margot monti kristin kemper kristin gundersen …...kristin kemper kristin gundersen lisa...

10
7 MYCOBACTERIUM AVIUMIN THE PYGMY RABBIT (BRACHYLAGUS IDAHOENSIS) Margot Monti Kristin Kemper Kristin Gundersen Lisa Harrenstien Oregon Zoo 4001 SWCanyonRd Portland, OR 97221 [email protected]. us ABSTRACT The pygmy rabbit (Brachylagus idahoensis) is a small burrowing lagomorph inhabiting the sagebrush habitat of eastern Washington, Oregon and northern Idaho. Due to habitat loss, the Oregon and Washington populations have become endangered. A joint conservation effort between the Washington Department of Wildlife, Washington State University, Northwest Trek Wildlife Park and the Oregon Zoo is attempting to determine what, if anything, can be done to reverse this process. It has been found that the Washington and Idaho populations, along with a purely captive population of animals cross-bred from the Washington and Idaho groups, are susceptible to disseminated Mycobacterium avium infection. A case summary of the 20 pygmy rabbits infected with M avium in captivity was prepared. Clinical signs of M avium in pygmy rabbits can include marked weight loss, pneumonia, altered blood values including lymphocytosis and hyperglobulinemia, and sometimes swollen elbow, stifle or hock joints with reduced range of motion. These joint lesions are caused by granulomas that contain acid-fast bacilli and test positive for M avium. M avium can also be cultured from the urine and (rarely) from feces. On necropsy, there are often diffuse granulomatous lesions containing M avium throughout the internal organs of the body. These are most consistently in the kidneys and joint swellings, but have also been found in many other organs. Because M avium is very resistant to anti-tuberculosis drugs and may persist in soil litter for many months, both treatment and prevention of the condition in the pygmy rabbit have been difficult. INTRODUCTION The pygmy rabbit (Brachylagus idahoensis) is the smallest rabbit in North America and is the only burrowing North American rabbit species. Pygmy rabbits are uniquely dependent upon sagebrush, which comprises up to 99% of their winter diet. They inhabit sagebrush-dense areas in Washington, Oregon, California, Nevada, Utah, Idaho, Montana and Wyoming. Two distinct subpopulations are recognized: the Columbia Basin pygmy rabbit and the Great Basin pygmy rabbit. .,. The Columbia Basin pygmy rabbit has been federally listed as endangered under the Endangered Species act since 2001. A subpopulation of pygmy rabbits native to the state of Washington, it has been isolated and distinct from the main population for thousands of years (WDFW, 1995). A recent sharp decline in the number of rabbits in this population was attributed primarily to AZVT 2 i h Annual Proceedings h

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Page 1: Margot Monti Kristin Kemper Kristin Gundersen …...Kristin Kemper Kristin Gundersen Lisa Harrenstien Oregon Zoo 4001 SWCanyonRd Portland, OR 97221 montim@metro.dst.or. us ABSTRACT

7

MYCOBACTERIUM AVIUMIN THE PYGMY RABBIT(BRACHYLAGUS IDAHOENSIS)

Margot MontiKristin KemperKristin GundersenLisa HarrenstienOregon Zoo4001 SWCanyonRdPortland, OR [email protected]. us

ABSTRACT

The pygmy rabbit (Brachylagus idahoensis) is a small burrowing lagomorph inhabiting thesagebrush habitat of eastern Washington, Oregon and northern Idaho. Due to habitat loss, theOregon and Washington populations have become endangered. A joint conservation effortbetween the Washington Department of Wildlife, Washington State University, Northwest TrekWildlife Park and the Oregon Zoo is attempting to determine what, if anything, can be done toreverse this process. It has been found that the Washington and Idaho populations, along with apurely captive population of animals cross-bred from the Washington and Idaho groups, aresusceptible to disseminated Mycobacterium avium infection. A case summary of the 20 pygmyrabbits infected with M avium in captivity was prepared. Clinical signs of M avium in pygmyrabbits can include marked weight loss, pneumonia, altered blood values includinglymphocytosis and hyperglobulinemia, and sometimes swollen elbow, stifle or hock joints withreduced range of motion. These joint lesions are caused by granulomas that contain acid-fastbacilli and test positive for M avium. M avium can also be cultured from the urine and (rarely)from feces. On necropsy, there are often diffuse granulomatous lesions containing M aviumthroughout the internal organs of the body. These are most consistently in the kidneys and jointswellings, but have also been found in many other organs. Because M avium is very resistant toanti-tuberculosis drugs and may persist in soil litter for many months, both treatment andprevention of the condition in the pygmy rabbit have been difficult.

INTRODUCTION

The pygmy rabbit (Brachylagus idahoensis) is the smallest rabbit in North America and is theonly burrowing North American rabbit species. Pygmy rabbits are uniquely dependent uponsagebrush, which comprises up to 99% of their winter diet. They inhabit sagebrush-dense areasin Washington, Oregon, California, Nevada, Utah, Idaho, Montana and Wyoming. Two distinctsubpopulations are recognized: the Columbia Basin pygmy rabbit and the Great Basin pygmyrabbit. .,.

The Columbia Basin pygmy rabbit has been federally listed as endangered under the EndangeredSpecies act since 2001. A subpopulation of pygmy rabbits native to the state of Washington, ithas been isolated and distinct from the main population for thousands of years (WDFW, 1995).A recent sharp decline in the number of rabbits in this population was attributed primarily to

AZVT 2ih Annual Proceedingsh

Page 2: Margot Monti Kristin Kemper Kristin Gundersen …...Kristin Kemper Kristin Gundersen Lisa Harrenstien Oregon Zoo 4001 SWCanyonRd Portland, OR 97221 montim@metro.dst.or. us ABSTRACT

habitat loss as a result of agricultural conversion and the burning of sagebrush to promote growthof grasses for cattle grazing. Currently, the 23 known remaining individuals are part of a jointcaptive breeding program involving the Washington Department of Fish and Wildlife,Washington State University, the Oregon Zoo and Northwest Trek Wildlife Park.

The Great Basin pygmy rabbit is not endangered. Individuals from. a Great Basin population inIdaho are being used as surrogates for the Columbia Basin captive breeding program.Techniques, protocols and procedures essential to the program such as capture, housing, pairingand release are tested and refined on the Great Basin individuals before they are utilized with theColumbia Basin animals.

The Columbia Basin pygmy rabbit captive breeding project was initiated in 2001 when 18rabbits were brought into captivity. Although captive breeding has produced 32 rabbits survivingpast emergence from burrows (at approximately 14 days of age), little net numerical gain hasbeen achieved. The breeding program has encountered many obstacles including low fecundityrates, lack of genetic diversity and disease. Coccidiosis often causes the deaths of young captiverabbits, and all captive rabbits surviving to adulthood periodically shed coccidial cysts. However,the most important disease of captive adult pygmy rabbits is mycobacteriosis due toMycobacterium avium, which has caused the death of 20 animals -:--including individuals fromthe Columbia Basin, Great Basin and an intercross population of rabbits -- as of April 2004.

Mycobacterium avium is a non-tuberculous mycobacterial species, meaning it is anenvironmental inhabitant and an opportunistic rather than an obligate pathogen. The bacteriareside in water, soil and avian feces. They are resistant to drying and so may live in soil litter formany months (Montali, 1978). They also tolerate chlorination and biocide use, and can thereforepersist in tap water as well (Primm, 2004).·

Though disease caused by M avium infection in mammals is rare (Primm, 2000), it has beenfound that some species of rabbit, swine, mink and marsupial display increased susceptibility tomycobacteriosis (Thoen, 1997). In most of these cases, M avium lesions are localized, butdisseminated mycobacteriosis has been seen in immunosuppressed individuals and populationsthat have experienced loss of genetic diversity (Cromie, 2000). The Columbia Basin pygmyrabbit population appears to exhibit both of these characteristics.

METHODS

A case summary. of the nineteen pygmy rabbits in which mycobacteriosis was reported wasprepared using Microsoft Excel. Clinical signs and bloodwork results from live animals arepresented, as are necropsy findings of granulomatous lesions containing acid-fast bacilli thatcultured positive for M avium.

Several methods have been utilized to diagnose M avium in captive pygmy rabbits:-- In-house acid-fast stains on suspect lesions (both pre-and post-mortem) to yield acid-

fast bacilli (AFB)-- Complete necropsy examinations on all expired animals=Mycobacterial cultures on feces, urine and granulomatous lesions collected on necropsy

8AZVT 2lh Annual Proceedings

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2

--Polymerase Chain Reaction (PCR) confirmation of M avium in AFB positive lesions

RESULTS

(Table 1 illustrates the findings.) Mycobacteriosis caused by M avium in captive pygmy rabbitsis characterized by non-specific signs of illness including anorexia, weight loss, lethargy anddiarrhea. Occasionally, signs such as lameness or neurological disease are associated withmycobacteriosis but are not specific for this disease process. The most common alteredhematology values included leukocytosis, heterophilia and hyperglobulinemia. These values canindicate a nonspecific inflammatory process that also could be attributed to the stress ofhandling. It is interesting to note that monocytosis and anemia, which would indicate chroniclesions, were not seen consistently. Necropsy results revealed that mortality caused by Mavium in pygmy rabbits is not typically localized to one particular organ, but is commonlydisseminated to several organs. Kidney and lung lesions seem to be the most common, but manyanimals also had lesions in the GI tract, liver, CNS and limb joints.

Treatment of pygmy rabbits suspected of having mycobacteriosis has been attempted usingsupportive care such as oxygen therapy and subcutaneous fluids. Additionally, a number ofantibiotics have been tried, including: trimethoprim sulfa (TMPS), enrofloxacin, azithromycinand rifampin. Currently a combination of azithromycin and rifampin is the treatment of choice,but sensitivities of the strain(s) of Miavium to these drugs are not known. In humans beingtreated for Mycobacterium avium complex, rifampin therapy can last up to two years(Harrington, 1999). As none of the pygmy rabbits has survived more than a few months afterfirst showing signs of the disease process, proper dosages and duration of treatment in pygmyrabbits has not. been determined. In addition, the stress of handling a rabbit for treatment evenonce a day can exacerbate an already compromised immune system.

Because mycobacterial infections are chronic and disseminated in the pygmy rabbit, it wouldappear that preventive efforts might be the best way to reduce the disease in the captivepopulation. A common source of exposure to the pathogen has not yet been positively identified-- results are pending on enclosure soil samples and water sources -- but future managementrecommendations for the population will include implementing an off-soil breeding program and

. offering the animals sterilized water in sterilized receptacles.

CONCLUSION

Diseases affecting small populations of highly endangered animals are of utmost concern.Therefore, there is little room for error in handling such populations. However, developingeffective protocols for handling such diseases can be a complicated and arduous process.Currently the etiology behind mortality-associated mycobacteriosis caused by Mycobacteriumavium in captive pygmy rabbits is unknown. Possible causes include high-level exposure to theopportunistic pathogen in the captive environment through soil or water, inherent immunedysfunction or immunosuppression of the species and decreased immunity due to loss of geneticdiversity. Mycobacteriosis is difficult to control in animal species, and years of therapy may benecessary before beneficial results are seen. Pygmy rabbits have a short life span and, therefore,such a time frame for treatment is not a viable option.

9AZVT 24'}, Annual Proceedings

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REFERENCESCromie RL, Brown MJ, Forbes NA et al. A comparison and evaluation of techniques fordiagnosis of avian tuberculosis in wildfowl. Avian Pathology 1993; 22: 617-630.

Harrington, R. MD and Spach, D.H. MD. Mycobacterium avium Complex, Current TreatmentOptions in Infectious Diseases 1999; 1: 71-80; available from www.biomedcentral.com/1523-3820/1/71 [accessed 31 May 2004]

Hayes D. Washington Pygmy Rabbit Recovery Plan Update. Olympia, WA: WashingtonDepartment of Fish and Wildlife; 2003.

Kemper, K and Gunderson, K. Clinical Data Summary of Captive Pygmy Rabbit Mortality.Unpublished as of May 2004.

Montali R, ed. Mycobacterial Infections of Zoo Animals. Washington DC: SmithsonianInstitution Press. 1978.

Primm, TP, Cam, Lucero and Falkingham, 1.0. III. Health Impacts of EnvironmentalMycobacteria. Clinical Microbiology Reviews 2004; 17: 98-106.

Thoen C. Tuberculosis. In Claneck BW, Barnes JH et al (eds): Diseases of Poultry. Ames, Iowa,Iowa State University Presss, 1997: 167-178.

Washington Department ofFish and Wildlife. Pygmy Rabbit Recovery Plan: ExecutiveSummary; www.wdfw.wa.gov/wlm/diversity/soc/recovery/pygrabitlpygrabit.htm: 1995[Accessed 8 May 2004]

ACKNOWLEDGEMENTSDr. Kristin Mansfield, Washington Department ofFish and WildlifeMitch Finnegan, DVM, The Oregon ZooNina Palmer, LVT, Bronx ZooVirginia Crossett, LVT, Louisville Zoo

10AZVT 24th Annual Proceedings

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MYCOBACTERIOSIS MORTALITY IN CAPTIVE PYGMY RABBITS (pg 1 of 4)

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Page 6: Margot Monti Kristin Kemper Kristin Gundersen …...Kristin Kemper Kristin Gundersen Lisa Harrenstien Oregon Zoo 4001 SWCanyonRd Portland, OR 97221 montim@metro.dst.or. us ABSTRACT

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Page 7: Margot Monti Kristin Kemper Kristin Gundersen …...Kristin Kemper Kristin Gundersen Lisa Harrenstien Oregon Zoo 4001 SWCanyonRd Portland, OR 97221 montim@metro.dst.or. us ABSTRACT

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NECROPSYGranulomatous lesion in:LungKidneyLiverMusculoskeletalLymph nodesHeartSpleenBrain/eNSMesenteryStomachlIntestineDiaphragmAdrenalSkin (Subcutaneous)Bone MarrowPancreasReproductive OrgansAdipose Tissue

Page 8: Margot Monti Kristin Kemper Kristin Gundersen …...Kristin Kemper Kristin Gundersen Lisa Harrenstien Oregon Zoo 4001 SWCanyonRd Portland, OR 97221 montim@metro.dst.or. us ABSTRACT

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Page 9: Margot Monti Kristin Kemper Kristin Gundersen …...Kristin Kemper Kristin Gundersen Lisa Harrenstien Oregon Zoo 4001 SWCanyonRd Portland, OR 97221 montim@metro.dst.or. us ABSTRACT

Proceedings of the24th Annual Meeting

of the

ASSOCIATION OF ZOO VETERINARY TECHNICIANS

25 August - 28 August 2004

Roosevelt Park Zooand

Holiday Inn Minot-RiversideMinot, North Dakota

Proceedings Edited byBonnie Soule, BS, CVT

Roger Williams Park ZooProvidence, RI 02907

-

Page 10: Margot Monti Kristin Kemper Kristin Gundersen …...Kristin Kemper Kristin Gundersen Lisa Harrenstien Oregon Zoo 4001 SWCanyonRd Portland, OR 97221 montim@metro.dst.or. us ABSTRACT

Library of Congress National Serials Program

Association of Zoo Veterinary TechniciansProceedings of the 24th Annual Conference of Zoo Veterinary Technicians

ISSN 1052-0732

2004 AZVT, Providence, RIAll Rights Reserved Printed in the United States of America