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The Plague and Hantavirus: Forgotten but Not Gone

Karras, David J. MD

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Dr. Karras is an associate professor of emergency medicine, the associate chairman for academic affairs, and the director of research in the department of emergency medicine at Temple University School of Medicine in Philadelphia, PA.

Two cases of bubonic plague showed up recently in New York City, but hantavirus has appeared all over the U.S. The term plague conjures images of widespread, horrifyingly painful deaths with victims succumbing to high fevers, respiratory distress, and necrotic skin ulcers. These images are accurate.

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Plague, also known as the Black Death, was one of the defining events of the European Middle Ages and Renaissance. During a two-year period in the 14th century, almost half of Western Europe's population was killed by the plague, and death rates exceeding 65 percent were reported in many major cities. Some 20 million deaths were attributed to this first wave of the Black Death in Europe. Epidemics and pandemics continued to strike and devastate European cities for the next 200 years. The plague ultimately emerged in the United States, with the most recent urban, rat-borne outbreak occurring in Los Angeles in the 1920s. A large plague epidemic last struck Europe just after World War II.

It may come as a surprise that the plague continues to be reported worldwide, with up to 3,000 cases reported annually and mostly in small villages in Africa, Asia, and South America. In the U.S., there continue to be sporadic cases of plague with up to 40 cases reported annually. Most cases of plague in the U.S. are found in the desert Southwest. As we have seen with other recent infectious disease outbreaks, however, rapid human travel raises the distinct possibility of plague outbreaks far from their sites of origin.

As a case in point, two cases of plague were reported in New York City in 2002. (MMWR 2003;52:725.) The victims were a married couple who had actually acquired the infection at their rural New Mexico home. Had there not been prompt identification and isolation of the disease, it is likely that health care workers and other contacts in New York might have contracted the disease.

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Modern Plague in the U.S.

Far from being a dead disease, plague continues to be a modern threat. The specter of plague being used as a weapon of bioterrorism further underscores the need for emergency physicians to recognize the illness and institute appropriate disease control measures. Like it or not, we are the vanguard in preventing widespread disease outbreaks, and we need to be vigilant in recognizing, treating, and containing diseases such as plague.

Plague is an infection by the bacterium Yersinia pestis, carried by rodent-infecting fleas. The rodent hosts serve as silent reservoirs of infection. While the great European plague outbreaks were caused by the fleas of common rats, sporadic modern cases have been linked to the fleas of other rodents, including prairie dogs, chipmunks, and ground squirrels. Domestic cats also may serve as sources of human infection after being infected by fleas or after eating infected rodents.

Untreated bubonic plague is associated with a mortality of about 50% and is fatal within a few days

Humans are usually exposed to plague through infected flea bites, resulting in bubonic plague. Two to six days after the bite, individuations develop a bubo, an exquisitely painful, swollen, hot lymph node in the axilla, groin, or neck, depending on the site of the initial flea bite. These pathognomonic buboes are 1 cm to 10 cm in length and not fluctuant. Patients are severely ill with fever, extreme fatigue, and headache. Untreated, plague septicemia ensues, characterized by shock, abdominal pain, and disseminated intravascular coagulation with diffuse hemorrhage. The bacterium may spread to the lungs, causing plague pneumonia and be transmitted further through infected respiratory droplets. The term Black Death refers to the purpuric skin lesions that may become necrotic and result in local gangrene. Untreated bubonic plague is associated with a mortality of about 50 percent, and is fatal within a few days.

As opposed to bubonic plague, pneumonic plague refers to infection acquired through inspiration of infected respiratory droplets. One to three days after exposure, infected individuals develop a fever, chills, and cough with bloody sputum. Patients with pneumonic plague have even faster disease progression and greater mortality.

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While other diseases clearly can present with swollen glands and fever, bubonic plague is uniquely associated with rapid onset of fever, toxic appearance, and the presence of painful, focal lymphadenitis without evidence of a skin lesion or ascending lymphangitis. Pneumonic plague, on the other hand, has no pathognomonic features, and suspicion often requires a history of exposure to another infected individual or large mammal.

All patients suspected of having plague should be placed in respiratory isolation, although there is probably little risk of transmission if the patient has no cough or other signs of respiratory infection. Public health officials should be emergently notified. Blood cultures and aspirates of buboes should be obtained and antibiotics initiated as soon as possible. The treatment of choice remains streptomycin, with tetracycline or chloramphenicol as alternatives.

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Hantavirus Lurking

Like plague, hantavirus lurks within rodents of the desert Southwest, sporadically causing human disease and intermittently making unexpected appearances far from its endemic region. Hantavirus pulmonary syndrome (HPS) first appeared in 1993 in the Four Corners region of New Mexico, Arizona, Colorado, and Utah. The initial outbreak involved 24 people and carried a 50 percent mortality. (New Engl J Med 1994;330:949.) The causative agent was quickly identified as a virus not previously known to cause human disease in the western hemisphere, termed Sin Nombre virus (SNV), or “virus without a name.”

Hantavirus continues to pose a highly fatal threat, with 384 proven cases over the past 12 years and a 36 percent overall mortality. It is no longer restricted to the desert Southwest. (Figure 1.) Furthermore, the disease has the potential to be transmitted from patients to physicians and from infected physicians to their own families. Emergency physicians across the U.S. need to be cognizant of the presentation of hantavirus.

The reservoir of hantavirus is the deer mouse, which even though healthy may continually excrete SNV in its urine, feces, and saliva and contaminate everything it contacts. Inspiration of aerosolized fomites, contact with contaminated objects, or consumption of contaminated food may result in transmission of hantavirus to humans. Humans are at particular risk of infection when opening or cleaning cabins and outbuildings that have been closed for the winter, particularly if mice have set up housekeeping.

HPS begins with a nonspecific prodrome lasting three to five days with fever, headache, malaise, and diarrhea. There are no pathognomonic signs of the disease at this time. After about a week of illness, patients suddenly develop profound increases in pulmonary vascular permeability, resulting in pulmonary edema and shock. Patients present with dyspnea, cough, tachypnea, and hypotension. Mechanical ventilation is usually required. Chest x-rays show interstitial infiltrates progressing to bilateral alveolar infiltrates and pleural effusions.

HPS can be difficult to diagnose. The telltale clues are unexplained pulmonary edema in a previously healthy individual with no apparent cause of adult respiratory distress syndrome. The presence of thrombocytopenia raises further the suspicion of HPS. Other infections with similar presentations in normal individuals include leptospirosis, Legionnaire's disease, mycoplasma, Q fever, and Chlamydia pneumonia, although the sudden cardiovascular collapse is far more abrupt, severe, and refractory with HPS.

Definitive diagnosis is not possible in the ED, and requires specific testing by the Centers for Disease Control and Prevention. South American hantavirus infections have been shown to be transmittable to health care workers, and respiratory and contact isolation is indicated for all suspected cases. There is no specific treatment or cure for HPS, and the only therapy is supportive. Antivirals and antibiotics are ineffective.

© 2005 by Lippincott Williams & Wilkins

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