Plague (disease)

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Yersinia pestis fluorescent.jpeg
Yersinia pestis seen at 200× magnification with a fluorescent label.
Specialty Infectious disease
Symptoms Fever, weakness, headache [1]
Usual onset1-7 days after exposure [2]
Types Bubonic plague, septicemic plague, pneumonic plague [1]
Causes Yersinia pestis [2]
Diagnostic method Finding the bacterium in a lymph node, blood, sputum [2]
Prevention Plague vaccine [2]
Treatment Antibiotics and supportive care [2]
Medication Gentamicin and a fluoroquinolone [3]
Prognosis~10% risk of death (with treatment) [4]
Frequency~600 cases a year [2]

Plague is an infectious disease caused by the bacterium Yersinia pestis . [2] Symptoms include fever, weakness and headache. [1] Usually this begins one to seven days after exposure. [2] In the bubonic form there is also swelling of lymph nodes, while in the septicemic form tissues may turn black and die, and in the pneumonic form shortness of breath, cough and chest pain may occur. [1]

Enterobacteriaceae family of bacteria

The Enterobacteriaceae are a large family of Gram-negative bacteria. This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria in the phylum Proteobacteria.

<i>Yersinia pestis</i> species of bacteria, cause of plague

Yersinia pestis is a gram-negative, nonmotile, rod-shaped coccobacillus bacteria, with no spores. It is a facultative anaerobic organism that can infect humans via the Oriental rat flea. It causes the disease plague, which takes three main forms: pneumonic, septicemic and bubonic plagues. All three forms were responsible for a number of high-mortality epidemics throughout human history, including: the sixth century's Plague of Justinian; the Black Death, which accounted for the death of at least one-third of the European population between 1347 and 1353; and the Third Pandemic, sometimes referred to as the Modern Plague, which began in the late nineteenth century in China and spread by rats on steamboats claiming close to 10,000,000 lives. These plagues likely originated in China and were transmitted west via trade routes. Recent research indicates that the pathogen may have been the cause of what is described as the Neolithic Decline, when European populations declined significantly. This would push the date to much earlier and might be indicative of an origin in Europe rather than Eurasia.

Fever common medical sign characterized by elevated body temperature

Fever, also known as pyrexia and febrile response, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using values between 37.5 and 38.3 °C. The increase in set point triggers increased muscle contractions and causes a feeling of cold. This results in greater heat production and efforts to conserve heat. When the set point temperature returns to normal, a person feels hot, becomes flushed, and may begin to sweat. Rarely a fever may trigger a febrile seizure. This is more common in young children. Fevers do not typically go higher than 41 to 42 °C.


Bubonic and septicemic plague is generally spread by flea bites or handling an infected animal. [1] The pneumonitic form is generally spread between people through the air via infectious droplets. [1] Diagnosis is typically by finding the bacterium in fluid from a lymph node, blood or sputum. [2]

Flea order of insects

Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that survive as external parasites of mammals and birds. Fleas live by consuming blood or hematophagy, from their hosts. Adult fleas grow to about 3 mm or .12 in long, are usually brown, and have bodies that are "flattened" sideways, or narrow, enabling them to move through their host's fur or feathers. They lack wings, but have strong claws preventing them from being dislodged; mouthparts adapted for piercing skin and sucking blood, and hind legs extremely well adapted for jumping. They are able to leap a distance of some 50 times their body length, a feat second only to jumps made by another group of insects, the superfamily of froghoppers. Fleas' larvae are worm-like with no limbs; they have chewing mouthparts and feed on organic debris left on their host's skin.

Airborne disease disease that is caused by pathogens and transmitted through the air

An airborne disease is any disease that is caused by pathogens that can be transmitted through the air. Such diseases include many of considerable importance both in human and veterinary medicine. The relevant pathogens may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, toilet flushing or any activities which generates aerosol particles or droplets. Human airborne diseases do not include conditions caused by air pollution such as Volatile Organic Compounds (VOCs), gases and any airborne particles, though their study and prevention may help inform the science of airborne disease transmission.

Sputum mucus that is coughed up from the lower airways

Sputum is mucus and is the name used for the coughed-up material (phlegm) from the lower airways. In medicine, sputum samples are usually used for naked eye exam, microbiological investigations of respiratory infections, and cytological investigations of respiratory systems. It is critical that the patient not give a specimen that includes any mucoid material from the interior of the nose. Naked eye exam of sputum can be done at home by a patient in order to note the various colors. Any hint of yellow color suggests an airway infection. Such color hints are best detected when the sputum is viewed on a very white background such as white paper, a white pot, or a white sink surface. The more intense the yellow color, the more likely it is a bacterial infection.

Those at high risk may be vaccinated. [2] Those exposed to a case of pneumonic plague may be treated with preventative medication. [2] If infected, treatment is with antibiotics and supportive care. [2] Typically antibiotics include a combination of gentamicin and a fluoroquinolone. [3] The risk of death with treatment is about 10% while without it is about 70%. [4]

Antibiotic drug used in the treatment and prevention of bacterial infections

An antibiotic is a type of antimicrobial substance active against bacteria and is the most important type of antibacterial agent for fighting bacterial infections. Antibiotic medications are widely used in the treatment and prevention of such infections. They may either kill or inhibit the growth of bacteria. A limited number of antibiotics also possess antiprotozoal activity. Antibiotics are not effective against viruses such as the common cold or influenza; drugs which inhibit viruses are termed antiviral drugs or antivirals rather than antibiotics.

Gentamicin chemical compound

Gentamicin, sold under brand name Garamycin among others, is an antibiotic used to treat several types of bacterial infections. This may include bone infections, endocarditis, pelvic inflammatory disease, meningitis, pneumonia, urinary tract infections, and sepsis among others. It is not effective for gonorrhea or chlamydia infections. It can be given intravenously, by injection into a muscle, or topically. Topical formulations may be used in burns or for infections of the outside of the eye. In the developed world, it is often only used for two days until bacterial cultures determine what specific antibiotics the infection is sensitive to. The dose required should be monitored by blood testing.

Globally about 600 cases are reported a year. [2] In 2017 the countries with the most cases include the Democratic Republic of the Congo, Madagascar and Peru. [2] In the United States infections occasionally occur in rural areas and the bacteria is believed to circulate among rodents. [5] It has historically occurred in large outbreaks, with the best known being the Black Death in the 14th century, which resulted in greater than 50 million dead. [2]

Democratic Republic of the Congo Country in Central Africa

The Democratic Republic of the Congo, also known as DR Congo, the DRC, DROC, Congo-Kinshasa, or simply the Congo, is a country located in Central Africa. It is sometimes anachronistically referred to by its former name of Zaire, which was its official name between 1971 and 1997. It is, by area, the largest country in Sub-Saharan Africa, the second-largest in all of Africa, and the 11th-largest in the world. With a population of over 78 million, the Democratic Republic of the Congo is the most populated officially Francophone country, the fourth-most-populated country in Africa, and the 16th-most-populated country in the world.

Madagascar island nation off the coast of Southeast Africa, in the Indian Ocean

Madagascar, officially the Republic of Madagascar, and previously known as the Malagasy Republic, is an island country in the Indian Ocean, approximately 400 kilometres off the coast of East Africa. The nation comprises the island of Madagascar and numerous smaller peripheral islands. Following the prehistoric breakup of the supercontinent Gondwana, Madagascar split from the Indian subcontinent around 88 million years ago, allowing native plants and animals to evolve in relative isolation. Consequently, Madagascar is a biodiversity hotspot; over 90% of its wildlife is found nowhere else on Earth. The island's diverse ecosystems and unique wildlife are threatened by the encroachment of the rapidly growing human population and other environmental threats.

Peru republic in South America

Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the west by the Pacific Ocean. Peru is a megadiverse country with habitats ranging from the arid plains of the Pacific coastal region in the west to the peaks of the Andes mountains vertically extending from the north to the southeast of the country to the tropical Amazon Basin rainforest in the east with the Amazon river.

Signs and symptoms

Bubonic plague

Swollen inguinal lymph glands on a person infected with the bubonic plague. The swollen lymph glands are termed buboes from the Greek word for groin, swollen gland: bubo. Plague -buboes.jpg
Swollen inguinal lymph glands on a person infected with the bubonic plague. The swollen lymph glands are termed buboes from the Greek word for groin, swollen gland: bubo.

When a flea bites a human and contaminates the wound with regurgitated blood, the plague carrying bacteria are passed into the tissue. Y. pestis can reproduce inside cells, so even if phagocytosed, they can still survive. Once in the body, the bacteria can enter the lymphatic system, which drains interstitial fluid. Plague bacteria secrete several toxins, one of which is known to cause beta-adrenergic blockade. [6]

Phagocytosis An endocytosis process that results in the engulfment of external particulate material by phagocytes. The particles are initially contained within phagocytic vacuoles (phagosomes), which then fuse with primary lysosomes to effect digestion of the par

In cell biology, phagocytosis is the process by which a cell – often a phagocyte or a protist – engulfs a large particle to form an internal compartment known as a phagosome. It is distinct from other forms of endocytosis, like pinocytosis, that involve the internalization of extracellular liquids. Phagocytosis is involved in the acquisition of nutrients for some cells. The process is homologous to eating at the level of single-celled organisms; in multicellular animals, the process has been adapted to eliminate debris and pathogens, as opposed to taking in fuel for cellular processes. An exception is the animal Trichoplax.

Lymphatic system a part of the defense system (immune system) of vertebrate animals against pathogens

The lymphatic system is part of the vascular system and an important part of the immune system, comprising a large network of lymphatic vessels that carry a clear fluid called lymph directionally towards the heart. The lymphatic system was first described in the seventeenth century independently by Olaus Rudbeck and Thomas Bartholin. Unlike the circulatory system, the lymphatic system is not a closed system. The human circulatory system processes an average of 20 litres of blood per day through capillary filtration, which removes plasma while leaving the blood cells. Roughly 17 litres of the filtered plasma is reabsorbed directly into the blood vessels, while the remaining three litres remain in the interstitial fluid. One of the main functions of the lymph system is to provide an accessory return route to the blood for the surplus three litres.

A toxin is a poisonous substance produced within living cells or organisms; synthetic toxicants created by artificial processes are thus excluded. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived from the word toxic.

Y. pestis spreads through the lymphatic vessels of the infected human until it reaches a lymph node, where it causes acute lymphadenitis. [7] The swollen lymph nodes form the characteristic buboes associated with the disease, [8] and autopsies of these buboes have revealed them to be mostly hemorrhagic or necrotic. [9]

Lymph node organ of the lymphatic system

A lymph node or lymph gland is an ovoid or kidney-shaped organ of the lymphatic system, and of the adaptive immune system, that is widely present throughout the body. They are linked by the lymphatic vessels as a part of the circulatory system. Lymph nodes are major sites of B and T lymphocytes, and other white blood cells. Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles and cancer cells. Lymph nodes do not have a detoxification function, which is primarily dealt with by the liver and kidneys.

Lymphadenopathy disorder of lymph nodes

Lymphadenopathy or adenopathy is disease of the lymph nodes, in which they are abnormal in size, number, or consistency. Lymphadenopathy of an inflammatory type is lymphadenitis, producing swollen or enlarged lymph nodes. In clinical practice, the distinction between lymphadenopathy and lymphadenitis is rarely made and the words are usually treated as synonymous. Inflammation of the lymphatic vessels is known as lymphangitis. Infectious lymphadenitis affecting lymph nodes in the neck is often called scrofula.

Bubo Inflammation of the lymph nodes

A bubo is defined as adenitis or inflammation of the lymph nodes and is an example of reactive lymphadenopathy.

If the lymph node is overwhelmed, the infection can pass into the bloodstream, causing secondary septicemic plague and if the lungs are seeded, it can cause secondary pneumonic plague. [10]

Septicemic plague

Septicemic plague resulting in necrosis PlagueTypes.jpg
Septicemic plague resulting in necrosis

Lymphatics ultimately drain into the bloodstream, so the plague bacteria may enter the blood and travel to almost any part of the body. In septicemic plague, bacterial endotoxins cause disseminated intravascular coagulation (DIC), causing tiny clots throughout the body and possibly ischemic necrosis (tissue death due to lack of circulation/perfusion to that tissue) from the clots. DIC results in depletion of the body's clotting resources, so that it can no longer control bleeding. Consequently, there is bleeding into the skin and other organs, which can cause red and/or black patchy rash and hemoptysis/hematemesis (coughing up/ vomiting of blood). There are bumps on the skin that look somewhat like insect bites; these are usually red, and sometimes white in the center. Untreated, septicemic plague is usually fatal. Early treatment with antibiotics reduces the mortality rate to between 4 and 15 percent. [11] [12] [13] People who die from this form of plague often die on the same day symptoms first appear.[ citation needed ]

Pneumonic plague

The pneumonic form of plague arises from infection of the lungs. It causes coughing and sneezing and thereby produces airborne droplets that contain bacterial cells and are likely to infect anyone inhaling them. The incubation period for pneumonic plague is short, usually two to four days, but sometimes just a few hours. The initial signs are indistinguishable from several other respiratory illnesses; they include headache, weakness and spitting or vomiting of blood. The course of the disease is rapid; unless diagnosed and treated soon enough, typically within a few hours, death may follow in one to six days; in untreated cases mortality is nearly 100%. [14] [15]


The Oriental rat flea (Xenopsylla cheopsis) engorged with blood after a blood meal. This species of flea is the primary vector for the transmission of Yersinia pestis, the organism responsible for bubonic plague in most plague epidemics in Asia, Africa and South America. Both male and female fleas feed on blood and can transmit the infection. Xenopsylla chepsis (oriental rat flea).jpg
The Oriental rat flea (Xenopsylla cheopsis) engorged with blood after a blood meal. This species of flea is the primary vector for the transmission of Yersinia pestis, the organism responsible for bubonic plague in most plague epidemics in Asia, Africa and South America. Both male and female fleas feed on blood and can transmit the infection.
A child bitten by a flea infected with the bacterium Yersinia pestis. Y. pestis, a member of the family Enterobacteriaceae, has caused the bite to become ulcerated. Ulceration of flea bite cause by yersinia pestis.jpg
A child bitten by a flea infected with the bacterium Yersinia pestis. Y. pestis, a member of the family Enterobacteriaceae, has caused the bite to become ulcerated.

Transmission of Y. pestis to an uninfected individual is possible by any of the following means. [16]

Yersinia pestis circulates in animal reservoirs, particularly in rodents, in the natural foci of infection found on all continents except Australia. The natural foci of plague are situated in a broad belt in the tropical and sub-tropical latitudes and the warmer parts of the temperate latitudes around the globe, between the parallels 55 degrees North and 40 degrees South. [16] Contrary to popular belief, rats did not directly start the spread of the bubonic plague. It is mainly a disease in the fleas ( Xenopsylla cheopis ) that infested the rats, making the rats themselves the first victims of the plague. Infection in a human occurs when a person is bitten by a flea that has been infected by biting a rodent that itself has been infected by the bite of a flea carrying the disease. The bacteria multiply inside the flea, sticking together to form a plug that blocks its stomach and causes it to starve. The flea then bites a host and continues to feed, even though it cannot quell its hunger, and consequently the flea vomits blood tainted with the bacteria back into the bite wound. The bubonic plague bacterium then infects a new person and the flea eventually dies from starvation. Serious outbreaks of plague are usually started by other disease outbreaks in rodents, or a rise in the rodent population. [17]


Since human plague is rare in most parts of the world, routine vaccination is not needed other than for those at particularly high risk of exposure, nor for people living in areas with enzootic plague, meaning it occurs at regular, predictable rates in populations and specific areas, such as the western United States. It is not even indicated for most travellers to countries with known recent reported cases, particularly if their travel is limited to urban areas with modern hotels. The CDC thus only recommends vaccination for: (1) all laboratory and field personnel who are working with Y. pestis organisms resistant to antimicrobials: (2) people engaged in aerosol experiments with Y. pestis; and (3) people engaged in field operations in areas with enzootic plague where preventing exposure is not possible (such as some disaster areas). [18]

A systematic review by the Cochrane Collaboration found no studies of sufficient quality to make any statement on the efficacy of the vaccine. [19]


If diagnosed in time, the various forms of plague are usually highly responsive to antibiotic therapy. The antibiotics often used are streptomycin, chloramphenicol and tetracycline. Amongst the newer generation of antibiotics, gentamicin and doxycycline have proven effective in monotherapeutic treatment of plague. [20]

The plague bacterium could develop drug-resistance and again become a major health threat. One case of a drug-resistant form of the bacterium was found in Madagascar in 1995. [21] Further outbreaks in Madagascar were reported in November 2014 [22] and October 2017 [23] .


Distribution of plague infected animals 1998 World distribution of plague 1998.PNG
Distribution of plague infected animals 1998

Globally about 600 cases are reported a year. [2] In 2017 the countries with the most cases include the Democratic Republic of the Congo, Madagascar and Peru. [2] It has historically occurred in large outbreaks, with the best known being the Black Death in the 14th century which resulted in greater than 50 million dead. [2]

Biological weapon

Plague has a long history as a biological weapon. Historical accounts from ancient China and medieval Europe detail the use of infected animal carcasses, such as cows or horses, and human carcasses, by the Xiongnu/Huns, Mongols, Turks and other groups, to contaminate enemy water supplies. Han Dynasty General Huo Qubing is recorded to have died of such a contamination while engaging in warfare against the Xiongnu. Plague victims were also reported to have been tossed by catapult into cities under siege.[ citation needed ]

In 1347, the Genoese possession of Caffa, a great trade emporium on the Crimean peninsula, came under siege by an army of Mongol warriors of the Golden Horde under the command of Janibeg. After a protracted siege during which the Mongol army was reportedly withering from the disease, they decided to use the infected corpses as a biological weapon. The corpses were catapulted over the city walls, infecting the inhabitants. This event might have led to the transfer of the plague (Black Death) via their ships into the south of Europe, possibly explaining its rapid spread. [24]

During World War II, the Japanese Army developed weaponised plague, based on the breeding and release of large numbers of fleas. During the Japanese occupation of Manchuria, Unit 731 deliberately infected Chinese, Korean and Manchurian civilians and prisoners of war with the plague bacterium. These subjects, termed "maruta" or "logs", were then studied by dissection, others by vivisection while still conscious. Members of the unit such as Shiro Ishii were exonerated from the Tokyo tribunal by Douglas MacArthur but 12 of them were prosecuted in the Khabarovsk War Crime Trials in 1949 during which some admitted having spread bubonic plague within a 36-km radius around the city of Changde. [25]

Ishii innovated bombs containing live mice and fleas, with very small explosive loads, to deliver the weaponized microbes, overcoming the problem of the explosive killing the infected animal and insect by the use of a ceramic, rather than metal, casing for the warhead. While no records survive of the actual usage of the ceramic shells, prototypes exist and are believed to have been used in experiments during WWII.[ citation needed ]

After World War II, both the United States and the Soviet Union developed means of weaponising pneumonic plague. Experiments included various delivery methods, vacuum drying, sizing the bacterium, developing strains resistant to antibiotics, combining the bacterium with other diseases (such as diphtheria), and genetic engineering. Scientists who worked in USSR bio-weapons programs have stated that the Soviet effort was formidable and that large stocks of weaponised plague bacteria were produced. Information on many of the Soviet projects is largely unavailable. Aerosolized pneumonic plague remains the most significant threat.[ citation needed ]

The plague can be easily treated with antibiotics, which some countries, such as the United States, have large supplies on hand if such an attack should occur, thus making the threat less severe. [26]

See also

Related Research Articles

Black Death Pandemic in Eurasia in the 1300s

The Black Death, also known as the Great Plague, the Black Plague, or the Plague, was one of the most devastating pandemics in human history, resulting in the deaths of an estimated 75 to 200 million people in Eurasia and peaking in Europe from 1347 to 1351. The bacterium Yersinia pestis, which results in several forms of plague, is believed to have been the cause. The Black Death was the first major European outbreak of plague, and the second plague pandemic. The plague created a number of religious, social and economic upheavals which had profound effects on the course of European history.

A human pathogen is a pathogen that causes disease in humans.

Pneumonic plague plague that results in infection located in lung, which results from direct inhalation of the bacillus and has symptom fever, has symptom chills, has symptom cough and has symptom difficulty breathing

Pneumonic plague is a severe lung infection caused by the bacterium Yersinia pestis. Symptoms include fever, headache, shortness of breath, chest pain, and cough. They typically start about three to seven days after exposure. It is one of three forms of plague, the other two being septicemic plague and bubonic plague.

Tularemia primary bacterial infectious disease that has material basis in Francisella tularensis, which is transmitted by dog tick bite (Dermacentor variabilis), transmitted by deer flies (Chrysops sp) or transmitted by contact with infected animal tissues.

Tularemia, also known as rabbit fever, is an infectious disease caused by the bacterium Francisella tularensis. Symptoms may include fever, skin ulcers, and enlarged lymph nodes. Occasionally, a form that results in pneumonia or a throat infection may occur.

Septicemic plague Human disease

Septicemic plague is one of the three main forms of plague. It is caused by Yersinia pestis, a gram-negative species of bacterium. Septicemic plague is a life-threatening infection of the blood, most commonly spread by bites from infected fleas.

Rat-bite fever is an acute, febrile human illness caused by bacteria transmitted by rodents, in most cases, which is passed from rodent to human by the rodent's urine or mucous secretions. Not to be confused with Rat fever which is usually alternative name for Leptospirosis. Alternative names for rat-bite fever include streptobacillary fever, streptobacillosis, spirillary fever, bogger, and epidemic arthritic erythema. It is a rare disease spread by infected rodents and can be caused by two specific types of bacteria. Most cases occur in Japan, but specific strains of the disease are present in the United States, Europe, Australia, and Africa. Some cases are diagnosed after patients were exposed to the urine or bodily secretions of an infected animal. These secretions can come from the mouth, nose, or eyes of the rodent. The majority of cases are due to the animal's bite. It can also be transmitted through food or water contaminated with rat feces or urine. Other animals can be infected with this disease, including weasels, gerbils, and squirrels. Household pets such as dogs or cats exposed to these animals can also carry the disease and infect humans. If a person is bitten by a rodent, it is important to quickly wash and cleanse the wound area thoroughly with antiseptic solution to reduce the risk of infection.

Yersiniosis is an infectious disease caused by a bacterium of the genus Yersinia. In the United States, most yersiniosis infections among humans are caused by Yersinia enterocolitica.

Bubonic plague Human and animal disease

Bubonic plague is one of three types of plague caused by bacterium Yersinia pestis. One to seven days after exposure to the bacteria, flu-like symptoms develop. These symptoms include fever, headaches, and vomiting. Swollen and painful lymph nodes occur in the area closest to where the bacteria entered the skin. Occasionally, the swollen lymph nodes may break open.

Human flea species of insect

The human flea – once also called the house flea – is a cosmopolitan flea species that has, in spite of the common name, a wide host spectrum. It is one of six species in the genus Pulex; the other five are all confined to the Nearctic and Neotropical regions. The species is thought to have originated in South America, where its original host may have been the guinea pig or peccary.

Theories of the Black Death are a variety of explanations that have been advanced to explain the nature and transmission of the Black Death (1347–51). A number of epidemiologists and since the 1980s have challenged the traditional view that the Black Death was caused by plague based on the type and spread of the disease. The confirmation in 2010 and 2011 that Yersinia pestis DNA was associated with a large number of plague sites has renewed focus on plague as the leading hypothesis, but has not yet led to a final resolution of all these questions.

Plague vaccine chemical compound

Plague vaccine is a vaccine used against Yersinia pestis. Killed bacteria have been used since 1890 but are less effective against pneumonic plague so that recently live vaccines of an attenuated type and recombination protein vaccines have been developed to prevent the disease.

African tick bite fever spotted fever that has material basis in Rickettsia africae, which is transmitted by ticks

African tick bite fever (ATBF) is a bacterial infection spread by the bite of a tick. Symptoms may include fever, headache, muscles pains, and a rash. At the site of the bite there is typically a red skin sore with a dark center. Onset usually occur 4–10 days after the bite. Complications are rare, however may include joint inflammation. Some people do not develop symptoms.

Cat-scratch disease Human disease

Cat-scratch disease (CSD) is an infectious disease that results from a scratch or bite of a cat. Symptoms typically include a non-painful bump or blister at the site of injury and painful and swollen lymph nodes. People may feel tired, have a headache, or a fever. Symptoms typically begin within 3-14 days following infection.

Sylvatic plague is an infectious bacterial disease caused by the bacterium Yersinia pestis that primarily affects rodents such as prairie dogs. It is the same bacterium that causes bubonic and pneumonic plague in humans. Sylvatic, or sylvan, means 'occurring in wildlife,' and refers specifically to the form of plague in rural wildlife. Urban plague refers to the form in urban wildlife.

Urban plague is an infectious disease among rodent species that live in close association with humans in urban areas. It is caused by the bacterium Yersinia pestis which is the same bacterium that causes bubonic and pneumonic plague in humans. Plague was first introduced into the United States in 1900 by rat–infested steamships that had sailed from affected areas, mostly from Asia. Urban plague spread from urban rats to rural rodent species, especially among prairie dogs in the western United States.

1924 Los Angeles pneumonic plague outbreak

The 1924 Los Angeles pneumonic plague outbreak began October 30, 1924, and was declared fully contained on November 13, 1924. It represented the first time plague had emerged in Southern California; plague outbreaks had previously arisen in San Francisco and Oakland. The Los Angeles outbreak began on October 30, lasted two weeks, and killed 30 people. Public health officials credited the lessons learned from the San Francisco outbreak coupled with swiftly implemented measures, including hospitalization of the sick and all their contacts, a neighborhood quarantine, and a large-scale rat eradication program, with saving lives.

21st century Madagascar plague outbreaks Outbreaks of plague in Madagascar during the 21st century

Madagascar has experienced two outbreaks of bubonic and pneumonic plague in the 21st century. In 2014, 40 died, and in 2017, 221 died.

Epidemiology of plague

Globally about 600 cases of plague are reported a year. In 2017 the countries with the most cases include the Democratic Republic of the Congo, Madagascar, and Peru.


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