8 March 2013 Science Briefs

SNAMP PUB #10: Canine distemper in an isolated population of fishers (Martes pennanti) from California

Article Title: Canine distemper in an isolated population of fishers (Martes pennanti) from California.

Authors: Keller, S. M., M. Gabriel, K. A. Kerio, E. J. Dubovi, E. Van Wormer, R. A. Sweitzer, R. H. Barrett, C. Thompson, K. Purcell, and L. Munson.

Research Highlights:


  • Although Pacific fisher is a candidate for listing under the Federal Endangered Species Act, little was previously known about how disease spread among them.

  • Four radio collared fishers with the same strain of canine distemper virus (CDV) died in our study population in spring and summer 2009.

  • Analysis of the infected animals revealed there were probably two separate disease outbreak events.

  • CDV infection was the primary cause of death for two animals, and predisposed the other two to death by other factors. These are the first reports of CDV in fishers.

  • The CDV strain from the four fishers were most similar to CDV from domestic dogs, but this did not directly implicate dogs as the source.


Background:
Currently, the Pacific fisher in Washington, Oregon and California is a candidate for listing under the Endangered Species Act. In California, there are two genetically distinct groups of fisher, one in northwestern California and the other in the southern Sierra Nevada, where there are fewer than 350 animals remaining. One pathogen of concern is canine distemper virus (CDV), which has resulted in the decline or near loss of small, isolated populations of various species including black-footed ferrets (Mustela nigripes). However, before this study there were no previous reports of the disease among fisher. This study describes the results of analysis of CDV infection in four free-ranging fishers and discusses how their virus strains are related.

All four fishers were part of a long-term population study and were monitored with radio-collars that reported when death occurred. Three fishers were recovered less than 6 miles (10 km) apart. A fourth fisher died during capture about 43 miles (70 km) from the others. Analysis of blood samples found distemper virus in the spleen, lungs, and kidneys of all four fishers.

Results:
Findings were consistent with previous reports in similar species. The three fishers that died near each other within the same month had the same type of CDV. The type of CDV that killed the fourth fisher four months later only differed genetically by 0.4%. No other fisher mortalities were noted during this time period.

The source of infection for the fishers in this study is unknown as no identical virus was found in the current California wildlife genetic bank (GenBank – found at: http://www.ncbi.nlm.nih.gov/genbank/), yet the timing and location of mortalities, as well as the high similarity of viruses, suggest that the infection was spread two different times from one or more similar species. The CDV strain from the four fishers was most similar to strains from domestic dogs, but this does not mean that dogs were the source of the infection.

More comprehensive studies are needed to find where CDV in fisher habitat comes from. Although where the infection came from, or how it spread, is still not known, the genetic information from the CDV viruses in the four fishers studied here are now on GenBank. This will provide information useful for research into future outbreaks, sources of infection, and how CDV is spread among fishers and other carnivores in this region. Ultimately, the goal is to protect fisher populations in the American west by learning more about how to prevent or reduce diseases.

Note: The published article includes one table and four figures providing information on the serological, histologic, immunohistochemical, and H gene nucleotide sequence of virus isolates used for the phylogenetic analyses.

Full Reference:
Keller, S. M., M. Gabriel, K. A. Kerio, E. J. Dubovi, E. Van Wormer, R. A. Sweitzer, R. H. Barret, C. Thompson, K. Purcell, and L. Munson. 2012. Canine distemper in an isolated population of fishers (Martes pennanti) from California. Journal of Wildlife Diseases 48(4): 1035–1041.

For more information about the SNAMP project and the Fisher Team, please see the Fisher Team site here.

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