Pathologic Findings in Loggerhead Turtles found with a Polyneuropathy in Coastal Waters off South Florida
Starting in October 2000, sub adult loggerhead sea turtles (Caretta caretta) showing clinical signs of a neurological disorder were found in waters off south Florida. Neurologic examination supported a diagnosis of neuromuscular junction transmission block and/or a severe demyelinating polyneuropathy that had spared axons and caused a conduction block of nerves. Seventeen turtles that were brought into rehabilitation facilities subsequently died and were necropsied. Using light microscopy, the most prominent lesions included tracheitis, proliferative pneumonia and spirorchidiasis. The tracheal and pulmonary lesions may be primary or secondary to chronic illness and a compromised immune system. Ulnar and sciatic nerves and biceps brachii and semi-membranosus muscles were collected and are being evaluated. A polyneuropathy may account for the tracheitis and pneumonia since these animals probably cannot clear inhaled material from their respiratory passages. The spirorchid trematode eggs and or adults were seen in a variety of tissues including spinal cord, meninges and brain. Eggs of these parasites were often surrounded by a granulomatous inflammatory response. Myocarditis was also seen in several cases with small round cells (probably lymphocytes) infiltrating the myocardium. A range of other lesions were seen in the various turtles evaluated. In a previous report, tracheitis and proliferative pneumonia have been associated with a specific herpes virus infection in green turtles (Chelonia mydas) in a turtle farm in the Cayman Islands; therefore tissues from an affected turtle were cultured for herpes virus and assayed by PCR for presence of herpes virus gene sequences. Plasma samples from affected turtles have been assayed by ELISA for specific antibody to a herpes virus isolated from green turtles. These tests have been negative to date.
At this time it is impossible to attribute the illness and epidemic to any one specific pathogen or toxin. However the neurospirorchidiasis has many similarities with neuroschistosomiasis as reported in humans. Spirorchidae and Schistosomatidae represent sister groups of intravascular trematodes. Neuroschistosomiasis is well described and a range of neurological defects have been reported in humans. Further, it is possible that these parasites may act as vectors for some other pathogen. Harmful algal toxins are known to cause neurologic disorders in a variety of marine animals and also may be involved in this outbreak. However, no other marine animal (e.g. Fish, other species of marine turtles or marine mammals) within the range of the ill loggerheads hag been similarly affected during the extent of this temporal event. If it is a toxin it would have to be localized in the prey base of these turtles, or these turtles have to be uniquely sensitive to this toxin. A final consideration is the possibility of jellyfish toxicosis or vector transmission by jellyfish of a toxin. Loggerheads have been seen at sea feeding upon large aggregates of jellyfish off the south Florida coasts.
This is an on going epizootic and the investigation is in its preliminary stages. There are many routes left to pursue in the examination of the many possible differentials we are currently considering.