Overview of Vaccination of Exotic Mammals

Overview of Vaccination of Exotic Mammals

By J. Jill Heatley, DVM, MS, DACZM, DABVP (Avian), Associate Professor, College of Veterinary Medicine, Texas A&M University ; Jeffrey Musser, DVM, PhD, Clinical Associate Professor, Texas A&M University

Exotic mammals are susceptible to many of the same infectious diseases that affect domestic mammals. However, vaccination of these species is often extra-label, because vaccines are tested and approved for use only in domestic species. Vaccination protocols recommended for exotic mammals are therefore based on limited published information, anecdotal experience, and relative risk of disease to the species from the infectious agent or vaccination itself. Reports of lack of seroconversion, antibody production, sustained protection, and induction of the disease resulting in morbidity and mortality in a variety of species, particularly for rabies and distemper, are common after vaccination of exotic mammals. Regardless, vaccination should be considered in captive wildlife and conservation programs based on a number of factors. Many diseases preventable by vaccination such as canine distemper virus, canine parvovirus, feline calicivirus, feline panleukopenia virus, and rabies virus have caused population declines or reduced host fitness in critically endangered mammals. Certainly, infectious disease outbreaks in small numbers of highly genetically valuable individuals can disastrously affect conservation projects. Unfortunately, the biology of many of these preventable diseases (incubation period, transmissibility, etc) in exotic mammals is often unknown. Captivity may enhance the risk of acquiring disease based on food sources, exposure to rodents and other disease hosts, and an unknown degree of exposure of other zoo animals, which is unlikely to occur in nature. Thus, due consideration of protection of captive nondomestic species, even those destined for release to the wild, is warranted. Core vaccines are designated as those that protect captive animals from life-threatening, globally distributed diseases. The determination of protection has largely been based on studies in domestic species; nonetheless, based on current knowledge, these vaccines deserve full consideration for inclusion into vaccination regimens for captive exotic mammals.

Individual animal safety dictates that inactivated or recombinant viral or bacterial vaccines are preferable to modified-live virus (MLV) vaccines, which have the potential to cause disease in exotic mammals and abortions in hoofstock. However, in select species, especially Old World apes, MLV vaccines have received sufficient use to warrant consideration based on the serious risk of morbidity and mortality. Use of MLV vaccines for rabies and distemper are generally contraindicated in exotic mammals. In particular, use of MLV distemper vaccines in exotic mammals may result in postvaccinal myelitis or distemper. Recently developed canary pox–vectored vaccines are the current vaccine of choice for distemper and appear both safe and efficacious. The following concepts should be considered before extra-label use of a vaccine in an exotic animal. Possession of the animal should be legal per state community and other applicable laws. Informed consent of the owner and discussion of the availability or lack of safety and efficacy trials associated with the use of this vaccine in the animal should be documented in the medical record. Use of product and vaccination procedures with record of previous success such as those used or recommended in zoo (Association of Zoos and Aquariums or American Association of Zoo Veterinarians) protocols, and those with publications supporting their safety and efficacy in the species, should be considered. Vaccination may be foregone in the face of lack of data to support that a certain disease occurs, despite antibody presence, in some species.

Vaccination protocols developed for exotic mammals should be determined with respect to number of animals, husbandry, relative value of animal and offspring, pregnancy, species susceptibility to a disease, likelihood of encountering disease, disease prevalence in the surrounding locality, ability to obtain useful products, information of reported or anecdotal benefits or disadvantages with usage of a vaccine in that species, housing and vector control programs, and zoonotic and infectious potential of the disease. As in domestic species, animals that are febrile or have other clinical signs of illness should not be vaccinated. Because a full vaccine dose is required to elicit a satisfactory immune response, remote vaccine administration should be weighed against anesthetic and disease risk. Some nondomestic mammals and their recommended vaccination protocols (eg, cervids, rodents, lagomorphs, camelids) are reviewed elsewhere in the Manual, and the reader should refer to the relevant chapters. In domestic mammals, young animals have differing vaccine schedules than those presented in Vaccinations Recommended for Exotic Mammals based on waning maternal antibodies. Consideration of the provided references and consultation with experts in zoo medicine and exotic mammal husbandry are recommended to develop vaccination protocols. Specific vaccine protocols should be developed for neonates. For apes, a youngster vaccination schedule, based on the human schedule, should include the killed polio series and Haemophilus vaccination (http://www.cdc.gov/vaccines/schedules/index.html).

Although titer determinations may be useful for evaluation of vaccination in exotic mammals, the lack of antibodies does not equate to lack of immune response. This method quantifies only the humoral immune response, not the cell-mediated aspect, and protective titer levels for exotic mammals have not been evaluated or established. Examples of titers that may be assessed include rabies, distemper, parvovirus, and leptospires, as well as the encephalitic viruses and many viruses affecting nonhuman primates that also affect people. Yearly and preshipment viral titers, which vary based on species, are recommended for all primates. Titers change based on natural disease exposure, independent of vaccination, may or may not confer protection from disease, and may also wane quickly, despite repeated exposure.