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RUPTURED AORTIC ANEURYSM IN A COYOTE (CANIS LATRANS) FROMSOUTH CAROLINAAuthor(s): Debra Lee MillerD.V.M., Ph.D., Joshua SchrecengostB.S., John KilgoPh.D., H. ScottRayM.S., and Karl V. MillerPh.D.Source: Journal of Zoo and Wildlife Medicine, 38(3):492-494. 2007.Published By: American Association of Zoo VeterinariansDOI: http://dx.doi.org/10.1638/2007-0002.1URL: http://www.bioone.org/doi/full/10.1638/2007-0002.1

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492

Journal of Zoo and Wildlife Medicine 38(3): 492–494, 2007Copyright 2007 by American Association of Zoo Veterinarians

RUPTURED AORTIC ANEURYSM IN A COYOTE (CANIS LATRANS)FROM SOUTH CAROLINA

Debra Lee Miller, D.V.M., Ph.D., Joshua Schrecengost, B.S., John Kilgo, Ph.D., H. Scott Ray,M.S., and Karl V. Miller, Ph.D.

Abstract: A radio-collared adult female coyote (Canis latrans) from South Carolina was found dead with no apparentsigns of trauma or struggle. Necropsy revealed a ruptured aortic aneurysm within the thoracic cavity as well as severeheartworm infection, with parasites present in the caudal vena cava. Histologically, inflammatory cell infiltrates werefrequent in the aneurysm and consisted of eosinophils, neutrophils, lymphocytes, plasma cells, and macrophages.Bacteria, fungi, and parasites were not found in the aneurysm. Death was due to exsanguination. This represents a firstreport of an aneurysm in a coyote.

Key words: Aneurysm, Canis latrans, coyote, Dirofilaria immitis, heartworm.

BRIEF COMMUNICATION

An adult female coyote (Canis latrans) that wasradio-collared as part of a field study in South Car-olina was found dead in June 2006. This study wasconducted on the U.S. Department of Energy’s Sa-vannah River Site, a 78,000-ha National Environ-mental Research Park located in Aiken and Barn-well counties in the Upper Coastal Plain. The ani-mal was captured and radio-instrumented on 15July 2005 and at that time was estimated to be atleast 4 yr of age. Upon recovery of the cadaver in2006, examination of the animal and the surround-ings revealed no external evidence of trauma andno local sign of struggle. The cadaver was frozenand transported to the University of Georgia’s Tif-ton Veterinary Diagnostic and Investigational Lab-oratory for a full necropsy.

Grossly the coyote was in fair flesh with subcu-taneous fat apparent throughout the body. No frac-tures or other evidence of trauma were observed.The thoracic cavity was filled with blood. Numer-ous canine heartworms (Dirofilaria immitis) werefound within the right ventricle, pulmonary arteries,and caudal vena cava (Fig. 1A). There was a ca.7-cm aneurysm of the aorta just cranial to the di-aphragm, with luminal lesions noted ca. 1–2 cmboth cranial and caudal to the site (Fig. 1B). Blooddissected within the vessel wall from the aneurysm

From The University of Georgia, College of VeterinaryMedicine, Veterinary Diagnostic and Investigational Labo-ratory, Tifton, Georgia 31793, USA (D. Miller); U.S. De-partment of Agriculture (USDA) Forest Service-SavannahRiver Site, 1 Mile inside Aiken Barricade, New Ellenton,South Carolina 29809, USA (Schrecengost, Kilgo, Ray);and The University of Georgia, Daniel B. Warnell Schoolof Forestry and Natural Resources, Athens, Georgia 30602,USA (Schrecengost, K. Miller). Correspondence should bedirected to Dr. Debra Lee Miller (millerdl@uga.edu).

to the base of the heart cranially and to the dia-phragm caudally but did not extend into the abdom-inal cavity. There was an 8-mm tear in the dia-phragm just to the right of the midline, approxi-mately 3 cm from its attachment to the body wall.Through this opening, approximately ¾ of theomentum had entered into the thoracic cavity, ef-fectively sealing the tear. The diaphragm compris-ing the perimeter of the tear was mildly thickened.There were few fibrous adhesions between theomentum and the pericardial sac and rarely be-tween the diaphragm and pleura of the thoracicwall. No other significant gross findings were not-ed.

Histologically, the lesion observed grossly (an-eurysm) in the aortic wall had extensive hemor-rhage and multifocal to occasionally transmural in-filtrates of mild numbers of eosinophils, neutro-phils, lymphocytes, plasma cells, and macrophages.Similar inflammatory foci were found in the lung,rarely accompanied by total obstruction (thrombo-sis) of vessels. Occasional pulmonary vessels hadhypereosinophilia and homogenization (sclerosis)of their wall and occasional protrusion of the wallinto the lumen. No parasites, fungi, or bacteria wereseen. The heart (myocardium) had a single inflam-matory infiltrate similar to those found in the an-eurysm. Pulmonary and hepatic congestion werepresent.

Death was due to severe intrathoracic hemor-rhage (exsanguination) secondary to the rupturedaortic aneurysm. The cause of this aneurysm re-mains unknown but may have been associated withparasites, given the presence of eosinophils in theinflammatory cell infiltrate, and may possibly havebeen potentiated by hypertension that developedsecondary to severe heartworm disease. The dia-phragmatic hernia was considered an incidentalfinding (based upon its presentation as a healed le-

493MILLER ET AL.—RUPTURED AORTIC ANEURYSM IN COYOTE

Figure 1. Caudal vena cava and aorta of a free-ranging adult female coyote (Canis latrans) from South Carolinathat died of a ruptured aortic aneurysm. A. Caudal vena cava showing the presence of heartworms (Dirofilaria immitis).B. Exposed luminal surface of the aorta showing the large aneurysm (arrows) with luminal lesions cranial (arrowheads)and caudal to the aneurysm.

494 JOURNAL OF ZOO AND WILDLIFE MEDICINE

sion), although it may have served as a complicat-ing factor and may have resulted from either a con-genital defect or past trauma.

Although their initial etiology and subsequentevolution often remain a mystery, aneurysms arethought to be caused by disease or focal weakeningof the vessel wall and are considered progressivelesions.4,6 They may develop in a variety of anatom-ic locations but generally occur in areas with pre-disposing factors, such as in the region of congen-ital defects, turbulent blood flow, parasite migra-tion, or neoplasia.4,6,7 Although a congenital etiol-ogy might be considered the initial cause of theaneurysm in this coyote, subsequent etiologies like-ly potentiated the rupture.

An aneurysm by itself is not necessarily fatal butcan become lethal over time as the vessel continuesto degenerate or thrombosis occurs. In dogs, thenematode Spirocerca lupi is the most commoncause of aortic thrombosis and results when para-sites migrate from the gastric arteries through theaortic wall en route to the esophagus.1 Spirocercalupi was entertained as a possible cause for the an-eurysm in this coyote; however, neither parasitesnor corresponding esophageal lesions were ob-served.

Heartworms have been documented in coyotesthroughout much of the United States.2,3,5,8 We havedocumented heartworms in other coyotes from theSouth Carolina study, as well as another infection-related fatality (Miller, unpubl. data). Heartwormswere not found within the vena cava of the otherinfected coyotes, and thus, caval syndrome wasconsidered as a possible complicating factor in thiscoyote. The course of events precipitating cavalsyndrome remains unclear, but in heartworm dis-ease it is thought to occur when heartworms mi-grate to the caudal vena cava and also accumulatein the right atrium and tricuspid area,9 in a mannersimilar to that observed in this coyote. The resultof these migrations is disruption of the tricuspidvalve, severe pulmonary hypertension, and right-sided heart failure,9 all of which contribute to dis-rupted blood flow and predispose the host to vas-cular thrombosis. Regardless of whether or not truecaval syndrome was present in this coyote, disrup-tion to blood flow was likely given the presence ofparasites in the caudal vena cava and pulmonaryhypertension.

In free-ranging mammals, death due to aortic an-

eurysm has been reported only in a Florida panther(Felis concolor) that was likewise radio-collared,7

which undoubtedly permitted discovery of the an-eurysm. Bacterial arteritis was the suspected etiol-ogy for aortic aneurysm in the panther. The etiol-ogy of the aneurysm in this coyote was not dis-cerned, but we surmise that it possibly was asso-ciated with parasites and may have been potentiatedby disruption of blood flow and pulmonary hyper-tension. This represents a first report of an aneu-rysm in a coyote.

Acknowledgments: The authors wish to thank thestaff of the Tifton Veterinary Diagnostic and In-vestigational Laboratory for assistance with speci-men analysis and Dr. Victoria Woshner for editorialassistance. Funding for the coyote telemetry re-search was provided by the U.S. Department of En-ergy–Savannah River Operations Office through theU.S. Forest Service–Savannah River under Inter-agency Agreement DE-AI09-00SR22188.

LITERATURE CITED

1. Gal, A., S. Kleinbart, Z. Aizenberg, and G. Baneth.2005. Aortic thromboembolism associated with Spirocer-ca lupi infection. Vet. Parasitol. 130: 331–335.

2. Holzman, S., M. J. Conroy, and W. R. Davidson.1992. Diseases, parasites and survival of coyotes in south-central Georgia. J. Wildl. Dis. 28: 572–580.

3. Nelson, T. A., D. G. Gregory, and J. R. Laursen.2003. Canine heartworms in coyotes in Illinois. J. Wildl.Dis. 39: 593–599.

4. Olsen, D., K. R. Harkin, M. N. Banwell, and G. A.Andrews. 2002. Postoperative rupture of an aortic aneu-rismal dilation associated with a patent ductus arteriosusin a dog. Vet. Surg. 31: 259–265.

5. Pappas, L. G., and A. T. Lunzman. 1985. Canineheartworm in the domestic and wild canids of southeast-ern Nebraska. J. Parasitol. 71: 828–830.

6. Pitt, M. P. I., and R. S. Bonser. 1997. The naturalhistory of thoracic aortic aneurysm disease: an overview.J. Cardiovasc. Surg. 12(Suppl.): 270–278.

7. Rotstein, D. S., S. K. Taylor, G. D. Bossart, and D.Miller. 2000. Dissecting thoracoabdominal aortic aneu-rysm in a free-ranging Florida panther (Felis concolorcoryi). J. Zoo Wildl. Med. 31: 208–210.

8. Sacks, B. N., and E. P. Caswell-Chen. 2003. Recon-structing the spread of Dirofilaria immitis in Californiacoyotes. J. Parasitol. 89: 319–323.

9. Strickland, K. N. 1998. Canine and feline caval syn-drome. Clin. Tech. Small Anim. Pract. 13: 88–95.

Received for publication 6 January 2007