Low Titers of Canine Distemper Virus Antibody in Wild Fishers (Martes pennanti) in the Eastern USA

Canine distemper (CD) virus (CDV) is a very contagious morbillivirus in the family Paramyxoviridae (Bernard et al. 1984; Greene and Appel 1990). The virus infects several families in the order Carnivora: Canidae, Mustelidae, Procyonidae, Hyaenidae, Ursidae, Viverridae, Felidae, Otariidae, Phocidae, and Mephitidae (Grachev et al. 1989; Mamaev et al. 1996; Deem et al. 2000; Kennedy et al. 2000; Williams 2001; Barrett et al. 2004), as well as families of the orders Cetartiodactyla (Artiodactyla; Cervidae and Suidae) and Primates (Cercopithecidae; Sun et al. 2010; Kameo et al. 2012). Canine distemper virus is transmitted mainly through aerosolization of respiratory exudate containing the virus, but other bodily secretions or excretions may be contagious if aerosolized (e.g., urine; Greene and Appel 1990), and the virus also has been transmitted through feces (Brown et al. 2006). The respiratory, gastrointestinal, integumentary, and central nervous systems are most commonly affected by CDV infections.

Fishers (Martes pennanti) are members of the family Mustelidae. Other mustelids are extremely susceptible to CDV (Deem et al. 2000), experiencing a mortality rate approaching 100% in some species (e.g., ferrets; Mustela putorius; Duplaix-Hall 1975; Wallach and Boever 1983; Bernard et al. 1984; Stephensen et al. 1997). Thus, fishers also may be susceptible to CDV infection and high mortality if infected. There have been relatively few reports about the incidence or epizootiology of CD in wild fishers. Five of 10 fishers trapped in New York (Monson and Stone 1976), three of 18 fishers from Maine (Frost and Krohn 1994), and one of 31 from northern California (Brown et al. 2006) were positive for the CDV antibody. Specific titers were not reported in any of these cases. Keller et al. (2012) reported the deaths of four fishers from California as being linked to CDV. The immunoglobulin M (IgM) and immunoglobulin G (IgG) antibody titers were reported in three of those fishers (IgM: 32, 32, and 8; IgG: 64, 128, and 32, respectively).

Understanding the potential diseases associated with wild-caught carnivores and the management of such diseases, as part of any reintroduction project, is important, especially when the diseases are considered contagious. Thus, the intent of prerelease management programs associated with care of animals intended for reintroduction should follow a process that is twofold: 1) maximize the health of the animals being relocated and 2) minimize the risk of introducing new pathogens or diseases into the areas of relocation (International Union for the Conservation of Nature, Species Survival Commission [IUCN/SSC] 2013). Reintroducing a species with a contagious disease can have a deleterious effect on wild and domestic animals at the relocation area. These concerns can be partially addressed by sampling the source population to be reintroduced through serologic studies to identify potential pathogens that may be transferred to the relocation area (Woodford 2000).

The Pennsylvania Fisher Reintroduction Project (PFRP) was implemented in 1994 to restore fishers to regions of their historic range in Pennsylvania. As part of the PFRP, 58 fishers were livetrapped from New Hampshire (n=55) and New York (n=3) and relocated to Pennsylvania. Prior to release, wild-caught fishers underwent a captive management program designed to evaluate their health and condition upon arrival at The Pennsylvania State University (PSU; University Park, Pennsylvania, USA), with primary focus on identification and treatment of preexisting injuries or diseases prior to release (Mitcheltree 1996; Mitcheltree et al. 1997). Upon initial entry into holding facilities at PSU, the 58 fishers were immobilized with an intramuscular injection of 100 mg of ketamine hydrochloride (Ketaset®, Fort Dodge Laboratories, Fort Dodge, Iowa, USA) to facilitate physical and clinical evaluation. As part of the screening, blood samples were collected from immobilized fishers to screen for CDV antibody. Blood samples were collected by jugular venipuncture, and serum was separated and frozen at −20 C. Serum samples were shipped on dry ice to the New York State Veterinary Diagnostic Laboratory at Cornell University (Ithaca, New York, USA), for serum neutralization testing (Appel and Robson 1973) to detect CDV antibody. Results of laboratory analyses were reported as percentage of fishers found positive and endpoint titers. Samples reactive at a dilution of ≥1:16 (Gese et al. 1997) were considered positive. Titers are expressed as the reciprocal of the greatest dilution found positive. The use of fishers and the procedures of this study were reviewed and approved by the PSU Institutional Animal Care and Use Committee (94RO57A1).

Five of the 58 (9%; all from New Hampshire) fishers had a weak-positive reaction for CDV antibody at a titer of 16 (Table 1). The remaining 53 (91%) fishers were negative for CDV antibody, with titers of 4 (n=44; 83%) or 8 (n=9; 17%).

Possible reasons for the weak-positive reactions in five of the fishers could be 1) a minimal immune response to CDV, 2) a fairly rapid loss of IgG antibody, 3) a long period of time since infection occurred, 4) exposure was recent, and high titers had not yet developed, or 5) a possible combination of reasons 1)–3) (Brown et al. 2006). Absence of antibody in the remaining 53 fishers may indicate that these fishers had 1) low or no exposure to CDV, 2) exposure was recent and the immune response had not developed, or 3) the wild population they came from experienced high or rapid mortality and fishers that were infected with CDV died before capture (Brown et al. 2006).

Reintroduction projects are only considered if the intended benefits of translocating the species will outweigh the risk of any negative impacts after translocation (IUCN/SSC 2013). Hence, procedures must be implemented to enhance the success of the translocation, including efforts to ensure that translocated animals are free of disease. Fishers used in the PFRP were typically held 10–14 d prior to release to monitor for clinical signs of disease. None of the fishers used in the PFRP showed clinical signs of CD or other disease, including the five fishers with low antibody titers. With the low antibody prevalence and none of the 58 fishers exhibiting any clinical signs of CD while being held at PSU prior to release, fishers reintroduced into Pennsylvania were at low risk of being infected with CDV when released and, thus, unlikely to contribute to the introduction of CDV at relocation areas.

Funds and support for the Pennsylvania Fisher Reintroduction Project were provided by the Pennsylvania Wild Resource Conservation Fund, the School of Forest Resources at the Pennsylvania State University, the US Department of Agriculture, Allegheny National Forest, and Pennsylvania Game Commission.