Ear Infections Part 1

dog scratching his ear

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If you have ever woken up in the middle of the night to your pet shaking its head and scratching its ears, you know how uncomfortable a pet can be when they have an ear infection. Ear infections have many causes. The key to treating the infection and stopping it from returning is understanding the primary, secondary, perpetuating and predisposing causes of ear infections. Join dermatologists Dr. Meagan Painter and Dr. Brittany Lancellotti to help you understand why your dog or cat is getting ear infections and how to stop them in their tracks so you can keep your animal happy and healthy.

Welcome Back, Dr. Painter!

[00:01:04] Dr. Lancellotti: Welcome, everyone, to today’s episode of Your Vet Wants You To Know. I’m joined by a special guest, Dr. Megan Painter. She was on episode 17- diet trials- when she talked about how to do a diet trial with your allergic animal, so that you could figure out whether or not they have a food allergy, and if that’s contributing to their allergic skin disease. Today, we’re going to be talking about ears. This is a big topic. Certainly, this is not going to be able to cover everything in just one episode, so we’re going to break it down into 2 parts for you. In the first episode, we are going to be talking about the different causes of ear infections and developing an approach where we can systematically go through and figure out why the animal’s getting those ear infections, so that they don’t come back. In the second episode, we’re going to talk about what your vet might do, what different diagnostics they might try, and what treatments they might try when using that systematic approach that we talk about in this episode. Join me in welcoming, today, Dr. Meagan Painter. Welcome! 

[00:02:04] Dr. Painter: Hey, everybody! Thanks so much for listening. I am very excited to be back with Dr. Lancellotti and Your Vet Wants You To Know. 

Dr. Meagan Painter

The Allergic Dog - A Course for Veterinarians

[00:02:14] Dr. Lancellotti: Dr. Painter, you’ve been pretty busy since the last time you came onto the show. You’ve been working on creating a course for primary care veterinarians (family vets) who want to know more about how to treat allergic dogs. Can you tell us a little bit about course? 

[00:02:28] Dr. Painter: Totally. Thanks so much! Yes. I just recently, in November, launched a course and community site for veterinarians who treat dogs with allergy called The Allergic Dog. In there, I have an eight hour course that’s race-approved, providing veterinarians with their continuing education credits and knowledge about how to treat and medically manage allergic skin and ear disease in dogs. It’s been very well received. Lots of veterinarians have signed up. I’m loving the feedback that people are giving for the course, and I’m just really proud of what’s in there- knowing that we can all advance the care of these dogs that we see each and every day. Pet owners are the listeners here, and you are certainly dealing with allergies firsthand- and so is your veterinarian. I think that the more we can advance our knowledge about how to treat these guys, the better off everyone will be. And I’m very committed to that, both as a professional and as a dermatologist. So, definitely encourage your veterinarian to check out the course, and if you’re a veterinarian, I look forward to welcoming you there, to learn about what we have to offer at theallergicdog.com. 

[00:03:39] Dr. Lancellotti: Yeah, this is an amazing resource for veterinarians. Dr. Painter, you are one of the most entertaining speakers that I have had the privilege of getting to enjoy lectures from. I would encourage anyone who has more interest in learning about how to treat allergic dogs- or if you’re a veterinarian listening- to check out theallergicdog.com to see if that course would be of interest to you.

Ear Infections are Frustrating!

Dr. Lancellotti: Thank you very much for joining us today, Dr. Painter. Tell me a little bit about why ear infections and ear disease are so important and why you’re passionate about this. 

[00:04:14] Dr. Painter: Ear disease is an incredibly common presentation for dogs with allergies. We see dogs with ear infections probably every day in our clinic, as dermatologists. Certainly, coming through urgent care and general practice, ear infections are often a presenting complaint as well. The reason is because they hurt. Dogs are miserable when they have ear infections. This is something that absolutely causes them to have discomfort. They’re up all night, their ears smell, their ears hurt them, they’re yelping when you touch their ear, etc. There are just so many ‘quality of life’ problems that occur when a dog has ear disease that warrants a pet owner to say, “Gosh, I need to help my dog and bring them in to the veterinarian.” But then I feel like when they get there, there are so many confusing and complexing issues that are all layered on top at one time. Why is the ear infection happening? What can we do about it? Which ear drops should we use? How do I clean the ear? There’s just so many questions that come up. I’m really glad that we have the opportunity in this podcast to dial down and simplify some of these complicating issues that we see, making it a little easier for everybody to understand, and helping these dogs to feel a lot better.

[00:05:39] Dr. Lancellotti: Absolutely. Our goal is to provide them with relief from the itch and the discomfort that they’re experiencing. Certainly, the owners need relief from the smell and they need to get sleep during the middle of the night, because that’s when the animals tend to get up and shake their heads and show how uncomfortable they are.

Why Do Dogs and Cats Get Ear Infections?

Dr. Lancellotti: Today, we’re going to be talking about a classification system that you and I learned, as dermatologists, during our residency. It’s a really helpful tool in simplifying how we approach these animals that have ear infections. Tell our listeners a little bit about what that classification system is, and then we’ll go through and talk about it in detail.

[00:06:19] Dr. Painter: Dr. Lancellotti and I shared many similar mentors. One of our mentors, Craig Griffin, is one of the geniuses of veterinary dermatology, and I believe that he actually came up with this system for understanding otitis externa. First of all, the otitis externa just refers to inflammation of the external ear canal, or including the flap (pinna). You can have infection, as well, when you have inflammation within the ears. Also, you can have just inflammation or just infection. We’ll talk all about that, but the reason that otitis externa occurs is because of this classification system.

There are really 4 overlapping things that we need to keep track of with the PSPP Classification System.

  • Primary causes
  • Secondary causes
  • Perpetuating causes
  • Predisposing causes

Keeping track of the primary, secondary, perpetuating, and predisposing causes to your dog’s ear disease is going to allow you to get ahead of it, instead of constantly being on that rollercoaster, where the infection itself doesn’t fully resolve or the problem never goes away completely. Or it just seems like you’re always spinning your wheels and treating the same thing over and over again, but nothing ever really goes away or gets better, it’s probably because there’s something in the PSPP system that you’re missing, and if that part is addressed, then you’ll have a much better likelihood of resolving that ear infection, rather than just putting a little hold on the symptoms so that it doesn’t get better. 

[00:08:03] Dr. Lancellotti: Yeah, that’s one of the things that I hear so commonly from owners. They get really frustrated that the infections just keep coming back. I spoke on episode 2 -food allergies- about Cookie, a black lab, who had these recurrent ear infections and they would clear up, but then just keep coming back as soon as they were cleared up. It wasn’t until we got down into this PSPP system and figured out the primary causes of the infection (not just the secondary infection, but why this is actually occuring). Once we went through PSPP, step by step, we were able to diagnose her with a food allergy and keep those infections under control. That’s a great example of how not to just treat the secondary infection that’s there, but also at work on the primary disease. So that’s definitely something that people can go back and listen to episode 2, if they’re more interested in learning about food allergies.

Diego's Terrible Ear Infections

swollen, red ear with scabs
Diego at his initial consult. Photo Courtesy of Dr. Meagan R. Painter.

Dr. Lancellotti: Dr. Painter, do you have any particular cases that come to mind when you think about ear infections and using this system to address what’s going on?

[00:09:12] Dr. Painter: Absolutely. One of my favorite cases of all time for ear disease is a dog named Diego. This dog was adopted by these two amazing humans who saw this dog online. He was being placed up for adoption by a single mom who could not take care of him. It was him and his brother. And these people adopted this dog and its brother- sight unseen. They never met the dog. They had no idea. They just knew this woman needed help, they wanted to help her, and they did. So they take Diego into their home and within like six minutes realized that he has the worst ear disease that they could imagine. They couldn’t touch him. He was reclusive in the home, and compared to his brother who did not have ear disease, he was kind of aggressive. He just didn’t want anyone near him. So, they went to the primary care to establish care and to say, “Hey, listen. We just have these two dogs. We want you to take a look,” and the primary care said “Oh my God! These are the worst ears. You have to get to a dermatologist,” and they found their way to me. And I’m so glad that they did. We were able to do so much for this dog because we were able to look at primary, secondary, perpetuating, and predisposing causes to his ear disease. And he really did have all four of these issues specifically layered on top of one another, making his ears within the ‘severe’ category. When I saw Diego, I actually couldn’t touch him. It wasn’t because he was aggressive. He was just very afraid and his ears hurt him so much that he would, essentially, alligator roll. You just could not go near this dog. 

[00:11:04] Dr. Lancellotti: Poor thing! 

[00:11:04] Dr. Painter: It was awful. And he was a love. Right? I mean, this dog was just a love and you knew that. But if you took one look at his ears, you said, “Oh my God!” It was both sides. The actual tissues in the ear were swollen, red, and there was horribly smelly yellow discharge and crusting around the ears. You couldn’t even see into that canal. It was so swollen and chronic. This didn’t happen overnight. This dog has been suffering with this for months, if not years. He was a several year old dog so I said to the owners, “These are some of the worst ears I’ve ever seen. We’re going to approach his case very systematically.” I laid out PSPP for them and said, “Here’s how we’re going to address each of these issues for your dog.” And he’s doing great. At this point, it’s several months later and his ears are as normal as they’re probably ever going to be. But he didn’t require surgery, which was something I was actually quite concerned he might need from our initial examination. We’ll walk through some of the things we talked about with, primary, secondary, perpetuating, and predisposing causes for his ear disease and apply it to other dogs, using him as an example. I was very worried we would never really be able to help him. I was worried that he’d never be comfortable again. And now, in the home and outside with other dogs, his whole attitude toward life has changed because his ears feel better. And that’s really all that we need, as veterinarians. I feel like, “Wow!” How ‘worth it’ this has been!” For the owners, as well. They really just adopted this dog with this issue, and were nervous about whether or not they’d be able to actually help him. 

[00:12:59] Dr. Lancellotti: Yeah. That’s amazing. To be able to see an animal come into their own personality, feel like themselves again, and enjoy being around their family- that’s the most important thing. Ear infections really affect the animal’s ability to do that comfortably, so I’m really excited to give owners the tools to help them figure out what’s going on with their animals ears. And for those veterinarians who are listening, Dr. Painter, you talk about Diego as a case study in your online course, The Allergic Dog, correct? 

[00:13:32] Dr. Painter: Yeah. He’s part of my steroids and the Atopica modules. I actually have like a twelve-page case study that you basically work through with me, so I decided to share all the emails, photographs, the next steps, medication decisions, and the cytology. Every aspect of his case is in that case study for the purpose of learning. I feel like his case, in particular, brings up so much about what we face with these really chronic ear cases that I thought it would be a very useful tool for learning.

What are the Primary Causes of Ear Infections?

the primary causes of ear infections are listed

[00:14:06] Dr. Lancellotti: Beautiful. So, when you were talking to Diego’s owners, you said you talked to them about PSPP. Let’s start with primary. What did you talk to Diego’s owners about? How did you explain primary causes of ear infections? 

[00:14:21] Dr. Painter: The primary cause of the ear infection is why the infection is happening. This is really important because a lot of people say, “My dog has an ear infection.” And then that’s kind of where the story ends. They don’t think that there was something that caused that ear infection, but there always is. Infections are not going to just come out of nowhere. There is a primary cause to having otitis externa, inflammation or infection in the ear. Examples of why inflammation can occur in the ear include environmentally driven allergy, and food allergy is a very common cause of otitis externa. We can have dogs have disorders where they’re actually not creating, or having a stabilization issue with their actual skin turnover (like a seborrheic type disorder), and also things like hypothyroidism and Cushing’s disease. Even certain tumors of the ear can be a primary cause of otitis externa. But the most common reason for a young (and otherwise healthy) dog to have an ear infection is going to be some type of allergy- usually either food, environmentally driven, or both. So it’s super important to recognize that it’s the primary cause that created that infection. 

[00:15:44] Dr. Lancellotti: Yeah, that’s right. These primary causes are the ones that can create disease in a normal ear. This normal ear should not have infections, but because of these primary diseases, the ear is then in a position where the secondary infections can occur. And oftentimes, that will make things worse in the ears. Working together with your family vet or with a veterinary dermatologist to figure out the primary cause is going to go a long way towards reducing the recurrence of these secondary infections. Here in Southern California, we have something called Fox tails or grass awns and those foreign bodies can actually get stuck in there, causing ear infections, as well. So being able to have someone actually look in the ear canal and see if there’s anything in there is helpful. But you are absolutely right. Allergic skin and ear disease is a very common cause of ear infections. So if you want more information about allergic skin disease, the first few episodes of the podcast are going to be really helpful in understanding this really challenging, lifelong disease, minimizing the amount of ear infections that keep coming back. That’s a primary cause.

What are Secondary Causes of Ear Infections?

secondary causes of ear infections

Dr. Lancellotti: What about secondary? What do we mean when we talk about a secondary cause? 

[00:17:04] Dr. Painter: Secondary causes are really your infection. This is the type of infection that’s present in the ear. Not every ear that appears to have inflammation is going to have infection. I have seen enough sterile inflammation cases of otitis externa (where you do cytology- swabbing the ear and using a microscope to see what kind of cells are there), and it’s just inflammatory cells- no infection type cells. But the majority of cases are going to have a secondary cause of otitis externa- usually, some type of bacterial overgrowth or some type of yeast overgrowth (and in some cases, both). So you can have a yeast infection in the right ear and a bacterial infection in the left ear. You can have yeast and bacteria in both ears or any combination of those things is possible for dogs with otitis externa. But the secondary problem is the infection because of that primary cause. First, you have food allergy, and now you have a yeast infection. That link is the most important link for everybody with a dog who’s facing ear disease to understand. There’s a Fox tail in the ear, therefore, you have a bacterial infection. You have food allergy, therefore, you have yeast infection in your ear. So it’s that allergy, that inflammatory process, that metabolic disorder– whatever that primary cause is- that’s leading to that secondary infection. And I think this is why you see pets go round and round again, because treating just the infection or just the secondary cause is not actually going to resolve the problem, because you have a primary problem that is still ongoing. And that’s really the ticket- helping to understand why those infections are there in the first place. 

[00:19:02] Dr. Lancellotti: Yeah, absolutely. Treating those secondary causes like bacterial and yeast infections is only one piece of getting this animal relief. But if you’re not figuring out what the primary cause is and why that secondary infection developed in the first place, it’s just a matter of time before that secondary infection comes back and you keep riding this rollercoaster of ear infections. So it’s really important to work with your veterinarian and figure out what the primary cause is, if you want to get control of these recurrent ear infections.

[00:19:38] Dr. Painter: And one quick little snippet about Diego at this time- he has food and environmental allergies, so he’s on a specific diet and he’s actually on immunotherapy. But allergy is a chronic relapsing condition. Yes, you’ve listened to episode 17 of Your Vet Wants You To Know, and you know all that there is to know about diet trials, and you still end up having a relapse. That’s normal. These things happen with allergic disease. It’s a chronic relapsing condition. You might still get some infection, but you certainly should have less, if the primary disease is being managed well. And that’s the whole point of what we do with medical management of allergic skin and ear disease- reducing that chance of getting these secondary problems because we’re treating the primary issue.

image of bacterial skin infection as seen under the microscope

What are Perpetuating Causes of Ear Infections?

[00:20:27] Dr. Lancellotti: Absolutely. I want to talk about our next letter in our acronym, PSPP, and that’s the perpetuating factors. These can be really frustrating. Tell our listeners a little bit about some of the perpetuating causes of ear infections are. 

[00:20:45] Dr. Painter: Perpetuating causes are things that just keep you up at night. These are the changes to the health of the ear that occurs because you have ear disease. Basically, this is what keeps the ball rolling downhill, forever and ever, if you’re not actually able to address them. They’re these little sticklers that, basically, promote infection and inflammation within the ear canal, preventing resolution of ear disease because there are changes to the ear itself. The most common things that we think of in this perpetuating category are chronic inflammatory change. Diego had horrendous ears that were swollen, hyperplastic, super red, and inflamed- chronic changes. Those changes didn’t occur overnight and aren’t going to resolve overnight either. Those are perpetuating causes of otitis externa. Other examples are glandular hyperplasia, where we can see the glands of the ear on overdrive. You just have so much production of wax and different debris in the ear, as a result of glandular hyperplasia. We can see the ear canal itself become calcified. So instead of that nice, soft cartilage of the external ear canal, you start to see even bone be laid down in the ear canal. Again, it’s just trying to protect itself, but it’s a perpetuating cause of ear disease that prevents us from being able to resolve this swiftly. Things like biofilm formation, infection of the middle ear, or stenosis (narrowing of the canal) are all examples of changes that are going to promote infection and inflammation within the canal. They’re not primary. They’re not secondary. They’re not the infection type. They’re things that just get in our way from resolving this infection and inflammation within the ear very readily. Basically, they’re just changes to the health of the ear that are going to promote infection and inflammation.

perpetuating causes of ear infections

[00:22:49] Dr. Lancellotti: There is so much to unpack in what you just said right there. These ears have chronic changes. And that’s the thing that I think people need to understand- these perpetuating factors are there because the ear infections have been there for long enough that we’re seeing changes to the anatomy and the normal functioning of the ear canal. You mentioned Biofilm, and this is something I talk to pet owners about quite a bit. Biofilm is this protective slime that certain bacteria and/or yeast will produce, making it more difficult for our topical therapy to actually clear infections. When we have biofilm, it perpetuates the infection in the ear canal because we’re just not able to clear that infection as effectively with the medications, which would otherwise be able to clear a normal infection if the biofilm wasn’t there. Typically, these are the animals that we talk about putting under anesthesia to do a deep ear cleaning and physically go in there and scrape the sides of the ear canal, removing biofilm and making our treatments more effective. You talked about the earwax-producing glands being overactive. That’s something that we will struggle with quite a bit, even after infection is gone. Those earwax-producing glands have been working so hard to pump out lots more ear wax, in an effort to fight off the infection, that even after we’ve cleared the infection, it is so important to establish a maintenance routine for cleaning that ear until the normal ear cleaning mechanism can be restored by the animal. Otherwise, ear wax is just going to keep building up inside of the ear canal and perpetuating the secondary infection, because it just creates a breeding ground where bacteria flourish. All of these things need to be addressed if we’re going to have successful outcomes, as far as reducing the recurrence of infection and making these animals feel good. 

[00:24:56] Dr. Painter: And I think it’s at this point that I’m sure most pet owners are like, “Oh my God,” because you go in and now you realize why it’s not that easy. Just sending you home with some drops is just probably not, in most cases, going to be enough for the rest of your dog’s life. If your dog truly has otitis externa with a primary cause that isn’t being resolved, it’s not something that’s just simple. Like, “Oh, yep. Throw some drops in. No big deal,” and we’ll be done- it’s a complex problem. And just having an understanding and respect for that- of how challenging this can be from a pet owner standpoint of trying to help your dog get better, but also from a veterinary standpoint that there are like 20 things that we have to keep track of- ear disease is a complicated problem in dogs and having everybody on the same page of recognizing that is really important.

What are the Predisposing Causes of Ear Infections?

[00:25:52] Dr. Lancellotti: We have one more part of our classification system- the predisposing factors. What are we talking about when we’re considering the predisposing factors? 

[00:26:01] Dr. Painter: I love predisposing factors because these are risk factors. Everybody says, “Well, he got an ear infection because he swims.” If you have listened, you probably will recognize that it was never mentioned as a primary cause. Swimming is not automatically going to set your dog up for ear infections. Swimming is a predisposing cause. So let’s say you have an allergic dog who swims, they’re at a heightened risk, but not every dog who swims gets ear infections. Similarly, we can see anatomy changes. Are you an English bulldog with the brachycephalic anatomy, the squished face, and small ear canals? Your whole head is just in anatomic change. Those dogs are at increased risk. Of course, the majority of English bulldogs (probably at some point) end up having issues with their ears, but not all of them, because that’s a predisposing cause. So again, these are risk factors for developing ear infections. They’re not the problem, but they amplify the problem. One of them is having a lot of hair and your ear canal. Not every standard poodle with lots of hair in their ear canal is going to develop ear infections, but certainly the food-allergic dogs will. And it might be something that makes it harder for us to clear that ear or makes them more likely to have refractory infections or infections that are much more difficult to treat.

[00:27:33] Dr. Lancellotti: Yeah, these are things to keep an eye out for- not necessarily the things that are going to be the major causes. If we’ve got an animal who is doing well and things are stable, if they go swimming or if they have more and more hair regrowth in their ear, that might kind of kick off having an ear infection. It’s something that we need to consider when we’re managing these patients that have chronic ear infections. 

[00:28:02] Dr. Painter: I’m not sure if we could throw more P words in there to help us facilitate this discussion on ear disease. But truly making a list and thinking about your dog in these categories really helps us all be on the same page of what exactly is going on, how the infection can be resolved, etc. Then, also think about if it’s not getting better. It helps to have this all laid out because what if the ear infection isn’t going away? We might have the wrong diagnosis of primary cause, have a perpetuating issue that’s in our way, or perhaps secondary infection is something that we just aren’t using the right therapeutic for. Again, being able to think of ear disease in this system really helps us be very methodical and systematic, so that we can, as veterinarians, help your dog get better so that veterinarians have a reliable system to help your dog improve.

Get Support for Understanding Your Pet's Ear Infections

[00:29:01] Dr. Lancellotti: And that’s so important- getting a veterinarian involved so that they have an understanding of your individual animal and its underlying factors are, to be able to come up with an appropriate treatment plan. That could mean working with your family veterinarian. Or if your animal is having chronic, frustrating skin and ear disease, finding a veterinary dermatologist near you would certainly be a fantastic resource, in figuring out the underlying causes and setting up a long-term plan, so that your animal can have long-term relief. If you have a pet that has had ear infections and you want to commiserate with some other owners, you can join our Facebook group, Your Vet Wants You To Know, where we talk about what’s going on with these allergic animals and get support from other members of the community. You can follow us on social media, as well, on Facebook and Instagram. For those of you who are interested in Dr. Painter’s course, that can be found at theallergicdog.com

Scratching the Itch

[00:30:20]Dr. Lancellotti: I like to end each episode with a segment called Scratching The Itch. This is something that is designed to highlight a product, a website, or a human interest story- something that just provides relief or makes you feel good. Hence, scratching the itch. Dr. Painter, do you have a ‘scratching the itch’ to share with our listeners today?

[00:30:39] Dr. Painter: I sure do. It’s not every day that the veterinary dermatologist is in the situation where one of their patients is going to need to be euthanized. We had a recent situation where one of my absolutely beloved patients became very ill and ‘end of life’ care was sought. I just want to give a plug for Lap Of Love. They are a national group that helps provide in-home euthanasia services for pet owners and (obviously) pets in need of that type of service. The care, respect, coordination, and just all that they did for this particular family was above and beyond. This wasn’t just one time. These people do this day in and day out and they’re incredible at their jobs. They’re so good at the service that they provide. For all of us that have a pet, the saddest part is that they need to pass and go to their rainbow bridge and wait for us. There are so many pets in my life that I’m excited to see again on the other side. But when we’re faced with that choice, having a trusted family veterinarian or our Lap Of Love service is really something that we should give thanks for. It truly is a humane service and just a true act of respect for all that our dogs and cats bring to our lives, and what they mean to us, providing them with that humane end.

[00:32:10] Dr. Lancellotti: Yeah, I absolutely love this company. They really have done a remarkable job at providing a service for pet owners to say goodbye to their animals in the most comfortable surroundings as possible. And to be able to provide some hospice care for these older animals, as well. I’ll have a link to Lap Of Love in the show notes, if people are interested in finding out about their service and getting some more information there. Thank you so much for mentioning them, Dr. Painter. 

[00:32:37] Dr. Painter: Absolutely. 

[00:32:38] Dr. Lancellotti: And when we come back for our next episode, we’re going to be diving deeper into this PSPP, and talking about what your veterinarian might actually do to investigate these specific causes in your pet. That will give you a lot more information there. I look forward to speaking with Dr. Painter more about this topic and for you to join us. Thank you so much, Dr. Painter. 

[00:33:03] Dr. Painter: You got it. Looking forward to the next talk. 

[00:33:05] Dr. Lancellotti: And I look forward to your next visit with Your Vet Wants You To Know.

References:

  1. Chan, Wei Yee, et al. “Biofilm Production by Pathogens Associated with Canine Otitis Externa, and the Antibiofilm Activity of Ionophores and Antimicrobial Adjuvants.” JOURNAL OF VETERINARY PHARMACOLOGY AND THERAPEUTICS, vol. 42, no. 6, Nov. 2019, pp. 682–92.
  2. Miller, William H., et al. Muller and Kirk’s Small Animal Dermatology. Saunders, 2013.
  3. O’Neill, Dan G., et al. “Frequency and Predisposing Factors for Canine Otitis Externa in the UK – a Primary Veterinary Care Epidemiological View.” Canine Medicine and Genetics, vol. 8, no. 1, Sept. 2021, p. 7.
  4. Paterson, Mrs Sue. “Allergic Canine Otitis Externa.” UK-Vet Companion Animal, vol. 20, no. 8, Aug. 2015, pp. 460–64.
  5. Zur, G., et al. “The Association between the Signalment, Common Causes of Canine Otitis Externa and Pathogens.” JOURNAL OF SMALL ANIMAL PRACTICE, vol. 52, no. 5, May 2011, pp. 254–58.

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