Canine Distemper Virus
Bennie Lye documents her analysis of the CDV outbreak of 2011.
If you've owned dogs or ferrets then the chances are you've heard of distemper, you may have even gone through the distressing experience of having your dog(s) or ferret(s) suffer from it, but what exactly is distemper and is it the same in ferrets as in dogs?
So what is distemper?
Canine Distemper is a viral disease that among other genesis of animals affects our much loved Mustelidae (ferrets). It is what's known as a single stranded RNA (ribonucleic acid) virus belonging to the family of 'paramyxovirus' and therefore a close relative of measles.
Do dogs and ferrets have the same symptoms?
Left: Distemper rash
Yes and no! For many years and even today on the internet, the information given to ferret owners on what symptoms and in which order, are the same as that for dogs. However, when in October 2011 a large scale out-break of distemper in ferrets appeared on the ferret scene it eventually became clear that one symptom in particular showed first and foremost in the majority of infected ferrets and that was a pink rash with black tips mainly in the abdominal area, worsening around the groin. It can also develop around the eyes and under the chin and in some cases can been seen all over the ferret's body.
This is invariably closely followed by crusting around the nose and swelling round the eyes either of which may or may not include a discharge, before finally, hard pad which is when the ferret's pads swell to sometimes twice their normal size and become 'crusty'.
Left: Swollen eyes and crusting of the nose.
Of course it has to be said that not all ferrets will have all these symptoms which is why if you suspect that this is a possibility then you should explain that to your veterinary practice when making an appointment so that they can put their 'suspected infectious diseases' protocols in place for your appointment thereby safe guarding other pets attending surgery.
Right: Crusting of the paws
If distemper is suspected then blood tests (serology for titre levels) and/or swabs (PCR test [polymerase chain reaction]) will be taken and sent away to a pathology laboratory for what's known as a histology report. Swabs are taken from eye/nose discharge if apparent, throat and anal. Also any faecal specimens are helpful as well.
During the 2011 outbreak, blood results came back inconclusive as the titre levels were compared to that of dogs and well, ferrets are NOT dogs. So what is the acceptable normal titre range for a ferret? If a ferret has been vaccinated will this always give a potentially 'false positive'? How long does it take for a distemper vaccine in a ferret to dissipate before giving a true reading? Months, years?
The first ferret to show signs of distemper had a distemper antibody titre 7 and so was considered negative for CDV, however all distemper antibody titre results <10 [< = less than] is considered negative as this is based on dogs. Incidentally this ferret's PCR came back positive - 'very high viral load of canine distemper virus'. One of my own ferrets, a never vaccinated two year old hob - titre levels came back <5; so are blood tests really relevant? If yes, then should the cut off point for ferrets be >5 [> = more than]? In America blood tests for distemper in ferrets are their first line of diagnosis, but then they tend to quantify symptoms in a different order of prevalence. Is this because they have a different strain so symptoms appear in a different order? If so, does this go for other countries as well? Different strains, different preference in order of symptoms? In Great Britain are swabs the best form of preliminary diagnosis?
Once a ferret with suspected or confirmed (by swab histology results) is put to sleep (pts) then tissue specimens of the small intestine, lung, bladder and pancreas in formal saline should to be taken and if possible a faecal sample as well. This is really the only way to get a final definitive diagnosis of distemper.
In October 2011 the first known reported case of potential CDV that I became aware of was a ferret called Ozzie, a 2.5 year old castrated albino hob. He presented with swollen muzzle, ventral dermatitis/erythema (redness) especially round prepuce (penis) and anal area, pruritic (itching), puffy eyes, hyper-keratotic (hard) pads.
(Incidently, on later investigation it appears that the first ferret to die of CDV was from another area and that was on 12th October 2011. A 2 year old albino hob who'd been vaccinated with a full vial of Canigen DHP two months earlier).
While an allergic reaction to a change in bedding was ruled out with piriton tablets, synulox (antibiotic) and metacam (pain killer) injection, distemper couldn't be ruled out, so swabs were taken for distemper pcr testing. The following day on the advice of the laboratory, a blood sample was taken and sent for a serology test.
The PCR test came back positive whilst the serology results gave a distemper antibody titre 7. Remembering that only titres >10 are considered positive, had the diagnosis rested on the serology test only then it would have been considered negative due to the reasons given earlier.
Unfortunately, Ozzie died a shortly afterwards, a fraction of his former weight, setting off a devastating chain of ferret deaths - 100+ in this particular welfare.
Ozzie was never post mortem'd (pm) but the NFWS only had to wait a few days when another ferret from the same welfare, a one year old, who'd been part of a group where a positive PCR test had been confirmed was pts, tissue samples taken and sent to the Society's consulting veterinary surgeon - Simon Thomas BSc BVetMed CVR CSAO MRCVS, Gatehouse Veterinary Hospital, who was the link with University of Glasgow School of Veterinary Medicine.
On 14th November 2011 the report came back stating "diagnosis of bronchointerstitial pneumonia and lymphoid depletion with prominent intracytoplasmic viral inclusion bodies in the lung and urinary bladder epithelium are consistent with the diagnosis of canine distemper virus infection. The lung lesions are relatively severe."
However at this welfare and along with reports from other ferret owners/welfares groups of ferrets didn't all show symptoms at the same time, giving many 'false' hopes of it being over. Symptoms took on average between 7 to 21 days to appear and not all ferrets within an infected group developed symptoms at the same time. There were several weeks between the first ferret(s) displaying signs of CDV and the last ferret(s); more confusingly, not all ferrets within an infected group showed symptoms or appeared to develop the illness.
Interestingly enough, two older ferrets which had been vaccinated a few years previously managed to survive, but was this because they went back to their owners before the CDV had run it's course and were maybe better isolated from the initial infected ferrets? But in that case why did some vaccinated ferrets die of CDV? Do some ferrets have a natural immunity to help mitigate the symptoms and if so does this make them carriers?
The more we look into and discover about CDV the more questions it seems to raise.
by Bennie Lye
(First published May 2014)