What Causes the Plague?
The bacterium (Yersinia pestis) that cause plague can be transmitted from a host such as a rat to a human through the bite of an animal or insect (such as a flea). These bites transport the zoonotic disease. The animal or insect that spreads the disease is referred to as a vector. More than 200 different rodents and other species can serve as hosts. Hosts can include domestic cats and dogs, squirrels, chipmunks, marmots, deer mice, rabbits, hares, rock squirrels, camels, sheep, and other animals.
The vector is usually the rat flea. Thirty different flea species have been identified as vectors of the plague. Other vectors of plague include ticks and human lice. Transmission can also occur when someone inhales plague-infected organisms that have been released into the air. Plague can be aerosolized, as in acts of terrorism, causing the inhalation (pneumonic) form of the disease. People infected with pneumonic plague can also transmit airborne plague through coughed droplets of their own respiratory fluid. Close contact with plague-infected tissue or fluid can also transmit plague-causing bacteria to humans.
- Types of plague:
- Bubonic plague: The bacteria that cause plague can thrive and grow in the flea's esophagus. This crowding of bacterial growth prevents food from entering the flea's stomach. To overcome starvation, the flea begins a blood-sucking rampage. Struggling to swallow, the flea vomits the plague-causing bacteria into the victim's skin during a bite. The germs invade nearby lymph glands in the bitten animal and produce an inflamed lymph node called a bubo. The plague spreads along the lymph system to every organ. In rare cases, plague spreads to the covering of the brain. Severe illness follows. Bubonic plague has a 13% death rate in treated cases and a 50%-60% death rate if left untreated. Bubonic plague is the most common form of plague.
- Pneumonic plague: Direct inhalation of the plague-causing germs results in pneumonic plague. Severe illness follows. The death rate for the pneumonic form of plague is 100% if not treated within the first 24 hours of infection. Plague bacteria may be released into the air as a weapon of biological warfare or terrorism causing this type of the disease, or plague may be transmitted person to person through the inhalation of droplets coughed from the lungs of a person with pneumonic plague. Transmission through direct contact is rare.
- Septicemic plague: This form of serious disease may occur quickly and causes severe blood infection throughout the body (primary). It is difficult to diagnose early because there are no buboes or lung abnormalities. This type of plague can also develop from one of the other types of plague (secondary). Septicemic plague has a 40% death rate in treated cases and about 100% in untreated cases.
- Risk factors: The following conditions may increase the likelihood of a person contracting a plague infection.
- Living in a rural area, especially in areas where plague is common
- Having contact with sick animals, dead animals, small rodents, or other possible hosts
- Participating in wilderness activities (such as camping, hiking, sleeping on the ground, hunting)
- Exposure to flea bites
- Exposure to naturally occurring plague in the community
- Employment as a veterinarian
- Outdoor activity during the summer months
- Travel: Anyone who has traveled recently in the southwestern and Pacific Coast regions of the U.S., particularly in New Mexico, Arizona, California, and Utah, might have had a flea bite. Although contracting plague while visiting another country is rare, doctors may suspect that a flea might have bitten a patient with plague-like symptoms who has recently traveled abroad to areas where plague is present.
- Animal contact: Close contact with infected animals and travel through rural areas are risk factors for contracting plague. Historically, rats have been the principal hosts of the plague. Currently in the U.S., ground and rock squirrels are the most common hosts. In recent years, the domestic cat has emerged as a prominent host of fleas that transmit the plague to veterinarians.
What Are the Symptoms and Signs of the Plague?
- Common general symptoms
- Bubo: This is an enlarged, tender, swollen lymph gland most commonly found in the groin, under the arms, or on the neck, depending on the locations of the flea bite.
- Skin: Bleeding into the tissues can turn tissue black. The medieval name black death is thought to have originated from the deeply darkened skin, bleeding, vomiting blood, and tissue death associated with septicemic and pneumonic plague. The initially rose-colored lesions most likely inspired the child's nursery rhyme "Ring Around the Rosy."
- "Ring around the rosy" -- rose-colored areas of skin
- "Pocket full of posies" -- sweet-smelling flowers that those tending the sick would carry to ward off the stench of disease
- "Ashes, ashes" -- impending death (or "A-choo, a-choo" -- The sneezing and coughing of those with pneumonic plague)
- "All fall down" -- death
How Do Health Care Professionals Diagnose Plague?
In making the diagnosis, a doctor performs certain blood tests such as cultures (growing the bacteria in the lab from samples of blood, sputum, and fluid from the bubo). Cultures require more than 48 hours to produce definitive results.
- A doctor may order an X-ray film of the chest, especially to see if plague has infected the lungs.
- If plague infection is discovered or suspected, an infectious disease specialist should be contacted for assistance.
- The Center for Disease Control and Prevention (CDC) may test samples with more sophisticated procedures. Typically, the CDC and the local Department of Health officials attempt to identify the source of the plague and begin procedures for preventing a potential plague epidemic.
What Is the Treatment for Plague?
If doctors suspect a patient may have plague, healthcare professionals will take precautions when dealing with the patient and will wear goggles, gloves, gowns, and masks.
- Patients are isolated and precautions taken not to infect others. Some patients may need help breathing and are given oxygen. They are kept away from others for two to three days after antibiotic treatment has started or until the infection is cleared.
- Most patients experience some degree of septic shock (low blood pressure), and specialists monitor this closely in an intensive care unit.
- Medical management of plague can involve a number of medications. Antibiotics must be given early in the infection to maximize the chance of the antibiotics killing Y. pestis bacteria. These antibiotics might include streptomycin sulfate in combination with tetracycline and other antibiotics.
- Well or asymptomatic contacts of people with the plague are followed up closely and may be given prophylactic antibiotics as a precaution against disease development.
What Is the Prognosis for the Plague?
Patients with plague may develop meningitis (infection and swelling of the brain), septic shock (dangerously low blood pressure with decreased function of the kidneys, brain, or other organs due to a serious system-wide blood infection), tissue death and bleeding, and swelling around the heart. All may lead to death.
- The death rate is about 13% for those treated for bubonic plague.
- A person with primary or secondary septicemic plague (infection in the bloodstream with associated shock symptoms) has an approximate 40% death rate, even when treated.
- Pneumonic plague has about a 100% death rate if not treated within the first 24 hours.
How Can I Prevent the Plague?
A previously used plague vaccine is no longer manufactured and not commercially available. It was only effective against the bubonic form of the illness. A small amount of vaccine is obtainable from the U.S. government under special conditions (for example, plague bacteria researchers).
- In general, to prevent contracting plague, people should avoid contact with wild animals. Controlling rat and flea populations where plague is found is also important.
- Avoid travel to areas where there is an outbreak of plague.
- Anyone who has had contact with a plague-infected patient (including hospital and rescue personnel) should be watched carefully for symptoms. At the first sign of illness (such as fever or swollen glands), doctors will begin antibiotic treatment.
- Pets and people who have come into contact with a plague-infected person may be given antibiotics under some circumstances as a preventive measure.