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Fox squirrels are an emerging urban, suburban, and agricultural vertebrate pest in California. They cause a diversity of damage to vegetation and property. Multiple introductions of fox squirrels into California have led to a rapid expansion of their range in the state. Fox squirrels at the University of California, Davis increased from none to an estimated 1,609 between 2001 and 2009. Damage due to the dense population of fox squirrels is increasing. There are several population control options available, but social considerations may limit the viable options to non-lethal methods. This paper provides an overview of the impacts of the introduced fox squirrel in California and on the University of California, Davis campus.

The term “vaccine” has traditionally been associated with establishing immunity (antibodies) to a disease. This immunity is usually developed following administration of killed microorganisms. Disease vaccines typically require 1 to 3 injections, depending on the antigen design and efficacy of the vaccine. The effectiveness of the disease vaccine depends on the immune response developed by the host following exposure to the disease organism. The immunocontraceptive vaccine GonaCon™ is designed to produce immunity to the “self” hormone (GnRH), which is essential to reproductive activity in the mammal. Antibodies to GnRH reduce its biological activity resulting in infertility of both sexes. GonaCon™’s effectiveness as a single-injection immunocontraceptive wildlife vaccine depends on 4 factors. The first is the use of a large foreign mollusk protein in the GnRH conjugate. Second is the design of mollusk/GnRH protein conjugate that presents the GnRH antigen in a repetitious fashion. This design mimics the “danger signal” found in bacterial pathogens to which the animal has been previously exposed. Third is the addition to the vaccine of micrograms of Mycobacterium avium, which is ubiquitous in the environment and activates memory cells. The fourth factor is use of a water-in-oil emulsion, which provides a depot at the injection site, allowing a slow release of the vaccine. With this formulation, the vaccine is presented to the body as a “chronic infection”, even though it is not infectious. The granuloma that normally develops at the injection site plays a prime role in the host’s defense against this “chronic infection”. A WHO report on the use of the alum adjuvant in human vaccines states that “development of a small granuloma is inevitable with vaccines adjuvanted with aluminum, and is to be considered necessary to the efficacy of the adjuvant.” Researching GonaCon™ for use in companion animals, NWRC has looked at many different adjuvants intended to reduce the injection site reaction while at the same time retaining an effective vaccine. This paper reports on the role of the adjuvant and the injection site on the effectiveness of the vaccine.

Greater demand for non-lethal means of alleviating human-wildlife conflict has led to an interest in contraception as a wildlife management tool. The development of a single-injection Gonadotropin-Releasing Hormone (GnRH) contraceptive vaccine by the USDA National Wildlife Research Center reduces logistical limitations and the cost of using a vaccine that requires 2 injections. This study assesses the efficacy of different GnRH-KLH (keyhole limpet hemocyanin) vaccine designs. Forty-two captive female black-tailed deer were divided into 3 groups. A control group was injected with saline solution, and 2 treated groups were given either GonaCon™, a GnRH vaccine paired with AdjuVac™ (an adjuvant containing 175 µg of killed Mycobacterium avium), or GnRH vaccine without AdjuVac™ (instead substituting DEAE-dextran/oil (DD) as the adjuvant). Pregnancy rates in deer treated with GonaCon™ were significantly reduced as compared to saline controls (P = 0.006). There was no significant difference between GnRH-DD compared to saline (P = 0.297). Significant difference was found between GonaCon™ and GnRH-DD (P = 0.055). Vaccinated does that remained fertile received booster injections according to treatment group and were administered either GonaCon™ containing 87 µg M. avium or GnRH-KLH conjugate bound to DEAE-dextran. Deer that received booster injections regardless of the adjuvant were 100% contracepted for 1 year. Six out of 10 deer that received a prime injection of GonaCon™ remained 100% contracepted for 3 years, suggesting that the killed M. avium in the adjuvant is essential for the success of GonaCon™ as a single-injection GnRH vaccine.

Traditional methods of prairie dog management are not always practical or acceptable. Therefore, other methods need to be developed to aid managers responsible for prairie dog management. Contraception is one such method being developed at the National Wildlife Research Center (NWRC). GonaCon™, an immunocontraceptive vaccine, has shown promise for other species when administered as a single shot. A laboratory dose-response study and a field study using GonaCon™ with black-tailed prairie dogs are being conducted concurrently at NWRC. DiazaCon™ is an oral contraceptive that resulted in a 47% reduction in the number of pups/adult in a preliminary field trial. However, treatment was administered late in the breeding season in that trial. A new field study is currently underway to examine the effects of DiazaCon™ on reproduction when administered to black-tailed prairie dogs just prior to the breeding season.

Changing cultural values and increasing urbanization in the United States are curtailing traditional wildlife management tools used to effectively manage conflicts between human and wildlife populations. Because of this trend, the USDA Wildlife Services, National Wildlife Research Center (NWRC) began developing wildlife contraceptives in 1991. Since that time, NWRC scientists have steadily worked toward the goal of developing and registering contraceptive products that are practical to use, safe for the treated animal, and present little risk to humans, nontarget animals, and the environment. Working cooperatively with Innolytics, LLC, OvoControl G™ was recently registered for reducing the hatchability of Canada goose eggs. Another product developed by the NWRC, the single-shot GonaCon™ Immunocontraceptive Vaccine is poised to begin the registration process. A third product, DiazaCon™, soon will be tested for field efficacy and should begin the registration process within the year. Between 1996 and the present, the regulatory agency responsible for wildlife contraceptives has been the Food and Drug Administration, Center for Veterinary Medicine (CVM). Working under this premise, the NWRC has progressed toward fulfilling CVM’s regulatory requirements by conducting field efficacy studies and a target animal safety study. NWRC explored various registration options with the CVM, and also with the USDA APHIS Center for Veterinary Biologics (CVB). Through this process, it became clear that wildlife contraceptives were incompatible with CVM’s regulatory process, and outside the regulatory authority of CVB. In response, CVM and the U.S. Environmental Protection Agency (EPA) negotiated an agreement on contraceptive uses. The EPA will assume regulatory authority of contraceptives used for wildlife and feral animals. The CVM will retain authority over all uses in captive animals including livestock, companion animals, and zoo animals.

High deer densities increase vehicle collisions, damage agricultural crops, and amplify the spread of zoonotic and animal diseases, intensifying human-deer conflict. In addition, deer impact on forest vegetation can influence the distribution and abundance of other wildlife species. Greater demand for non-lethal means of animal damage control has led to an interest in contraception as a wildlife management tool. The development of a single-injection Gonadotropin-Releasing Hormone (GnRH) contraceptive vaccine by NWRC reduces logistical limitations and cost of using immunocontraception as compared to a vaccine that requires two injections. This study assessed the efficacy of two different GnRH-KLH (keyhole limpet hemocyanin) vaccine designs in a single-injection study, to determine if Mycobacterium avium bacterium in the adjuvant is necessary for the success of a single-injection contraceptive vaccine. Forty-two captive female black-tailed deer were divided into 3 groups. Control deer were injected with saline solution, one treatment group received GonaCon™ (a GnRH-KLH vaccine paired with AdjuVac™ adjuvant that contains a small quantity of killed M. avium bacterium), and the second treatment group received GnRH-KLH vaccine with DEAE-Dextran/oil as the adjuvant. Contraceptive success was evaluated by monitoring progesterone, pregnancy specific protein, antibodies to GnRH-KLH conjugate and to Johne’s bacterium (M. avium), and actual pregnancy rates. Pregnancy rates were significantly different based on treatment (X² = 9.389; df = 2; P = 0.009). Pregnancy rates in deer treated with GonaCon™ were significantly reduced as compared to saline controls (P = 0.006), but there was no significant difference between GnRH-DD compared to saline (P = 0.297). Significant difference was found between GonaCon™ and GnRH-DD (P = 0.055). Results suggest that M. avium in the AdjuVac™ adjuvant is essential for the success of the single-injection GnRH vaccine GonaCon™. The development of a single-injection vaccine will increase the practicality and lower the cost of using immunocontraception as a tool to control deer populations.

As part of the program to develop contraceptive tools to control populations of over-abundant wildlife species, the NWRC has developed a single-injection gonadotropin-releasing hormone (GnRH) immunocontraceptive vaccine, GonaCon™. GonaCon™ has been tested and shown to provide contraceptive effects lasting 1-3 years in many pest species including white-tailed deer, domestic and feral pigs, bison, wild horses, cats, dogs, and California ground squirrels. GonaCon™ contains a GnRH peptide conjugated to keyhole limpet hemocyanin combined with AdjuVac™, an adjuvant also developed at the USDA National Wildlife Research Center. Immunization against GnRH prevents the circulating GnRH from stimulating the release of pituitary luteinizing hormone and follicle-stimulating hormone. This process of immuno‑neutralization of GnRH effects a temporary non‑surgical castration in both males and females. Contraceptive and behavioral effects of GonaCon™ are discussed for a variety of species.

Tree squirrels (Sciurus spp.) are highly successful immigrants to urban and suburban areas in North America and Europe, causing both economic and ecological damage. Control of such invasive populations is challenging but of increasing importance to local managers. We studied an invasive population of fox squirrels (S. niger) and applied an immunocontraceptive vaccine in an experimental study of demographic control. Here we integrate our data into a simple stage-structured population model to simulate population reduction under 2 treatment levels (60 and 80% of females, respectively) for vaccines lasting from 1 to 5 years. Contraception can be an effective means of reducing fox squirrel populations if the vaccine is effective for ≥2 years or if ≥71% of the females are treated. Over a 15-year period, fewer individuals require treatment at a treatment rate of 0.8 versus 0.6 due to a declining population size. This study illustrates how a simple population model may guide local resource managers in the design of control strategies for invasive species.

Immunocontraceptive vaccines have shown some promise for fertility control of white-tailed deer (Odocoileus virginianus) in urban and suburban habitats where traditional methods of population control may not be applicable. Currently, the only contraceptive vaccine approved by the U.S. Environmental Protection Agency for use in white-tailed deer is GonaCon™ Immunocontraceptive Vaccine, but it is registered for use via hand-injection only. It has been suggested that remote-delivery of immunocontraceptives would be more cost-effective than hand-injection, but there is the potential for incomplete injection from a syringe-dart. Therefore, the purpose of our research was to: (1) conduct a dart configuration assessment trial to determine the ideal syringe-dart configuration for remote-delivery of GonaCon to white-tailed deer and (2) use the determined syringe-dart configuration in a subsequent trial to evaluate the vaccine efficacy when administered to female white-tailed deer via hand-injection versus syringe-dart. We saw comparable results with regard to vaccine dispersal during the dart configuration assessment and the efficacy trial; syringedart injected deer presented vaccine deposits and reaction sites both subcutaneously and intramuscularly, whereas, hand-injected deer presented vaccine deposits and reaction sites only intramuscularly. One year after administration, 4 of 5 deer treated with syringe-darts were pregnant, compared to 3 of 6 deer that received hand-injections. Anti-GnRH titers were negatively related to pregnancy status. We did not observe a high level of vaccine efficacy with the syringe-dart delivery method we used. Therefore, we recommend further research of syringe-dart delivery of GonaCon with a larger sample size where the vaccine is deployed in a single bolus similar to a hand-injected presentation. [ABSTRACT FROM AUTHOR]

Tree squirrels (Sciurus spp.) are highly successful immigrants to urban and suburban areas in North America and Europe, causing both economic and ecological damage. Control of such invasive populations is challenging but of increasing importance to local managers. We studied an invasive population of fox squirrels (S. niger) and applied an immunocontraceptive vaccine in an experimental study of demographic control. Here we integrate our data into a simple stage-structured population model to simulate population reduction under 2 treatment levels (60 and 80% of females, respectively) for vaccines lasting from 1 to 5 years. Contraception can be an effective means of reducing fox squirrel populations if the vaccine is effective for ⩾2 years or if ⩾71% of the females are treated. Over a 15-year period, fewer individuals require treatment at a treatment rate of 0.8 versus 0.6 due to a declining population size. This study illustrates how a simple population model may guide local resource managers in the design of control strategies for invasive species. [ABSTRACT FROM AUTHOR]

Highlights: [•] Simultaneous administration of GonaCon™ and rabies vaccine did not affect immunogenicity. [•] Local injection site reactions were less frequent and intense than an earlier formulation. [•] GonaCon™ did not negatively impact the delivery of healthy pups. [•] Studies that monitor female dogs through multiple breeding cycles are needed. [ABSTRACT FROM AUTHOR]

The article presents a study to determine the effects of a contraceptive vaccine on eastern gray squirrels (EGS). The administration of vaccine was through a combination of pelage characteristics of body weight. The animals were trapped in seasons and were killed for necropsy to evaluate histologic changes in testes and ovaries. The study reveals that treated EGS males had testicular, prostatic and epididymal atrophy when compared to controlled EGS males while there were no histologic changes in EGS females. The study demonstrates the potential of the GonaCon™ to control EGS population.

Abstract: Management of prairie dogs in the past has included poisoning, fumigants, barriers, and relocation. Because of the diverse attitudes related to prairie dog management, nonlethal methods that allow the existence of prairie dogs but help minimize damage related to population growth need to be developed. GonaCon™ is an immunocontraceptive vaccine that elicits antibodies to native GnRH; this prevents the secretion of reproductive hormones necessary for sperm and oocyte production. Prairie dogs were vaccinated with 0.1, 0.2, or 0.4mL of the GonaCon™ emulsion intramuscularly in the upper thigh containing 100, 200, or 400μg GnRH conjugate, respectively. Control animals were vaccinated with 0.4mL saline emulsion in the upper thigh. Blood samples (≤1mL) were taken from the femoral vein once pretreatment and at 1, 2, 3, 4, 6, and 15 months post-vaccination. Age (adult or juvenile) did not affect immune response to GonaCon™. Antibody titers were higher in the 200 and 400μL GonaCon™ groups than in the 100μL group, and there was no difference between the 200 and 400μL GonaCon™ groups. No adverse effects of GonaCon™ were noted on weight or blood chemistry parameters during the study. GonaCon™ will likely contracept prairie dogs for ≥1 year in the field using either 200 or 400μg conjugate. GonaCon™ could be incorporated into management plans to help maintain prairie dog populations while reducing habitat degradation due to overpopulation. [ABSTRACT FROM AUTHOR]

Abstract: Parenteral vaccination campaigns are integral to the elimination of canine rabies. To maximize herd immunity in dogs, immunocontraception provided at the time of rabies vaccination should reduce fecundity and dog abundance. GonaCon™ has been used successfully as an immunocontraceptive in a variety of mammals, and by inference, the dog would be an ideal candidate for testing. As an initial step in evaluating a combination-vaccination program, we assessed the effects of GonaCon™ on rabies virus neutralizing antibody production in dogs after administration of a veterinary rabies vaccine. Eighteen feral/free ranging dogs were included in this initial study: six were given GonaCon™ only, six were given rabies vaccination only, and six received GonaCon™ and rabies vaccination. Antibody levels were evaluated over 82 days. The use of the immunocontraceptive GonaCon™ did not affect the ability of dogs to seroconvert in response to the rabies vaccine. Thus, GonaCon™ provides a potential immunocontraceptive for use in combination with rabies vaccine to increase herd immunity and address dog population over abundance to better manage rabies. [Copyright &y& Elsevier]