime water has a significant inhibitory effect on the development of Ae. albopictus, which increases with the age of mosquito larvae. The results imply that quicklime can be possibly used for the prevention and control of Ae. albopictus. The field control effect of quicklime on Ae. albopictus needs further verification.

Objective To analyze the correlation between density indices of Aedes larvae in key provinces of China, and to provide scientific evidence for the prevention and control of Aedes-borne diseases. Methods The Breteau index (BI), container index (CI), house index (HI), and mosquito ovitrap index (MOI) of Aedes larvae in Guangdong, Yunnan, and Zhejiang provinces of China from 2005 to 2017 were collected, and a database was established. A correlation analysis was performed using SPSS 13.0 software. Results In Guangdong province, there was a positive correlation between BI in 2016 and 2017 and MOI in the same period ( r=0.853 and 0.771, respectively, P<0.05). In Zhongshan, BI in 2016 and 2017 was positively correlated with MOI in the same period ( r=0.741 and 0.918, respectively, P<0.05), and there was a positive correlation between BI and CI, BI and HI, CI and HI, and HI and MOI in 2016 ( r=0.841, 0.990, 0.797, and 0.736, respectively, P<0.05). In Shantou, the four density indices in 2016 were all positively correlated with each other ( r=0.964, 0.982, 0.988, 0.772, 0.776, and 0.805, respectively, P<0.05). There was a positive correlation between BI and CI, BI and HI, and CI and HI in 2016 in Zhanjiang ( r=0.986, 0.998, and 0.980, respectively, P<0.05). In Yunnan province, there was a positive correlation between BI and CI, BI and HI, and CI and HI in 2014 and 2016 ( r=0.988, 0.978, and 0.973, respectively, P<0.05). There were a positive correlation between BI and CI, BI and HI, and CI and HI in 2016 and 2017 in Menghai county ( r=0.973, 0.982, 0.994, 0.954, 0.995, and 0.971, respectively, P<0.05). In Hekou county, BI was positively correlated with HI in 2016 ( r=1.000, P<0.05), and there was a positive correlation between BI and CI, BI and HI, and CI and HI in 2017 ( r=0.962, 0.945, and 0.961, respectively, P<0.05). In Longchuan county, there was a positive correlation between BI and HI in 2016 and 2017 ( r=1.000 and 0.974, respectively, P<0.05). During 2005-2010 in Yiwu, Zhejiang province, the four density indices of Aedes larvae were positively correlated with each other ( P<0.05), except between BI and CI in 2007 and between BI and CI, BI and HI, and CI and HI in 2008 ( P>0.05). In Fenghua, there was a positive correlation between BI and CI, BI and HI, and CI and HI in 2011 ( r=1.000, 0.994, and 0.993, respectively, P<0.05). In Cixi, there was a positive correlation between BI and CI, BI and HI, and CI and HI in 2011 ( r=0.980, 0.993, and 0.962, respectively, P<0.05). Conclusion The correlation between the density indices of Aedes larvae in different years in key provinces of China has spatial and temporal specificity, and the results can provide basic data for risk assessment and sustainable control of Aedes vectors and related diseases in different provinces of China.

Objective To understand distribution patterns and influencing factors for the interval between onset and diagnosis of typhus in China, and to provide a scientific basis for accurate prevention and control of typhus. Methods Descriptive statistical methods were used to analyze the distribution patterns of the interval between onset of disease and diagnosis. The Kruskal-Wallis H test was conducted for statistical difference analysis. Multivariate logistic regression was used to analyze the influencing factors. Results A total of 29 211 typhus cases were reported in China from 2005 to 2017. Those cases were from 29 provinces (autonomous regions and centrally administered municipalities). The median interval between onset of disease and diagnosis was 7 days. The interval was between 0 and 20 days for 92.20% of the cases. The median interval between onset of disease and diagnosis was 6 days for males and 7 days for females. Students and scattered children had longer time intervals between onset of disease and diagnosis than others. Hebei, Guangdong, and Shandong provinces had shorter time intervals, while Sichuan and Liaoning provinces had longer time intervals. Conclusion There is a long interval between onset and diagnosis of typhus in China. To accurately diagnose, treat, prevent, and control typhus, action should be taken to specifically address this issue.

Objective To investigate the species compositions of rodents and the chigger mites on their body surface and the infection rate of Orientia tsutsugamushi in rodents in Yongcheng, Henan province, China, and to provide a scientific basis for the prevention and control of scrub typhus in Yongcheng. Methods Rat traps were used to capture rodents and to collect ectoparasites from the body surface of rodents in different survey sites and different habitats in Yongcheng in October 2017. Nested PCR was used to detect nucleic acid of O. tsutsugamushi. The rodent density, chigger infestation rate, chigger index, and pathogen infection rate were calculated. Results A total of 110 rodents were captured with a capture rate of 12.21%. Apodemus agrarius accounted for 90.00%. A total of 1 249 chigger mites were collected from rodents. The chigger infestation rate and chigger index were relatively high in the forest along the riverbank, wetland, and mountain forest. Leptotrombidium scutellare (96.86%) was the dominant chigger mite species, which was mainly parasitic on the body surface of A. agrarius. The O. tsutsugamushi positive rate of rodent was 10.48%. Apodemus agrarius, Rattus norvegicus, and Mus musculus were detected O. tsutsugamushi positive with nPCR. Orientia tsutsugamushi in Yongcheng belonged to Kawasaki molecular type. Conclusion This study confirms that there are some epidemic foci of scrub typhus with host rodents in Yongcheng, which have the same hosts and vectors as the surrounding epidemic foci of scrub typhus.

Objective To investigate the data on scrub typhus cases reported in Pinggu district of Beijing, China, in 2008-2018 and the epidemiological characteristics of scrub typhus, and to provide a scientific basis for the prevention and control of scrub typhus. Methods The data on scrub typhus cases reported in 2008-2018 were collected from the information system of Chinese Center for Disease Control and Prevention to analyze the epidemiological characteristics of scrub typhus. Results A total of 899 scrub typhus cases were reported in Pinggu district in 2008-2018, with a mean annual incidence rate of 18.70/100 000. The incidence rate of scrub typhus increased from 2008 to 2015 and then gradually decreased. Of all cases, 99.33% were reported in September to November of each year, suggesting that Pinggu district was an autumn-type epidemic area for this disease. This disease was mainly reported in patients aged 50-65 years, accounting for 52.73% of all cases. The disease was most prevalent among farmers, accounting for 77.20% of all cases. The highest incidence rate was found in Wangxinzhuang town and Daxingzhuang town. Conclusion There is a high incidence rate of scrub typhus in Pinggu district. Therefore, the key populations should be monitored in autumn and prevention and intervention measures should be adopted to reduce the development and prevalence of scrub typhus.

Objective To investigate the division of the distribution areas for summer- and autumn-type scrub typhus in China by analyzing the seasonal distribution characteristics of reported scrub typhus cases in China from 2006 to 2018, and to provide a scientific basis for research, prevention and control of scrub typhus vectors. Methods The data of scrub typhus cases reported in China were collected and analyzed, to identify the seasonal and geographical distributions of these cases. Results From 2006 to 2018, the incidence rate of scrub typhus in China increased year by year, with local cases in 31 provincial regions. As for seasonal distribution, the onset of this disease was observed throughout the year, and 88.87% of all cases were observed in June to November. The autumn-type epidemic areas were north to the line from Taihu Lake in Jiangsu to Central Anhui, Southern Henan, and Xi'an in Shaanxi province, and the summer-type epidemic areas were Eastern Tibet, Yunnan, Southern Sichuan, Western Hunan, Southern Jiangxi, and Southern Zhejiang. There was a transitional zone between these two types of epidemic areas. Conclusion The incidence rate of scrub typhus in China has been on the rise since 2006. This disease occurs in different seasons in northern and southern China, with summer- and autumn-type epidemic areas and a transitional zone between them. Therefore, targeted investigation should be performed in different areas for precise intervention.

Objective To investigate the infestation of bed bugs in China, and to provide a scientific basis for risk assessment and effective prevention and control of bed bugs. Methods The bed bug surveillance data were collected from the National vectors Surveillance in China in 2018. The occurrence of bed bug infestation was compared between different provinces or habitats. Results Bed bug surveillance was carried out in 13 provinces (autonomous regions, centrally administered municipalities) via field investigation and telephone survey. A total of 1 537 units were investigated on site, of which 11 had bed bug, infestation giving a positive infestation rate of 0.72%. A total of 17 332 standard rooms were investigated; among them, 31 (0.18%) had bed bugs. The habitats with the highest positive rates, in sequence, were dormitories in construction site, student dormitories, residential areas, nursing homes, and hotels. Conclusion Bed bugs are widely distributed in China, and the density of bed bugs in most areas was still at a relatively low level. The results of investigation indicated that construction site dormitories, residential areas, and student dormitories are the foci of bed bug infestation surveillance in the future.

Objective To investigate the density and seasonal variation of ticks captured from human settlement and surroundings in China, and to provide a basis for risk assessment and scientific prevention and control of ticks and tick-borne diseases. Methods The tick surveillance data in 2018 were collected from 53 surveillance sites of the National Vectors Surveillance in China. The dominant species of ticks were analyzed, and the density and seasonal variation of ticks were compared between different hosts, habitats, and provinces. Results Haemaphysalis longicornis was detected most frequently in 2018. Among the host animals, sheep and cattle had the highest tick index, and the tick index of urban pet dogs increased from 0.04 in 2017 to 0.15 in 2018. The tick density in surroundings of villages was higher than that in scenic areas. The highest index of on-host ticks was observed in July, and the highest density of questing ticks was observed in August; their secondary peaks were observed in April to May, and on-host ticks had an additional peak in September. Conclusion Haemaphysalis longicornis was the predominat species of ticks in human habitats and surroundings in China, sheep and cattle were dominant host animals, and surroundings of villages are the dominant habitat of ticks. There were 3 peaks in the curve of the index of on-host ticks and 2 peaks in the curve of the density of questing ticks. There was an increase in the tick index of urban pet dogs from 2017 to 2018. These results suggest that tick prevention and control should be strengthened for rural domestic animals and in surroundings of villages, as well as in early spring and the middle of the year. Tick infection in urban pets should not be neglected.

Objective To investigate the common species, population density, and seasonal variation of cockroaches in residential areas and surroundings in China and the surveillance results of cockroaches based on the sticky trap method versus visual observation, and to provide a scientific basis for the prevention and control of cockroaches infestations. Methods The cockroach surveillance data were collected from national surveillance sites of the National Vectors Surveillance in China in 2018. The population density was compared between different species or cockroaches in different habitats or provinces, and its seasonal variation was analyzed. Results The cockroach infestation rate monitored by the sticky trap method was 6.70%, and among the predominant cockroaches, Blattella germanica was the predominant species and accounted for 94.81%, Periplaneta americana accounted for 2.11%, and other cockroaches accounted for 3.08%. The cockroach infestation rate was 3.58% according to visual observation, with 1.13% for Periplaneta and 2.71% for Blattella. Conclusion Blattella germanica is the dominant species in human habitats and surroundings in China. The cockroach infestation rate monitored by the sticky trap method is higher than that monitored by visual inspection, and visual inspection is more sensitive to the density surveillance of Periplaneta. The surveillance results suggest that surveillance and control of cockroaches should be strengthened in open markets and restaurants.

Objective To analyze the Aedes surveillance data of the National Vectors Surveillance in China of 23 provinces, autonomous regions, or municipalities directly under the central government in 2018, and to provide a scientific basis for sustainable control of Aedes-borne diseases in China. Methods The national Aedes surveillance data was statistically analyzed using SPSS 18.0 software. Results In 2018, the mean Breteau index (BI) of Aedes mosquitoes was 3.25, and the mean mosquito ovitrap index (MOI) was 5.19. In category I provinces with the high dengue risk, the mean BI of Hainan throughout the year, that of Zhejiang from the first half of April to the first half of November, that of Fujian from April to November (except the second half of April), that of Yunnan from the first half of July to the first half of October, and that of Guangxi from June to August and the second half of September were all higher than 5, indicating a risk of dengue transmission; the BI of 9 surveillance cities in Guangdong from March to November indicated a risk of dengue transmission; the mean MOI of Guangxi from the first half of May to the second half of September and that of Guangdong from the second half of May to the first half of October were all higher than 5, indicating a risk of dengue transmission. In category Ⅱ provinces with the medium dengue risk, the BI of Hubei and Sichuan from May to September, that of Shanghai from June to September, and that of Chongqing, Anhui, Jiangxi, Henan, and Hunan from May to October indicated a risk of dengue transmission; the BI of Jiangsu indicated no risk of dengue transmission during the study period. The MOI of Guizhou from June to September, that of Henan in July and September, and that of Hunan in July indicated a risk of dengue transmission. In category Ⅲ province with the low dengue risk, the BI of Shaanxi from July to September, that of Shandong from July to August, and that of Hebei from June to September were higher than 10, indicating a risk of dengue outbreak; the MOI of Beijing in August indicated a risk of dengue transmission. The adult density of Aedes in Guangxi from the second half of May to the second half of September (except the first half of July and the first half of September), that of Hainan from April to October, that of Ningbo, Zhejiang, from August to October, that of Hangzhou from July to November, that of Chongqing from May to September, that of Hubei and Jiangsu from June to September, that of Sichuan in July, and that of Shaanxi from July to August were higher than 2 mosquitoes per net per hour. Conclusion In 2018, the dengue transmission risk varies in different months in the three categories of provinces in China. Overall, the southern provinces have higher risk than the northern provinces, and the eastern coastal provinces have higher risk than the central and western provinces. It is suggested that Aedes surveillance and risk assessment should be strengthened in key provinces and cities to ensure sustainable control of Aedes for the prevention and control of Aedes-borne diseases in China.

Objective To analyze the mosquito surveillance data of the National Vectors Surveillance in China in the 31 provincial regions (provinces, autonomous regions, or municipalities directly under the central government) in 2018 and investigate the species composition, distribution, and seasonality of mosquito vectors, and to provide a basis for the risk analysis of mosquito-borne diseases and mosquito vector control program. Methods In 2018, the lamp trapping method, double mosquito net method, Breteau index (BI) method, scoop capture method, and route method were used to capture mosquitoes and record their numbers. The mosquito vector surveillance data throughout 2018 were collected from 90 national surveillance sites in the 31 provincial regions and analyzed by Excel 2013. Results In 2018, the dominant mosquito species in China's residential areas were Culex pipiens/Cx. pipiens quinquefasciatus, which accounted for 60.25% of all captured mosquitoes, followed by Cx. tritaeniorhynchus, Anopheles sinensis, Aedes albopictus, and Ae. aegypti, which accounted for 21.64%, 7.19%, 2.61%, and 0.23%, respectively. In all habitats, livestock sheds had the highest mosquito density, reaching 31.96 mosquitoes/lamp·night, followed by livestock farms and rural households, with 13.08 and 11.32 mosquitoes per lamp per night, respectively; the mosquito density was relatively low in parks, hospitals, and residential areas. The adult mosquito density began to increase during April to May, remained high during June to September, and declined in October; the density of mosquito larvae increased slightly earlier than that of adult mosquitoes. More Ae. albopictus was captured with the double mosquito net method than with other methods in all habitats, especially during June to September. Rural natural villages had the highest BI (22.04). Conclusion The mosquito surveillance data of the National Vectors Surveillance in China in 2018 showed a certain risk of mosquito-borne diseases such as dengue fever, Japanese encephalitis, and malaria in the residential areas of China. The mosquito density in livestock sheds was much higher than that in livestock farms, suggesting that intensive livestock production pattern may avoid mosquito infestation. The peak season of mosquitoes was from June to September, but larvae positive water bodies were found in early investigations, so mosquito vector control should be carried out early and continuously. Rural natural villages had a high mosquito density, and the risk of mosquito-borne diseases do exist. It is recommended to strengthen mosquito vector surveillance in order to provide accurate data for target mosquito control and provide a scientific basis for effective control of mosquito-borne diseases in China.

Objective To investigate the composition and distribution of rodents, their trend of seasonal variation, and the density of rodents in different habitats in China, and to provide an scientific basis for the development of rodent control programs. Methods The rodent surveillance data of the National Vectors Surveillance in China in 2016 were collected and analyzed to investigate the composition of rodent species. The density of rodents was compared across species, habitats, and provinces. Seasonal variation of density was analyzed. Results Among the rodents captured in China in 2016, Rattus norvegicus had the highest density of 0.30 rodents/100 traps, followed by Mus musculus with a density of 0.09 rodents/100 traps. There was a fluctuation in the total density of rodents. Among the three habitats, rural areas had a significantly higher density of rodents than the other two habitats, and residential areas had the lowest density. Xinjiang Uygur Autonomous Region had the highest density of rodents (1.68 rodents/100 traps), followed by Guangdong province. The total density of rodents in China showed an approximately unimodal distribution, with higher densities from March to October. The dominant species R. norvegicus had a relatively low density in March and a significantly higher density than the other species in other months, and R. rattoides had a relatively low density throughout the year. Seasonal variation of rodents varied across species. Conclusion The national rodent surveillance in China in 2016 indicated there were slight fluctuations in the total rodent density throughout the year and seasonal variation of the rodent density varied across species and provinces. The above findings imply that different prevention and control measures should be taken based on surveillance and the local rodent borne diseases risks.