Introduction

Plague is a zoonosis affecting rodents and transmitted by fleas from rodents to other animals and humans. Early symptoms may include lymphadenitis near the site of the flea bite, which is called bubonic plague. It often occurs in the groin, armpit or neck. Infected lymph nodes are inflamed, red and swollen, tender and may contain pus, and they are usually accompanied by a fever. All types of plague, including the cases with minor lymphadenopathy, could progress to septic plague, with infections in various parts of the body, including meninges through the blood stream. Secondary pneumonic infection can cause pneumonia, mediastinitis or pleural effusion. Secondary pneumonic plague is particularly important in the control of the outbreak because the aerosol transmission is the source of primary pneumonic plague and pharyngeal plague. Further human-to-human transmission can lead to local outbreaks or devastating pandemics. Plague, if untreated, has a fatality rate of 30 to 60%.  

Epidemiology

In Taiwan, the first case of plague was reported in 1896, and thereafter cases had been reported every year. Large epidemics occurred in 1901 and 1904, with more than 4,000 reported cases and more than 3,000 reported deaths respectively. Nevertheless, after the implementation of long-term epidemic prevention and control measures by the government, no confirmed case was reported during 1918 to 1945. However, plague re-emerged in Taiwan in 1946 and resulted in 14 cases. Consequently, the government implemented extensive control measures. Since 1948, no confirmed case has been reported in Taiwan. 

Plague Surveillance in Taiwan

1. Taiwan National Infectious Disease Statistics System-Plague
2. Fever screening at international airports and seaports.
3. Self–reporting through the toll–free 1922 hotline or local public health authority. 

Transmission

Humans contract bubonic plague mainly through the bites of infected fleas (especially Xenopsylla cheopis, Indian rat flea), or inadvertently contact with the pus when handling infected animals (especially rats and rabbits) or tissues of infected corpse. The transmission of pneumonic plague and pharyngeal plague is through aerosols. Human could be infected through inhalation with pathogenic infective materials from patient with primary pneumonic plague or pneumonia developing from bubonic plague. 

Symptoms

Fever, chills, headache, malaise, collapse, leukocytosis, and at least one of the following clinical symptoms:

(A) Local lymphadenitis (bubonic plague).

(B) Sepsis with inconspicuous lymphadenopathy (septic plague).

(C) Pneumonic plague: developed from bubonic plague or septic plague by blood circulation (secondary pneumonic plague) or aerosolized infective materials inhalation (primary pneumonic plague).

(D) Pharyngitis and cervical lymphadenitis caused by exposure to larger infective materials or ingestion of infected tissues (pharyngeal plague).  

Prevention

1. The primary ways to ward off infection are to avoid flea bites, direct contact with infectious tissues, and exposure to areas where patients with pneumonic plague resides.

2. In plague-endemic areas, inform the public the transmission of the disease. Advise them to prevent rodents from entering the houses and avoid contacting and handling carcasses. Report to the health authorities when such animal carcasses are identified.

3. Regularly investigate the rodent population, and assess the prevalence and control the outbreak.

4. Remove rodents and fleas: flea removal must be practiced before or at the same time with rodent removal. Doing so is because when rats die, the parasitic fleas are likely to jump to the new host (human) and continue to suck blood.

5. Ships from or port warehouses in the endemic area must repel and remove rodents and fleas.

6. Vaccination provides protection against the disease for several months. At-risk individuals are recommended to receive the vaccine. Laboratory personnel and disease control personnel who handle the infected animals must implement necessary protective measures to prevent infection. 

FAQs

1. What is plague?
Plague is a zoonosis caused by the bacterium, Yersinia pestis,of rodents and their fleas.

2. How is plague transmitted?
Plague can be transmitted to humans in the following ways: flea bites, contact with contaminated fluid or tissue, or inhalation of infective materials.   

3. What is the treatment for plague?
Proper antibiotics are essential. The earlier the antibiotics are used, the lower the fatality rate is.

4. What can be done to reduce the risk of contracting plague?
The primary ways to prevent infection are to avoid flea bites, direct contact with infectious tissues, and exposure to patients with pneumonic plague. In addition, receiving vaccination according to the recommendations of the health authorities is also effective at reducing the risk of infection.

More Information

1. WHO|Plague
2. USA CDC|Plague