A non-intervention controlled study on the safety of distemper vaccines in ferrets. (Draft version).
Introduction
Canine distemper (CD) is a disease that occurs in members of the Canidae, Procyonidae and Mustelidae families (Crook and Gorham 1958, Dinnes 1980, Woodford 2000). Although the prevalence of CD is currently low in domestic animals, many ferrets are used in pest control and are at risk of contracting CD not only from dogs, but also from foxes and wild Mustelidae (Crook and Gorham 1958, Budd 1981).
The causative agent for canine distemper, Canine Distemper Virus (CDV), is a single stranded RNA Morbillivirus, in the Paramyxoviridae family. CDV is shed in urine, faeces, skin scurf, and in conjunctival, nasal and oral exudates, materials (Gorham and Brandly 1953) and can be transmitted by direct contact with infected animals and infected materials (Gorham and Brandly 1953. Shen and Gorham 1978), and by aerosol exposure to infected body fluids (Crook and others ).
Viable CDV has been recovered from inert materials for as long as 20 minutes after contact with an infected animal (Gorham and Brandly 1953), and CDV in infected tissues has been shown to retain infectivity for days at 25°C, and for weeks at 2 - 4°C (Shen and Gorham 1980). CDV is therefore relatively robust, and the disease is highly contagious.
The symptoms of CD are severe, and there is no effective treatment for CD (Pearson and Gorham 1999). Consequently, the mortality rate for CD in ferrets is high, approaching 100% (Fox and others 1999, Pearson and Gorham 1999 Lewington 2000, Wimsatt and others 2001), and prevention by vaccination is recognised as essential by the majority of veterinary practitioners (Pearson and Gorham 1999, Lewington 2000, Brown 2001).
In the US, two monovalent CD vaccines are licensed for ferrets, Fervac-D (United Vaccines, Inc, Madison, W1), a modified-live virus vaccine of chick cell origin and Purevax (Merial, Athens, GA) a canary pox vectored recombinant vaccine. In the UK, no CD vaccine is currently licensed for use in ferrets, and no monovalent CD vaccine is available. In consequence, many UK vets elect to vaccinate ferrets against CD using multivalent dog canine distemper vaccines, even though it has been suggested that use of multivalent vaccines in ferrets may lead to vaccine-induced disease (Finkler 1999).
There has been a number of anecdotal reports of anaphylactic reactions following vaccination of ferrets against distemper in the US (Lewington 2000, Brown 2001). These anecdotal reports have been substantiated by a recent retrospective study of the medical records of ferrets in the US, in which Greenacre (2003) found that anaphylactic reactions including generalized hyperemia, hypersalivation, and vomiting, had been reported at an incidence of 5.6% following vaccination against distemper. Such observations have led to concern in many ferret owners about the safety of distemper vaccination, to the extent that some UK ferret owners are now electing not to vaccinate their ferrets against CD (personal communications from ferret owners in the UK).
Despite the concerns about the risk of distemper vaccination of ferrets, and even though CD can be easily disseminated and is almost invariably fatal, a large scale study has not been undertaken to evaluate the safety in ferrets of the distemper vaccines that are currently in use in Europe. The following large scale non-intervention study was carried out with the intention of providing UK veterinary surgeons and ferret owners with information on the safety of CD vaccines currently in use in ferrets, thus enabling them to make an informed decision on vaccinating ferrets against canine distemper.
Safety was evaluated using adverse events occurring in the one month period following vaccination and noted on a study specific questionnaire by ferrets owners. Control data was obtained by ferrets owners recording adverse events occurring over a random one month period in non-vaccinated ferrets.