White-tailed deer farming is an established and growing industry in Pennsylvania. Managers of deer farming operations often struggle with animal health problems, the most common of which is pneumonia associated with Fusobacterium sp. infection. Fusobacterium is a genus of anaerobic, gram negative, rod-shaped bacteria that have been associated with many infectious disease processes in humans and animals. It is important to the deer industry, as well as the cattle and sheep industries, to more clearly understand fusobacterial disease pathogenesis and determine effective treatment and prevention strategies. The objectives of the following series of studies were: (1) to determine the current management practices and animal health problems on white-tailed deer farms in Pennsylvania, (2) to phenotypically and genotypically characterize a set of Fusobacterium isolates from white-tailed deer and evaluate their association with disease in the host, and (3) to determine the pathogenicity of Fusobacterium varium to the respiratory tract of mice and to evaluate this system as a model for pulmonary fusobacterial infection of deer.
A total of 28 clinical strains of Fusobacterium spp. were isolated at necropsy over a two-year period from the respiratory tract of cervids, including white-tailed deer, elk, and reindeer. Isolates were identified as F. varium (21/28, 75%), F. necrophorum subsp. funduliforme (5/28, 17.9%), and F. necrophorum subsp. necrophorum (2/28, 7.1%). Using PCR-based detection of virulence genes, all F. varium isolates were negative for the promoter region of the leukotoxin operon of F. necrophorum and the hemagglutinin-related protein gene of F. necrophorum. In the necropsy population no significant differences in gross or microscopic lesions were detected across Fusobacterium species, suggesting similar potential for virulence, however, toxicity to bovine polymorphonuclear leukocytes was not observed in any F. varium strains, perhaps indicating that a virulence factor other than leukotoxin is involved in the pathogenesis of F. varium infection. F. varium was less susceptible to many antimicrobials than were the F. necrophorum subspecies. These data suggest that F. varium may be a significant pathogen in deer and may require different treatment and prevention methods than F. necrophorum.
C57BL/6 mice and BALB/c mice were inoculated intranasally with various strains and varying dosages of F. varium to evaluate the pathogenicity of F. varium to the respiratory tract of mice and to determine the utility of this system as model of fusobacterial pneumonia. Prior to inoculation, mice were pre-treated with either 0.2 mg dexamethasone intraperitoneally once daily for four days, 10 μg of lipopolysaccharide (LPS) of E. coli 055:B5 intranasally one time, or no pre-treatment. Following inoculation mice were observed for morbidity and mortality for fourteen days. No mice infected with F. varium showed clinical illness or died. No mice infected with F. varium developed gross or microscopic lesions. The bacterium was recovered from the blood of one mouse, but was not recovered from blood or lung of any other mice. Antifusobacterial IgM or IgG were not produced in serum by 14 days in response to infection. Pre-existing antibodies detected in pooled serum bound similarly with proteins of two F. necrophorum subspecies and three F. varium strains, but did not bind to proteins of similar size from other common bacterial pathogens including Escherichia coli, Pasteurella pneumotropica, Arcanobacterium pyogenes, and Clostridium perfringens. No serum antibodies were detected in BALB/c mice. These results suggest that F. varium is not highly pathogenic to the respiratory tract of mice, and does not result in a humoral immune response following intranasal inoculation.
In conclusion, the results of this series of studies suggest that fusobacterial species, specifically F. varium, are not highly pathogenic to the respiratory tract and are unable to establish lung infection alone without some severe predisposing condition. Management changes on deer farms should be instituted in an effort to minimize stress, overcrowding, nutritional imbalance, and environmental contamination, while maximizing immunity through colostrum and vaccination, and developing effective preventive health and biosecurity programs with routine veterinary consultation. (Abstract shortened by UMI.)