Plague - Causes, Symptoms and Treatments

Plague, also known as the Black Death. is an acute infection that occurs in several forms. Bubonic plague, the most Common. causes the characteristic swollen, and sometimes suppurating, lymph glands (buboes) that give this infection its name. Other forms include septicemic plague, a severe, rapid systemic form, and pneumonic plague, which can be primary or secondary to the other two forms. Primary pneumonic plague is an acutely fulminant, highly contagious form that causes acute prostration, respiratory distress, and death - in many cases within 2 to 3 days after onset.

Without treatment, mortality is about 60% in bubonic plague and approaches 100% in both septicemic and pneumonic plagues. With treatment, mortality is approximately 18%, largely due to the delay between onset and treatment and the patient's age and physical condition.

Bubonic plague is notorious for the historic pandemics in Europe and Asia during the Middle Ages, which in some areas killed up to two-thirds of the population. This form is rarely transmitted from person to person. However, the untreated bubonic form may progress to a secondary pneumonic form, which is transmitted by contaminated respiratory droplets (coughing) and is highly contagious. In the United States, the primary pneumonic form usually occurs after inhalation of Y. pestis in a laboratory.

Sylvatic (wild rodent) plague remains endemic in South America, the Near East, central and Southeast Asia, north central and southern Africa, Mexico, and western United States and Canada. In the United States, its incidence has been rising, a possible reflection of different bacterial strains or environmental changes that favor rodent growth in certain areas. Plague tends to occur between May and September; between October and February it usually occurs in hunters who skin wild animals. One attack confers permanent immunity.

Causes of Plague:

Plague is caused by the gram-negative, nonmotile, nonspomlating bacillus Yersinia pestis (formerly called Pasteurella pestis). It's usually transmitted to humans through the bite of a flea from an infected rodent host, such as a rat, squirrel, prairie dog, or hare. Occasionally, transmission occurs from handling infected animals or their tissues.

Signs and symptoms of Plague:

The incubation period, early symptoms, severity at onset, and clinical course vary in the three forms of plague. In bubonic plague, the incubation period is 2 to 6 days. The milder form begins with malaise, fever, and pain or tenderness in regional lymph nodes, possibly associated with swelling. Lymph node damage (usually axillary or inguinal) eventually produces painful, inflamed, and possibly suppurative buboes. The classic sign of plague is an excruciatingly painful bubo. Hemorrhagic areas may become necrotic; in the skin, such areas appear dark - hence the name"Black Death."

This infection can progress extremely rapidly: A seemingly mildly ill person with only fever and adenitis may become moribund within hours. Plague may also begin dramatically, with a sudden high fever of 103° to 106 0 F (39.5 0 to 41.1 0 C), chills, myalgia, headache, prostration, restlessness, disorientation, delirium, toxemia, and staggering gait. Occasionally, it causes abdominal pain, nausea, vomiting, and constipation, followed by diarrhea (frequently bloody), skin mottling, petechiae, and circulatory collapse.

In primary pneumonic plague, the incubation period is 2 to 3 days, followed by a typically acute onset, with high fever, chills, severe headache, tachycardia, tachypnea, dyspnea, and a productive cough (first mucoid sputum, later frothy pink or red).

Secondary pneumonic plague, thc pulmonary extension of the bubonic form, complicates about 5% of cases of untreated plague. A cough producing bloody sputum signals this complication. Both the primary and secondary forms of pneumonic plague rapidly cause severe prostration, respiratory distress and, usually, death.

Septicemic plague usually develops without overt lymph node enlargement. In this form, the patient shows toxicity, hyperpyrexia, seizures, prostration, shock, and disseminated intravascular coagulation (DIC). Septicemic plague causes widespread nonspecific tissue damage­such as peritoneal or pleural effusions, pericarditis, and meningitis - and is rapidly fatal unless promptly and correctly treated.

Diagnosis of Plague:

Because plague is rare in the United States, it's commonly overlooked until after the patient dies or multiple cases develop. Characteristic buboes and a history of exposure to rodents strongly suggest bubonic plague.

Stained smears and cultures of Y. pestis obtained from a needle aspirate of a small amount of fluid from skin lesions confirm this diagnosis.

Postmortem examination of a guinea pig inoculated with a sample of blood or purulent drainage allows isolation of the organism. Other laboratory findings include a white blood cell count of over 20,000/ul with increased polymorphonuclear leukocytes, and hemoagglutination reaction (antibody titer) studies. Diagnosis should rule out tularemia, typhus, and typhoid.

In pneumonic plague, diagnosis requires a chest X-ray to show fulminating pneumonia, and stained smear and culture of sputum to identify Y. pestis. Other bacterial pneumonias and psittacosis must be ruled out. Stained smear and blood culture containing Y. pestis are diagnostic in septicemic plague. However, cultures of Y. pestis grow slowly; so, in suspected plague (especially pneumonic and septicemic plagues), treatment should begin without waiting for laboratory confirmation. For a presumptive diagnosis of plague, a fluorescent antibody test may be ordered.

Treatment of Plague:

Antimicrobial treatment of suspected plague must begin immediately after blood specimens have been taken for culture and shouldn't be delayed for laboratory confirmation. Generally, treatment consists of large doses of streptomycin, the drug proven most effective against Y. pestis. Other effective drugs include gentamicin, doxycycline, and chloramphenicol. Penicillins are ineffective against plague.

In both septicemic and pneumonic plagues, life-saving antimicrobial treatment must begin within 18 hours of onset. Supportive management aims to control fever, shock, and seizures, and to maintain fluid balance.

After antimicrobial therapy has begun, glucocorticoids can combat life-threatening toxemia and shock; diazepam relieves restlessness; and if the patient develops DIC, treatment may include heparin.

Special considerations and Prevention tips of Plague:

Patients with plague require strict isolation, which may be discontinued 48 hours after antimicrobial therapy begins unless respiratory symptoms develop.

• Use an approved insecticide to rid the patient and his clothing of fleas. Carefully dispose of soiled dressings and linens, feces, and sputum. If the patient has pneumonic plague, wear a gown, mask, and gloves. Handle all exudates, purulent discharge, and laboratory specimens with rubber gloves. For more information, consult your infection control officer.
• Give medications and treat complications, as ordered.
• Treat buboes with hot, moist compresses. Never excise or drain them because this could spread the infection.
• When septicemic plague causes peripheral tissue necrosis, prevent further injury to necrotic tissue. Avoid using restraints or armboards, and pad the bed's side rails.
• Obtain a history of patient contacts so that they can be quarantined for 6 days of observation. Administer prophylactic tetracycline as ordered.
• Report suspected cases of plague to local public health department officials so they can identify the source of infection.

To help prevent plague, discourage contact with wild animals (especially those that are sick or dead), and support programs aimed at reducing insect and rodent populations. Recommend immunization with plague vaccine to travelers to or residents of endemic areas, even though the effect of immunization is transient.