Plague is a natural disease of epidemic origin and is a virulent infectious disease characterized by rapid onset, rapid spread, high death rate and strong contagiousness, and is a Class A infectious disease under the Prevention and Control of Infectious Diseases Law of the People’s Republic of China. It has caused three pandemics in the world, and the number of deaths is countless. The plague has been found to have originated in 201 counties (cities) in 17 provinces and autonomous regions, covering an area of more than 600,000 square kilometers. In a world where plague is active, 106 cases of human plague were found in five provinces, including Qinghai, Xinjiang, Tibet, Yunnan, and Inner Mongolia from 1991 to 1994, with a death rate of 24.5%.
I. Caused diseases and transmission
The pathogenic bacterium of plague is Yersinia pestis, which belongs to the family Enterobacteriaceae and the genus Yersinia. The bacterium spreads through its end host rodents to intermediate host fleas, and then spreads the pathogen to humans or animals through flea bites and contact with humans or susceptible animals.
The main hosts and vectors of plague are rodents and fleas, and fleas are the main vectors of plague.
However, in recent years, the emergence of new animals and vectors infected with plague bacteria, and even new pathogens, has been reported. The emergence of new host animals, the sources of plague infection (storage hosts) are wild rats, gophers, foxes, wolves, cats, leopards, etc., of which the genera weasel and dry otter are the most important. The number of infected animals found in China has increased from 57 species in 1990 to 87 species in 2006, especially the probability of infecting and spreading plague in animals such as herding dogs, domestic cats, horse deer, yaks and rabbits which have close contact with people has increased.
Second, there are three common types of diseases caused
Glandular plague, septicemic plague and pneumonic plague.
1.Glandular plague: The pathogenic bacteria inserted through the bite contact route will first invade the lymph nodes, resulting in swelling, necrosis and abscesses, mostly in the inguinal lymph nodes, a process called glandular plague.
2, septicemic plague: the pathogenic bacteria invade the blood stream due to massive multiplication, the formation of bacteremia, sepsis, this process is called septicemic plague. There can be high fever (39-40 ℃), small bleeding spots on the skin mucosa, if not rescued in time can die in 2-3 days.
3, pneumonic plague: pathogenic bacteria accumulate in the lungs through the bloodstream and cause pneumonia after multiplying in alveolar macrophages, a process called pneumonic plague. Pneumonic plague is secondary to glandular plague and septicemic plague, and the patient develops high fever and coughs up sputum with a large number of Yersinia pneumoniae in the sputum. A patient or animal with pneumonic plague can spread the pathogenic bacteria through proximal airborne droplet transmission, leading to an epidemic of plague. Most of the sensitive animals and people infected with Yersinia pestis die within a week after infection.
III. Bioterrorism
Bioterrorism refers to the use of biological warfare agents as weapons of terrorist attack to cause outbreaks and epidemics of virulent infectious diseases, resulting in the disabling and death of populations and causing social unrest.
Yersinia pestis is one of the priority pathogens that may pose a threat to national and public safety. The World Health Organization and the U.S. military have been using Yersinia pestis as a biological weapon for prevention and control.
In March 2005 at the first International Criminal Police Organization (Interpol) International Conference against Bioterrorism, Interpol has made it clear that bioterrorism has become one of the greatest global security threats, and once the wrongdoers use Yersinia pestis to make biological warfare agents, this will pose a great threat to human life and health and the stability of society.
IV. Pathogenetic examination
Yersinia pestis is extremely infectious. Specimens should be handled in strict compliance with the biosafety operation procedures, in a Class III biosafety laboratory, and with strict personal protection.
1, smear: typical form of gram-negative short thick rod, the two ends of the bacterium is bluntly rounded and densely stained, also easy to be colored by aniline dye. No flagellum, can be distinguished from other bacteria in this genus. Does not form bacilli. In the smear or print prepared from fresh animal viscera that died of plague, phagocytosis can be seen inside and outside the typical morphology of the bacterium, and there is a pod membrane.
2, culture characteristics: parthenogenic anaerobic. Optimal growth temperature 27 ℃ ~ 30 ℃, in the ordinary medium can grow, but the growth is slow, in the nutrient medium containing blood or tissue fluid, after 24 hours ~ 48 hours to form visible colonies. Toxic strains form gray-white, mucoid colonies. In the broth medium precipitation growth and formation of bacterial film, the liquid is generally not cloudy, slightly shaken, bacterial film sinking stalactite, this feature has some significance in the identification.
Combined with the clinical symptoms, once the initial judgment or confirmation of plague is made, the clinician should be notified immediately and reported to CDC.
V. Prevention and control measures
Yersinia pestis can be transmitted among animals, between animals and people, and between people and people, among which the most important is the transmission between animals. Therefore, controlling the transmission between animals is the key to prevention.
People in the infected area should be well protected, injected with attenuated vaccine, idea personal hygiene, and prevent flea bites.
Patients should be strictly isolated, and each type of plague should be isolated separately. Pneumonic plague patients should be kept in one room for one person, and the room should be free of rats and fleas. Health care workers entering the ward where plague patients are admitted should be well protected. They are required to wear protective clothing, hats, N95 masks and gloves, eye protection, isolation clothes and rubber boots when entering the isolation room. Do good hand hygiene. Wear full-scale respiratory protection when performing close operations on patients.
Disinfect the ward environment with chlorine disinfectant or peracetic acid, and disinfect patient excreta thoroughly.
VI. Treatment
Plague should be forcibly treated with antibacterial drugs, and the mortality rate of untreated patients reaches more than 50%.
Currently, gentamicin and streptomycin are preferred for clinical treatment. Post-exposure prophylaxis is generally chosen from doxycycline. Depending on the site of infection, specimens such as lymph node puncture fluid, blood and sputum are collected and sent for examination. Since plague is a virulent infectious disease, once the initial judgment or diagnosis is made, the clinic should be notified immediately, the patient should be isolated and treated, and the source of infection should be identified as soon as possible in cooperation with the Center for Disease Control, and if necessary, the infected area should be sealed off to prevent the spread of the disease.
It is important to note that streptomycin-resistant and multi-drug-resistant strains have emerged abroad. The emergence of multi-drug resistance in plague will pose a major threat to the treatment of plague and is a serious public health problem.