Health & Medical

Rats do not need to be anywhere near your dog for your dog to catch leptospirosis from them. The bacteria pass out in infected urine and then survive for days or weeks in warm, wet soil and slow-moving water, so the puddle at the edge of the bridleway can still be a problem long after whatever contaminated it has wandered off. Once that clicks, most of the confusing parts of this disease start to make sense.

Leptospira are thin, spiral bacteria carried in the urine of rats, mice, voles, hedgehogs, cattle, deer, pigs and plenty of other mammals. Dogs pick them up by drinking from or wading through contaminated water, by walking on wet contaminated ground and then licking their feet, or through a cut or a graze. Canals, ditches, flooded fields, farm puddles, slow rivers and stagnant garden water are the usual suspects. Cold, fast-moving water is less of a risk. Frozen ground is less of a risk. A mild, soaking autumn following a hot summer is when a lot of practices start seeing cases.

The early signs look like almost anything

Here is the frustrating part. A dog in the first day or two of leptospirosis is simply off. Not eating breakfast. Flat. Possibly feverish, possibly vomiting once or twice, sometimes stiff and sore through the muscles and reluctant to jump into the car. Any owner would put that down to something scavenged on a walk, and most of the time they would be right.

The sign that deserves more weight than it usually gets is a sudden change in thirst. A dog that drains the water bowl twice in an evening when it normally lasts all day, or who starts asking to go out at three in the morning, is telling you something about the kidneys. Put that together with lethargy and vomiting and you have a dog who should be seen the same day. Not after the weekend.

What comes next can move quickly. Leptospira head for the kidneys and the liver. Acute kidney injury is the most common serious outcome, and some dogs stop producing urine altogether. Others turn jaundiced, with yellowing visible in the whites of the eyes, the gums and the skin inside the ear flaps. A smaller group develop clotting problems or severe lung involvement, which is every bit as bad as it sounds. Treatment means antibiotics plus proper supportive care, usually several days of intravenous fluids in hospital, and occasionally dialysis at a referral centre. Dogs caught early do meaningfully better than dogs caught late, which is exactly why vets get twitchy about vague symptoms that are getting worse rather than better.

It can move from your dog to your household

Leptospirosis is zoonotic. People catch it too, usually through contact with infected urine or contaminated water, and in humans it ranges from a flu-like illness to something genuinely dangerous. If your dog is being investigated or treated for it, your vet will talk you through handling urine with gloves, cleaning up accidents with disinfectant rather than a quick mop, washing hands properly, and keeping the dog away from young children and from anyone pregnant or immunosuppressed while they are still shedding. This is not a reason to panic and it is absolutely not a reason to consider rehoming a treated dog. It is a reason to take the hygiene advice seriously for the couple of weeks it matters, and to mention the diagnosis to your own doctor if someone in the house becomes unwell.

What the vaccine does and does not cover

The lepto vaccine is the odd one out on the dog vaccine card, and that trips people up. Core vaccines such as distemper and parvovirus produce long-lasting protection, which is why many dogs now go three years between those boosters. Leptospirosis protection does not behave that way. Immunity is relatively short-lived, so the vaccine needs repeating every year to be worth much at all.

The other detail worth understanding is that Leptospira comes in many serovars, and a vaccine only covers the ones it contains. An L2 vaccine protects against two serogroups; an L4 covers four, adding strains that have become more relevant across parts of Europe. Neither is a blanket shield against everything a dog could meet. So a vaccinated dog who becomes unwell has not necessarily been failed by the vaccine, and a vaccinated dog showing the classic picture still needs testing. Which product suits your dog depends on where you live, where you travel and what your vet is seeing locally. That is a conversation, not a default setting.

Whether any of this matters much for your own dog comes down to lifestyle, and it is worth being honest about it. A terrier who swims in canals, a gundog working wet stubble, a farm dog, a dog living somewhere rats are simply part of the landscape: high exposure, easy decision. A small dog who walks on city pavements and never puts a foot in standing water sits at the other end, though not at zero, because urban rats exist and heavy rain moves things around. Most dogs land somewhere in between. Talk it through with your vet, keep your dog out of stagnant water where you reasonably can, carry drinking water on walks so they are not tempted, and treat a suddenly thirsty, listless dog as something to act on rather than sleep on.