Overview
Plague is an infectious disease caused by Yersinia pestis bacteria, usually found in small mammals and their fleas. The disease is transmitted between animals via their fleas and, as it is a zoonotic bacterium, it can also transmit from animals to humans.
Humans can be contaminated by the bite of infected fleas, through direct contact with infected materials, or by inhalation. Plague can be a very severe disease in people, particularly in its septicaemic and pneumonic forms, with a case-fatality ratio of 30% - 100% if left untreated.
Although plague has been responsible for widespread pandemics throughout history, including the so-called Black Death that caused over 50 million deaths in Europe during the fourteenth century, today it can be easily treated with antibiotics and the use of standard preventative measures.
Plague is found on all continents except Oceania but most human cases since the 1990s have occurred in Africa. Democratic Republic of Congo, Madagascar and Peru are the three most endemic countries.
Symptoms
People infected with plague usually develop influenza-like symptoms after an incubation period of 3–7 days. Symptoms include fever, chills, aches, weakness, vomiting and nausea.
There are 3 main forms of plague.
Bubonic plague is the most common and is caused by the bite of an infected flea. The plague bacillus, Y. pestis, enters at the bite and travels to the nearest lymph node to replicate. The lymph node becomes inflamed, tense and painful, and is called a bubo. With advanced infections, the inflamed lymph nodes can turn into suppurating open sores. Bubonic plague cannot be transmitted from human to human.
Septicaemic plague occurs when infection spreads through the bloodstream. It may result from flea bites or from direct contact with infective materials through cracks in the skin. Advanced stages of the bubonic form of plague will also lead to direct spread of Y. pestis in the blood.
Pneumonic plague – or lung-based plague – is the most virulent and least common form of plague. Typically, it is caused by spread to the lungs from advanced bubonic plague. However, a person with secondary pneumonic plague may form aerosolized infective droplets and transmit plague to other humans. This is usually fatal.
Treatment
Untreated plague can be rapidly fatal, so early diagnosis and treatment is essential for survival and to reduce complications. Antibiotics and supportive therapy are effective against plague if patients are diagnosed in time.
Laboratory testing is required to confirm infection. This includes identifying the causative bacteria in a sample of pus from a bubo, blood or sputum. WHO does not recommend vaccination except for high-risk people such as laboratory personnel and health care workers.
Preventive measures include informing people when zoonotic plague is present in their environment and giving advice on how they can protect themselves. They should be advised to take precautions against flea bites and not to handle animal carcasses. People, especially health workers, should also avoid direct contact with infected tissues such as buboes, or close exposure to patients with pneumonic plague.
credit/source: https://www.who.int/health-topics/plague#tab=tab_1
Plague
Cause
The plague bacillus, Yersinia pestis.
Transmission
Plague is a zoonotic disease affecting rodents and transmitted by fleas from rodents to other animals and to humans. Direct person-to-person transmission does not occur except in the case of pneumonic plague, when respiratory droplets may transfer the infection from the patient to others in close contact.
Nature of the disease
Plague occurs in three main clinical forms:
- Bubonic plague is the form that usually results from the bite of infected fleas. Lymphadenitis develops in the drainage lymph nodes, with the regional lymph nodes most commonly affected. Swelling, pain and suppuration of the lymph nodes produces the characteristic plague buboes.
- Septicaemic plague may develop from bubonic plague or occur in the absence of lymphadenitis. Dissemination of the infection in the bloodstream results in meningitis, endotoxic shock and disseminated intravascular coagulation.
- Pneumonic plague may result from secondary infection of the lungs following dissemination of plague bacilli from other body sites. It produces severe pneumonia. Direct infection of others may result from transfer of infection by respiratory droplets, causing primary pulmonary plague in the recipients.
Without prompt and effective treatment, 50–60% of cases of bubonic plague are fatal, while untreated septicaemic and pneumonic plague are invariably fatal.
Geographical distribution
There are natural foci of plague infection in rodents in many parts of the world. Wild rodent plague is present in central, eastern and southern Africa, South America, the western part of North America and in large areas of Asia. In some areas, contact between wild and domestic rats is common, resulting in sporadic cases of human plague and occasional outbreaks.
Risk for travellers
Generally low except in rural areas of countries or areas at risk, particularly if camping or hunting or if there is contact with rodents.
Prophylaxis
A vaccine effective against bubonic plague is available exclusively for individuals with a high occupational exposure to plague; it is not commercially available in most countries.
Precautions
Avoid any contact with live or dead rodents.
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