Practice of integrated vector surveillance of arthropod vectors, pathogens and reservoir hosts to monitor the occurrence of tropical vector-borne diseases in 2020 in Zhejiang Province, China

Development and field evaluation of a novel sugar bait device for controlling residential vector mosquitoes in Zhejiang Province, China

Background

Mosquito-borne diseases pose serious public health threats in Zhejiang Province, China, and vector control is believed to be the primary method for reducing transmission. Due to severe resistance problems, effective and sustainable methods without chemical insecticides are urgently required to control mosquito vectors. Attractive toxic sugar baits (ATSB) are newly developed methods to control mosquitoes in recent decades with the core element sugar bait, which was invented according to the sugar-feeding behavior of mosquitoes. In this study, we developed a Novel Sugar Bait Device (NSBD) trap by combining sugar bait and physical adhesive capture technology. The study aimed to evaluate the effect of the NSBD trap on controlling mosquitoes in residential environments and to identify the optimal sugar solution concentration in the sugar bait of the NSBD for real use.

Methods

Four residential villages in Ningbo City with similar geographic environments and mosquito densities were selected for field trials in 2022. One village (site 1) was designated as the control group, and three villages (sites 2-4) served as the test groups to assess the effectiveness of NSBD traps with different sugar solution concentrations (6, 8, and 10%) in the sugar bait. Larval and adult mosquito densities were monitored monthly before and semi-monthly after the trials using the CDC light trap and larval pipette method.

Results

Before the trials, we monitored mosquito density for 3 months to confirm the baseline mosquito density among the four sites, and no statistical differences in adult and larval mosquitoes were found (adult, F = 3.047, p > 0.05; larvae, F = 0.436, p > 0.05). After the trials, all NCBD traps effectively controlled larval and adult mosquito densities, with the highest standard decrease rates of larval and adult mosquito densities at 57.80 and 86.31%, respectively, observed in site 4. The most suitable sugar solution concentration in the sugar bait was 10%.

Conclusion

NSBD traps effectively controlled mosquitoes in residential environments during field trials. Without the use of insecticides, this may be a promising choice for mosquito vector control to prevent mosquito-borne diseases.

Epidemiological characteristics and prediction model construction of hemorrhagic fever with renal syndrome in Quzhou City, China, 2005-2022

Background

Hemorrhagic fever with renal syndrome (HFRS) is one of the 10 major infectious diseases that jeopardize human health and is distributed in more than 30 countries around the world. China is the country with the highest number of reported HFRS cases worldwide, accounting for 90% of global cases. The incidence level of HFRS in Quzhou is at the forefront of Zhejiang Province, and there is no specific treatment for it yet. Therefore, it is crucial to grasp the epidemiological characteristics of HFRS in Quzhou and establish a prediction model for HFRS to lay the foundation for early warning of HFRS.

Methods

Descriptive epidemiological methods were used to analyze the epidemic characteristics of HFRS, the incidence map was drawn by ArcGIS software, the Seasonal AutoRegressive Integrated Moving Average (SARIMA) and Prophet model were established by R software. Then, root mean square error (RMSE) and mean absolute error (MAE) were used to evaluate the fitting and prediction performances of the model.

Results

A total of 843 HFRS cases were reported in Quzhou City from 2005 to 2022, with the highest annual incidence rate in 2007 (3.93/100,000) and the lowest in 2022 (1.05/100,000) (P trend<0.001). The incidence is distributed in a seasonal double-peak distribution, with the first peak from October to January and the second peak from May to July. The incidence rate in males (2.87/100,000) was significantly higher than in females (1.32/100,000). Farmers had the highest number of cases, accounting for 79.95% of the total number of cases. The incidence is high in the northwest of Quzhou City, with cases concentrated on cultivated land and artificial land. The RMSE and MAE values of the Prophet model are smaller than those of the SARIMA (1,0,1) (2,1,0)12 model.

Conclusion

From 2005 to 2022, the incidence of HFRS in Quzhou City showed an overall downward trend, but the epidemic in high-incidence areas was still serious. In the future, the dynamics of HFRS outbreaks and host animal surveillance should be continuously strengthened in combination with the Prophet model. During the peak season, HFRS vaccination and health education are promoted with farmers as the key groups.

The ecological and etiological investigation of ticks and rodents in China: results from an ongoing surveillance study in Zhejiang Province

OBJECTIVES

This study aimed to analyze the population density of vector ticks and reservoir hosts rodents, and to investigate the relevant pathogen infection in Zhejiang Province, China.

METHODS

In this surveillance study, the data of ticks density were collected with the tick picking method on animal body surface and the drag-flag method, while the rodent density with the night trapping method. The samples of ticks were examined for the severe fever with thrombocytopenia syndrome virus (SFTSV), and blood serum and organs from rodents were subjected for SFTSV, hantavirus, Leptospira, Orientia tsutsugamushi (O. tsutsugamushi) and Yersinia pestis (Y. pestis) screening in the laboratory.

RESULTS

From 2017 to 2022 in Zhejiang Province, 16,230 parasitic ticks were found in 1848 positive animals, with the density of parasitic ticks of 1.29 ticks per host animal, and a total of 5,201 questing ticks were captured from 1,140,910 meters of vegetation distance with the questing tick density of 0.46 ticks/flag·100 m. Haemaphysalis longicornis (H. longicornis) was the major species. A total of 2,187,739 mousetraps were distributed and 12,705 rodents were trapped, with the density of 0.58 per 100 trap-nights. Rattus norvegicus was the major species. For SFTSV screening, two groups nymphal ticks of H. longicornis were tested to be positive. For the rodents samples, the Leptospira had a positive rate of 12.28% (197/1604), the hantavirus was 1.00% (16/1604), and the O. tsutsugamushi was 0.15% (2/1332). No positive results were found with SFTSV and Y. pestis in the rodents samples.

CONCLUSION

Findings from this study indicated that the ticks and rodents were widely distributed in Zhejiang Province. Particularly, the positive detection of SFTSV, Leptospira, hantavirus and O. tsutsugamushi in ticks or rodents from this area suggested that more attention should be paid to the possibilities of relevant vector-borne diseases occurrence.

Evaluation of the effectiveness of the human-baited double net traps and BG traps compared with the human landing catches for collecting outdoor Aedes albopictus in China

Dengue fever is one of the biggest threats to public health in China, causing huge disease burden and economic loss. Aedes-mosquito surveillance could be a cornerstone for predicting the risk of Aedes-borne diseases and evaluating the effect of vector management during diseases outbreaks. The human landing catch (HLC) method is regarded as the "gold standard" for catching Aedes mosquitoes, but it potentially exposes field professionals to vectors of known or unknown pathogens. Human-baited double net (HDN) was recommended to replace HLC for emergency monitoring in China when Aedes-borne diseases break out, but it had been reported with low efficiency for capturing Aedes mosquitoes. In this study, we compared HLC with HDN and BG traps for field Aedes albopictus monitoring, with the aim of evaluating the effectiveness of HDN replacing HLC and finding an effective and safe alternative to the HLC for monitoring Aedes albopictus. Six sites in Hangzhou, Shaoxing, and Yiwu, Zhejiang Province, China, were chosen to conduct outdoor HLC, HDN, and BG trap catches from June to October 2021. The tests were performed 3 h apart: 8:30-9:30 AM, 16:30-17:30 PM, and 17:30-18:30 PM. A total of 2330 adult mosquitoes were collected, and Aedes albopictus was the most abundant species in all three catches with 848(98.95%), 559(97.39%) and 867 (96.44%) caught in HLC, HDN and BG traps respectively. Compared to HLC, HDN collected significantly less Ae. albopictus and Ae. albopictus females per trapping period (P < 0.001, P < 0.001), whereas no statistical differences were found between the HLC and BG trap (P = 0.970, P > 0.05). Statistically significant positive spatial correlations for Ae. albopictus sampling was found between HLC and HDN traps (r = 0.543, P < 0.001) and HLC and BG traps (r = 0.658, P < 0.001). In conclusion, both the BG trap and HDN have a significant positive spatial correlation with HLC, making them safer alternatives to HLC for Ae. albopictus monitoring in China. However, with better a sampling efficiency, being less labor intensive, and no human-baited attraction bias, the BG trap could be a better choice than the HDN trap.