Section 5 -

Pulmonary Manifestations of Potential Biowarfare Agents David H. Walker

The opportunity to make the correct diagnosis of the index case of a bioterrorism event quite probably could be that of a pathologist examining an autopsy or lung biopsy. Recognition of the potential exposure of a large group of persons would enable early treatment in the prodromal stage or even prophylaxis with greatly reduced morbidity and mortality. The goal of this presentation is to prepare pathologists to identify the pulmonary lesions of anthrax, pneumonic plague, pneumonic tularemia, glanders, typhus, Q fever, and brucellosis. The most likely means of dispersal of the microbial weapon would be as an aerosol although ingestion of contaminated food or water is also possible. Pulmonary involvement by some of these diseases is pneumonic (e.g., plague, tularemia, Q fever) with primary growth of the inhaled bacteria in airspaces. Pulmonary involvement in some other diseases, however, follows hematogenous spread to the lungs whether after initial inhalation, ingestion, or other means of transmission (e.g., anthrax, secondary plague or tularemic pneumonia, glanders, typhus, brucellosis). Infectious agents that have scarcely been considered as threats might be used (e.g., coccodioidomycosis, histoplasmosis, or blastomycosis, which develop easily prepared spores, or tuberculosis, influenzavirus A, or SARS-coronavirus, which are transmissible from person-to-person). Inhalational Anthrax Inhalational anthrax provides a clear example of the challenge and importance of a timely diagnosis. The incubation period is extremely variable (2-43 days), owing to dose and variable delay in germination of inhaled spores. During the 3-4 days after onset, mild fever, malaise, non-productive cough, and precordial discomfort resemble many other illnesses. Thereafter sudden onset of dyspnea followed by cyanosis, stridor, rales, pleural effusions, and hypotensive shock, the fulminant phase, leads to death 24 hours later despite contemporary intensive care. Diagnosis of the index case, even at neuropsy, can alert physicians to provide early treatment and prophylaxis to other exposed persons. Grossly there are usually massive hemorrhagic pleural effusions, hemorrhages in the mediastinum, tracheobronchial lymph nodes, and tracheobronchial submucosa, gelatinous edema of the mediastinum and parietal pleura, perihilar extension of mediastinal hemorrhages and edema into the lung, and in half of the cases significant peripheral pulmonary hemorrhagic consolidations. Microscopically, the gelatinous edema contains abundant fibrin, lymphatic vessels are frequently dilated and focally obstructed by bacteria and inflammatory cells, and there is minimal accumulation of inflammatory cells in the hemorrhages or edematous lesions. The peripheral hemorrhagic lesions contain only a small amount of fibrin and few macrophages. They are likely caused by vasculitis and hematogenous spread of Bacillus anthracis to the lungs. During the incubation period, anthrax spores are transported by alveolar macrophages to mediastinal lymph nodes where they germinate, proliferate, secrete toxins, cause vasculitis and hemorrhage, and spread into the blood. Anthrax causes respiratory failure mainly by compressive atelectasis owing to pleural effusions with significant hematogenous hemorrhagic pneumonia in some patients, but bronchopneumonia caused by primary germination and growth of B. anthracis in the lungs does not occur. Pneumonic Plague After an incubation period of 1-3 days, patients who have inhaled Yersinia pestis from a bioweapon or aerosol generated by a coughing patient develop high fever followed by chest pain, dyspnea, hemoptysis, and fulminant death. Chest radiographs reveal multiple bilateral nodular consolidations that grossly represent nodules of necrosis and hemorrhage that may be lobular, lobar or multilobar. Microscopic examination reveals necrotizing lobular pneumonia with many 0.5-1 x 1-2 μm gram negative bacilli with bipolar safety pin appearance by gram, methylene blue, Wayson and Wright-Giemsa stains. The alveoli also contain a protein-rich exudate, few neutrophils, and no fibrin. There is also necrosis of alveolar walls and adjacent pleuritis. Pneumonic Tularemia After inhaling a low dose of Francisella tularensis, patients develop fever, dry cough, and malaise. Bronchoscopy reveals focal-to-diffuse hemorrhagic erosions of the bronchial mucosa. Chest radiographs demonstrate patchy, segmental, or subsegmental consolidation, pleural effusions, hilar lymphadenopathy in 50%, and cavitation in 20% (best observed by CT examination). At necropsy, gross examination shows bronchopneumonia, hilar lymphadenopathy, and pleural effusions. Microscopically there is acute necrotizing hemorrhagic pneumonia. Alveoli contain edema, fibrin, a mixed exudate with macrophages and necrotic neutrophils. Thrombosis of arteries and veins is associated with infarction and cavitation. Lungs in late deaths are characterized by fibrosis, calcification, and/or granulomatons inflammation. The draining lymph nodes contain sheets of bacteria, stellate abscesses with geographic necrosis and later pallisading granulomas. Glanders Less known than melioidosis caused by Burkholderia pseudomallei, glanders caused by B. mallei is a more severe biothreat with all infections manifesting illness and 95% lethality. Melioidosis causes symptoms in only 0.1% of infections, namely those with host factors such as renal disease. Glanders is a disease of equines that was eradicated from the United States and Canada in the first half of the 20th century, but persists elsewhere. Human glanders usually manifests as an acute disease with fever, headache, and myalgia followed by septic death with a pustular rash in many patients who survive longer than two weeks. Whether infection enters via percutaneous inoculation or inhalation, the lungs are involved by hematogenous spread. In acute septic death 10-13 days after exposure, half of patients develop interstitial pneumonia. In deaths 15-25 days after percutaneous inoculation, all patients develop pulmonary lesions, usually military granulomas, often hemorrhagic suppurative pneumonia and obliterative endarteritis. At 37-49 days, half of the patients manifest miliary granulomas, and the other half, obliterative endarteritis. Inhalational transmission causes bronchial inflammation, and in deaths occurring more than 100 days after exposure, there is severe lobular pneumonia. The obliterative endarteritis that occurs in half of cases surviving longer than two weeks resembles the pathology of septic emboli. The multiple pulmonary nodules are associated with waxy central necrosis and a surrounding zone of hemorrhage. Microscopy reveals well formed granulomas and vascular occlusion by fibrin with angiocentric inflammation. Infarction is a component of some of the pulmonary and myocutaneous lesions. Q Fever The usual route of infection by Coxiella burnetii is via inhalation of aerosol of spore-like bacteria. Although only 40% of infections are symptomatic, 4.4% of patients are hospitalized with pneumonia. The stability of the agent, extremely low dose infectivity, and acutely incapacitating illness in many patients led to its weaponization. There is abrupt onset of chills, fever, fatigue, and headache with non-productive cough in a variable portion (4-90%) of cases. Chest radiographs in patients with Q fever pneumonia may demonstrate segmental or subsegmental consolidation, rounded opacity, atelectasis, pleural effusion, or hilar lymphadenopathy. The major pulmonary target cells of C. burnetii are alveolar macrophages, where the bacteria thrive in acidic phagolysosomes. Microscopy reveals bronchioloalveolitis, interstitial and alveolar infiltrates of macrophages, lymphocytes, a few PMNs, fibrin, and RBCs. The lesion resolves slowly and in the late stage has been characterized as a pseudotumor. Pulmonary Involvement in Vasculotropic Rickettsioses Rickettsia prowazekii, R. rickettsii, R. typhi, and R. conorii are highly infectious by low dose aerosol, have extracellular forms that with stable infectivity, and cause lifethreatening disease. Typhus and Rocky Mountain spotted fever have case-fatality rates similar to category A agents. Their potential threat as agents of bioterror has been underestimated. Rickettsioses acquired by aerosol are clinically indistinguishable from naturally vector-borne infections. Patients present with fever, headache, and myalgia with rash appearing on day 3-5 or later. Cough occurs in a third or more of cases of epidemic typhus, Rocky Mountain spotted fever, and murine typhus. The most severe cases manifest respiratory and neurologic involvement. Fatal disease is frequently associated with adult respiratory distress syndrome. There is extensive infection of endothelial cells of the pulmonary microcirculation by rickettsiae, causing increased vascular permeability and non-cardiogenic pulmonary edema. At necropsy the lungs are edematous and diffusely consolidated. Histopathologic lesions include interstitial pneumonia and edema, alveolar edema fibrin, hemorrhages, and macrophages, diffuse alveolar damage often with hyaline membranes, edema of the interlobular septa, and lymphohistocytic vasculitis. Pulmonary Manifestations of Brucellosis Pulmonary abnormalities occur infrequently in brucellosis. In a series of 1500 cases of brucellosis, nine patients manifested fever and productive cough and six had rales. Chest radiographs revealed patchy infiltrates or consolidation in five patients, pleural effusions in three, noncasesting granulomas in one, and interstitial pneumonia in one. Rhesus monkeys infected by inhalation of aerosol containing Brucella melitensis developed little pulmonary pathology. Cultures containing 103 or more bacteria were obtained in three of six animals. One animal showed mild multifocal interstitial pneumonia containing lymphocytes, plasma cells, PMNs, and multinucleated grant cells, and another monkey had focal pneumonia with alveolar, macrophages, eosinophils, few PMNs, and protein-rich edema. These lesions are most likely the result of hematogenous spread of brucella to the lungs. Immunohistologic Diagnoses Immunohistochemical methods are available at the CDC to diagnose anthrax, plague, tularemia, Q fever, brucellosis and Rocky Mountain spotted fever. References Guarner, J., and Zaki, S.R. (2006). Histopathology and immunohistochemistry in the diagnosis of bioterrorism agents. J Histo Cyto 54: 1, 3-11. Guarner, J., Jernigan, J., Shieh, W., Tatti, K., Flannagan, L., Stephens, D., Popvic, T., et al. (2003). Pathology and pathogenesis of bioterrorism-related inhalational anthrax. Am J Pathol 163: 701-709. Grinberg, L., Abramova, F., Yampolskaya, O., Walker, D., Smith, J. (2001). Quantitative pathology of inhalational anthrax I: quantitative microscopic findings. Mod Pathol 14: 482-495. WALKER DH. (2006). Mycoplasma, Chlamydial, Rickettsial and Ehrlichial Pneumonias. In: Tomashefsski J, Cagle P, Farver C, Fraire A, editors. Dail and Hammar Pulmonary Pathology. 3rd ed. (In press). Mense, M.G., Borschel, R.H., Wilhelmsen, C.L., Pitt, M.L., Hoover, D.L. (2004). Pathologic changes associated with brucellosis experimentally induced by aerosol exposure in rhesus macaques (Macaca mulatta). AJVR, 65: 5, 644-652.