Overview.
Francisella pneumonia, also known as tularemia, is a common infectious disease of animals in the United States. Its causative agent, Francisella tularensis, is a widespread parasite of many wildlife, domestic animals, and birds. Tick and deer fly bites are the primary mode of transmission. Like other bubonic plagues, tularemia primarily involves the skin and local lymph nodes and is characterized by a focal purulent and granulomatous inflammatory reaction throughout the body. Pulmonary involvement is usually secondary to bacteremia or as a result of primary inhalation of the causative agent. In ulcerative granulomas due to Francisella tularensis, the lungs are involved in 10% to 15% of cases.
Etiology
Francisella tularensis belongs to the genus Francisella of the family Salicaceae. It is fragile, tiny gram-negative coccobacilli, non-powered, without pods in culture, but can appear in the secretion of the living body, it is difficult to grow on ordinary medium, and it grows best in the medium rich in serum, sugar and cystine. The suitable growth temperature is 36～37℃, pH6.8～7.2. It is not heat-resistant, and is more tolerant to low temperature, and is generally considered to have endotoxin.
Tularemia franciscana cell membrane has a variety of proteins and polysaccharide antigens, in addition, also has a similar role with other gram-negative bacteria endotoxin. The causative organisms may enter the body through breaks in the skin or mucous membranes, causing localized suppurative infections of the lymph nodes and occasionally bacteremia, with the bacteria spreading with the bloodstream to other organs, including the lungs. Unexplained rhabdomyolysis often occurs with bacteremia and pneumonia. Bacteria entering from the GI tract can cause pharyngitis and inflammation of the gastrointestinal tract. Bacterial inhalation via the respiratory tract may cause primary pneumonia, which manifests itself as multisite inflammation, necrosis, and a tendency toward granuloma formation.
Epidemiology
The epidemic is widespread all over the world, and the natural source of the epidemic is mainly in the northern hemisphere. It was first reported in 1957 in China, and only a small epidemic has been reported. Most cases tend to have a history of contact with infected animals before the onset of the disease, such as winter outdoor activities: hunting, traveling or other outdoor activities. Many animals carry the bacterium, especially squirrels and rabbits being the most important, and animal-to-animal transmission is through tick or deer fly bites. Human transmission occurs through contact with infected animals or the bite of arthropods such as ticks and deer flies, and in some cases through the consumption of contaminated meat or inhalation of airborne droplet particles from infected birds or animals. Direct human-to-human transmission is theoretically possible, such as from contact with a person with plague pneumonia, but no cases of transmission by this route have been reported.
Symptoms
Pneumonia caused by the spread of bacteria through the bloodstream usually occurs in the first 2 to 3 weeks of the disease and is characterized by coughing, coughing up white or bloody sputum, chest pain, and shortness of breath, and is often accompanied by fever and limited ulcerative granuloma formation. Primary pneumonia due to aspiration, in addition to cough and shortness of breath, occasionally involves the pleura and causes pleural effusion. Complications of bacteremia.
Examination
Gram staining and culture in sputum and pleural effusion are not easy to find pathogenic bacteria, but direct fluorescein labeling antibody staining is positive, double serum agglutination test is very helpful for etiological diagnosis, i.e., double serum in the acute and recovery period, antibody titer has more than 4-fold increase, such as single serum in the recovery period with antibody potency of more than 1:160, there should be a high degree of suspicion that there is an active focus of the disease in vivo, and the antigenic skin test is helpful for the diagnosis, but the preparation of the antigen is not easy. Antigen skin test is also helpful for diagnosis, but the preparation of antigen is not easy.
In the first 2~4 hours of fever, X-ray may not show any abnormality, but later there are lung infiltrating foci and enlarged hilar lymph nodes, which may involve the pleura and cause pleural effusion. X-ray changes in this disease are disproportionate to the physical signs, i.e., diffuse bronchopneumonia, unilateral or bilateral pleural effusions, but the physical signs are relatively mild. The central ovoid dense shadow that used to be a characteristic feature is now rarely found.
Diagnosis
Diagnosis is based on a history of animal contact in an infected area or a history of arthropod bites in an infected area, and the presentation of fever, skin lesions, and enlarged, tender lymph nodes, which should lead to a high suspicion of tularemia. If cough, shortness of breath, chest pain, etc., X-ray confirmation of lung involvement, etiological diagnosis feasible direct fluorescein labeling antibody staining and serum agglutination test.
Differential diagnosis
There are many diseases that easily resemble Francisella pneumonia and must be differentiated. Such as ① non-bacterial pneumonia: psittacosis, Q fever, mycoplasma pneumonia; ② bacterial pneumonia: plague pneumonia, tuberculosis; ③ systemic deep fungal infection.
Treatment
1.Drug treatment
Penicillin is ineffective for Francisella pneumonia. Aminoglycosides, tetracyclines, chloramphenicol are sensitive. Streptomycin is the drug of choice. Gentamicin is another effective drug. Tetracycline or chloramphenicol is also effective in this disease and is suitable for patients who cannot tolerate aminoglycosides.
2. Chinese medicine treatment
Pneumonia herbal prescription – wind-heat offending the lungs (symptoms of pneumonia) cough, phlegm, fever, asthma, nasal discharge, no sweating, thin white tongue coating, floating pulse. Clearing heat and removing toxins, and penetrating the surface with pungent coolness. This is a case of wind-heat offending the lungs, so the treatment is mainly to promote the penetration of the evil by pungency and coolness, supplemented by clearing heat and removing toxins.
Prognosis
Early diagnosis and timely treatment generally have a good prognosis.
Prevention
Pay attention to self-protection when coming into contact with animals in infected areas, e.g. wearing gloves, wearing protective clothing or spraying insecticides to prevent contact and transmission.