Experimental Oral Administration of Canine Adenovirus (Type 2) to Raccoons (Procyon lotor)

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Experimental Oral Administration of Canine Adenovirus (Type 2) to Raccoons (Procyon lotor) A. N. Hamir, N. Raju and C. E. Rupprecht Vet Pathol 1992 29: 509 DOI: 10.1177/030098589202900604 The online version of this article can be found at: http://vet.sagepub.com/content/29/6/509

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Vet Pathol 29:509-513 (1992)

Experimental Oral Administration of Canine Adenovirus (Type 2) to Raccoons (Procyon lotori A. N.

HAMIR,

N.

RAJU, AND

C. E.

RUPPRECHT

Laboratory of Large Animal Pathology, New Bolton Center, University of Pennsylvania, Kennett Square, PA 19348 (ANH); Department of Pathology, Michigan State University, East Lansing, MI 48824 (NR); and Thomas Jefferson University, Department of Microbiology, Center for Neurology, Philadelphia, PA 19107 (CER) Abstract. Canine adenovirus type 2 (CAV2) has been proposed for recombinant vaccines to control rabies in wild animals. To evaluate the suitability of CAV2 as a safe vector for the genetically engineered vaccines, seven wild-caught raccoons (three males and four females) were administered CAV2 per os. Two of the animals were euthanatized on each of post-infection days 3,6, and 14, and one was euthanatized on day 21. Two other control raccoons (a male and a female) were also euthanatized on day 21. Microscopic pulmonary lesions of multi focal necrotizing bronchiolitis with basophilic intranuclear inclusions were seen in 3/4 raccoons euthanatized on post-infection days 3 and 6. Ultrastructural examination of lungs with pulmonary lesions revealed hexagonal viral particles characteristic of adenoviruses. CAV2 is potentially pathogenic for raccoons, and this susceptibility should be of concern to developers ofrecombinant vaccines who intend to use CAV2 as a vaccine vector. Key words: Adenovirus; raccoons; recombinant vaccines.

During the past decade, the mid-Atlantic area of the United States has been experiencing an epizootic of rabies in its wild raccoon population. 14 The epizootic has not only spread to other wildlife but also has spilled over to companion and farm animals in the area. I O. 12 To counteract this outbreak, an oral vaccinia-rabies glycoprotein (V-RG) recombinant virus vaccine was developed. 19 The V- RG virus has not only been shown to be safe for raccoons and other nontarget wild and domestic animals but also has been effective under experimental conditions in protecting raccoons against challenge by street rabies virus for at least 6 months after oral vaccination." The vaccine has been given approval by the United States Department of Agriculture (USDA) for limited field trials in Virginia, Pennsylvania, and New Jersey. The use of vaccinia virus as a vector for other genes appears to be somewhat controversial," and therefore alternate virus vectors have been proposed for wildlife rabies vaccines. 1 1,16.20 One such potential vector system is the canine type 2 adenovirus, the benefits of which have been described.v-" When administered orally, this virus did not produce any noticeable clinical signs in raccoons." Because a sequential pathologic study was not performed in this experiment, it is unknown whether the adenovirus is completely nonpathogenic for raccoons or other wild animals. To verify this hypothesis we conducted the following experiment to

study the pathologic changes (if any) in raccoons that were orally administered canine adenovirus. Materials and Methods Virus The Manhattan seed strain of canine adenovirus type 2 (CAV2) was obtained from Dr. L. E. Carmichael, Cornell University, Ithaca, New York. The CAV2 was propagated in a canine kidney cell line (DK) obtained from the American Type Culture Collection (Rockville, MD, USA) for a minimum of five continuous passages. Virus was harvested from DK cells by low-speed centrifugation (1,000 x g). Animals Nine adult raccoons (Nos. 1-9; four males and fivefemales) were used for this study. The animals were originally wild caught in Ohio and were maintained in captivity for a minimum of 6 months before inclusion into the experiment. They were sedated by an intramuscular inoculation of ketamine/xylazine (10 mg and 2 mg/kg, respectively). Seven of 77 the raccoons (Nos. 1-7) were given 2.0 ml of CAV2 (10 TCID",Iml) per os as described previously," and the two controls (Nos. 8, 9) received vaccine diluent (phosphate-buffered saline) per os (Table I). Animals were observed daily for potential clinical signs attributable to CAV2 immunization, and blood samples were obtained on days 0, 14, and 21 for CAV2 neutralizing antibody tests, determined by the inhibition of cytopathic effect (CPE). Two raccoons per day were euthanatized by intravenous barbiturate overdose on

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Hamir, Raju, and Rupprecht

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Table 1. Serologic and histopathologic findings for raecoons experimentally inoculated with canine adenovirus type 2 (CAV2) and control raccoons, Euthanasia RacGroup coon Sex (days postNo. infection) Oral CAV2

M F F F M F M M F

infec-

tion

Pulrno-

Postinfection

nary lesions]

< 1: 5 < 1: 5 0 < 1: 5 < 1: 5 +