Surprisingly large number of people may have marker for tick-linked meat allergy
Surprisingly large number of people may have marker for tick-linked meat allergy
令人惊讶：大量人群可能携带蜱虫叮咬引发的红肉过敏标志物
In some parts of the US, up to 30 percent of people may carry the antibody behind a red meat allergy spurred by tick bites, far exceeding the estimated number of people who actually have the allergy, according a study published in Morbidity and Mortality Weekly Report. The findings suggest far more Americans than previously thought may be at risk of the allergy, which can make having a hamburger for dinner a potentially life-threatening choice. 根据发表在《发病率与死亡率周报》（Morbidity and Mortality Weekly Report）上的一项研究，在美国部分地区，高达 30% 的人可能携带由蜱虫叮咬引发的红肉过敏抗体，这一比例远超实际患有该过敏症的人数估计。研究结果表明，面临这种过敏风险的美国人远比此前认为的多，而这种过敏可能让晚餐吃个汉堡都变成潜在的致命选择。
The Centers for Disease Control and Prevention has previously estimated that only 0.14 percent of the US population (up to 450,000 people) has the allergy. But the study also highlights how little we understand about this unique disease—and the challenges of accurately diagnosing it. 美国疾病控制与预防中心（CDC）此前估计，仅有 0.14% 的美国人口（约 45 万人）患有此种过敏症。但这项研究也凸显了我们对这种独特疾病的了解依然匮乏，以及准确诊断该病所面临的挑战。
The study surveyed blood donations for the disease’s key antibody, which is in a class dubbed IgE and specifically attacks a double-sugar molecule called galactose-α-1,3-galactose, also known as alpha-gal. This disaccharide is found decorating the cells of nonprimate mammals, including cows and pigs, but it’s also released in the saliva of ticks, particularly the lone star tick (Amblyomma americanum). 该研究通过检测献血样本来寻找该疾病的关键抗体。这种抗体属于 IgE 类，专门攻击一种名为半乳糖-α-1,3-半乳糖（galactose-α-1,3-galactose，简称 alpha-gal）的双糖分子。这种双糖存在于非灵长类哺乳动物（包括牛和猪）的细胞表面，但也会通过蜱虫（尤其是孤星蜱，Amblyomma americanum）的唾液释放出来。
People bitten by ticks can develop IgE antibodies against alpha-gal, which can sometimes trigger an allergic response to eating red meat as well as other animal products, such as dairy and gelatin. The allergy, called alpha-gal syndrome, is notorious for its delayed onset, flaring between two and six hours after a meal—making it difficult for people to connect the reaction to food. 被蜱虫叮咬的人可能会产生针对 alpha-gal 的 IgE 抗体，这有时会在食用红肉以及其他动物产品（如乳制品和明胶）时引发过敏反应。这种被称为“alpha-gal 综合征”的过敏症以其延迟发作而闻名，通常在进食后两到六小时内发作，这使得人们很难将过敏反应与食物联系起来。
Symptoms can include hives, nausea, vomiting, abdominal cramps, diarrhea, and/or signs of a severe allergic response called anaphylaxis, which can be marked by trouble breathing, throat tightening, swelling tongue or lips, dizziness, weak pulse, and a drop in blood pressure. 症状可能包括荨麻疹、恶心、呕吐、腹部绞痛、腹泻，和/或被称为过敏性休克的严重过敏反应迹象，其特征可能包括呼吸困难、喉咙紧缩、舌头或嘴唇肿胀、头晕、脉搏微弱以及血压下降。
Alpha-gal syndrome was only first described in the early 2000s, and researchers still have a slew of questions about it, including why some people develop alpha-gal IgE antibodies and why only some of those who have the antibody seem to have the allergy. Early on, researchers realized there were people with so-called asymptomatic sensitization to alpha-gal. In other words, there are people with the antibody against the carbohydrate who don’t seem to have an allergic response to meat. Alpha-gal 综合征直到 21 世纪初才首次被描述，研究人员对其仍有许多疑问，包括为什么有些人会产生 alpha-gal IgE 抗体，以及为什么只有部分携带该抗体的人会出现过敏症状。研究人员很早就意识到，有些人对 alpha-gal 存在所谓的“无症状致敏”。换句话说，有些人虽然携带针对这种碳水化合物的抗体，但似乎并不会对肉类产生过敏反应。
This became clear in 2007 when researchers reported that many cancer patients were having severe allergic reactions to a cancer treatment called cetuximab—a monoclonal antibody drug that just happened to contain alpha-gal. The allergic response was first noticed when cetuximab was used in patients from Tennessee and North Carolina, where there are established populations of the lone star tick. While the cancer patients had alpha-gal IgE antibodies and the same allergic reaction to the drug as seen with alpha-gal syndrome, the cancer patients didn’t report problems eating meat. 这一点在 2007 年变得清晰，当时研究人员报告称，许多癌症患者在接受一种名为西妥昔单抗（cetuximab）的癌症治疗时出现了严重的过敏反应——这是一种恰好含有 alpha-gal 的单克隆抗体药物。这种过敏反应最初是在田纳西州和北卡罗来纳州的患者使用西妥昔单抗时被发现的，而这些地区正是孤星蜱的常驻地。虽然这些癌症患者体内有 alpha-gal IgE 抗体，且对该药物的过敏反应与 alpha-gal 综合征相同，但他们并未报告在食用肉类时出现问题。
New estimates
新的估计
To date, researchers still don’t know how common alpha-gal antibodies are, hence the new MMWR study. A group of researchers, led by infectious disease experts at the University of North Carolina at Chapel Hill, collected samples from 3,000 blood donations across 10 states, with 300 samples per state. They tested the samples for the antibody and used the data to make population-level estimates for the antibody’s prevalence. 迄今为止，研究人员仍不清楚 alpha-gal 抗体有多普遍，因此才有了这项新的 MMWR 研究。由北卡罗来纳大学教堂山分校的传染病专家领导的研究小组，从 10 个州的 3,000 份献血样本中进行了采集，每个州 300 份。他们对样本进行了抗体检测，并利用这些数据对该抗体在人群中的流行率进行了估算。
Six of the states were firmly in lone star tick territory: Arkansas, Kentucky, Missouri, South Carolina, Tennessee, and Virginia. There were also two states out of the tick’s range, New Mexico and Washington, and two states with regions that may have the ticks, Minnesota and Maine. 其中 6 个州处于孤星蜱的明确活动范围内：阿肯色州、肯塔基州、密苏里州、南卡罗来纳州、田纳西州和弗吉尼亚州。此外还有两个州处于蜱虫活动范围之外（新墨西哥州和华盛顿州），以及两个部分地区可能存在蜱虫的州（明尼苏达州和缅因州）。
The researchers found, as expected, that alpha-gal antibodies were most common in the states with the lone star tick. Of the six states in the tick’s territory, South Carolina had the lowest estimated prevalence of 5.5 percent. The other five ranged from 21.5 percent (Tennessee) to 31.2 percent (Arkansas). Collectively, the five top states had a prevalence estimate of 24 percent. The two states that only had some regions estimated to be in range for the tick, Maine and Minnesota, had prevalence estimates of 10.6 percent and 5.4 percent, respectively. Estimates for New Mexico and Washington, outside the tick’s range, were lowest, at 1.9 percent and 1.1 percent, respectively. 研究人员发现，正如预期的那样，alpha-gal 抗体在有孤星蜱的州最为常见。在处于蜱虫活动范围的 6 个州中，南卡罗来纳州的估计流行率最低，为 5.5%。其余 5 个州的流行率从 21.5%（田纳西州）到 31.2%（阿肯色州）不等。总体而言，这 5 个州的总流行率估计为 24%。缅因州和明尼苏达州这两个仅有部分地区被认为处于蜱虫活动范围内的州，其流行率估计分别为 10.6% 和 5.4%。处于蜱虫活动范围之外的新墨西哥州和华盛顿州的估计值最低，分别为 1.9% 和 1.1%。
The researchers did not have data from the blood donors to know if they had been diagnosed with alpha-gal syndrome or not. But the prevalence in the donors and the modeled population-level estimates far exceed the estimated number of people with alpha-gal syndrome. The results suggest asymptomatic sensitization to alpha-gal may be common, while alpha-gal syndrome is not, the researchers conclude. 研究人员没有从献血者那里获得数据来了解他们是否被诊断出患有 alpha-gal 综合征。但献血者中的流行率和模拟的人群水平估计值远超 alpha-gal 综合征患者的估计人数。研究人员总结称，这些结果表明，对 alpha-gal 的无症状致敏可能很常见，而 alpha-gal 综合征则不然。
This poses a risk for alpha-gal syndrome to be overdiagnosed and for patients to unnecessarily restrict their diets if clinicians rely solely on the antibody’s presence. The researchers stress that a diagnosis should only be given if people report symptoms after meals with red meat. Clinical guidelines recommend that people suspected of alpha-gal syndrome do a trial period of avoiding meat to see if symptoms improve before getting a diagnosis. 如果临床医生仅依赖抗体的存在进行诊断，这会带来 alpha-gal 综合征被过度诊断以及患者不必要地限制饮食的风险。研究人员强调，只有在人们报告食用红肉后出现症状时，才应做出诊断。临床指南建议，怀疑患有 alpha-gal 综合征的人应进行一段时期的禁肉试验，以观察症状是否改善，然后再进行诊断。
On the other hand, researchers still don’t know what proportion of people with antibodies have alpha-gal syndrome or are at risk of developing it later, possibly after additional tick bites. It’s also unclear if having alpha-gal IgE antibodies poses other risks. For instance, some small studies have linked alpha-gal IgE antibodies to higher risks of coronary artery disease. The researchers behind the new study suggest such alpha-gal antibody surveillance data can help identify areas with high prevalence ripe for further research. 另一方面，研究人员仍不清楚携带抗体的人群中有多少比例患有 alpha-gal 综合征，或者在未来（可能在再次被蜱虫叮咬后）患病的风险有多大。目前也不清楚携带 alpha-gal IgE 抗体是否会带来其他风险。例如，一些小型研究已将 alpha-gal IgE 抗体与更高的冠状动脉疾病风险联系起来。这项新研究的研究人员建议，此类 alpha-gal 抗体监测数据有助于识别流行率较高的地区，从而为进一步研究提供条件。