In July of 2007 an adult wild female manatee (Trichechus manatus latirostris) was rescued near the Isles of Capri, Florida. Upon arrival to the Miami Seaquarium, Key Biscayne, FL, she was evaluated for head trauma after sustaining severe injuries from a boat propeller. Initial clinical signs included a swollen forehead, a flaccid muzzle, dysphasia, an absent papillary light reflex bilaterally, hyperesthesia to the lumbar area, no pain response to the flippers, and anorexia. When placed in the pool, she had no use of her flippers and struggled to breathe while surfacing the water. The paddle was fully functional, thus it was assessed that the spinal cord was not completely severed.
Within one week function to the flippers and the pupillary light reflex returned, but the manatee had complete deficits of motor function to the muzzle and swallow reflex. Radiography revealed that the atlas was fractured on both sides. After consulting with a manatee anatomist, we suspected that the peripheral nerves were severed as they exited the cranium (see Figure 1). The cranial nerves are peripheral nerves and have the potential capacity to regenerate unlike the axons of the central nervous system (CNS), which lack Schwann cells.2,3 Human case studies have suggested that peripheral nerves can regenerate at an estimated rate of 1 mm/day.1 In theory, this manatee could potentially regenerate her nerve loss; however, given the severity of her injuries, her prognosis was guarded.
She was initially treated with injectable broad spectrum antibiotics, a decreasing dose of steroids, and gastroprotectants. Since it was evident that she could not swallow, nasogastric tubing commenced upon arrival to the facility. She was tube-fed once daily for nearly three months as her only source of nutrition and water. To minimize stress, the maximum volume we could tube was 2 ½ liters. Externally, she looked and acted like a completely normal manatee (except for eating and drinking). After three months of therapy, the manatee finally began showing twitches to her upper muzzle and a few swallowing gulps upon tubing, but still lacked the ability to prehend food and remained anorexic. A few days later, she began to grasp lettuce leaves slowly with her muzzle and soon after, was foraging lettuce on a consistent basis. She was released with normal muzzle motor function and ability to swallow four months after her rescue.
Figure 1. Courtesy of Sentiel A. Rommel, MS, PhD
We would like to thank the Florida Fish and Wildlife Conservation Commission. We truly feel that the speed in which they brought this manatee into our critical care facility was paramount to her survival. We would also like to thank Dr. Sentiel A. Rommel for his input on this case and for providing the illustration.
1. Bailey B.J., J.T. Johnson, and S.D. Newlands (eds.). 2006. Head & Neck Surgery-Otolaryngology 4th edition, Vol. 1, Lippincott Williams & Wilkins, Philadelphia; Pp. 209-210.
2. Brecknell J.E., and J.W. Fawcett. 1996. Axonal regeneration. Biol Rev Camb Philos Soc 71(2): 227-255.
3. Fenrich K., and T. Gordon. 2004. Canadian Association of Neuroscience review: axonal regeneration in the peripheral and central nervous systems-current issues and advances. Can J Neurol Sci 31 (2): 142-156.