Willie is a middle-aged Jack Russell. He was neutered five or six years ago so quite why he has taken to wandering off is a mystery.

It was soon clear from his owner's story how much anxiety Willie's behaviour was causing. Even with a microchip and a collar with a disc with his name and address on it his escapades were terrifying because of the worry that he would get run over or worse.

A minor change in his owner's lifestyle had meant that he spent more time on his own in his owner's garden surrounded by fields. Probably his bad habits started with boredom and a desire to go dustbin raiding at the neighbouring farm. The immediate cause of his arrival on my consulting room table was the terrible diarrhoea that had afflicted him during the night. He had woken his owner with urgent demands to rush outside several times. He was a little quieter than usual but that was all.

When I examined him his abdomen was tender and his bottom sore, but he his temperature was normal and there was no tightness in his skin to suggest he was dehydrated, just a rather dry mouth.

Diarrhoea is a symptom of many illnesses in dogs. Parvovirus, distemper and hepatitis, the serious infections we vaccinate dogs against, can all start with diarrhoea. Fortunately Willie was vaccinated so I was able to put these to the back of my mind, together with poisonings and liver and kidney disease since he was not ill in himself.

Many of the dogs I see with diarrhoea have caught less serious germs from other dogs on their morning walk, in kennels or wherever else they mix with other dogs or sniff where they have been. These infections are not life-threatening but they are unpleasant and need treatment.

Another set of my patients have diarrhoea that is not infectious at all but persists or recurs and is connected with disease of the small or large bowel or with some form of food allergy or sensitivity. Willie had none of these.

On his latest trip around the countryside he had chewed the remains of an extremely decomposed dead rabbit before tipping over a dustbin containing some elderly lamb casserole. He had thorough-going food poisoning. The gone-off meat he had eaten had given him a large dose of bacterial toxins, and his bowels were now doing their level best to get rid of them as soon as possible.

When I had explained what was wrong to his owners, I gave Willie an injection to slow down the violent movements within his bowel, and some kaolin medicine to absorb any of the toxins that were left. I also gave his owners a packet of powder to make up an electrolyte drink in water to replace the fluids he was losing.

A phone call the next morning confirmed he was much better. Now he is restricted to walks under close supervision until he learns not to run away.

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