Plague is a serious, infectious disease usually transmitted by the bites of rodent fleas. It was the scourge of our early history. There are three major forms of the disease: bubonic, septicemic, and pneumonic. Plague has been responsible for three great world pandemics, which caused millions of deaths andsignificantly altered the course of history. A pandemic is a disease that occurs throughout the entire population of a country, a people, or the world. Although the cause of the plague was not identified until the third pandemic in1894, 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.

The first great pandemic appeared in 542 A.D. and lasted for 60 years. It killed millions of citizens, particularly along the MediterraneanSea. This sea was the busiest, coastal trade route at that time and connected what is now southern Europe, northern Africa, and parts of coastal Asia.

The second pandemic occurred during the 14th century, and was called "the black death" because its main symptom was the appearance of black patches on theskin. It was also a subject found in many European paintings, drawings, plays, and writings of that time. The connections between large, active trading ports, rats coming off the ships, and the severe outbreaks of the plague was known by the people. This was the most severe of the three, beginning in the mid 1300s with an origin in central Asia and lasting for 400 years. About a fourth of the entire European population died within a few years after plague was first introduced.

The final pandemic began in northern China, reaching Canton and Hong Kong by1894. From here, it spread to all continents, killing millions.

The great pandemics of the past occurred when wild rodents spread the diseaseto rats in cities, and then to humans when the rats died. Another route forinfection came from rats coming off ships that had traveled from heavily infected areas. Generally, these were busy, coastal or inland trade routes.

Curiously, between 10 and 50 Americans living in the southwestern United States contract plague each year during the spring and summer. The last rat-borneepidemic in the United States occurred in Los Angeles in 1924-25. Since then, all plague cases in this country have been sporadic, acquired from wild rodents or their fleas. Plague can also be acquired from ground squirrels and prairie dogs in parts of Arizona, New Mexico, California, Colorado, and Nevada.Around the world, there are between 1,000 and 2,000 cases of plague each year. Recent outbreaks in humans occurred in Africa, South America, and southeast Asia.

Some people and/or animals with bubonic plague go on to develop pneumonia (pneumonic plague). This can spread to others via infected droplets during coughing or sneezing.

Plague is one of three diseases still subject to international health regulations. These rules require that all confirmed cases be reported to the World Health Organization (WHO) within 24 hours of diagnosis. According to the 1998regulations, passengers on an international voyage who have been to an area where there is an epidemic of pneumonic plague must be placed in isolation forsix days before being allowed to leave.

Fleas carry the bacterium Yersinia pestis. When a flea bites an infected rodent, it swallows the plague bacteria. The bacteria is passed on when the fleas, in turn, bite a human. Humans also may become infected if they havea break or cut in the skin and come in direct contact with body fluids or tissues of infected animals.

More than 100 species of fleas have been reported to be naturally infected with plague; in the western United States, the most common source of plague isthe ground squirrel flea.

Since 1924 there have been no documented cases in the United States of human-to-human spread of plague from droplets. All but one of the few pneumonic cases have been associated with handling infected cats. While dogs and cats canbecome infected, dogs rarely show signs of illness and are not believed to spread disease to humans. However, plague has been spread from infected coyotes(wild dogs) to humans.

Two to five days after infection, patients experience a sudden fever, chills,seizures, and severe headaches, followed by the appearance of swelling or "buboes" in armpits, groin, and neck. The most commonly affected sites are thelymph glands near the site of the first infection. As the bacteria multiply in the glands, the lymph node becomes swollen. As the nodes collect fluid, they become extremely tender. Occasionally, the bacteria will cause an ulcer atthe point of the first infection.

Bacteria that invade the bloodstream directly (without involving the lymph nodes) causes septicemic plague. (Bubonic plague also can progress to septicemic plague if not treated appropriately.) Septicemic plague that does not involve the lymph glands is particularly dangerous because it can be hard to diagnose the disease. The bacteria usually spread to other sites, including the liver, kidneys, spleen, lungs, and sometimes the eyes, or the lining of the brain. Symptoms include fever, chills, prostration, abdominal pain, shock, and bleeding into the skin and organs.

Pneumonic plague may occur as a direct infection (primary) or as a result ofuntreated bubonic or septicemic plague (secondary). Primary pneumonic plagueis caused by inhaling infective drops from another person or animal with pneumonic plague. Symptoms, which appear within one to three days after infection, include a severe, overwhelming pneumonia, with shortness of breath, high fever, and blood in the phlegm. If untreated, half the patients will die; if blood poisoning occurs as an early complication, patients may die even before the buboes appear.

Life-threatening complications of plague include shock, high fever, problemswith blood clotting, and convulsions.

Plague should be suspected if there are painful buboes (inflamed lymph nodes), fever, exhaustion, and a history of possible exposure to rodents, rabbits,or fleas in the western states. The patient should be isolated. Chest x-rays are taken, as well as blood cultures, antigen testing, and examinationof lymph node specimens. Blood cultures should be taken 30 minutes apart, before treatment.

As soon as plague is suspected, the patient should be isolated, and local andstate departments notified. Drug treatment reduces the risk of death to lessthan 5%. The preferred treatment is with antibiotics such as streptomycin administered as soon as possible. Alternatives include gentamicin, chloramphenicol, tetracycline, or trimethoprim/sulfamethoxazole.

Plague can be treated successfully if it is caught early. Untreated pneumonicplague is almost always fatal, however, and the chances of survival are verylow unless specific antibiotic treatment is started within 15-18 hours aftersymptoms appear. The presence of plague bacteria in a blood smear is a gravesign, and indicates septicemic plague.

Plague vaccines have been used with varying effectiveness since the late 19thcentury. Experts believe that vaccination lowers the chance of infection andthe severity of the disease. However, the effectiveness of the vaccine against pneumonic plague is not clearly known.

Vaccinations against plague are not required to enter any country. Because immunization requires multiple doses over a 6-10 month period, plague vaccine is not recommended for quick protection during outbreaks. Moreover, its unpleasant side effects make it a poor choice unless there is a substantial long-term risk of infection. The safety of the vaccine for those under age 18 has not been established. Pregnant women should not be vaccinated unless the need for protection is greater than the risk to the unborn child. Even those who receive the vaccine may not be completely protected. This is why it is important to protect against rodents, fleas, and people with plague.

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