There is growing information available regarding duration of immunity for core vaccines in both domestic and nondomestic species. Vaccination protocols in nondomestic canids have frequently followed guidelines developed for the domestic dog; however, these protocols can be inappropriate for nondomestic canids such as the African wild dog (Lycaon pictus), leaving some animals susceptible to infectious disease and others at risk for contracting vaccine-induced disease. In this study, red wolves (Canis rufus) were vaccinated against canine distemper virus (CDV) and canine parvovirus (CPV) and vaccination titers were followed annually for 3 yr. One hundred percent of wolves developed and maintained a positive titer to CDV for 3 yr and 96.9% of wolves developed and maintained a positive titer to CPV for 3 yr. Seroconversion for canine adenovirus was sporadic. The results of this study support decreasing the frequency of vaccine administration in the red wolf population to a triennial basis.
There is growing information regarding the efficacy and duration of vaccines in both domestic and nondomestic species. Guidelines first established in 2003 (and modified most recently in 2011) by the American Animal Hospital Association for the vaccination of domestic dogs (Canis familiaris) have led to reductions in the frequency of administration of combination canine distemper, parvovirus, adenovirus types 1 and 2, and parainfluenza vaccines.15,16,24 Similar guidelines have been established for domestic cats (Felis catus) by the American Association of Feline Practitioners.3 As a result of these studies, many zoologic medicine practitioners have moved toward a longer time interval between vaccination boosters for canid, felid, and other zoologic species. Recent publications have supported this approach in southern sea otters (Enhydra lutra nereis),10 tigers (Panthera tigris), and lions (Panthera leo),17 whereas others have reported that some species do not develop an appropriate immune response to vaccination. Those species may require modifications to the type of vaccine administered or more frequent administration than every 3 yr.12,14,17,18,23 In some instances, most notably with modified live canine distemper virus (CDV) vaccines, vaccination has induced disease in nondomestic species.5–7,11,13,19–22 The occurrence of such adverse events underscores the importance of developing appropriate vaccination protocols for nondomestic species.
The current Association of Zoos and Aquariums (AZA) Canid Taxon Advisory Group's (TAG) recommendation for vaccination of large canids does not specify the frequency of administration of multivalent combination vaccines.4 These guidelines recommend that large canid pups receive vaccinations protecting against parvovirus and distemper beginning at 6–9 wk of age with boosters administered every 2–3 wk through 16–20 wk of age; however, the frequency of administration after the animal is 1 yr of age is not defined.4 Historically, Point Defiance Zoo & Aquarium (PDZA), site of the largest population of captive red wolves, has vaccinated red wolves (Canis rufus) on an annual basis for CDV and canine parvovirus (CPV), with occasional vaccination against canine adenovirus (CAV) if multivalent vaccines were utilized. A previous study on red wolf response to vaccination for CPV and CDV indicated that this species could mount an immune response to vaccination with an anticipated duration greater than 1 yr.9 This study sought to determine the efficacy and duration of two single-agent, modified live vaccines (CDV and CPV) for red wolves using serologic data over a 3–4-yr interval. Serologic response to vaccination with CAV is also included.
MATERIALS AND METHODS
This study was reviewed and approved by PDZA's Animal Welfare Committee and the United States Fish and Wildlife Service. A total of 32 adult wolves with a mean age of 3 yr (range 2–11 yr) located at four separate facilities completed the study. Red wolves included in the study were managed primarily at PDZA's off-site red wolf facility near Tacoma, Washington. Other facilities that contributed data to this project include Wolf Haven International in Tenino, Washington; Rosamond Gifford Zoo in Syracuse, New York; and the Endangered Wolf Center in Eureka, Missouri.
Wolves were considered eligible for the study if they met the following criteria: 1) the animal received the recommended juvenile vaccination series with canine distemper, parvovirus, and rabies vaccination and 2) the wolf must have received an additional set of boosters for canine distemper, parvovirus, and rabies 1 yr after completing the juvenile series. The recommended juvenile vaccination series consisted of at least three inoculations with canine distemper combination products and canine parvovirus administered at 3-wk intervals; the inoculations were recommended to start at 8 wk of age and continue through the final vaccination set including rabies at 16 wk of age.
All wolves received booster vaccination for CPV and CDV at the beginning of the study, in 2007 or early 2008. These vaccines were a modified live canine distemper vaccine (1.0 ml, s.c., Galaxy-D, Schering-Plough Animal Health Corporation, Omaha, Nebraska 68103, USA) labeled for use in domestic dogs and ferrets, and a single-agent, nonadjuvant, recombinant modified live canine parvovirus vaccine (1.0 ml, s.c., Recombitek Canine Parvo, Merial, Duluth, Georgia 30096, USA) labeled for use in domestic dogs. Neither vaccine was administered again for the remainder of the study, although wolves received annual leptospirosis and triennial rabies vaccination as indicated by location and vaccine history. The types of vaccines used prior to the beginning of this study could not be determined for all wolves but it is anticipated that several wolves received combination multivalent canine products that resulted in serum antibodies specific for CAV.
Samples were collected from each animal on an annual basis from fall 2007 through fall 2011. Whole blood was collected from wolves during routine annual examination, via the jugular or saphenous vein. Blood was placed into a red-top serum separator tube and allowed to clot 15–30 min at room temperature before centrifugation. Serum was separated from the clot and frozen at −86°C until all samples for the year had been collected. Serum was sent to the Washington Animal Disease Diagnostic Lab in Pullman, Washington, for titer determination. CDV and CPV titers were determined by indirect immunofluorescence assay and CAV by serum neutralization (SN) assay. Titers were considered positive at ≥1 : 25 for CPV IgG, ≥1 : 5 for CPV IgM, ≥1 : 50 for CDV IgG, and ≥1 : 10 for IgM. Serum neutralization titers were considered positive at >≥1 : 4 for CAV IgG.
Of the 32 wolves that completed the study, 100% of the animals developed and maintained a positive IgG titer to CDV. Thirty-one of 32 (96.9%) wolves developed and maintained a positive IgG titer to CPV. Ten of 32 (31.25%) developed and maintained a positive SN IgG antibody titer to CAV.
For CDV IgM, eight animals (25%) developed a positive titer at different time periods during the course of the study. Only one animal (3.1%) developed and maintained a positive IgM titer over the course of the study. Two animals had a positive titer during year 1 but not years 2 and 3, three animals developed a positive titer during year 3 (9.4%), one animal developed and maintained a positive titer during years 2 and 3, and one animal had a positive titer during year 2.
For CPV IgM, 3 (9.4%) wolves developed a positive titer during year 1 of the study and had negative titers during the remaining years of the study. The remainder of wolves did not show a positive IgM titer to CPV.
CDV and CPV are important disease concerns for both captive and free-ranging red wolves and vaccination protocols have been designed to minimize the risk of disease outbreak in both populations. Although there have been no published reports of CPV or CDV causing outbreaks of morbidity or mortality within these groups, a high percentage of wild wolf pup mortalities and serologic evidence in free-ranging red wolves support natural-exposure infection to both diseases in this critically endangered species.1 Infrequent cases of mortality from either disease have been reported (Waddell, pers. comm.) and include necropsy findings in a wild juvenile male in 2011 that were supportive of fatal parvovirus infection (U.S. Fish and Wildlife Service, R. Harrison, pers. comm.). In 2013, two of five littermates in a captive litter of red wolf neonates died from a mixed adenovirus, herpesvirus, and coronavirus infection leading to fatal sepsis in the pups. The dam had been routinely vaccinated for infectious disease, including CAV, suggesting a failure of passive transfer for this litter. In a published mortality survey for captive red wolves, three of the wolves had necrotizing enteritis, with lesions that were similar to those of animals affected with CPV, although no virus could be definitively identified.2 As a critically endangered population, the loss of individuals from preventable infectious disease further compounds difficulties in the recovery of this species.
There is a small but growing field of information available on the duration of immunity of nondomestic mammalian species following vaccination.10,14,17 Currently, AZA's Canid TAG recommends that large canids be vaccinated against CPV, rabies, and CDV, with leptospirosis and coronavirus vaccination administered as indicated.4 Although recommendations exist for frequency of vaccination in pups, the frequency for adults is not identified. Gaps in knowledge regarding the safety of certain vaccines in canid species are likely the reason for the lack of adult vaccination frequency recommendations. Historically, vaccines (in particular, modified live CDV vaccines) have induced disease and caused mortality in several species, including African hunting dog (Lycaon pictus), black-footed ferret (Mustela nigripes), maned wolf (Chrysocyon brachyurus), red panda (Ailurus fulgens), European mink (Mustela lutreola), and kinkajou (Potos flavus).5–7,11,13,19–21 These losses justify attempts to quantify the duration of immunity in nondomestic species in order to to reduce the risk of vaccine-induced disease by decreasing the number of vaccines administered over an individual's lifetime.
One hundred percent of the wolves that completed the current study maintained a 3-yr positive titer to CDV at levels that are considered supportive of seroconversion or natural-exposure infection in the domestic dog. Nearly 97% of study animals maintained a positive 3-yr titer to CPV at levels considered protective from disease for the domestic dog. Of the 32 wolves followed during this study, only one individual failed to develop or maintain a titer through the course of the study. Comparatively, in 2007, Acton reported that 100% of animals demonstrated seroconversion to CDV with only 46.7% of free-ranging wolves demonstrating seroconversion to CPV.1 These variable results between seroconversion studies for CPV are likely secondary to types of vaccine administered, and highlight the importance of vaccine-specific serologic studies for management of both captive and wild endangered species.
Despite a lack of immunity challenge studies, it is anticipated that titers that are protective for domestic dogs would also be protective for the red wolf. Effective immunity for CDV requires a combination of both humoral and cell-mediated response, although antibody titers are considered predictive of immunity.8 Although positive antibody titers are not considered as predictive of immunity for CPV in domestic dogs, positive results have been correlated to protective immunity.8 Additionally, some animals with low CPV titers may still mount a protective immune response, suggesting humoral immunity is not solely responsible for protection against CPV.8 During the course of this study, no wolves at any facility included in the study developed CDV or CPV, despite outbreaks of these diseases in local wildlife (e.g., raccoons) and dogs (PDZA). However, sporadic positive IgM titers for both CPV and CDV identified during the course of the study may reflect natural-exposure infection of these individuals to either virus, as none of the wolves were revaccinated during the course of the study. Natural-exposure infection to either virus during the course of this study cannot be excluded as a cause of the sustained serologic response. As vaccine-induced distemper has been a concern for other large canid and nondomestic zoo species, it is relevant to note that none of the study wolves developed vaccine-induced disease.
Although vaccines administered at the beginning of this study were monovalent, modified live CPV and CDV, a small percentage of the wolves in the study had positive IgG titers for CAV. Due to insufficient historic vaccination information for some study individuals it was difficult to determine what vaccine products were received prior to the study. Serologic findings support evidence that some wolves received combination booster products containing CAV. These vaccines would appear to offer protective immunity for >3 yr as none of the wolves received a booster vaccination for CAV during the course of the study.
This study demonstrates that red wolves are capable of mounting a positive serologic response for ≥3 yr for both CDV and CPV. Although not all of the wolves exhibited protective titers for CPV, 97% of the wolves in this study did have protective titers at numbers that would be sufficient to prevent or minimize disease outbreaks within the population. Further research into the efficacy and duration of protective immunity to CAV is indicated, and recommendations for the use of this product cannot be made based on the results of this study. Triennial vaccination of red wolves for CDV and CPV should provide adequate protective immunity after animals have completed standard juvenile vaccination protocols.
This manuscript is dedicated to our friend, colleague, mentor, and red wolf advocate Dr. Holly Hogan Reed. The authors would like to thank Point Defiance Zoo Society for providing financial support for this project, and PDZA for support from keeper and veterinary staff necessary for wolf handling and sample processing.