以共享健康為基礎之風險評估法量化親水性產氣單胞菌抗藥性對水產養殖物種—人類—環境健康系統之衝擊

Abstract

產氣單胞菌(Aeromonas spp.)引發之運動性產氣單胞菌病為臺灣持續發生之水產養殖疾病，其中親水性產氣單胞菌(Aeromonas hydrophila)為最受關注之致病菌。且用於治療此疾病之氧四環素(Oxytetracycline)與水域中親水性產氣單胞菌出現抗生素抗藥性(Antibiotic resistance)具連結性。水產養殖大量使用抗生素引發抗生素抗藥性，進一步威脅水生動物與人類健康，此問題建議須以共享健康(One Health)之觀點加以探討。然，目前仍缺乏定量模式合適地評估與環境殘留抗生素相關之抗生素抗藥性之健康風險。有鑑於此，本研究計畫之目的可分為：(1)建立以共享健康為基礎之研究法，以了解環境殘留之氧四環素引起親水性產氣單胞菌抗藥性之衝擊，(2)推估水域氧四環素濃度以評估在氧四環素壓力下抗生素抗藥性篩選風險，(3)評估親水性產氣單胞菌造成水產養殖物種感染之風險與人類抗藥性基因轉移之風險，及(4)提出控制策略模式以管理於人類—動物—環境介面之抗生素抗藥性相關風險。 本研究推估水產養殖氧四環素使用量做為多介質逸壓模式重要輸入參數，以推估養殖池與河川水體之氧四環素濃度。其中氧四環素濃度與四環黴素抗藥性(tetracycline resistance, tetR)之關係及親水性產氣單胞菌濃度與健康效應之關係以建構之劑量反應模式描述。本研究亦發展細菌族群動態模式以量化水環境四環黴素抗藥性於親水性產氣單胞菌之傳輸。藉連結逸壓模式、劑量反應模式及族群動態模式，可評估水域中四環黴素抗藥性基因篩選之風險、水產養殖物種感染親水性產氣單胞菌之風險及人類四環黴素抗藥性基因(tetracycline resistance genes, tetR genes)轉移之風險。最後，本研究不僅可為環境健康提出控制措施模式，以減緩四環黴素抗藥性造成之衝擊；亦可評估控制策略對動物與人類健康之效應。如此，得以共享健康之觀點提出控制策略與建議，以管理四環黴素抗藥性於人類—動物—環境介面造成之衝擊潛能。 本研究呈現蘭陽溪、朴子溪、曾文溪、鹽水溪、阿公店溪、高屏溪及東港溪流域與環境健康相關之氧四環素濃度、四環黴素抗藥性基因篩選風險及控制策略之結果。研究結果顯示，養殖池與河川之最高氧四環素濃度分別於蘭陽溪與阿公店溪流域，其推估值分別為497.93 ± 193.03 μg L−1與10.10 ± 3.19 μg L−1。當氧四環素濃度高於2.59 μg L−1 (95%信賴區間: 0.97–4.21 μg L−1)極可能增加水環境四環黴素抗藥性基因篩選之風險。風險評估之結果顯示，幾乎所有養殖池之風險商數中位數皆高於1，顯示氧四環素之殘留極可能引發四環黴素抗藥性基因篩選。控制策略模式模擬結果指出，於超越風險為0.5之條件下，欲確保蘭陽溪流域養殖池之四環黴素抗藥性基因篩選速率低於百分之十之篩選效應極為困難，其於春、夏及秋季氧四環素排放速率減少之最低百分比皆需高於90%。另一方面，應優先管控阿公店溪於春季與夏季之氧四環素濃度，其氧四環素排放速率應減少之百分比則分別為67%與25%。 本研究根據建構之細菌族群動態模式，可推估與水溫相關之抗藥性獲得數(resistance acquisition number, R0)。推估結果顯示，四環黴素抗藥性基因於親水性產氣單胞菌之傳輸能力受限於高於26°C之水溫。族群動態模擬結果顯示，應關注具高水活性、低水溫及pH介於5至8之水環境，其可能具較高之四環黴素抗藥性親水性產氣單胞菌族群。本研究亦發現水中氧四環素濃度超過7.14–18.87 μg L−1，極可能增大四環黴素抗藥性親水性產氣單胞菌之比例。 本研究進一步以位於朴子溪流域之東石鄉做為以共享健康為基礎之研究地區，評估動物與人類暴露親水性產氣單胞菌之健康風險。研究結果顯示，環境具四環黴素抗藥性親水性產氣單胞菌且持續暴露氧四環素可能使養殖蝦具有較高的感染風險，其第九十五百分位之相對風險介於1.25至1.34。另一方面，於秋季在養蝦池工作之人員與沿海區域游泳之泳客，其四環黴素抗藥性基因轉移風險推估值分別介於5.48×10−5–2.81×10−4與1.94×10−6–6.41×10−6，超過每年可接受之風險10−6。因此，研究結果指出四環黴素抗藥性親水性產氣單胞菌藉由此些暴露途徑造成之健康風險應受到關注。控制策略模式模擬結果顯示，為確保養殖池與朴子溪之環境健康，建議於秋季氧四環素排放速率應分別減少79%與21%。然，如欲同時保護養殖蝦與人類健康，除減低氧四環素排放速率，親水性產氣單胞菌之濃度亦需減低70–99%。 總結來說，藉建構以共享健康為基礎之整合型風險評估架構，可系統性評估與四環黴素抗藥性相關之健康風險。本論文提供以風險為基礎之控制策略，不僅利於關注具四環黴素抗藥性基因篩選高風險之環境，亦有助於在水產養殖物種—人類—環境系統探討健康風險，以達到共享健康之目標。本研究提出之定量研究法可提供公衛決策與水產養殖抗生素管理指引。

Motile aeromonad disease caused by Aeromonas spp, most notably Aeromonas hydrophila, have been continuously reported in aquaculture industry across Taiwan. The antibiotic approved to treat the disease is oxytetracycline (OTC), which has been linked to the emergence of antibiotic resistance in A. hydrophila in aquatic environment. The issue of antibiotic resistance driven by a massive use of antibiotics in aquaculture further threatening aquatic animal and human health has been suggested to be addressed from a One Health perspective. However, there is a lack of quantitative models to properly assess health risk of antibiotic resistance associated with environmentally relevant antibiotic residues. Therefore, the purpose of this dissertation was fourfold: (i) to formulate a One Health-based methodology to understand the impact of OTC residues-induced antibiotic resistance in A. hydrophila, (ii) to estimate OTC concentration in water environment and to assess risk of antibiotic resistance selection under OTC stresses, (iii) to assess aquaculture species-associated infection risk and human-associated resistance gene transfer risk posed by A. hydrophila, and (iv) to propose the control measure models on managing antibiotic resistance-related risks at a human–animal–environment interface. In this dissertation, amount of aquaculture-used OTC was estimated as a critical input parameter in a multimedia fugacity model to estimate environmental concentrations of OTC residues in aquaculture ponds and rivers. The dose–response models were used to describe the OTC concentration–tetracycline resistance (tetR) and A. hydrophila–health outcome relationships. A bacterial population dynamic model was developed to quantify the tetracycline resistance transmission among A. hydrophila in water environment. By incorporating the fugacity, dose–response, and population dynamic models, tetR genes selection risk in aquatic environment, aquaculture species-associated A. hydrophila infection risk, and human-associated tetR genes transfer risk could be assessed. Finally, the control measure models not only could be developed on reducing the impact of tetracycline resistance in environment, but also could be used to evaluate the effect of control strategies on animal and human health. Interventions and recommendations could be proposed from the perspective of One Health to manage the potential impact of tetracycline resistance at a human–animal–environment interface. Results related to environmental health included OTC concentration estimates, tetR genes selection risk, and the control measures among Lanyang, Potzu, Tsengwen, Yenshui, Agongdian, Kaoping, and Tungkang river basins. The maximum OTC concentration estimates in aquaculture ponds and rivers were 497.93 ± 193.03 μg L−1 in Lanyang river basin and 10.10 ± 3.19 μg L−1 in Agongdian river basin. When OTC concentration was higher than 2.59 μg L−1 (95% confidence interval: 0.97–4.21), it is highly likely to increase the tetR genes selection risk in water environment. In aquaculture ponds, almost all median risk quotients (RQs) were higher than 1, indicating that OTC residues were highly likely to induce tetR genes selection. Simulation results from the control measure model indicated that, at exceedance risk (ER) of 0.5, to ensure tetR genes selection rates in aquaculture ponds situated at Lanyang river basin lower than 10% increase in tetR genes selection rate was extremely difficult. The results showed that minimum reductions in OTC emission rates in spring, summer, and autumn were higher than 90%. On the other hand, OTC concentrations during spring and summer in Agongdian River should be given priority to be controlled by reducing 67% and 25% of OTC emission rate, respectively. Based on the constructed bacterial population dynamic model, water temperature-dependent resistance acquisition number (R0) could be derived. The results indicated that tetR transmissibility among A. hydrophila was restricted at water temperatures > 26°C (R0 < 1). Simulation results from the population dynamics showed that higher population of tetracycline-resistant A. hydrophila should be payed attention to the environment with higher water activity, lower water temperature, and pHs ranging from 5–8. Notably, it was found that fraction of tetracycline-resistant A. hydrophila would be highly likely to be amplified when OTC concentration in the water environment exceed 7.14–18.87 μg L−1. Furthermore, health risks were assessed for animals and human exposed to A. hydrophila in One Health-based study regions, i.e., Dongshi Township, situated at Potzu river basins. Results showed that given tetracycline-resistant A. hydrophila and continuous OTC exposure, it was likely that farmed shrimp would have higher risk being infected with 95%-tile relative risk (RR) estimates of 1.25–1.34. One the other hand, tetR genes transfer risks for human working in shrimp ponds (5.48×10−5–2.81×10−4) and swimming in coastal areas (1.94×10−6–6.41×10−6) during autumn exceeded acceptable risk 10−6 per year, indicating that health risk posed by tetracycline-resistant A. hydrophila via these exposure routes was alarming. To ensure environmental health for aquaculture ponds and Potzu River, OTC emission rates were recommended to be reduced by 79% and 21% during autumn, respectively. However, to protect health of farmed shrimp and human, reductions in OTC emission rate together with concentration of A. hydrophila (70–99%) were recommended. In conclusion, the integrated One Health-based risk assessment framework is developed to systematicly assess tetracycline resistance-related health risks. In this dissertation, risk-based control strategies not only could be provided to zero-in on environment with high tetR genes selection risk but also could be proposed to achieve One Health goals for addressing health risks in an aquaculture species–human–environmental system. The quantitative methodology can inform public health decision-making and antibiotic stewardship in aquaculture.