History
An approximately 2-year-old 2.2-kg (4.8-lb) sexually intact male stray cat was evaluated because of expiratory dyspnea. On examination, the cat also had coarse crackles heard on thoracic auscultation, hyperthermia (rectal temperature, 40°C [104°F]; reference range, 36.7°C to 38.9°C [98.1°F to 102.0°F]), and dehydration (approx 8%). Thoracic radiography was performed (Figure 1).
Right lateral (A) and ventrodorsal (B) thoracic radiographic images of a 2.2-kg (4.8-lb) sexually intact male stray cat evaluated for severe expiratory dyspnea.
Citation: Journal of the American Veterinary Medical Association 257, 4; 10.2460/javma.257.4.375
Right lateral (A) and ventrodorsal (B) thoracic radiographic images of a 2.2-kg (4.8-lb) sexually intact male stray cat evaluated for severe expiratory dyspnea.
Citation: Journal of the American Veterinary Medical Association 257, 4; 10.2460/javma.257.4.375
Right lateral (A) and ventrodorsal (B) thoracic radiographic images of a 2.2-kg (4.8-lb) sexually intact male stray cat evaluated for severe expiratory dyspnea.
Citation: Journal of the American Veterinary Medical Association 257, 4; 10.2460/javma.257.4.375
Formulate differential diagnoses and treatment strategies from the history, clinical findings, and Figure 1—then turn the page →
Radiographic Findings and Interpretation
Thoracic radiographic findings included multifocal lung opacification with a mild mixed bronchointerstitial and alveolar pattern and a more severe generalized pattern of multiple pulmonary soft tissue nodular opacities with irregular hazy margins (Figure 2). Moderate hyperinflation of the lung lobes was observed, with the diaphragm extending caudal to the 13th ribs. The cardiovascular structures appeared radiographically normal. In the included portion of the abdomen, the liver appeared enlarged and extended caudal to the costal arch with displacement of the gastric axis.
Same radiographic images as in Figure 1. Multiple soft tissue nodular opacities (arrows) with irregular hazy margins and areas of alveolar infiltrate are evident throughout the lung fields. There is moderate hyperinflation of the lungs, with the diaphragm extending caudal to the 13th ribs, and the liver (asterisk; A) appears enlarged.
Citation: Journal of the American Veterinary Medical Association 257, 4; 10.2460/javma.257.4.375
Same radiographic images as in Figure 1. Multiple soft tissue nodular opacities (arrows) with irregular hazy margins and areas of alveolar infiltrate are evident throughout the lung fields. There is moderate hyperinflation of the lungs, with the diaphragm extending caudal to the 13th ribs, and the liver (asterisk; A) appears enlarged.
Citation: Journal of the American Veterinary Medical Association 257, 4; 10.2460/javma.257.4.375
Same radiographic images as in Figure 1. Multiple soft tissue nodular opacities (arrows) with irregular hazy margins and areas of alveolar infiltrate are evident throughout the lung fields. There is moderate hyperinflation of the lungs, with the diaphragm extending caudal to the 13th ribs, and the liver (asterisk; A) appears enlarged.
Citation: Journal of the American Veterinary Medical Association 257, 4; 10.2460/javma.257.4.375
On the basis of findings from physical and radiographic examinations, the differential diagnosis list included nonspecific pneumonia (parasitic, bacterial, fungal, or protozoal), noncardiogenic edema, pulmonary hemorrhage, or neoplastic infiltrate. The predominant nodular alveolar lung pattern observed lacked specificity and could have been caused by any of several pathological processes.
Treatment and Outcome
Ceftriaxone sodium (40.0 mg/kg [18.2 mg/kg], IV), lactated Ringer solution (44 mL/kg/h [20 mL/lb/h], IV), and supplemental oxygen (2 L/min delivered through a facemask) were administered; however, the cat died within an hour after initial evaluation. Key results of necropsy included multifocal to coalescing nodular lesions in the pleural surface and parenchyma of all lung lobes but no lymphadenomegaly (Figure 3). Histologic evaluation of lung tissue samples revealed a mixed inflammatory infiltrate surrounded by multifocal bacterial colonies associated with diffuse alveolar edema. The bacterial colonies were observed in foci of alveolar necrosis and in the bronchial lumen. In addition, the cat had lymphocytic cholangiohepatitis. Bacterial culture was performed on samples of liver, bile, and lung. The samples of liver and bile yielded no bacterial growth; however, colonies of Yersinia pestis were cultured from lung tissue.
Photograph of the isolated lungs and trachea of the cat in Figures 1 and 2 from the dorsal perspective showing multifocal to coalescing nodular pulmonary lesions (0.3 to 0.5 cm in diameter).
Citation: Journal of the American Veterinary Medical Association 257, 4; 10.2460/javma.257.4.375
Photograph of the isolated lungs and trachea of the cat in Figures 1 and 2 from the dorsal perspective showing multifocal to coalescing nodular pulmonary lesions (0.3 to 0.5 cm in diameter).
Citation: Journal of the American Veterinary Medical Association 257, 4; 10.2460/javma.257.4.375
Photograph of the isolated lungs and trachea of the cat in Figures 1 and 2 from the dorsal perspective showing multifocal to coalescing nodular pulmonary lesions (0.3 to 0.5 cm in diameter).
Citation: Journal of the American Veterinary Medical Association 257, 4; 10.2460/javma.257.4.375
Comments
Pneumonic plague is a disease caused by the bacterium Y pestis, a gram-negative coccobacillus of the Enterobacteriaceae family. Typically, plague occurs in rodent-infested areas where fleas are active year-round. For instance, Xenopsylla cheopis fleas feed on Y pestis bacteremic rodents and are efficient vectors, spreading Y pestis to other mammals.1 The 3 most endemic countries are the Democratic Republic of Congo, Madagascar, and Peru,2 and several foci are located in the Brazilian northeast. The only country that is considered free of plague is Australia.2 The cat of the present report was a stray found in southern Brazil.
The pulmonary form of plague, pneumonic plague, which affected the cat in the present report, is the most severe clinical form, has the poorest prognosis, and often occurs secondary to the other 2 forms: bubonic and septicemic. Although pneumonic plague can also be a primary manifestation of the infection, this form is much less likely in cats. The bubonic form, however, is the most common form in cats and humans, and infected cats are a primary source of human infection.3
The primary radiographic finding in the cat of the present report was a nodular alveolar lung pattern. This finding was consistent with findings in people with pneumonic plague in that for a brief period during the infection process, infected people may have radiographically unilateral small nodular pulmonary infiltrates, and these lesions rapidly progress to large areas of bilateral alveolar infiltrates or nodular lesions that can be associated with disseminated intravascular coagulation, acute respiratory distress syndrome, or plague pneumonitis.4 Similarly, a study5 of 10 monkeys experimentally exposed to Y pestis shows that radiographic evidence progressed from small, single nodular opacities detected in lungs 3 days after experimental exposure to Y pestis to larger areas of alveolar infiltrates and multifocal opacities detected on the following day. Thoracic radiography of the cat in the present report also revealed areas of alveolar infiltrate and small nodular opacities like those detected in monkeys with early-stage disease.5
In humans, typical histopathologic characteristics of pneumonic plague include lobar pneumonia; diffuse presence of bacilli, inflammatory infiltrates, or both; and necrotic areas.6 Similarly, the cat in the present report had a mixed inflammatory infiltrate surrounded by multifocal bacterial colonies in the bronchial lumen and in foci of alveolar necrosis.
Findings in the cat of the present report underscored that, although rare, pneumonic plague should be a differential diagnosis for the combination of severe respiratory disease and radiographic evidence of multifocal nodular pulmonary alveolar infiltrates in cats in areas where Y pestis is endemic. When treating cats with suspected or known infection with Y pestis, all involved personnel must follow strict safety measures. Streptomycin is the treatment of choice, with alternatives being gentamicin, doxycycline, tetracycline, or chloramphenicol.7
References
1. Chomel B. Plague. In: Greene CE, ed. Infectious diseases of the dog and cat. 4th ed. Philadelphia: WB Saunders, 2012;469–476.
2. World Health Organization. Plague. Available at: www.who.int/news-room/fact-sheets/detail/plague. Accessed Feb 14, 2019.
3. Eidson M, Thilsted JP, Rollag OJ. Clinical, clinicopathologic, and pathologic features of plague in cats: 119 cases (1977–1988). J Am Vet Med Assoc 1991;199:1191–1197.
4. Alsofrom DJ, Mettler FAJ, Mann JM. Radiographic manifestations of plague in New Mexico, 1975–1980: a review of 42 proved cases. Radiology 1981;139:561–565.
5. Layton RC, Brasel T, Gigliotti A, et al. Primary pneumonic plague in the African Green monkey as a model for treatment efficacy evaluation. J Med Primatol 2011;40:6–17.
6. Reeder MM, Palmer PES. Plague. In: The radiology of tropical diseases with epidemiological, pathological and clinical correlation. 7th ed. Baltimore and London: Williams and Wilkins, 1981;623–632.
7. Centers for Disease Control and Prevention. Plague: information for veterinarians. Available at: www.cdc.gov/plague/healthcare/veterinarians.html. Accessed Feb 18, 2019.
