Recently I read in an abstract in the CAB Abstracts Database that “Dog poisoning caused by grape or raisin consumption has been increasing recently. The first cases of poisoning were documented around 1989, several tens cases have been registered yearly in the world since 2003”. The author writing in a Czech veterinary journal is correct in saying that the first report of
raisin poisoning in dogs was fairly recent, and there appears to be no recorded cases before 1989.
Raisin poisoning can be very serious with most affected dogs developing vomiting and/or diarrhoea within 6-12 hr of eating the grapes or raisins. Other signs include lethargy, anorexia, abdominal pain, weakness, dehydration, polydipsia, and tremors (shivering). Oliguric or anuric renal failure
can develop within 24-72 hr after eating the raisins, and once anuric renal failure develops, most dogs die or are destroyed. Some dogs develop transient elevations in serum glucose, liver enzymes, pancreatic enzymes, serum calcium, or serum phosphorus develop in some dogs.
The Merck veterinary manual recommends that affected dogs should be given an emetic as soon as possible to try and eliminate the fruit, followed by
doses of activated charcoal. With large ingestions or in cases where vomiting and/or
diarrhoea has spontaneously developed within 12 hr of ingestion of grapes or raisins, aggressive fluid diuresis for 48 hr is recommended. Renal function and fluid balance should be monitored during fluid administration. For oliguric dogs, urine production may be stimulated by using dopamine and/or furosemide. Anuric dogs are unlikely to survive unless peritoneal dialysis or haemodialysis is performed, and even then the prognosis is guarded.
The interesting thing about raisin/grape poisoning is why it has only been reported in recent years? Dogs have not suddenly become more greedy and less discerning in what they choose to eat. Also the availability of raisins in
houses would have been greater in the past when more people baked fruit cakes and their own Christmas puddings at home. I far as I know, dogs (some breeds in particular) have always been great opportunists when it comes to raiding the
larder, so its hard to belief that they never had the chance to eat raisins
before 1989. Could it be that raisins have changed in some way? Or is it just that cases
of raisin poisoning did occur in the past and were just not reported? Some authors have suggested that a mycotoxin
contaminating the raisins may be to blame for the poisonings. Would some change
in the processing of raisin and grapes be responsible? If the toxin can cause
kidney failure in dogs does it have an adverse effect in humans? As yet no toxin has been identified, so
suggesting a mycotoxin is just speculation. So, looking at the literature on a particular topic, like raisin poisoning, may not provide all the answers we would like, but it does help to us to ask the right questions.