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Antibiotic resistance, like global warming, is a threat to our future that keeps popping up in the media. The topic moved centre-stage today, with the long awaited publication of a major report that specifies the severity of the risk, and the measures that need to be taken to avert the threat. It's a long report, at 84 pages, and it's worth reading for those with a serious interest in the subject, but here's the gist of what's being said.

Giving medication to pets is not easy. In a typical case of a dog with a skin condition, I may send the owner home with three types of tablets to be given twice daily for ten days. As I write up the final details of the patient’s file, I sometimes reflect that I have sent the owner away with a challenging task to complete.

Natalie Kent asked:

My 8 year old pug has just been diagnosed with Pseudomonas in his nose. He's been having problems with his nose for about a year,   discharge, blocked up etc. Vet did a nose swab and found this bacteria. He's been on marbocyl antibiotics for 2 weeks and it's not       completely gone away, still a bit of discharge and a bit stuffy but vet refuses to give any more tablets, what else would you suggest?

Reply:

Hi Natalie, thanks for your question. Because of the conformation of their skull and nasal passages, Pugs are prone to a range of different breathing problems, and may suffer from recurrent nasal infections, so I’ll start by discussing the anatomy of the nasal passages and the defects Pugs typically suffer from. Pseudomonas is a particularly nasty bacterium that can be very difficult to treat effectively, so I’ll also talk about appropriate antibiotic therapy and the reasons why the symptoms may not have resolved. Finally, I’ll look at different ways forward for your dog.

What is the “normal” anatomy of a dog’s nose and airway? When a dog breathes in, the air flows through the nostrils (also known as the “nares”) into the nasal chambers. The left and right sides are separated by a dividing wall (the “nasal septum”) so what affects one side doesn’t always reach the other; and they are separated from the mouth by the bone of the hard palate (the ridged roof of the mouth). These chambers aren’t open – they are almost filled with scrolls or swirls of bone called the conchae (because they look a bit like sea shells), leaving only a narrow space in between for air to flow. This is important because even a small amount of fluid or swelling of the tissues here can make a dog very congested and uncomfortable. Behind these 2 chambers is a common space where left and right nasal chambers meet called the nasopharynx; the floor of this is made up of a strong muscular band called the soft palate. When breathing, the soft palate prevents food from entering the nasal passages. The air then flows through the larynx (voicebox), down the trachea (windpipe) and into the lungs. Opening out of the airways in the skull are the sinuses; these are hollow spaces inside the bone that make the head lighter and easier for the dog to carry around. There are 2 sets – on each side of the skull is a frontal sinus (in the forehead) and maxillary sinus (in the upper jaw, just above the tooth roots). So what’s different about pugs? Dogs can be divided into 3 different groups of breeds, based on their skull shape:

• Dolichocephalic – dogs with long noses, e.g. Greyhounds
• Mesocephalic (also known as mesaticephalic) – dogs with medium noses (most dogs, e.g. Labradors)
• Brachycephalic – dogs with short noses (e.g. Pugs).

As one of the most extreme brachycephalic breeds, Pugs almost always suffer from some degree of Brachycephalic Airway Obstruction Syndrome. This is a condition caused by selective breeding over many generations for an abnormally short skull, and includes a range of conditions such as:

• Nostril Stenosis – narrowing of the nostrils.
• Elongated Soft Palate – over-long soft palate that blocks the airway.
• Everted Laryngeal Saccules – folds of flesh that stick out into the voicebox, blocking airflow.
• Hypoplastic Trachea – where the windpipe is a little too narrow.

These are all caused by excessive amounts of soft tissue – in the course of breeding for the modern Pug, we’ve been very successful in shrinking their bones, but not so much the soft tissues around them. As a result, Pugs have loads of extra folds of tissue in their nasal chambers and airways, making breathing a little more difficult. That’s all very interesting, but why did my dog get the infection in the first place? There are a number of possible reasons, but let’s start with the most obvious – with lots of extra soft tissue in their noses, all those little crevices, nooks and crannies are perfect for bacteria to find a home and start to grow! Other possible underlying causes include:

• Foreign bodies – dogs are particularly prone to getting things stuck up their noses, like grass seeds or even bits of food.
• Tooth infection – because the roots of some of the upper teeth are right next to the maxillary sinuses, an infection of the tooth can cause sinusitis and nasal infection.
• Fungal infections – fairly rare in the UK, but they do occur.
• Polyps – benign growths in the nasal chambers or pharynx.
• Tumours – malignant growths of the airways.

These conditions aren’t uncommon in dogs, and often result in secondary bacterial infection. Once the infection is resolved, however, the symptoms may persist or recur because the underlying problem has not been addressed. What is Pseudomonas? Pseudomonas is a Gram Negative bacterium (meaning it has a double cell membrane as well as a cell wall) that commonly causes skin, ear and sometimes nasal infections. It is a very tough organism, and is prone to rapidly developing resistance to antibiotics. This means that in most cases, a prolonged (usually 2-6 weeks) course is required to ensure that it is completely eliminated. Exactly what antibiotic to use will depend on the results of the culture and sensitivity swab which your vet did – judging by what you’ve said, it would seem that this particular infection was susceptible to marbofloxacin (Marbocyl), a fluoroquinolone antibiotic commonly used against these bacteria. So why hasn’t the treatment worked? There are a number of possible reasons. Firstly, it may simply be that the course wasn’t long enough – however, your vet is right to be cautious about just handing out more antibiotics; overuse of antibiotics in animals or people is one of the main drivers of antibiotic resistance. A second possibility is that the course was long enough, but the Pseudomonas is now resistant to marbofloxacin; I’ve seen this happen before when treating these infections. You give an antibiotic that the bacterium is proven to be sensitive to, and within a week or two, the test results show that they have gained resistance to it. Alternatively, there may have been other bacteria on that nasal swab that didn’t show up because there were so many Pseudomonas. In that case, if they weren’t susceptible to marbofloxacin, they’ll still be there causing problems even once the Pseudomonas are all dead. Finally, and given the duration of the problems you’ve been having I’d say this is the most likely, there may be another underlying problem (such as a nasal polyp, a foreign body, dental disease, or even his nasal conformation and anatomy) that is causing the symptoms. OK, what should I do next? I think the most important thing is to find out what’s going on inside your dog’s nose right now. You know that some weeks ago there was a Pseudomonas infection; however, you’ve got no idea if that’s still the case and that treatment has failed (and if so, why); or if the symptoms are ongoing despite the successful treatment because the Pseudomonas were themselves only secondary to something else. The first step would be for your vet to repeat the nasal swab (if possible, using the same laboratory) and see how the results are different – what bacteria are growing there now, and what antibiotics they are susceptible to. The next thing to consider would be direct visualisation of the nasal chambers under anaesthetic; this usually involves rhinoscopy (putting a camera or endoscope up the nose) and/or retrograde visualisation (looking at the back of the nose with an endoscope or mirror) to see if there’s anything stuck there, or any masses or polyps growing. This isn’t always easy in pugs and may require referral to a specialist; however, your vet will be able to perform X-rays of the skull and nasal chambers, as often polyps and tumours are often clearly visible on an X-ray of this region. I think it’s very important for you to discuss your concerns with your vet, and talk about further diagnostics – you really need to sort out what’s going on in that nose to make him comfortable again and to hopefully avert any more serious consequences! All the best, I hope you can get this sorted out quickly. David Harris BVSc MRCVS