Yersinia pestis pneumonia

　　1. Etiology

　　Yersinia pestis belongs to the genus Yersinia of the family Enterobacteriaceae, a bipolar Gram-negative small rod-shaped bacterium without flagella, spores, and with a capsule. Facultative anaerobic. It grows well on blood agar or MacConkey medium, producing typical rough colonies. The bacterium has various antigens, among which F, T, and V are related to pathogenicity and immunogenicity. Yersinia pestis in China can be divided into 5 groups (A-E) with 17 ecotypes. The bacterium has weak resistance, especially sensitive to heat and dryness, and can be killed by sunlight, roasting, and commonly used disinfectants. It can survive at low temperatures for 10-20 days in pus, for a month in fleas, and for several weeks to several months in cadavers.

　　2. Pathogenesis

　　After bacteria enter the body, they can rapidly reproduce while producing a polysaccharide capsule, which can resist phagocytosis and杀菌 by non-allergenic phagocytes. Pathogenic factors also include endotoxins and other antigens. After entering the body, the bacteria first reproduce locally in the regional lymph nodes or at the site of skin bitten by fleas, causing hemorrhagic necrotic lymphadenitis, followed by sepsis. Secondary pneumonia is caused by bacterial involvement in the lungs due to sepsis, hence it occurs in the well-vascularized lung base. Bacteria can cause primary pneumonia through inhalation via the respiratory tract.

　　1. Pleural effusion:The pleural cavity is a potential space between the visceral and parietal pleurae. Normally, the pleural cavity contains a small amount of lubricating fluid, whose production and absorption are often in dynamic balance. When suffering from plague Yersinia pneumonia, the accumulation of fluid increases, leading to pleural effusion, which is exudative in nature.

　　2. Sepsis, septic shock:Manifested as fever, chills, tachycardia, changes in consciousness, and increased white blood cells.

　　3. Severe cases can lead to respiratory failure:It causes severe impairment of lung ventilation and (or) gas exchange function, resulting in inability to perform effective gas exchange, leading to hypoxia with (or without) carbon dioxide retention, thereby causing a series of physiological and metabolic disorders.

　　Secondary pneumonia depends on the mode of transmission, usually appears after adenoid plague without obvious skin lesions. Respiratory system involvement generally occurs 3 to 7 days after fever, manifested as cough, shortness of breath, cyanosis, hemoptysis, chest pain, and a few wet rales at the base of the lung. It may also be complicated by pleural effusion. Primary aspiration pneumonia occurs after contact with plague pneumonia patients, and respiratory symptoms such as shortness of breath, cyanosis, emaciation, and coughing up frothy sputum appear quickly, followed by hemoptysis. It may also cause obvious toxic blood symptoms and mental symptoms, with death cases presenting with severe cyanosis, hence the name 'Black Death'.

　　Preventive measures include burying dead animals, spraying against fleas in the plague area, and reminding people not to enter the infected area. Confirmed patients should report to the health and epidemic prevention agency immediately as an 'emergency epidemic'. Suspected patients should be isolated immediately, and any person who has come into contact with the patient, especially those who have had face-to-face contact with patients with this disease accompanied by coughing, should be given prophylactic treatment, which is tetracycline taken orally, 2g per day, for 5 to 10 days. Isolation of the patient should continue until the sputum bacterial culture is negative. For staff who often come into contact with this bacterium, vaccination is effective and necessary.

　　1. Blood leukocyte count:Generally (10-20) × 10^9/L, marked left shift, even leukemoid reaction.

　　2. Etiological examination:Gram-negative bipolar coccobacilli can be found in sputum, and cultures of sputum, blood, or lymph node aspirates can be positive. Direct fluorescent antibody staining: This method is to detect antigens of pathogenic bacteria in the specimen and has the characteristic of rapidity, which can be used as an etiological diagnosis.

　　3. Hemagglutination test:Detect serum antibodies with F1 antigen, the titer of serum antibodies in the acute and convalescent phases increases by 4 times, or a single serum titer exceeds 1:16, which has diagnostic significance.

　　4. X-ray:Presented as nodular shadows at the base of both lungs, patchy hazy infiltrative shadows, enlargement of hilar and mediastinal lymph nodes, occasionally pleural effusion, primary pneumonia due to aspiration, patchy shadows can be seen within 24 hours of onset, and further changes such as ARDS or pulmonary edema may occur.

　　Provide patients with semi-liquid diet and sufficient fluids. Available foods include: thick rice porridge, lotus root starch, almond tea, strainer wheat porridge; steamed egg custard, egg flower soup, meat soup with eggs, milk with eggs; various milk and dairy products: cheese, almond tofu, yogurt, ice cream, cocoa milk, milk with lotus root starch; soy milk, strainer bean soup; vegetable water, strainer vegetable soup, tomato juice; fresh fruit juice, boiled fruit water, fruit tea, jelly; clear chicken soup, clear meat soup, liver soup, etc., or glucose and normal saline intravenous infusion can be given to facilitate the excretion of toxins.

　　1. Strict isolation:Rodent and flea control in the patient's room. The excrement of the patient should be thoroughly disinfected, and medical personnel should have strict protective measures.

　　2. Antibiotic treatment:For plague, streptomycin can be used, 2g daily, intramuscular injection. Tetracycline can be added, oral, 2g daily. For pulmonary plague and septicemic plague, combined medication is recommended. Gentamicin can replace streptomycin for intravenous injection. For patients with renal dysfunction or other reasons who cannot use streptomycin or gentamicin, chloramphenicol intravenous injection can be used, 3g daily. The fever will subside rapidly within 3 days of medication, but the bacteria in the lymph nodes may still survive. After the fever subsides, the medication can be appropriately reduced, and the medication should be continued for 10 days. Single drug therapy is effective, and combined medication is not required.