Conference 16 - 2016 Case: 1 20170125

Signalment:

Eight-month-old, Dorset ewe, (Ovis aries).This ewe was enrolled in a research study in which it underwent surgery and MRI the following day, both under general anesthesia. The ewe initially recovered normally, displaying brief weakness in the hindlimbs immediately after surgery. However, over the next two weeks, it gradually became dull and lethargic, dehydrated, inappetent, and weakened despite supportive care. The animal was found recumbent, hypothermic, tachycardic, and dyspneic 13 days after surgery and died before it was able to be euthanized.

Gross Description:

The major gross lesion was in the lungs. The right cranial lung lobe was half normal size, mottled dark red to black, and firm on palpation. The cranial aspect of the right middle lung lobe appeared similarly. Dissection of the bronchial tree did not reveal the presence of foreign material. Additionally, several ulcers, up to 1 x 2 cm, were present in the trachea.

Histopathologic Description:

The lung is markedly hypercellular, owing to filling of alveoli by degenerate inflammatory cells, amorphous and fibrillar eosinophilic material (edema and fibrin, respectively), basophilic streaming nuclear and eosinophilic cytoplasmic debris, and myriad gram-positive bacterial rods. In some regions, well-defined areas with architectural preservation without cellular detail (coagulative necrosis) are present. Bronchi and bronchiole lumina frequently contain abundant bacteria and sloughed bronchial epithelium. Interlobular septa are thickened up to 2mm wide by fibrin and edema, and blood vessels were congested and contained bacteria. The pleura is expanded up to 3x normal with blood.

Morphologic Diagnosis:

Broncho-pneumonia, multifocal, subacute, severe, necrotizing.

Lab Results:

Bacterial culture of the lung yielded a pure culture of Trueperella pyogenes.

Condition:

Choriomeningoencephalitis/Borrelia burgdorferi

Contributor Comment:

All findings in this case were consistent with bronchopneumonia caused by Trueperella pyogenes (formerly Arcanobacterium pyogenes), a gram-positive non-motile, non-sporeforming, short, rod-shaped bacterium.⁶ Trueperella pyogenes is one of the most common opportunistic pathogens in domestic livestock and is often commensal flora in the mammary gland, upper respiratory, urogenital, and gastrointestinal tracts.^6,10 Although T. pyogenes can act as a primary pulmonary pathogen, infection usually follows physical or microbial trauma which overcomes the pulmonary defense mechanisms, allowing for colonization of the lungs.^1,8 The pneumonia was initially suspected to be due to aspiration shortly after recovery from anesthesia, but foodstuff was not present in the respiratory tract. The reason for the infection was likely due to a combination of stressors, including what was interpreted as intubation-associated ulceration of the trachea. Trueperella pyogenes produces and utilizes a variety of virulence factors to colonize, damage, and persist within a variety of tissues in the host. The most important factor is pyolysin (PLO), a cytolysin, which is able to bind to and create pores in the cell membranes of erythrocytes, polymorphonuclear cells, and macrophages resulting in cell lysis.⁶ Trueperella pyogenes mutants lacking the PLO gene were unable to cause an intraperitoneal infection in mice injected with 10⁸bacteria, whereas replacement of the PLO gene to the T. pyogenes mutants restored full virulence.⁵ Additional virulence factors used by T. pyogenes include fimbriae¹³, extracellular matrix binding proteins specific for collagen⁴, fibrinogen, fibronectin⁵, and exoenzymes including DNases¹¹, proteases¹², and neuraminidases⁷ which degrade host nucleic acids, proteins, and acid residues, respectively.

Note: Multiple different tissue sections of lung were used for the slides submission; therefore, not all the participants will receive similar serial microslide sections.

JPC Diagnosis:

Lung: Bronchopneumonia, necrotizing and fibrinosuppurative, multifocal to coalescing, severe, with marked alveolar and septal edema and numerous large colonies of bacilli, Dorset sheep, Ovis aries.

Conference Comment:

This case demonstrates the characteristic gross and histologic lesions associated with bacterial bronchopneumonia. Conference participants described the suppurative inflammation filling bronchi and bronchioles surrounded by multifocal to coalescing areas of necrosis, and readily identified numerous large colonies of bacilli within the areas of inflammation. Participants discussed the differential diagnosis for large colony forming bacteria in tissue section to include: Yersinia sp, Actinomyces sp., Actinobacillus sp., Corynebacterium sp, Staphylococcus sp., Streptococcus sp., and T. pyogenes. Trueperella pyogenes is one of the most common opportunistic pathogens present on the mucosal surfaces of domestic animals.^1,2,5,8 The bacterium induces suppurative inflammation within a wide variety of organs and is an important cause of abortion, arthritis, endocarditis, mastitis, osteomyelitis, and pneumonia resulting in significant losses in production animals.^2,4 Additionally, T. pyogenes is widespread in the wild animal population and has been reported as an important cause of cerebral abscesses in young male white-tailed deer as a consequence of antler development and conspecific aggression between bucks. Mortality can reach up to 35% in affected free-ranging adult male deer.³

As mentioned by the contributor, while T. pyogenes can be a primary pathogen, it is usually associated with physiologic trauma to a mucosal membrane, concurrent primary infection, or immune suppression.^1,2,3,8 As postulated by the contributor in this case, there well may be an association with placement of the endotracheal tube. Other common commensal organisms of the ruminant upper respiratory tract that can cause opportunistic bronchopneumonia include Mannheimia haemolyica, Pasteurella multocida, and Bibersteinia trehalosi. Causes of primary infectious pneumonia in sheep include parainfluenza virus 3, respiratory syncytial virus, and Bordetella parapertussis, which can predispose sheep to secondary infection by the commensal bacteria mentioned above.^1,3,8 Mycoplasma ovipneumoniae is another important primary etiologic agent involved in chronic enzootic pneumonia; also known as chronic non-progressive pneumonia, it is a multi-factorial disease complex affecting lambs less than one-year-old. Mycoplasma ovipneumoniae usually causes a mild, subclinical infection that results in poor growth unless complicated by stressors such as over-crowding, inclement weather, or poor air quality.^1,2,3,8

Another primary cause of pneumonia in sheep includes the maedi-visna virus, which results in lifelong persistent viral infection and leads to ovine progressive pneumonia (OPP), encephalitis, arthritis, and mastitis in sheep. This lentivirus is a member of the family Retroviridae, and is closely related to caprine arthritis-encephalitis virus. First reported in Iceland, the maedi (respiratory form) occurs in sheep older than three years, while the visna (neurologic form) occurs in younger sheep.^1,9 The respiratory form is characterized by interstitial pneumonia with prominent perivascular and peribronchial lymphoid nodules. This slowly progressive pneumonia is often complicated by secondary bacterial infection, especially T. pyogenes.¹ Peste des petits ruminants (PPRV), a morbillivirus, has also been reported to cause primary respiratory disease in small ruminants in Africa and parts of Asia. This virus primarily affects the cranioventral lung lobes and causes a bronchointerstitial pneumonia.^1,8,9

References:

1. Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. 6th ed. Vol. 2. Philadelphia, PA: Elsevier; 2016:557-560.
2. Cohen BS, Belser EH, et al. Isolation and genotypic characterization of Trueperella (Arcanobacterium) pyogenes recovered from active cranial abscess infections of male white-tailed deer (Odocoileus virginianus). J Zoo Wildl Med. 2015; 46(1):62-67.
3. Dassanayake RP, Shanthalingam S, Herndon CN, et al. Mycoplasma ovipneumoniae can predispose bighorn sheep to fatal Mannheimia haemolyticapneumonia. Vet Microbiol. 2010; 145:354-359.
4. Esmay PA, et al. The Arcano-bacterium pyogenes collagen-binding protein, CbpA, promotes adhesion to host cells. Infect Immun. 2003; 71(8):4368-74.
5. Jost BH, Billington SJ. Arcano-bacterium pyogenes: Molecular pathogenesis of an animal opportunist. Antonie Van Leeuwenhoek. 2005; 88(2):87-102.
6. Jost BH, Songer JG, Billington SJ. An Arcanobacterium (Actinomyces) pyogenes mutant deficient in production of the pore-forming cytolysin pyolysin has reduced virulence. Infect Immun. 1999; 67(4):1723-8.
7. Jost BH, Songer JG, Billington SJ. Cloning, expression, and characterization of a neuraminidase gene from Arcanobacterium pyogenes. Infect Immun. 2001; 69(7):4430-7.
8. Lopez A, Martinson SA. Respiratory system, mediastinum, and pleurae. In: Pathologic Basis of Veterinary Disease. Zachary JM ed. 6th ed. St. Louis: Elsevier; 2017:537-540.
9. MacLachlan NJ, Dubovi EJ, eds. Fenners Veterinary Virology. 4th ed. London, UK: Elsevier; 2011:267-268,308-323.
10. Queen C, Ward AC, Hunter DL. Bacteria isolated from nasal and tonsillar samples of clinically healthy Rocky Mountain bighorn and domestic sheep. J Wildl Dis. 1994; 30(1):1-7.
11. Ramos, CP, Foster G, Collins MD. Phylogenetic analysis of the genus Actinomyces based on 16S rRNA gene sequences: description of Arcanobacterium phocae sp. nov., Arcanobacterium bernardiae comb. nov., and Arcanobacterium pyogenes comb. nov. Int J Syst Bacteriol, 1997; 47(1):46-53.
12. Takeuchi S, Kaidoh T, Azuma R, Assay of proteases from Actinomyces pyogenes isolated from pigs and cows by zymography. J Vet Med Sci. 1995; 57(5):977-9.
13. Yanagawa R, Honda E Presence of pili in species of human and animal parasites and pathogens of the genus Corynebacterium. Infect Immun. 1976; 13(4):1293-5.