Abstract
In 2010, 71 of the 767 Florida manatee (Trichechus manatus latirostris) carcasses examined by Florida Fish and Wildlife Commission's Marine Mammal Pathobiology Laboratory staff were noted to have macroscopic 1–5 mm diameter, flat to slightly elevated black or discolored lesions on the parietal pleura. Prior to this time, pleura specks had only been recorded once in 2009.1 The most common cause of death associated with this clinical finding was cold stress syndrome (85% [60/71; 95% CI 74–92]); followed by cause of death remaining undiagnosed (7% [5/71; 2–16]), other natural diseases (6% [4/71; 2–14]), and manatees that died due to anthropogenic misadventure (3% [2/71; 0.3–10]). If clinical significance can be confirmed, the persistent occurrence of parietal pleural specks in animals dying of cold stress may be a useful post mortem indicator of this complex disease.
Of the several samples taken from histology quality carcasses and submitted for microscopic analysis, only two were successfully preserved for examination. This may have been due to human error during the tissue preparation phase or, more likely, a breakdown of the lesions when placed in 10% neutral buffered formalin solution. Lesion destruction did not occur when stored in 70% ethanol. In one manatee (MNW1019), projections were noted on the parietal pleura that contained a moderate amount of macrophages with cytoplasmic globular hemosiderin pigmentation. A previous intrathoracic or pleural hemorrhage was speculated as initiating cause; a theory supported by findings from other examined carcasses where red lesions were thought to be coagulating erythrocytes. In the other animal (MNW1069), the parietal pleura was considered normal. In humans, these types of respiratory-associated lesions have been linked with pollution and asbestos-related mesothelioma.2 In birds, pollutant inhalation has been the initiator of lesions in the respiratory system.3 In green sea turtles, discrete coelomic pigmentation has been confirmed to be due to spirorchiid parasite egg granulomas forming in peripheral vessels and when green adipose tissue atrophies result in macroscopic concentration of pigment giving a black speck appearance.4
The origin of these specks in Florida manatees is unknown and in cold stress animals there was no predilection to the acute (55% [33/60; 42–68]) or chronic (45% [27/60; 32–58]) form of this syndrome. Determining why black specks are being found in manatees may provide a link to the pathogenesis of cold stress syndrome; particularly the role of respiratory compromise which in turn may help improve current treatment regimes of this endangered species. Finally, the role of the environment as a co-factor in the recent emergence of this lesion, including the role of inhalation pollutants, is warranted.
Acknowledgements
The authors wish to thank Mr Brandon Bassett for data retrieval from the FWC Database; and the FWC and UF Aquatic Animal Health programs for funding support.
References
1. Florida Fish and Wildlife Conservation Commission. 2010. Manatee mortality database. Florida Fish and Wildlife Conservation Commission, St Petersburg.
2. Mitchev K, Dumortier P, De Vuyst P. 'Black spots' and hyaline pleural plaques on the parietal pleura of 150 urban necropsy cases. American Journal of Surgical Pathology 2002; 26: 1198–1206.
3. Tully T. Avian respiratory diseases: clinical overview. Journal of Avian Medicine and Surgery 1995; 9: 162–174.
4. Flint M, Patterson-Kane JC, Limpus CJ, Work TM, Blair D, Mills PC. Post mortem diagnostic investigation of disease in free-ranging marine turtle populations: a review of common pathological findings and protocols. Journal of Veterinary Diagnostic Investigation 2009; 21: 733–759.