8 Case Studies on Infectious Diseases of Dogs

Case A Otitis externa in a dog

Introduction

Otitis externa/media is a common problem in dogs, especially those with floppy ears and living in the Tropics. Dogs that swim may develop “swimmer’s ear”. This is associated with a build-up of warm moisture in the ear that allows yeasts and bacteria to overgrow on a softened skin. Ear infections are more complicated when the dogs are suffering from atopy (a genetic predisposition to developing allergies to environmental substances) and an allergic disease like a food hypersensitivity.

The case study below serves to explore the causes, epidemiology, pathogenesis, diagnosis and treatment of this common disease.

History

Jasmine the Springer Spaniel has been visiting the vet every 3 months to be treated for recurrent ear infections. Jasmin’s owner believes that there will never be a cure and has sought your advice as a last resort. Jemima is now 7 years old and scratches her ears almost constantly. After a thorough clinical history taking, you decide that a shotgun (empirical) approach i.e. just giving a more powerful treatment is not going to work. You decide with your client’s support to perform a full diagnostic work-up.

In the clinical history, you learn that Jemima goes daily for a walk along the beach and takes great pleasure in swimming and catching a ball in the waves. She is fed a diet of Hill’s Canine Adult large Pellets and is fed treats such as meat scraps from the table, dental chews and commercial meat strips “Smackos”. Jemima’s owner also complains that she smells and scratches a lot spreading hair all over the house.  Jemima is mainly an indoor dog and is treated like one of the family. She has been on a number of ear drops and ear cleaners that seem to help a bit initially but later on don’t work. The owner admits that it is not easy to treat her as the ears are sore and she becomes very wriggly and even tries to bite when she is treated.

Otoscopic examination of the left ear of Jemima

Otitis predispositions

What factors could be predisposing to Jemima’s otitis? Provide an explanatory statement for each predisposing factor you write down. To assist you, the link will bring you to a review article by Donald MacTaggart, Assessment and management of chronic ear disease. In Practice, September 2008.

An example of a factor is: Excessive moisture in the ears. Explanatory statement : Jemima swims a lot exposing her ears to moisture. Her ear flaps keep the moisture in, where it gets warm, leading to skin maceration and allowing the normal microflora in the ear to overgrow.

Diagnostic Plan

Numerically order (1- 8) what you would do to obtain a diagnosis as well as the value of that diagnostic procedure. Don’t include those tests as a number, if you won’t use them.

You performed a clinical examination and found her to be healthy except for the fact that she tilted her head a bit to the right and the parotid, cervical and postauricular lymph nodes were enlarged.

You then examined Jasmin’s ears and find that both ears are inflamed, with the right ear being severely inflamed, (as shown in the picture below right). The right ear canal was narrowed due to thickening and inflammation. This meant that you could not see the ear drum even with an otoscope. She found the ear examination very painful. The left ear was reddened but less thickened and painful. It is shown in the picture below on the left. The ear drum could be observed and was found to be intact. There was a brown sticky exudate from the left ear.

Left ear appearance

Clinical appearance of Jemima’s right ear

Further investigations

Based on your findings , what would be the most immediate major concern that you would have? The link will bring you to a review article by Donald MacTaggart, Assessment and management of chronic ear disease. In Practice, September 2008.

1. That the right ear drum has ruptured and there has been spread of the infection to the middle and possibly the inner ear
2. That Jemima has a resistant bacterial infection
3. That the owner is not compliant in preventing infection and treating the infection
4. That the infection in the right ear is too far progressed for treatment
5. That Jemima is also suffering from a food allergy

With the owner’s permission you anaesthetise Jasmin and examine the ears more thoroughly. Since the right ear drum is very narrowed and full of exudate, you clean the ears with a solution of warm sterile normal saline solution. However, before you do that you collect swabs of both ear canals to perform cytology on and if needed bacterial and fungal cultures and identification. You Gram’s stain the exudate from both ears.

Gram’s stain of the exudate from the right ear.

Results from the right ear

Below is a list of possible causes of otitis in dogs. Select from the list below what could be the infectious agent perpetuating the otitis.

1. Aspergillus niger
2. Corynebacterium species
3. Escherichia coli
4. Klebsiella species
5. Malassezia yeast
6. Proteus species
7. Pseudomonas aeruginosa
8. Staphylococcus pseudintermedius
9. Staphylococcus aureus
10. Streptococcus canis

Results from the left ear

The exudate from the left ear had only a few inflammatory cells present, but a lot of epithelial cells. Trapped in the epithelial cells was a mixed population of microorganisms. Which microorganisms may be associated with infection in this ear? Hint: They usually cause a sticky brown exudate in the ear canal.

Gram’s stain of the left ear. It has less inflammatory cells and more epithelial cells present.

1. Aspergillus niger
2. Corynebacterium species
3. Escherichia coli
4. Klebsiella species
5. Malassezia yeast
6. Proteus species
7. Pseudomonas aeruginosa
8. Staphylococcus pseudintermedius
9. Staphylococcus aureus
10. Streptococcus canis

You discover that the ear drum of the right ear has ruptured. Thus, you radiograph the ear and find that the infection has spread to the middle ear. You decide, based on the history and clinical examination, that immediate antibiotic therapy is warranted.

Notes

What route of antibiotic administration would you use? Provide reasons for your choice.

Antibiotic choice

Based on the right ear exudate cytology, what antibiotic would you select for empirical treatment? The antibiotics shown below are all used to treat otitis media.

1. a) Amoxicillin with clavulanate (potentiated penicillin)
2. b) Cephalexin (1st generation cephalosporin)
3. c) Cefovecin (like a 2nd generation cephalosporin)
4. d) Clindamycin (lincosamide)
5. e) Enrofloxacin (fluoroquinolone)
6. f) Ticarcillin (Antipseudomad penicillin)
7. g) Trimethoprim sulphadiazine (potentiated sulphonamide)

Notes on antibiotic choice

Write short notes on your choice of antibiotics

You send the swabs for bacterial and fungal culture and identification and antimicrobial susceptibility testing. The left ear yields a heavy growth of Malassezia pachydermatitis, moderate growth of Corynebacterium auriscanis and a light growth of Pseudomonas aeruginosa. The right ear yields a heavy pure growth of Pseudomonas aeruginosa.

Pseudomonas aeruginosa cause of otitis

Pseudomonas aeruginosa is a common perpetuator of chronic otitis in dogs. Provide at least 3 reasons for this.

The antimicrobial susceptibility results of the isolated are shown below.

Susceptibility testing of the yeast M. pachydermatis

Antibiotic choice

What antibiotic would you select. Bear in mind that at least 3 weeks of treatment are required.

1. Amoxicillin with clavulanate (potentiated penicillin)
2. Cephalexin (1st generation cephalosporin)
3. Cefovecin (like a 2nd generation cephalosporin)
4. Clindamycin (lincosamide)
5. Enrofloxacin (fluoroquinolone)
6. Gentamicin
7. Ticarcillin (Antipseudomad penicillin)
8. Trimethoprim sulphadiazine (potentiated sulphonamide)

Route of administration

Select the route of administration

• Topical
• Systemic

Treatment of the left ear

What antibiotic/fungal combination would you select?

1. Topical: Marbofloxacin/Clotrimazole
2. Topical: Fusidic acid/Framycetin/Nystatin
3. Topical: Gentamicin/Clotrimazole
4. Topical: Neomycin/Thiostreptone/Nystatin
5. Topical: Polymixin B/Miconazole
6. Systemic: Itraconazole
7. Systemic: ketoconazole

Other treatments

Why is using a good ear cleaner an excellent adjunct therapy to antibiotics and antifungals?

Ear cytology pictures

Dog ear cytology Gram’s stain

Interpret Gram’s stain above

1. Epithelial cells and Gram positive cocci in clumps and chains
2. Neutrophils and Gram negative cocci in clumps
3. Epithelial cells and Gram negative and Gram positive cocci in chains and individually
4. Neutrophils and Gram positive cocci in clumps and chains

DiffTMQuik stain

Above is a DiffQuik stain of an ear what do you see?

1. Ear wax = cerumen
2. Gram negative cocci
3. Gram positive cocci
4. Intracytoplasmic cocci
5. Inflammatory protein debris
6. Neutrophils
7. Squamous epithelial cells
8. Red blood cells

Gram’s stain of ear sediment

Label the arrows in the picture above

Describe the Bacteria seen on this Gram’s stain x100 magnification of the dog Val’s left ear.

From the list below, select two bacteria that have the morphological appearance of the bacteria observed in the picture above.

1. Actinomyces species
2. Corynebacterium species
3. Dermatophilus congolensis
4. Escherichia coli
5. Klebsiella species
6. Mycobacterium species
7. Nocardia species
8. Proteus species
9. Pseudomonas aeruginosa
10. Staphylococcus pseudintermedius
11. Staphylococcus aureus
12. Streptococcus canis

Case history B

Johnny, a male desexed French Bulldog 11 months of age developed pyrexia (fever), pain in the left elbow with diffuse soft tissue swelling. A septic arthritis is suspected.

Cytology results:

Sample consists of a large population (obtained from 200 cell differential count) of neutrophils 94% which appear mostly non-degenerative with few degenerate, and macrophages 6% which are frequently leukophagic. No infectious organisms were detected. There is moderate numbers of ruptured cells and apoptotic bodies present. The background is eosinophilic, granular and clumped.

Even though no bacteria were noted, should a bacterial culture be performed? Provide a reason for your answer.

Joint fluid was collected and submitted for culture. Below is a Gram’s stain x100 magnification of the fluid obtained

Mark on the picture any bacteria

From the list below, select two bacteria that have the morphological appearance of the bacteria observed in the picture above.

A modified acid-fast stain of the sample

1. Actinomyces species
2. Corynebacterium species
3. Dermatophilus congolensis
4. Escherichia coli
5. Klebsiella species
6. Mycobacterium species
7. Nocardia species
8. Proteus species
9. Pseudomonas aeruginosa
10. Staphylococcus pseudintermedius
11. Staphylococcus aureus
12. Streptococcus canis

Additional samples included blood, chin abscess and urine

Below is a Gram’s stain of what was cultured from all samples.

Make a diagnosis and provide reason for your diagnosis

The results from an antibiotic disk diffusion test are below

1. a) Based on the results, what antibiotic would you select?

1. b) In a few sentences describe the origins of this bacterium and the role it plays in infections

Case study C: Using laboratory data for urinary tract infections in dogs

1. Why is Escherichia coli a common cause of UTIs in dogs?

Cystitis is more common in female dogs with females representing 80% of the positive cultures. However urinary tract infections occur in male dogs, especially middle-aged dogs

2. Cystitis is associated with which other disease in male dogs?

3. What is a bacterial L-form and why is it significant?

Pictures below are of urine sediment cytology.

4. Compare them and see if you can observe any patterns that will assist you in clinical practice.

Case A. Left DiffQuik, Right Gram’s stain

Case B. Left DiffQuik, Right Gram’s stain

Observation:

5. What antibiotic should be used empirically to treat Gram-positive coccal infections?

6. When would bacterial cultures be useful in Gram-positive infections?

7. What antibiotic should be used empirically to treat Gram-negative bacilli Infections?

8. For what Gram-negative bacillus should a different antibiotic be selected and should never be treated empirically?

Case study D Kennel cough syndrome in dogs

Tim is a seven-month-old Golden Retriever male pup. He has been going to doggy day care once a week for two months and within a week of being there he had developed a dry hacking cough and fever response. Tim is otherwise healthy and has received a full puppy course of vaccinations. He has been tested for heartworm and is heartworm antigen negative. Potentiated sulphonamides and anti-inflammatories were prescribed with some improvement and a reduction in fever. However, Tim is still coughing.

Answer the following questions related to kennel cough

Bordetella bronchiseptica infections primary cause infections of the bronchial tree and most infections are treated with supportive therapy and not antibiotics.

1. What viral diseases predispose dogs to Bordetella bronchiseptica infections?

2. What bacterial agents are common opportunistic pathogens in kennel cough?

3. Are antibiotics always necessary and under what clinical circumstances should antibiotics be prescribed?

Haematology, serum biochemistry and urinanalysis were performed with no significance findings. A bronchoalveolar lavage (BAL) was performed and the fluid thus collected was thick with clumps of pus in it.

DiffQuik stained cytology of the pus is shown in the image below.

Describe any abnormal findings.

Label the arrows in the images above

Bordetella bronchiseptica was cultured from the BAL. Mycoplasmal and fungal cultures were negative.

Based on antibacterial susceptibility results, it was decided to treat Tim with nebulized gentamicin (6.9 mg/kg in 3mL saline) BID for 5 days and oral doxycycline (5mg/kg) BID for two weeks. This resulted in clinical cure.

What is the advantage of administering gentamicin via nebulizer?

Why would doxycycline be an effective treatment?

4. Vaccination is considered to be important in the prevention of kennel cough syndrome in dogs. Even though it is a non-core vaccine, it is a requirement before sending dogs for boarding

Select from the list of vaccines below, your preferred vaccine and motivate your choice. (Bear in mind, there is no one correct answer – this is for you to reason it out) Base it on:

• Co-morbidities
• Timing of vaccination
• Duration of immunity
• Potential adverse effects
• Route of administration