Pathology of Eastern Equine Encephalitis in Emus (Dromaius novaehollandiae)

Eastern equine encephalitis virus (EEEV) is an important cause of encephalitis in horses and human beings in the eastern and southern United States and has been recognized infrequently in other mammalian species. Numerous species of free-living passerine and columbiform birds serve as natural hosts for the virus.y Outbreaks of the disease have been reported in domestic avian species including pheasants, turkeys, ducks, chukars, and pigeons. This paper describes the pathological findings accompanying an epornitic of EEEV involving two separate flocks of emus (Dromaius novaehollandiae). From late August to late October 199 1, 13 of 24 birds from a single farm in south central Louisiana (flock 1) experienced acute mortality. Two birds were presented dead (case Nos. 3, 10) and the remaining 1 1 birds died or were euthanatized subsequent to presentation (case Nos. I , 2,4-9, 1 1-1 3). Two additional clinically affected birds from the same flock recovered. The ages of the affected birds ranged from 18 months to 3 years and both sexes were represented. Most birds died without premonitory signs, but copious hemorrhagic diarrhea and emesis of blood-tinged ingesta were sometimes observed in the terminal stages of the disease. Details of the epidemiology, clinical history, and treatment outcome associated with the outbreak of EEEV infection in this first flock are described elsewhere.x In late October 199 I , another outbreak of EEEV infection occurred at an emu farm (flock 2) approximately 50 miles east of the first location. There was no sex predilection and the seven birds dying from this flock were between 2 and 4 years of age. The short course of the disease and clinical signs displayed by these birds were similar to those seen in flock 1. Complete necropsies were performed on three of the birds (case Nos. 14-1 6) and representative sections of liver, lung, heart, proventriculus, ventriculus, small and large intestine, kidney, adrenal gland, spleen, brain, and gonad from four birds (case Nos. 17-20) were submitted by the refemng veterinarian in neutral buffered 10% formalin. Eastern equine encephalitis virus was isolated from liver, spleen, and intestine as previously describedx from a total of 1 1 birds comprising members of both flocks (case Nos. 4-8, 11-1 3, 14-16). Representative sections of liver, lung, heart, proventriculus, ventriculus, small and large intestine, kidney, adrenal gland, spleen, brain, and gonad were collected from all birds undergoing complete necropsy and were fixed routinely in neutral buffered 10% formalin. These tissues as well as those from case Nos. 17-20 were paraffin embedded, and 4-5-pm sections were stained with hematoxylin and eosin for histologic examination. In all necropsied birds (case Nos. 1-16), there was gross evidence of hemorrhage involving the small and large intestine. Petechial to ecchymotic serosal hemorrhages were consistently present. Occasionally suffusive serosal hemorrhages were present, resulting in diffuse, dark reddish-purple discoloration of the intestinal tract. Intestinal lumens contained unclotted to partially digested blood in varying but usually copious quantities. The mucosa was intensely reddened with thin, brownish-red fibrinous material adherent to it. Gross abnormalities in the liver were present in six birds (case Nos. I , 9-12, 14-1 6). Marked congestion and petechial to ecchymotic subcapsular hemorrhages were often observed. Other livers had accentuated lobular patterns and a tan to brown mottling of the parenchyma. Less frequently encountered gross lesions included splenomegaly, myocardial hemorrhage, foamy fluid in the trachea, and pale streaks in the pelvic limb muscles. One bird (case No. 11) had petechial hemorrhages on the serosa of the oviduct and the renal capsules. Blood was found free in the abdominal cavity in another bird (case No. 8). Microscopic lesions in the liver and spleen were consistently present in all 20 birds. In the liver, marked, diffuse congestion and hemorrhage resulted in disruption of hepatic cords, obliteration of the lobular architecture, and individualization of hepatocytes. There was widespread individual necrosis of individual hepatocytes. Many sections had multifocal areas of coagulative necrosis (Fig. l) . Pyknotic nuclei and karyorrhectic nuclear debris were present in the sinusoids and parenchyma. Remaining hepatocytes had moderate cytoplasmic vacuolation consisting of foamy to coalescing clear vacuoles. Occasional multifocal aggregates of necrotic lymphocytes were found throughout the hepatic parenchyma in most cases. The majority of these lymphocytes were often obliterated, consisting of indistinct foci of karyorrhectic debris. Occasional small to moderate numbers of heterophils and degenerate mononuclear inflammatory cells were diffusely scattered throughout the necrotic areas. Occasional necrosis of hepatic arteries was observed. Histologic changes in the spleen consisted of severe, diffuse lymphocytic necrosis with moderate to marked amounts of karyorrhectic debris scattered throughout the sections. Fibrinoid degeneration of sheathed arterioles with necrosis of endothelial macrophages was a consistent finding (Fig. 2). Postmortem autolysis precluded ideal adequate interpretation of intestinal changes in some birds; however, intestinal lesions were recognized in 16 birds (case Nos. 1-7, 9, 11, 12, 14-1 9). These consisted of, in decreasing order of frequency, large amounts of cell debris in both the lamina propria and proprial lymphatics, multifocal areas of hemorrhage and infiltration of small numbers of heterophils into the lamina propria, and necrosis of proprial lymphoid follicles. Streaming of blood and proteinaceous fluid from vessels of the vil-