台灣地區低致病性禽流感H5亞型病毒及2009年流行之H1N1病毒在肉豬及禽畜業工作人員的血清偵測

Serological Surveillance on 2009 Pandemic Influenza H1N1 Viruses and LPAI H5 among Swine and Animal-related Workers in Taiwan

蔡孟玲(Men-Lin Tsai)

指導教授 ： 金傳春

國立臺灣大學/公共衛生學院/流行病學與預防醫學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.00484

摘要

流行性感冒(簡稱流感)病毒具八段基因，且極易發生抗原漂變(drift)、移變(shift)及基因重組，因此常在動物或人群間變異傳播、適應而造成大規模流行。臺灣家禽曾出現「低」致病性禽流感H5亞型(簡稱LPAI H5)的流行，在2003年造成農業經濟損失甚鉅。而2009年美洲冒出禽、人、豬三重組的新型流感H1N1病毒(簡稱pH1N1/09)，即在豬群上經重組後，迅速適應而傳播至人，終造成人際間全球大流行。由於豬呼吸道細胞可同時感染來自禽及人兩宿主的流感病毒，致使豬可成為流感病毒基因重組與種間傳播的媒介。本研究目的以血清學監測臺灣肉豬及禽畜業相關人員對2009年新型H1N1病毒及本土低致病性H5禽流感病毒的感染，期能了解流感病毒可能跨越兩宿主族群傳播的關係與感染的危險/保護因子。
內容含三部分：(一) 2008到2010年間，在A縣牧場內收集846支經濟用豬血清，進行LPAI H5及pH1N1/09的血清抗體監測；（二）2010年收集同縣1,354名禽畜業人員血清也進行此兩流感病毒的抗體監測；及（三）找出人與豬感染之危險及保護因子。作法上，禽流感病毒的血球凝集抑制(hemagglutination inhibition, HI)抗體測試是採自2008年A縣活禽市場分離得的LPAI H5病毒，並測血清對馬紅血球凝集抑制力(抗體效價≧1:20為陽性)；pH1N1/09的HI抗體是採自備製新流感疫苗的2009年A/California/7/2009 (H1N1)病毒株，以其對火雞紅血球凝集抑制力(抗體效價≧1:40為陽性)。
結果發現，自2008年8月到2010年5月間，豬隻的此新流感H1N1病毒抗體總盛行率為19.1% (162/846) [三年各為8.9% (20/225)、2009年8月3.4% (10/291)及40.0% (132/330) ]；而豬場的此病毒抗體總盛行率為51.7% (31/60)[各為53.3% (8/15)、22.7% (5/22)及78.3% (18/23)]；均遠高出該豬群/豬場的本土低致病性H5抗體總盛行率(p<0.0001)，且僅一隻來自2008年的豬為低致病性H5抗體陽性(0.12%，1/846)。多變項分析控制年度變項後，發現此三年豬飼養於沿海區為其感染此新流感H1N1病毒的危險因子 [勝算比(Odds Ratio, OR)=2.33，95% 信賴區間(confidence interval, CI)=1.51-3.59，p=0.0001]，而良好的飼養管理為保護因子(OR=0.99，95% CI=0.98-0.995，p=0.0006)。以多變項分析單2010年檢測結果後，發現另有非一貫式飼養也是危險因子(OR=2.88，95% CI=1.45-5.72，p=0.0025)，其餘結果雷同(養於沿海：OR=3.43，95% CI=1.71-6.88，p=0.0005；管理好：OR=0.96 ，95% CI=0.95-0.97，p<0.0001)。
2010年10月動物相關產業人員的此新H1N1流感病毒抗體總盛行率為21.42% (290/1,354)，而未打新流感疫苗的之此病毒抗體陽性率為16.4% (138/841)，均高於其低致病性H5抗體陽性率1.77% (24/1,354) (p<0.0001)。以多變項分析控制年齡及打pH1N1/09疫苗兩變項後，發現豬相關工作者的pH1N1/09抗體陽性風險較其他人員為高(OR=1.50，95% CI=1.11-2.02，p=0.0084)，而牧場場主(OR=0.071，95% CI=0.50-0.99，p=0.042)、屠夫或營業員(OR=0.32，95% CI=0.14-0.73，p=0.0061)為保護因子；在未打新流感疫苗者控制年齡後，牧場員工(OR=1.62，95% CI= 1.06- 2.47，p=0.0257)及獸醫師(OR=4.72，95% CI=1.51-14.83，p=0.0078)較易感染；相反地，較高的身體質量指數(Body Mass Index，BMI) (OR=0.91，95% CI= 0.86- 0.97，p=0.003)及從事禽工作(OR=0.64，95% CI=0.43-0.96，p=0.0299)較不易感染。另控制年齡後，人感染低致病性H5流感的危險因子為從事禽業(OR= 3.40，95% CI=1.21-9.56，p=0.0205)，而保護因子為居住在豬舍密度較高(≧1.58 pig house/km2)區(OR=0.28，95% CI=0.11-0.76，p=0.0121)。
本研究的結論是2009年新流感病毒較禽流感H5病毒極易在臺灣中部跨越感染人及豬群，因外來新流感H1N1大流行後期的臺灣豬群抗體盛行率明顯高於2009年第一波流行及2008年的背景值；反之，臺灣禽的本土低致病性H5禽流感病毒較少在豬群間感染。有鑑於豬為流感病毒跨宿主傳播與基因重組的重要橋樑，未來更應加強豬及相關產業人員的流感病毒及血清偵測，且將同牧場的豬群及人群配對比較，迅速掌握流感病毒在臺灣禽畜業的動向；並探究新流感病毒是否較動物流感病毒有取代優勢力及其機轉。

關鍵字

流行性感冒 ； 血清學偵測 ； 2009年新型流感 ； 低致病性H5亞型禽流感 ； 豬 ； 動物相關產業人員 ； 牧場 ； 跨種傳播 ； 人畜共通傳染病 ； 全球流行 ； 台灣

並列摘要

Influenza A viruses (IAVs) involving eight gene segments can infect many different hosts and are capable to have inter-species transmission among mammals, avian and humans. These viruses have changed continuously year by year and are also capable to emerge novel virus after antigenic shift occasionally. Pigs having receptors for both avian and mammalian influenza viruses are susceptible to infection of these viruses, and thus may serve as a mediator of inter-species transmission of IAVs between human and avian populations. In Taiwan, a large-scale outbreak of low pathogenic avian influenza (LPAI) H5 viruses occurred in 2003 causing great economic loss. Furthermore, the 2009 emerged triple-reassorted pandemic H1N1 viruses (pH1N1/09) with swine- and avian-origin gene segments rapidly spread human-to-human populations leading to pandemics. Therefore, the specific aims of this study were to investigate possible inter-species transmission of LPAI H5 and the pH1N1/09 viruses among economic swine and animal-related workers in Taiwan through serological surveillance and to search for the risk and protective factors for the infections of these two animal-origin influenza viruses.
To approach above issues, this study involved three parts: (1) to conduct a serological surveillance of the pH1N1/09 and LPAI H5 influenza in 846 pigs in County A of central Taiwan from August 2008 to May 2010 (2) to find out the likelihood in acquiring the two viral infections among 1,354 animal-related workers in County A in 2010 by measuring their antibody serotiters; and (3) to investigate factors associated with the two viral infections in these two different host populations, particularly environmental conditions that may reflect local geographical differences in seroprevalence rates of pH1N1/09.
To investigate the epidemiological importance of inter-species transmission in central Taiwan, both 846 swine serum samples (60 farms) from 2008 to 2010, and 1354 human sera from animal-related workers in 2010 were collected in County A. These samples were screened by modified hemagglutinin inhibition (HI) assays using turkey RBCs and the California/7/2009 (H1N1) vaccine strain for measuring anti- pH1N1/09 HI antibody, and the titers >1:40 regarded as seropositive. On the other hand, horse red blood cells (RBCs) and the locally Taiwanese low pathogenic avian influenza (LPAI) H5N2 viruses (Duck/Taiwan/DV1237/2008, isolated from ducks in County A) were used to measure anti-H5 HI antibody, and serotitiers >1:20 determined as seropositive. Risk and protective factors for acquiring both infections in swine and animal-related human populations were further analyzed by univariate and multivariate analyses.
The overall seroprevalence rates of anti-pH1N1/09 in swine populations and swine farms were 19.1% (162/846) and 51.7% (31/60), respectively; with significant increase in 2010 [40.0% (132/330 samples); 78.3% (18/23 farms)] compared to those in 2008 [8.9% (20/225 samples); 53.3%, (8/15 farms)] and in 2009 [3.4%, (10/291 samples); 22.7%, (5/22 farms)] (p<0.0001). These overall seroprevalence rates of the 2009 novel influenza virus in swine were significantly higher than those of LPAI H5 [0.12% (1/846 samples); 1.7% (1/60 farms), (p<0.0001)]. Similar trends in significant differences between these two animal-originated viruses also occurred for pH1N1/09 infection in animal-related workers [21.4% (290/1,354) in all workers and 16.4% (138/841) in non-pH1N1/09 vaccinated workers on pH1N1/09 infection, versus 1.8% (24/1,354) on LPAI H5, p<0.0001].
Multivariate analysis after controlling the study year shows that the risk factor for swine to acquire the pH1N1/09 infection during the past three years was raised swine along the coast [Odds Ratio (OR)=2.33, 95% confidence interval (CI)=1.51 -3.59, p=0.0001], whereas the protective factor was appropriate swine farm management (OR=0.99, 95% CI=0.98-0.995, p=0.0006). The risk and protective factors in the 2010’s pH1N1/09 infection in swine remained the same [raised along the coast (OR=3.43, 95% CI=1.71-6.88, p=0.0005) and well management (OR=0.96, 95% CI=0.95-0.97, p<0.0001)], in addition to another risk factor of the farrow-to-finish raised farm type (OR=2.88, 95% CI=1.45-5.72, p=0.0025).
Regarding to human infection, after controlling age and receiving the pH1N1/09 vaccine, the multivariate analysis reveal that the only statistically significant risk factor for acquiring the 2009 pH1N1 infection among animal-related workers was swine-related labor (OR=1.50, 95% CI=1.11-2.02, p=0.0084), whereas the protective factors were the low-risk occupations [farm’s owners (OR=0.071, 95% CI=0.50-0.99, p=0.042) and slaughters or sellers (OR=0.32, 95% CI=0.14 -0.73, p=0.0061)]. Among those pH1N1/09-unvaccinated workers, the high-risk occupations increased the risk of acquiring this infection [swine farm’s employees (OR=1.62, 95% CI=1.06-2.47, p=0.0257) and veterinarians (OR=4.72, 95% CI=1.51-14.83, p=0.0078)] in contrast, avian-related labors (OR=0.64, 95% CI=0.43-0.96, p=0.0299) and higher body mass index (BMI) (OR=0.91, 95% CI=0.86-0.97, p=0.003) were protective factors. On the other hand, the only risk factor for acquiring the LPAI H5 infection among animal-related workers after controlling age was avian-related labors (OR=3.40, 95% CI=1.21-9.56, p=0.0205), whereas the only protective factor was living in areas with higher densities of pig houses (OR=0.28, 95% CI=0.11-0.76, p=0.0121).
In conclusion, swine populations did strikingly increase the infection of pH1N1/09 in central Taiwan in 2010 after the occurrence of the 2009 pandemic in human in 2009. On the contrary, LPAI H5 virus isolated in County A that had not been adapted to swine populations yet leading that the seroprevalenc of this H5 virus infection was extremely low in animal-related workers. This first seroepidemiological study in both swine and swine workers in the same county can provide us more clues on inter-species transmission of important novel influenza viruses in this island where poultry density ranked the highest. Since Taiwan has been the HPAI-free area domestically and has not had outbreaks of novel influenza among human or swine populations, virological and serological surveillance to detect novel influenza viruses in farms and high risk populations with animal exposures in the countryside should be reinforced continuously. In addition, future research needs to focus on serological surveillance of influenza viruses among paired animal-related workers and their farm animals and investigating the mechanism involved in novel influenza viruses to become selection advantageous viruses for replacing the localized animal influenza viruses.

並列關鍵字

influenza virus ； serological surveillance ； pH1N1/09 ； LPAI H5 ； swine ； animal-related people ； farm ； inter-species transmission ； zoonosis ； pandemic ； Taiwan

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