Plague

What is plague, how is it spread, and how is it treated?

In the mid-fourteenth century, a single infectious disease killed 25 to 30 percent of the European population and came to be known as the Black Death. Three such epidemics have been recorded, causing a death toll of 200 million (almost equal to the entire population of the United States today!). This infectious disease, the plague, has not been eradicated. The most common form of plague is bubonic, meaning the lymph glands in the groin, armpit, and neck swell (that is, form buboes). The bubonic plague bacteria, Yersinia pestis, are carried by rats, other rodents, or less commonly, domestic animals such as cats. A person could catch the plague by handling an infected animal, but more commonly, the disease is spread when a flea that has bitten an infected animal later bites a human. It is also possible to catch the plague by inhaling droplets coughed by a person who has the plague. The symptoms of bubonic plague begin two to six days after exposure. Initial signs of plague are the same as those for a dozen other diseases: fever, chills, muscle aches, nausea, exhaustion, sore throat, and headache. Antibiotics taken early in the course of the disease are quite effective. If untreated, plague ends in death 50 to 60 percent of the time. The cause of death is the overwhelming inflammatory response that leads to breathing difficulties, clotting abnormalities, shock, and organ failure.

Wild rodents continue to carry plague in rural areas of the Americas (including the western third of the U.S.), Asia, and Africa, and southeastern Europe near the Caspian Sea, but plague rarely spreads to humans from them. Urban outbreaks of plague-from rats living near humans-have been rare and relatively small over the past several decades. In fact, from 1980 to 1994, worldwide only just over 1,000 cases were reported each year on average. Usually, the disease occurs in areas of extreme poverty, not tourism.

Plague prevention really comes down to a few measures. In plague infected areas,

• Avoid the animals that carry plague (fleas, rats, rabbits, squirrels, chipmunks), especially if they are sick or dead.

• Make food and shelter inaccessible to rodents. Keep garbage covered.

• Regularly use flea powders on domestic animals.

• Use insect repellents on persons. Use insect repellent with DEET on exposed skin and repellent with permethrin on clothing.

• Use insecticides in home, recreational, and work environments when local animals or fleas have been found to be carrying plague.

• If you are at high risk of exposure, consider taking preventive antibiotics, such as doxycycline or tetracycline for adults and trimethoprim-sulfamethoxazole for children less than 10.

How effective is plague vaccine, and who should get it?

Studies have not been done to directly measure the value of plague vaccine. The low incidence of plague among vaccinated U.S. military personnel exposed to plague in Vietnam suggests that the vaccine protects against flea-borne plague.

No country currently requires plague vaccine for entry. The ACIP recommends that only persons at very high risk should consider getting plague vaccine. Specifically, this includes lab workers who routinely deal with the bacteria and field workers who have regular contact with wild rodents or their fleas in plague-infected areas.

Two doses should be given one to three months apart. The third dose is given five to six months after dose two. For persons with ongoing exposure, boosters one, two, and three are given every six months; thereafter boosters should be given every year or two.

Who should not get the vaccine?

• Persons with a history of a severe allergic or systemic reaction following a prior dose of plague vaccine or any of its components should not receive the vaccine.

• Persons with a moderate or severe acute illness should postpone vaccination.

• Children younger than 18 years old should not receive the vaccine.

• Pregnant women should avoid this vaccine. A pregnant woman should only receive the plague vaccine if it is clearly needed.

What are the vaccine risks and side effects?

Plague vaccine produces more severe side effects than most vaccines, and repeated doses of the vaccine increase the probability of the side effects. About 30 percent of vaccine recipients experience pain, swelling, and redness at the plague vaccine injection site. This begins soon after the shot and usually resolves within two days. About 20 percent experience malaise, headache, fever, and swollen lymph glands for a day or two after receiving the plague vaccine. Severe allergic reactions and other moderate to severe reactions such as severe headache, joint pain, or shaking chills occur infrequently (about 4 in 1,000) after plague vaccine.

Additional notes

Cholera vaccine and the injected typhoid vaccine often cause side effects much as plague vaccine does. Theoretically, getting these vaccines at the same time could lead to a bigger reaction. If you have time to separate these vaccinations by a week or more and still get all the vaccines you need before leaving, you may be more comfortable.