Investigation of Chronic Disease in a Captive Mara Colony

1
Investigation of Chronic Disease in a Captive
Mara Colony

• Mexico

2
Index Case

• July 21, 2001
• 2 year old captive born male mara (Dolichotis
  patagonum) died shortly after presenting with
  weakness and anorexia

3
Index Case-cont

• Animal had disseminated fungal infection
  affecting mostly the liver, adrenal and lymph
  nodes
• Cytology evaluation of the lymph node, adrenal
  and liver revealed numerous cytoplasmic
  yeast-like organisms
• 2-4 um in diameter
• Clear halo surrounding them
• In the cytoplasm of phagocytic cells and
  adrenocortical cells
• Gomoris methenamine silver stain positive
• Histoplasma capsulatum var capsulatum was
  isolated from spleen

4
Case Confirmation

• Gross necropsy findings
• Histological findings
• Other testing
• Special stains
• Transmission electron microscopy
• Organism isolation
• Exoantigen test
• Immunohistochemistry

5
Establishing Endemic Levels

• Intradermal testing
• Common test in humans and equine
• Test location on abdomen
• 18/29 animals negative at 72 hours
• No clinical, hematolgical, radiographic or
  immunologic evidence of histoplasmosis in these
  animals
• No prior cases of histoplasmosis in this
  collection

6
Is There An outbreak?

• There is no evidence of histoplasmosis previous
  to these cases in the entire collection
• Is there the probability that more animals in the
  mara colony could have been exposed ot the
  disease?
• Maras use dens dug in the ground, each den is
  used several times by different females
• The intradermal testing, that is the only
  practical way to detect positive animals, was
  negative.

7
Descriptive Epidemiology

• Herd history
• Environmental factors

8
Herd History

• Mara colony at park for gt20 years
• 1997 5 animals from Argentina added to group
• 1 male, 4 females
• Reproduction good since introduction (66 births)
• During time of the index case
• Herd composed of 29 animals

9
Environmental Factors

• Diet
• Water ad libitum
• Oranges, carrots, chopped alfalfa and rabbit
  pellets
• Enclosure
• 120m2
• Fenced with 1.20m high wire mesh and bamboo on
  one side
• Sandy substrate
• Often see squirrels (Spermophilus variegatus),
  Mice (Mus musculus) and various birds inside the
  enclosure.
• Often see opossum (Didelphis virginiana),
  ringtail cat (Bassariscus astutus) and stray cats
  (Felis domesticus) inside the park.
• Several wild colonies of insectivorous bats
  (Tadarida brasiliensis)

10
Subsequent Cases

• April 25, 2002
• Died after presenting with progressive weight
  loss
• Severe granulomatous typhlocolitis and moderate
  granulomatous gastrohepatic lymphadenitis
• Similar organisms in the cytoplasm of macrophages

11
Case 2

• Gross necropsy findings
• Thickening of the large intestinal mucosa
• Watery to mucoid small intestinal contents
• Histopathology
• Severe, chronic grnaulomatous and fibrosing
  hepatitis and adrenalitis with foci of
  necrosuppurative inflammation
• Granulomatous typhlocolitis
• Adrenocortical cells had abundant similar
  organisms in their cytoplasm with no associated
  lesion
• Histoplasma capsulatum var. capsulatum was
  isolated from the liver and adrenal gland.

12
Is This An Outbreak?

• Retrospective review of 54 animals revealed no
  other lesions compatible with Histoplasmosis
• Previously non-tested animals were tested with
  high-dose antigen testing
• All animals negative
• Investigate immune status of animals and
  contamination status of environment

13
Immune Status and Environment

• No previous evidence of histoplasmosis in this
  mara colony
• High probability that more animals in the colony
  could have been exposed to disease
• Intradermal testing is the only practical way to
  test these animals
• questionable accuracy
• Immunological status of the colony would
  contribute to presence of disseminated
  histoplasmosis in more animals

14
Hypotheses

• Unusual susceptibility of this species to the
  disease
• Low immunological status of the group
• Predisposing them to disease
• High environmental contamination

15
Investigate Hypothesis

• Review literature for similar cases
• Environmental Investigation

16
Literature Review

• No reports of disseminated histoplasmosis in
  maras or any rodent species
• Report of a localized mucocutaneous
  histoplasmosis in a rabbit
• Reports of histoplasmosis affecting the skin and
  lymph nodes of Badgers in Europe

17
Environmental Investigation

• Environmental sampling of mara areas
• No growth
• Mice inoculated with extracts of environmental
  samples DID seroconvert
• Demonstrates presence of organism in the
  enclosure
• 2 bat colonies in the park were sampled
• No culture growth
• NO seroconversion in mice

18
Environmental Investigation

• Climatic conditions of park does not promote the
  proliferation of the fungus
• Sandy substrate, low humidity, lack of bird or
  bat droppings
• But indirect evidence of fungal presence was
  found
• Bats play an important role in fungal
  dissemination
• Abundance of insectivorous bats in park
• Other carnivorous wild animals in the park could
  disseminate the fungus
• Serology is pending

19
Treatment and Intervention

• Disinfect
• Foot baths with phenolic base products
• Dedicated tools to affected areas
• 80cm of dirt removed from enclosure and replaced
• Disinfection of holding area
• Communicate to staff
• Provided with masks
• Review of personal hygiene
• Quarantine
• All maras moved to quarantine

20
Long Term

• Control of immune status of the colony
• Review sex ratio and demographics
• Review genetics
• Monitor wild bat colonies within the park

21
References

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