Undiagnosed deaths, crocodiles - Australia (NT)(03)

International Society for Infectious Diseases
<http://www.isid.org>

Deaths in juvenile farmed crocodiles in northern Australia associated
with chlamydial infection
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Outbreaks of disease causing high mortality in farmed saltwater
crocodiles on 2 properties in the Darwin region have been thoroughly
investigated at the Berrimah Veterinary Laboratories.  Over 3000
juveniles in the 2-5 month age group died in the period from June to
August 2006. Full necropsies were performed on 57 typically affected
animals.  On both farms fatally affected animals consistently had
fibrinous pharyngitis and conjunctivitis with pharyngeal fibrinous
exudate frequently causing death by laryngeal obstruction.

Histopathology on a wide range of tissues including conjunctiva,
pharynx, liver, and spleen was performed in 32 cases. In most animals
lesions were confined to the conjunctiva, pharynx, and upper
esophagus. The microscopic lesions were similar at all mucosal sites
and essentially consist of lymphoplasmacytic inflammation, epithelial
hyperplasia and erosion. PCR for family Chlamydiaceae was positive on
specimens of conjunctiva (13/13 animals) and pharyngeal mucosa (5/5
animals) forwarded to the Tropical and Aquatic Animal Health
Laboratory, Townsville.  DNA sequence analysis for speciation/strain
typing of the Chlamydiae is being performed at the Queensland
University of Technology and the University of Melbourne.

There has been comment, previously reported on ProMED, of the
possibility of poxvirus infection being responsible for the lesions.
Poxvirus was excluded early in the investigation, since the
characteristic histological changes produced by this virus group were
not found in any of the cases examined. Furthermore, thin section
electron microscopy on pharyngeal and conjunctival mucosa from 3
typically affected animals failed to detect viral particles, pox
virus or otherwise.

An interesting difference between crocodiles and mammalians, which
may account for more widespread chlamydial lesions, is the presence
of columnar non-ciliated mucosal epithelium (favored by chlamydiae)
lining the crocodile pharynx and esophagus.  Since the poxvirus group
usually infects stratified squamous epithelium, they would be
unlikely candidates for conjunctival/pharyngeal disease in
crocodiles.  Viral infection however has not been completely
dismissed and isolation attempts on the affected specimens are continuing.

Factors which appear to account for the high mortality in juvenile
crocodiles with fibrinous pharyngitis are the anatomical features of
the pharynx/larynx and the inability to cough, both factors making
these animals highly susceptible to laryngeal obstruction by exudate.
The buildup of exudate associated with mucosal damage likely
partially accounts for the poor clinical response to antibiotic
treatment.  Note also that animals with pharyngeal lesions are
inapparent; thus oral medication must be force-fed. Parenteral
administration of antibiotics is poorly tolerated by juvenile crocodiles.

--
Ian Jerrett BVSc MACVSc
Veterinary Pathologist
Berrimah Veterinary Laboratories
Darwin, Northern Territory
Australia