September 07, 2016

Canine Distemper Virus Infection in Giant Pandas

In late 2014 and early 2015, five giant pandas at a rescue center in China died of canine distemper virus infection.
By Laurie Anne Walden, DVM, ELS
In late 2014 and early 2015, five giant pandas at a rescue center in China died of canine distemper virus (CDV) infection. A panda that had been previously vaccinated against CDV was infected but did not develop clinical signs. Details of the outbreak were recently published in Scientific Reports.
The first panda to show clinical signs presented with limb convulsions and jaw trembling on December 3, 2014, and died 7 days later. Four other pandas, all of whom were housed in the same or adjacent areas, presented with convulsions between December 24, 2014, and March 14, 2015. In these 4 pandas, the time from symptom onset to death ranged from 12 to 34 days. Pandas testing positive for CDV were treated with antiserum. Sixteen pandas that were not infected with CDV were isolated on December 26, 2014, and given a canarypox-vectored CDV vaccine.
Clinical signs in addition to convulsions included mucopurulent ocular discharge, footpad hyperkeratosis, and nasal hyperkeratosis. On necropsy, the lungs of one panda appeared grossly congested, with small white surface patches. Histopathological analysis revealed interstitial pneumonia with congestion, widening of alveolar septa, and infiltration of multinuclear macrophages into alveoli. These findings are consistent with those reported in other species infected with CDV.
In all of the pandas that died, CDV RNA was detected by reverse transcription–polymerase chain reaction testing of nasal swab, fecal, urine, and blood samples collected at the time of disease onset and of internal organ samples collected after death. CDV RNA was also found in nasal swab samples and blood of a sixth panda that did not have clinical signs of infection. None of the five pandas that died had detectable serum neutralizing antibodies to CDV. However, the sixth panda, who had received a vaccine against CDV in 2012, had a high antibody titer.
Genome sequencing indicated that the CDV virus involved in the outbreak had high levels of nucleotide identity to various strains previously isolated from dogs, foxes, mink, and raccoon dogs (a wild canid indigenous to eastern Asia). One gene included a substitution that has been associated with highly virulent CDV strains capable of infecting multiple host species.
“Universal CDV vaccination of captive giant pandas may be warranted but must be also weighed against potential vaccination risks,” write the authors. Pandas are not routinely vaccinated against CDV because of limited supplies of the canarypox-vectored vaccine and possible risks associated with the live-attenuated vaccine. The authors recommend further studies of CDV vaccine safety and efficacy in giant pandas. “The documentation of a CDV outbreak among captive giant pandas in China suggests that heightened surveillance and CDV vaccination should be considered in all facilities housing captive giant pandas for successful conservation of this endangered species,” they conclude.
Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC.

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