Hawksbill Turtle (Eretmochelys imbricate) with mycobacteriosis (M. marinum)
Registry case number TARZ-9624.1
The sub-adult, male hawksbill turtle was found nearly dead on Shellharbour beach. The person who found the animal poured water over its head and it moved its flippers, but was profoundly weak and lethargic. The animal was transported to Taronga Wildlife Hospital where it was found to have erythematous skin, extensive carapace algae, numerous erosions on its plastron and large skin erosion on the top of its head. The turtle was treated with fluids, B vitamins and fortum, but was found dead the next morning.
External examination: The carapace is markedly covered in algae. The scales along the lateral aspects of the carapace are lifting along the margins. There is a thick, tan L shaped ulcer with a raised central region. There are numerous 2 – 3 cm long ulcers along the plastron. The skin is erythematous.
Muscle mass: emaciated
Fat deposits: absent
Internal examination: The spleen is markedly enlarged and nodular, measuring 12 x 8 cm. On cut section the tissue is composed of firm to hard white foci admixed with friable brown parenchyma. Focally there is a wedge shaped region of black, necrotic appearing tissue with a maximum width of 3 cm.
Throughout the lungs there are multiple 1-1.5cm diameter white nodules and other less defined firm white areas of parenchyma. The pulmonary tissue is wet and exudes a frothy, purulent appearing discharge.
The gall bladder is distended with bile and there appear to be fibrin plaques along the serosal surface. The gall bladder is readily manually expressed into the small intestine. The bile duct is markedly thickened and very firm, with a tan mural plaque.
There are 1cm diameter tan nodules dangling from the most caudal papillae of the oesophagus. A 1.3 cm diameter tan, thick plaque is present in the adjacent gastric mucosa. The distal gastric mucosa is extensively eroded and then there are several 1-1.5cm diameter fibrin plaques thickening the mucosa near the gastric/oesophageal junction. The duodenal mucosa is black. Throughout the intestinal tract there are severe and extensive areas of erosion and ulceration, admixed with thick, tan fibrin plaques. At approximately the junction of the small and large intestines there is a 1.5 x 1.8 cm diameter mural mass, which on cut section has a thin connective tissue capsule and a caseous white centre. The mucosa in this area is markedly eroded.
Multifocal 3-4 mm tan plaques are firmly adherent to the bladder mucosa.
The gastrointestinal tract contains scant ingesta and no plastics are evident.
The tissues are well preserved.
Lesions are not evident within the following tissues: small intestine, skeletal muscle, thyroid gland (C), oesophagus (F)
The following observations are notable:
Spleen (A, B): The tissue is nearly indistinguishable and contains scant lymphoid tissue. The tissue us composed largely of streaming reticuloendothelial cells, macrophages, and foci of coagulation to caseation necrosis. Where lymphoid aggregares are present, they contain large numbers of pyknotic and karyorrhectic nuclei.
Lung (A): The pulmonary interstitium is multifocally and extensively thickened with granulomas and granulomatous inflammation. The granulomas have central caseous debris surrounded by rims of macrophages and multinucleate giant cells, then peripheral circles of connective tissue bearing lymphocytes, plasma cells and scattered granulocytes. Interstitial foci of granulomatous inflammation are predominantly composed of macrophages and multinucleate giant cells. Multifocally, these infiltrates extend into adjacent airways. While in other foci there are merely aggregates of macrophages, multinucleate giant cells and cellular debris evident in airways. The epithelium of many smaller airways is tall cuboidal rather than squamous.
ZN stain (A): Beaded, long acid fast bacilli are evident individually, and in clusters throughout the splenic parenchyma and within macrophage and multinucleate giant cell aggregates within the pulmonary interstitium and airways. Acid fast bacilli are not evident within the central caseous material or inner layer of the large pulmonary granulomas, but they are evident within macrophage and multinucleate giant cell aggregates at the periphery of the granulomas.
Myocardium (B): Multifocally within the myocardium and along the endocardium there are aggregates of macrophages that have foamy cytoplasm. Some of these foci contain eosinophilic, fibrinoid material and cellular debris.
Liver (D): Multifocally and extensively, the hepatic cords have been replaced with aggregates of macrophages and multinucleate giant cells that have abundant foamy cytoplasm. Eosinophilic, fibrinoid material is evident within some of these foci. Kupffer cells contain brown cytoplasmic pigment and there is occasional erythrophagocytosis.
Stomach (D): The gastric mucosa contains extensive haemorrhage. The villar tips are lost and in some areas the margin of viable and non-viable tissue contains necrotic cells. Large colonies of bacteria are evident within the non-viable tissue. Multifocal intestinal crypts contain sloughed epithelial cells, or aggregates of granulocytes. Some of these crypts are segmentally lined with squamous epithelium.
Cloaca (E): The cloacal wall is markedly thickened and necrotic. There is a transmural infiltrate of round cells with moderate quantities of eosinophilic cytoplasm, admixed with granulocytes. This infiltrate extends into the adventitia and onto the coelomic surface. The mucosa is segmentally intact and proliferative, and then it is necrotic and coated with bacterial colonies, before being completely consumed by the thick cellular infiltrate.
Duodenum (E): The intestinal wall is segmentally intact, containing only a small number of lamina proprial aggregates of macrophages. The remaining segment of intestine is markedly distended by a thick cellular infiltrate, as described in the cloaca above. Foci of coagulation to caseation necrosis are evident throughout the tissue.
Bile duct (F): The bile duct wall is markedly thickened by a cellular infiltrate and extensive necrosis that has effaced much of the mucosa. The infiltrate is composed of a mixture of granuloyctes and round cells with mild cytoplasm. Bacteria are scattered throughout the portions of tissue near to the lumen of the bile duct.
Large intestine/small intestine – site of mural granulomas (F): The tissue is markedly and diffusely thickened with an infiltrate of granulocytes and macrophages, as described above, with extensive foci of caseation to coagulation necrosis. The infiltrate is more granulomatous near the serosa and more granulocytic near the lumen. Serosal blood or lymphatic vessels contain foci of necrosis often containing bacterial colonies. Scant remnant mucosa is visible.
Brain – sagittal section (G): Small clusters of macrophages bearing waxy brown pigment are evident in Virchow-Robbin space.
Skin – wound on top of head (H): The epidermis is mildly thick and it is covered with a thick layer of compact keratin, which often contains branching, non-parallel sided fungal hyphae. Focally, there is a cavitating wound that breaches the epidermis and extends deep into the dermis. The centre of the lesion contains caseous cellular debris and large numbers of bacterial colonies. The margin of the wound consists only of exposed viable dermis, which sometimes contains scattered necrotic cells. The keratin layer at the margins of the wound is markedly thickened, containing an exudate of granulocytes. Fungal elements may be present within the keratin layer, but do not appear to be present within the exudate in the cavitating wound.
Acid fast bacteria are evident within splenic and pulmonary impression smears.
Multisytemic granulomas – mycobacteriosis – M marinum
Enteritis – fibrinonecrotising, severe, extensive
Wound – dorsal head
The turtle was found to have marked splenomegally and granulomas in the walls of the intestine and bile duct. Acid fast bacteria were found within impression smears of these lesions at the time of necropsy. Microscopic examination of the tissues identified granulomatous inflammation throughout many organs. The lesions in the stomach and gall bladder walls were chronic and severe, with necrosis and haemorrhage of what little mucosa remained. There were some large granulomas in the lungs, which did not appear to contain acid fast bacteria, and may have been caused by a separate process.
This is an interesting case of disseminated mycobacteriosis in a free ranging turtle. The most severe and chronic appearing mycobacterial lesion was in the intestinal tract, which suggests that the digestive tract was the portal of infection for this animal.