Frequently Asked Questions: What is plague?
Plague is an infectious disease that affects rodents, certain other animals, and humans. It is caused by the Yersinia pestis bacteria. These bacteria are found in many areas of the world, including the United States.
How do people become infected with plague?
People most commonly acquire plague when they are bitten by a flea that is infected with the plague bacteria. People can also become infected from direct contact with infected tissues or fluids while handling an animal that is sick with or that has died from plague. Finally, people can become infected from inhaling respiratory droplets after close contact with cats and humans with pneumonic plague.
What are the different forms of plague?
There are three forms of plague:
Bubonic plague: Patients develop sudden onset of fever, headache, chills, and weakness and one or more swollen, tender and painful lymph nodes (called buboes). This form is usually the result of an infected flea bite. The bacteria multiply in the lymph node closest to where the bacteria entered the human body. If the patient is not treated with appropriate antibiotics, the bacteria can spread to other parts of the body.
Septicemic plague: Patients develop fever, chills, extreme weakness, abdominal pain, shock, and possibly bleeding into the skin and other organs. Skin and other tissues may turn black and die, especially on fingers, toes, and the nose. Septicemic plague can occur as the first symptoms of plague, or may develop from untreated bubonic plague. This form results from bites of infected fleas or from handling an infected animal.
Pneumonicplague: Patientsdevelopfever, headache, weakness, and a rapidly developing pneumonia with shortness of breath, chest pain, cough, and sometimes bloody or watery mucous. Pneumonic plague may develop from inhaling infectious droplets or from untreated bubonic or septicemic plague that spreads to the lungs. The pneumonia may cause respiratory failure and shock. Pneumonic plague is the most serious form of the disease and is the only form of plague that can be spread from person to person (by infectious droplets).
What is the basic transmission cycle of plague
Fleas become infected by feeding on rodents, such as chipmunks, prairie dogs, ground squirrels, mice, and other mammals that are infected with the bacterium Yersinia pestis. Fleas transmit the plague bacteria to humans and other mammals during a subsequent feeding. The plague bacteria survive briefly (a few days) in the blood of rodents and for longer periods in the fleas. An illustration of plague ecology in the United States is available.
Could one person get plague from another person?
Yes, when a person has plague pneumonia they may cough droplets containing the plague bacteria into air. If these bacteria-containing droplets are breathed in by another person they can cause pneumonic plague. Human-to-human transmission is rare and typically requires direct and close contact with the person with pneumonic plague.
What is the incubation period for plague?
A person usually becomes ill with bubonic plague 2 to 6 days after being infected. Someone exposed to Yersinia pestis through the air would become ill within 1 to 3 days.
When bubonic plague is left untreated, plague bacteria can invade the bloodstream. When plague bacteria multiply in the bloodstream, they spread rapidly throughout the body and cause a severe and often fatal condition called septicemic plague. Untreated bubonic plague can also progress into an infection of the lungs, causing pneumonic plague. If plague patients are not given specific antibiotic therapy, all forms of plague can progress rapidly to death.
一个人通常在感染后 2 至 6 天患上腺鼠疫。有人通过空气接触鼠疫耶尔森菌，1～3 天内就会发病。当淋巴腺鼠疫未经治疗时，鼠疫细菌可侵入血液。当鼠疫细菌在血液中繁殖时，它们迅速扩散到全身，并引起一种严重的、通常是致命的情况，称为败血性鼠疫。未经治疗的腺鼠疫也可发展为肺部感染，引起肺鼠疫。如果鼠疫患者不给予特殊的抗生素治疗，各种形式的鼠疫都可以迅速进展至死亡。
How is plague diagnosed?
The first step in plague diagnosis is an evaluation by a health worker. If the health worker suspects plague, samples of the patient’s blood, sputum, or lymph node aspirate are sent to a laboratory for testing. Once the laboratory receives the sample, preliminary results can be ready in less than two hours. Laboratory confirmation will take longer, usually 24 to 48 hours. Often, presumptive treatment with antibiotics will start as soon as samples are taken, if plague is suspected.
鼠疫诊断的第一步是由卫生工作者进行评估。如果卫生工作者怀疑有鼠疫，患者的血液、痰液或淋巴结抽吸物的样本会被送到实验室进行检测。一旦实验室收到样本，初步结果可在两小时内完成。实验室确认需要更长时间，通常为 24 至 48 小时。通常情况下，如果怀疑有鼠疫，一旦取样，就会开始抗生素的假定治疗。
How many cases of plague occur in the United States? Globally?
Plague was first introduced into the United States in 1900. Between 1900 and 2012, 1006 confirmed or probable human plague cases occurred in the United States. Over 80% of United States plague cases have been the bubonic form. In recent decades, an average of 7 human plague cases are reported each year (range: 1-17 cases per year). Plague has occurred in people of all ages (infants up to age 96), though 50% of cases occur in people ages 12–45. Worldwide, between 1,000 and 2,000 cases each year are reported to the World Health OrganizationExternal (WHO), though the true number is likely much higher.
鼠疫于 1900 年首次传入美国。1900 年至 2012 年间，美国发生 1006 例确诊或可能的人间鼠疫病例。超过 80% 的美国鼠疫病例是腺鼠疫。近几十年来，平均每年报告 7 例人间鼠疫病例（范围：每年 1-17 例）。尽管 50% 的病例发生在 12-45 岁的人群中，但所有年龄的人（96 岁以下的婴儿）均发生过鼠疫。在世界范围内，每年向世界卫生组织 (WHO) 报告的病例数在 1,000 至 2,000 例之间，但实际数字可能要高得多。
What is the death rate of plague?
In the pre-antibiotic era (1900 through 1941), mortality among those infected with plague in the United States was 66%. Antibiotics greatly reduced mortality, and by 1990-2010 overall mortality had decreased to 11%. Plague can still be fatal despite effective antibiotics, though it is lower for bubonic plague cases than for septicemic or pneumonic plague cases. It is hard to assess the mortality rate of plague in developing countries, as relatively few cases are reliably diagnosed and reported to health authorities. WHO cites mortality rates of 8–10%, however some studies (WHO, 2004) suggest that mortality may be much higher in some plague endemic areas.
在前抗生素时代（1900 年至 1941 年），美国鼠疫感染者的死亡率为 66%。抗生素大大降低了死亡率，到 1990-2010 年总死亡率已降至 11%。尽管使用了有效的抗生素，鼠疫仍然可能是致命的，尽管它在腺鼠疫病例中的发病率低于败血症或肺鼠疫病例。很难评估发展中国家的鼠疫死亡率，因为可靠诊断并向卫生部门报告的病例相对较少。WHO 引用的死亡率为 8-10%，然而一些研究 (WHO，2004) 表明在一些鼠疫流行区死亡率可能高得多。
How is plague treated?
Plague can be successfully treated with antibiotics. Once a patient is diagnosed with suspected plague they should be hospitalized and, in the case of pneumonic plague, medically isolated. Laboratory tests should be done, including blood cultures for plague bacteria and microscopic examination of lymph node, blood, and sputum samples. Antibiotic treatment should begin as soon as possible after laboratory specimens are taken. To prevent a high risk of death in patients with pneumonic plague, antibiotics should be given as soon as possible, preferably within 24 hours of the first symptoms.
用抗生素可以成功地治疗鼠疫。一旦患者被诊断为疑似鼠疫，他们就应该住院治疗，如果是肺鼠疫，就应该进行医学隔离。应做实验室检查，包括血培养鼠疫菌和淋巴结、血、痰标本镜检。实验室标本采取后，应尽早开始抗生素治疗。为防止肺鼠疫患者的高死亡风险，应尽早给予抗生素治疗，最好在首次出现症状的 24 小时内给予。
Is the disease seasonal in its occurrence?
Yes. Although cases can occur at any time of the year, most cases in the United States are acquired from late spring to early fall.
Where is plague most common in the United States?
Plague occurs in rural and semi-rural areas of the western United States. Plague is most common in the southwestern states, particularly New Mexico, Arizona, and Colorado.
Who is at risk for getting plague in the United States?
Human plague occurs in areas where the bacteria are present in wild rodent populations. The risks are generally highest in rural and semi-rural areas, including homes that provide food and shelter for various ground squirrels, chipmunks and wood rats, or other areas where you may encounter rodents.
Is a vaccine available to prevent plague?
A plague vaccine is not available. New plague vaccines are in development but are not expected to be commercially available in the immediate future.