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Nasty Infectious Diseases You Want To Avoid - Plague

Updated on December 31, 2008

The scourge of early history, plague is a serious infectious disease transmitted by the bites of rat fleas. There are three major forms of the disease: bubonic, septicemic, and pneumonic, each of which can occur alone or together as the disease moves throughout the body. Plague types differ as to what part of the body the disease affects. Bubonic plague is centered in the lymphatic system, creating swelling lymph nodes, or buboes, from which it gets its name. Septicemic plague indicates that the disease has entered the bloodstream. Pneumonic plague occurs when the bacteria enters the lungs.

Plague has been responsible for three great pandemics, which caused millions of deaths around the world and significantly affected the course of history. Although the cause of the plague was not identified until the third pandemic in 1894, scientists are virtually certain that the first two pandemics were plague because a number of the survivors wrote about their experiences and described the symptoms, including the appearance of buboes.

The first great pandemic began in A.D. 542 during the reign of Emperor Justinian, and lasted for about 60 years. Plague affected parts of the Mediterranean region most heavily, and an estimated tens of millions of citizens died.

The second pandemic was nicknamed the 14th century got plague died. because its primary symptom was black patches on the skin caused by bleeding around the buboes (swollen lymph glands). This was the most severe and historically significant of the three; it began in the mid-1300s in central Asia, and some historians believe it lasted for more than 400 years. About one fourth of the entire population of Europe died vent disease. within a few years after plague was first introduced into the continent in 1347. The Middle and Far East also suffered during this time. The final pandemic (or Modem Pandemic) began in northern China, reaching Canton and Hong Kong in 1894. From here, plague quickly spread to all of the continents, spreading death among millions. The bacteria also became established during this pandemic in wild rodent flea populations in areas that previously were plague-free, including some parts of North and South America and southern Africa.

Recent outbreaks among humans have occurred in Africa, South America, and Southeast Asia. It is also found among ground squirrels, prairie dogs, and marmots in parts of Arizona, New Mexico, California, Colorado, and Nevada. Between 10 and 50 Americans each year contract plague during the spring and summer months. The last ratborne epidemic in the United States occurred in Los Angeles in 1924-25; since then, all plague cases in the United States have been sporadic, acquired from wild rodents or their fleas.

Rock squirrels and their fleas are the most frequent sources of human infection in the southwestern states. In the Pacific states, the California ground squirrel and its fleas are the most common source. Many other rodents (prairie dogs, deer mice, wood rats, chipmunks, and other squirrels) suffer plague outbreaks and can sometimes infect humans.

Each of the great pandemics eventually came to an end, probably due to a number of factors. Seasonal or weather changes can adversely affect the survival of rodent hosts and fleas, together with control measures aimed at controlling rodents and fleas, sanitation measures, and use of antibiotics to prevent disease.

Major epidemics are most likely to occur when rats live closely with humans in poverty-stricken areas with poor sanitation and also share habitat with wild rodents infected with plague bacteria. Major outbreaks of primary pneumonic plague are most likely to occur under crowded conditions.

Cause - Fleas found on rodents may carry the bacterium Yersinia pestis (formerly Bacillus pestis or Pasteurella pestis). More than 100 species of fleas have been reported to be naturally infected with plague; in the western United States, the most important source of plague is the ground squirrel flea. On a global basis, the most important is the oriental rat flea. The great pandemics of the past occurred when wild rodents spread the disease to rats in cities and then to humans when the rats died. A bite from an infected flea leads to bubonic plague; pneumonic plague is a complication of bubonic plague but is also spread via infected droplets during coughing. Since 1924, there has been no documented case of human-to-human transmission of plague from droplets in the United States. All but one of the few pneumonic cases have been associated with handling infected cats. Dogs and cats can become infected after capturing or eating infected rodents. Dogs rarely exhibit signs of illness and are not known to transmit the disease to humans. However, plague has been transmitted from infected coyotes to humans. Cats often survive severe at the point of first infection. disease, and can pass their infections to humans via direct contact or the inhalation of infectious droplets from cats with plague pneumonia. Person-to-person transmission without symptoms is very unlikely, but close contacts with pneumonic plague patients could lead to contraction of the disease through exposure to infected droplets.

Symptoms - Two to five days after infection, patients experience sudden fever, shivering, seizures, and severe headaches followed by buboes, which are smooth, oval, reddened, and very painful swellings in the armpits, groin, or neck. Pneumonic plague causes severe, overwhelming pneumonia, with shortness of breath, high fever, and blood in the phlegm. (Onset of these symptoms begins only one to three days after exposure.) If untreated, half the patients will die, and if blood poisoning occurs as an early complication, patients may die before the buboes appear. The most commonly affected sites are the lymph nodes nearest the site of first infection. As the bacteria multiply in the lymph nodes, they become swollen; as they collect fluid, they become extremely tender. If the bacteria invade the bloodstream, they can spread to other sites, including liver, kidneys, spleen, lungs, and sometimes the meninges and eyes. Occasionally, the bacteria will cause an ulcer at the point of first infection.

Diagnosis - Findings of a painful bubo, together with fever, exhaustion, and a history of possible exposure to rodents, rabbits, or fleas in the western United States, leads to a diagnosis of plague. As soon as a diagnosis is suspected, the patient should be isolated, and known. local and state health departments should be notified. Blood cultures and examination of lymph node specimens can help diagnose the disease.

Treatment - Plague can be treated successfully if it is caught early. Untreated pneumonic plague is almost always fatal, and the chances of survival are very low unless specific antibiotic treatment is started within 15 to 18 hours after symptoms appear.

Prevention - Untreated pneumonic plague patients can pass on their illness to close contacts throughout the course of the illness. All plague patients should be isolated for 48 hours after antibiotic treatment begins. Pneumonic plague patients should be completely isolated until sputum cultures are negative. Residents of areas where plague occurs in the wild animals should make sure their home is rodent-proof. Anyone working in a rodent-infested area should use insect repellent on skin and clothing; pets should be treated with insecticidal dust and kept indoors. Handling sick or dead animals (especially rodents, rabbits, and cats) should be avoided. Plague vaccines have been used since the late 19th century, but their effectiveness has not been proven. Field experience indicates that vaccination lowers the incidence and severity of disease caused by the bites of infected fleas. But the degree of protection against primary pneumonic infection is not known.


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