Morphology, arrangement, and gram stain of the bacterium
Bubonic plague is a natural focal quarantine infection, which is characterized by high fever, severe intoxication, immunosuppression, possible damage to internal organs, and generalization of the condition. The causative agent of this disease is the bacterium Yersinia pestis (Demeure et al., 2019). Sources and reservoirs of infection include infected people, rats, rabbits, foxes, camels, domestic cats, etc. The carrier is a flea in whose digestive tract Y. pestis multiplies. Insects become infected 3-5 days after infection and remain so for up to a year (Barbieri, 2021). After a flea bite, the contents of the stomach, burdened with bacteria, float to the wound’s surface. The plague bacillus is characterized by a morphologically isolated nucleus, as well as a lack of mobility, and the bacterium is stained bipolar (Demeure et al., 2019). The ways of airborne, fecal-oral, and contact-household transmission are also explained.
Symptoms, diagnosis, and treatment of the disease
Symptoms of bubonic plague include weakness, headache, sleep disorders, anxiety, movement inconsistency, sometimes delusion, and hallucinations. The disease is also characterized by damage to the gastrointestinal tract, that is, vomiting, diarrhea, and abdominal pain (Barbieri, 2021). In addition to the general symptoms, people have small red spots. They are localized, where there were bites of small animals or insects. Gradually, the speck becomes larger, filled with pus and blood (Demeure et al., 2019). A pimple is formed, which bursts after a particular time. The patient has specific symptoms characteristic of a more complex form of the disease, such as enlarged regional lymph nodes, inflammatory processes in tissues, and clusters of inflamed lymph nodes – buboes.
Diagnosis of the bubonic plague does not present any particular difficulties, whereas the clinical diagnosis of the primary pulmonary form is doubtful, and primary septic is practically impossible. Bacterioscopic, bacteriological, biological, serological, and molecular research methods are used (Demeure et al., 2019). The material for the study can be any environment of the body, such as blood, bubonic punctate, sputum, ulcers, urine, and vesicle contents. During the bacteriological examination, pure culture is isolated and identified. For this purpose, the studied material is sown on nutrient media. The obtained physical data of the lungs are feeble, and signs of lobular or focal pneumonia are visible on the X-ray (Demeure et al., 2019). Cardiovascular insufficiency increases, expressed by tachycardia, and a gradual decrease in blood pressure and cyanosis develops.
All forms of plague are treatable if detected early enough. The plague microbe is sensitive to many sulfonamide drugs and antibiotics but shows resistance to penicillin (Barbieri, 2021). The patient’s treatment consists of two main directions. The first is etiotropic therapy, which is carried out using antibiotics including aminoglycosides, tetracyclines (Barbieri, 2021). The doses of antibiotics depend on the form of the disease. Another direction is pathogenetic therapy, which in plague is reduced to detoxification and correction of metabolic disorders, which is observed with the development of infectious and toxic shock. Additionally, symptomatic treatment with analgesics and antispasmodics are carried out, and vitamin therapy is prescribed.
Incubation period, duration of illness, and convalescence period
The incubation period is usually 2-5 days but varies from a few hours to 12 days (Demeure et al., 2019). The duration varies, and in some people, it can be cured entirely, while in others, a fatal outcome can occur 18-24 hours after infection (Barbieri, 2021). In many cases, recovery can happen in 2-4 days with timely treatment.
Chemotherapeutic agents (drugs) used for treatment
With the beginning of the use of antibiotics, the prognosis of the disease has become more favorable, although there are no reliable treatments. Streptomycin is most effective in all forms of plague and has fewer side effects compared to other antibiotics. The dose depends on the form of the disease, the severity of the course and the time of initiation of treatment. Streptomycin in the treatment of bubonic plague is administered in doses of 0.5-1.0 g 3 times a day (World Health Organisation, 2022).
Vaccines available?
There is no bubonic plague vaccine in the USA, while in other countries these vaccines can only be provided for those people who have a risk of contracting bubonic plague at work.
How is the bacterium transmitted?
The causative agent of this disease is the bacterium Yersinia pestis. Sources of infection include infected people, rats, rabbits, foxes, domestic cats, etc. The carrier is a flea in whose digestive tract the bacterium multiplies. Insects become infected 3-5 days after infection and remain so for up to a year (World Health Organisation, 2022). After a flea bite, the contents of the stomach, burdened with bacteria, float to the wound’s surface. The main risk factors for bubonic plague infection include living in endemic areas, military service, rat control classes, barn work, and veterinary work.
How can the bacterium/illness be avoided?
Prevention consists primarily in informing the population about the foci of the spread of plague among animals. In this case, it is recommended to beware of flea bites and not to touch the corpses of animals. People should also avoid direct contact with infected tissues and patients suffering from the plague (Demeure et al., 2019). Preventive measures also involve the prevention of the importation of infection from other countries and the occurrence of the disease in areas that are not affected by the plague. If the spread of infection is detected within a particular region, anti-plague institutions carry out deratization and disinfections measures. In the case of detection of patients with the bubonic form of plague in focus, restrictive measures are introduced; when detecting patients with the pulmonary form, quarantine is introduced.
Any additional distinguishing/notable features of the bacterium and/or disease
In the past, the plague caused large-scale pandemics accompanied by high mortality. In the XIV century, one of the forms of the epidemic, known as the Black Death, claimed the lives of 50 million people, resulting in the death of a quarter of the population of Europe (Bramanti et al., 2019). The disease is caused by the plague bacillus Yersinia pestis — a type of gram-negative spore-forming bacteria, facultative anaerobes. Plague pathogens secrete exotoxins and endotoxins, which are contained in the bodies and capsules of bacteria. Bacterial aggression enzymes facilitate their penetration into the body. The wand can penetrate even through intact skin. In the ground, the plague bacillus does not lose its viability for up to several months. It survives up to one month in the corpses of animals and rodents.
Bacteria are resistant to low temperatures and freezing. The causative agents of the plague are sensitive to high temperatures, the acidic reaction of the environment, and sunlight, which kill them only in 2-3 hours (Demeure et al., 2019). The ability of the plague bacillus to form a capsule and anti-phagocytic mucus does not allow macrophages and leukocytes to fight it actively. As a result, the pathogen multiplies rapidly in the organs and tissues of humans and animals. The causative agents of the plague, through the damaged skin and further along the lymphatic pathways, penetrate the lymph nodes, which become inflamed and form conglomerates (Demeure et al., 2019). The penetration of the pathogen into the bloodstream and its massive reproduction leads to the development of bacterial sepsis.
References
Barbieri, R. (2021). Origin, transmission, and evolution of plague over 400 y in Europe.PNAS, 118(39), 1-3.
Bramanti, B., Dean, K., Walløe, L., & Stenseth, N. (2019). The third plague pandemic in Europe. Proceedings of the Royal Society, 286(1901), 1-8.
Demeure, C.E., Dussurget, O., Mas Fiol, G., Le Guern, A., Savin, C., & Pizarro-Cerdá, J. (2019). Yersinia pestis and plague: An updated view on evolution, virulence determinants, immune subversion, vaccination, and diagnostics. Genes Immunity, 20(1), 357–370.
World Health Organisation. (2022). Plague.