Abstract

Introduction

A 10-year (1992–2003) retrospective analysis of Mycobacterium avium ss. paratuberculosis (MAP) on a 15-acre mixed species display at Busch Gardens Tampa Bay (BGT) was conducted. Nyala (Tragelaphus angasii), impala (Aepyceros melampus), and Thomson’s gazelle (Gazella thomsonii) all commingled on this display for many years until the herds were removed in 2002 for renovations and as a medical management tool to help control MAP.

Methods and Materials

Records were reviewed to estimate the running totals of herd numbers on the display from 1992 to 2003. As some records are incomplete, these are best estimates but should be fairly accurate. Fecals were collected routinely from these herds and submitted for culture to the Johne’s testing center at the School of Veterinary Medicine at the University of Wisconsin. In addition fresh and/or frozen tissues from necropsies were submitted for culture. Positive cultures are reported out as Mycobacterium spp. and the species confirmed by PCR probe. Acid fast stains were routinely performed on the following tissues: lymph nodes (submandibular, mesenteric, and ileocecal junction), ileocecal valve, small intestine, and large intestine. Blood was collected from 12 Thomson’s gazelles and submitted to evaluate IFN-gamma production by blood mononuclear cells in response to stimulation with mycobacterial antigens.

Results

Table 1 details the prevalence of animals MAP culture positive from the common display from 1992–2003. The youngest age for a positive fecal culture for each species was a Thomson’s gazelle at 19 months, a nyala at 20 months, and an impala at 23 months. In one subset of 15 nyala that were culture positive on fecals, only six had positive cultures from tissues and none of them were positive by direct fecal PCR only. The most common place to find acid-fast organisms was in the lymph nodes, followed by small intestinal sections then large intestines and finally the ileocecal valve. In the same subset of 15 fecal culture positive nyala, 13 had acid fast organisms in lymph node tissue, 7 had acid fast organisms in small intestine, 2 in large intestines, and 2 in the ileocecal valve. In a subset of 13 impala, seven were positive on both fecal and tissue culture, five animals were positive on tissue culture but negative on fecal culture and one was positive on fecal culture but negative on tissue culture. The results of the IFN-gamma testing indicated that the antibodies for cattle IFN-gamma do not detect gazelle IFN-gamma. (Ray Waters, DVM, PhD personal communication).

Table 1. Prevalence of culture positive animals (fecal and tissue) 1992–2003

Discussion

Higher prevalence was found in impala and nyala than in Thomson’s gazelle even though all three species inhabited this display at the same time. Nyala are primarily browsers, Thomson’s gazelle are primarily grazers and impala are intermediate. As grazers Thomson gazelle seem more likely to ingest the MAP organisms. Thomson gazelle may have an inherenit resistance to infection to MAP and that could be due to more exposure to the MAP organism. Nutrition could play a role in the difference in prevalenceincidence from one species to the other. A pelleted diet and forage were provided to all species in addition to pasture but there may have been a difference in what was selected by each species and how diets met requirements for the species. The smaller species, Thomson’s gazelle, were often excluded from feeding at communal troughs. Examples of socially dominant animals having nutritional deficiencies are not unheard of in captive settings. The impala and nyala were also noted to have hypocalcemia issues on a herd basis whereas the Thomson’s gazelle did not. This may have been from an imbalance in the concentrate to roughage ratio consumed by the two more dominant species. Animals with lowered calcium diets are at an increased risk of contracting MAP.¹ In the subset of 15 nyala histopathology was actually more sensitive at finding the organism than tissue culture. Table 2 demonstrates the relative risk (odds ratio) of developing Johne’s disease in reference to the species with the lowest incidence. Impala are approximately four times as likely to develop Johne’s disease given the same exposure while nyala are approximately five times as likely to, compared to Thomson gazelles. Continued investigation into a species-specific quantitative PCR for incorporation into a Johne’s-specific diagnostic is ongoing. The role of hypocalcemia in predisposing ruminants to Johne’s disease is also being looked at in the broader scope of overall ruminant health and nutrition.

Table 2. Relative risk of having MAP culture positive sample between the three species on a common pasture at Busch Gardens Tampa Bay

Literature Cited

1.  Stabel JR, Goff JP, Ackermann MR. Dietary calcium modulates Mycobacterium paratuberculosis infection in beige mice. Vet Immunol Immunopathol. 1998;66:377–390.