Two-year-old, hermaphrodite, veiled chameleon, (Chamaeleo calyptratus).Initially the
chameleon exhibited open mouth breathing and declining appetite, eventually
requiring forced feeding. The patient returned to the clinic 4 weeks later with
severe dehydration and obvious weight loss. The chameleon was euthanized at
chameleon was in good nutritional condition with normal muscle mass and
moderate coelomic adipose stores. A small amount of clear red-tinged fluid was
present in the coelom. Diffuse red discoloration was evident in the expanded
lungs and the liver was mottled tan and red with slight rounding of the
margins. Ovotestes were present bilaterally. Mucoid content was evident in the
lumen of the stomach and the colon; the intestinal content was otherwise scant.
The faveolar septa are expanded with moderate to marked congestion of the
vasculature and myriad slender bacilli are present within the lumina of blood
vessels; bacteria are both free within the lumina and present within the
cytoplasm of macrophages. Hemorrhage, intravascular fibrin thrombi and necrotic
cellular debris often accompany the bacterial colonies and scattered small
aggregates of epithelioid macro-phages are present multifocally in the septa.
In areas, there is necrosis of the faveolar epithelium and erythrocytes,
proteinaceous fluid and cellular debris are noted with the faveolar spaces. The bacteria are acid-fast
with the Ziehl-Neelsen stain. Similar
intravascular bacteria and occasional small aggregates of macrophages
containing bacteria are present in most organs (liver, pancreas, kidney, brain,
spleen, skeletal muscle, adrenal glands, small intestine and ovotestes).
Necrotizing and histiocytic
interstitial pneumonia, diffuse, subacute, with myriad
intravascular/intrahistiocytic acid-fast bacilli and intravascular fibrin
Sections of lung were
submitted for bacterial culture. Primary culture on a sheep
blood agar plate after 48 hour aerobic incubation at 37oC
resulted in heavy growth of tiny smooth cream-colored colonies. Grams
stain revealed pleomorphic gram-positive bacilli. The
bacteria were acid-fast with the Ziehl-Neelsen stain. The
isolate was sent to the National Reference Centre for Mycobacteriology (Public
Health Agency of Canada). Based on 16s and hsp65 gene
sequencing, the isolate had 100% sequence identity to Mycobacterium
chelonae chemovar niacinogenes.
are ubiquitous in nature and can be isolated from the soil, dust, water and
bioaerosols.1 Reptiles are generally thought to acquire
mycobacterial infections via ingestion or through defects / penetrating injury
in the skin.11 In this chameleon, there was a localized area of
intestinal ulceration and granulomatous enteritis, suggesting that infection
may have been acquired through the intestinal tract. In
reptiles, like most species, mycobacterial infections tend to be chronic with
rare acute infections reported.5 The typical gross lesions are
grey-white nodules in multiple organs. Microscopically, early lesions are
composed of organized collections of foamy macrophages that with time may
become chronic granulomas composed of a mixture of epithelioid macrophages,
lymphocytes, plasma cells, and multinucleated giant cells often surrounding a
central region of necrosis and occasionally with a surrounding wall of fibrous
connective tissue.11 In this case, there were a few small early
granulomas in multiple organs including the brain, lung, liver, kidneys and
intestine. More striking, however, was the presence of myriad intravascular
bacteria in multiple organs and frequent intravascular fibrin thrombi. These
changes are compatible with acute to subacute infection with acute bacteremia
and disseminated intravascular coagulation.
Mycobacteria are broadly divided into two groups: Mycobacterium tuberculosis complex and non-tuberculous myco-bacteria.2 While only non-tuberculous mycobacteria have been reported to cause infections in reptiles, several different species have been associated with these infections. These include M. confluentis, M. chelonae, M. haemophilum, M. hiberniae, M. neoarum, M. confluentis, M. nonchromogenicum, M. marinum, and M. thamnopheos.2,5,11 The most common causes of mycobacteriosis in reptiles are reported to be M. marinum, M. chelonae and M. thamnopheos.5 The isolate in this case was confirmed to be M. chelonae chemovar niacinogenes.
Non-tuberculous mycobacteria are classified into four Runyon groups according to growth rate and pigmentation.5 Runyon group I mycobacteria are slow growing and form pigment in the light following growth in the dark. Runyon group II organisms are also slow growing bacteria; these bacteria form pigment in the dark following growth in the light. Runyon group III bacteria are slow growing and do not form pigment in the dark or light. Fast growing non-pigmented mycobacteria are placed in Runyon group IV. These mycobacteria form mature colonies on solid agar within 7 days, while bacteria in Runyon groups I to III take longer periods of time for cultivation.2 Most mycobacteria which infect reptiles fall into Runyon groups I and IV.5 Mycobacterium chelonae is a rapidly growing mycobacteria belonging to Runyon group IV.4 Rapidly growing mycobacteria are relatively resistant to standard disinfectants and antibiotic treatment and are increasingly recognized as opportunistic pathogens in humans.1,2
In reptiles, M. chelonei has been reported in association with osteoarthritis in a Kemps Ridley sea turtle,4 with stomatitis and subcutaneous granulomas in a boa constrictor,6 and with disseminated infection in a loggerhead sea turtle8 and a veiled chameleon.9 There is a single report of this bacterium causing acute fatal sepsis and disseminated intravascular coagulation in an eastern spiny softshell turtle8 with lesions very similar to those described in this case. Because of poor response to treatment and the zoonotic potential, euthanasia is often recommended for reptiles with myco-bacterial infections.
Lung: Pneumonia, histiocytic and necrotizing, multifocal to
coalescing, moderate, with numerous intrahistiocytic and intravascular bacilli, veiled
chameleon, Chamaeleo calyptratus.
The contributor provides an outstanding review of non-tuberculous
Mycobacteria in reptiles. Mycobacteria spp. are a large genus
comprised of over 100 species of obligate pathogenic, potentially pathogenic,
and environmental saprophytic bacteria.6 They are all
morphologically similar and are composed of aerobic, gram-positive, acid-fast,
non-spore forming bacilli.6 Conference participants were impressed
by the large numbers of intrahistiocytic and intravascular thin filamentous
bacilli that stain slightly basophilic on hematoxylin and eosin stained tissue
section. These bacilli are intensely acid-fast positive with Fite-Faraco and
Ziehl-Neelsen acid-fast stains, run by the Joint Pathology Center prior to the
conference. Mycobacterium chelonae infection,
confirmed by the contributor as the cause of rapid disseminated disease in this
animal, is an opportunistic and potentially zoonotic pathogen that is
characterized by rapid growth and high resistance to antibiotics.1,2
As mentioned by the contributor, spontaneous non-tuberculous Mycobacteria sp., including M. avium, M. chelonae, M. szulagai, M. fortuitum, M. marinum, M. hemophilum, M. kansasii, and M. ulcerans have been reported to be the classic etiologic agents that cause histiocytic granulomas snakes, turtles, lizards, and crocodiles and should top the list of differential diagnoses for lesions similar to this case.2,5,10,11 The obligate intracellular bacteria, Chlamydophila pneumoniae, can also occasionally infect reptilian species and induce histiocytic granulomas and should be considered as a differential diagnosis. Additionally, relatively recently described Chlamydia-like bacteria Parachlamydia acanthamoebae and Simikania negevensis, have been sporadically reported to form histiocytic granulomas in reptiles as well.11
While histiocytic granulomas in reptiles are often induced by intracellular bacteria, such as in this case, heterophilic granulomas in reptiles are caused by extracellular pathogens, including most bacterial and fungal etiologies. Tissue injury can also induce heterophilic granulomas in reptiles.5 Heterophilic granulomas are characterized by accumulation and degranulation of heterophils leading to a central area of necrosis, stimulating a strong macrophage foreign body-like response. Caseocalcareous nodules, lymphoid infiltration, and peripheral fibrosis, typical of mammalian granulomas, have not been observed in reptilian heterophilic granulomas.5 Both histiocytic granulomas and heterophilic granulomas can progress to chronic granulomas, characterized by a fibrous connective tissue capsule, lymphocytes and plasma cell infiltration, and a central area of necrosis with a prominent lamellated appearance.5
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