July 23, 2010

In the Spotlight – Revisiting a Past Disease Investigation

A Case from the Southeastern Cooperative Wildlife Disease Study (SCWDS) Archives. What is Your Diagnosis?

From April 2010 SCWDS Brief: "On January 5, 2010, SCWDS was asked by U.S. Fish and Wildlife Service personnel to assist in the investigation of the death of an endangered Key deer held at a South Florida petting zoo. The deer died suddenly, and a postmortem examination was conducted by the attending veterinarian. Lesions included multifocal necrosis of the liver and severe pulmonary edema. Tissues were sent to a private pathology laboratory, and clinicians there described a vasculitis thought to be consistent with hemorrhagic disease (HD).

Almost immediately after we contacted the clinician regarding this deer, the other Key deer in the facility became feverish and lethargic. It died within two days, in spite of supportive care and the administration of antibiotics. The clinician again performed a necropsy and described subcutaneous hemorrhages and edema in the wall of the small intestine and associated mesentery. Samples of frozen and formalin-fixed tissues were submitted to SCWDS for evaluation.

In this case, the origin of the deer suggested that HD was an unlikely cause of death. Although we regularly find circulating antibodies to HD viruses in Key deer, indicating exposure, we have never identified a clinical case of HD in these animals. This probably is due to a combination of factors. Deer in the extreme South are exposed to the viruses of HD on a regular basis from birth and, therefore, have a high degree of herd immunity. In that situation, deer are not likely to develop clinical HD.

In addition, experimental results suggest that white-tailed deer that populate these areas of high exposure may be genetically resistant to these viruses. The maintenance of the deer in a mixed-animal collection and a second look at the description of the vasculitis in the first deer increased our suspicion that another disease had killed these deer.

Formalin-fixed tissues from the second deer were examined microscopically using standard techniques. This examination revealed all major organs had severe vasculitis. These lesions were characterized by massive accumulations of lymphocytes and a particular degenerative change to arteries called fibrinoid necrosis. This combination of lesions is suggestive of…"

Source: SCWDS Briefs, April 2010 Issue, pages 6-7