(EXAM 2) Lecture 8: Eye and ear infections- I

What is the primary clinical relevance of Moraxella bovis?

Moraxella bovis is the causative agent of infectious bovine keratoconjunctivitis (IBK).

What is the significance of Moraxella bovoculi in IBK?

Moraxella bovoculi is isolated from animals affected by IBK and possesses RTX toxin, but its pathogenicity remains unproven.

How is Moraxella ovis clinically relevant?

Moraxella ovis has been isolated from both healthy animals and those with keratoconjunctivitis.

Which Moraxella species is a member of the normal oral flora of dogs and has been isolated from dog bite wounds in humans?

Moraxella canis

What is the clinical significance of Moraxella cuniculi?

It has been isolated from cases of IBK, often in association with other organisms.

Which Moraxella species is associated with conjunctivitis in horses?

Moraxella equi

Which Moraxella species has been isolated from various pathological conditions in animals, including goats, dogs, pigs, and aborted equine fetuses?

Moraxella lacunata; its pathogenicity is unknown.

What is the significance of Moraxella phenylpyruvica in veterinary medicine?

It has been isolated from multiple sites in farm animals, but its pathogenicity is uncertain.

Which two Moraxella species have been isolated from the upper respiratory tract of healthy goats?

Moraxella boevrei and Moraxella caprae

What are the early clinical signs of infectious bovine keratoconjunctivitis (IBK)?

Blepharospasm, lacrimation, conjunctivitis, and photophobia.

What are the progressive ocular signs seen in IBK?

Keratitis, corneal opacity and ulceration, with occasional panophthalmitis and permanent blindness.

What happens to the cornea in mild cases of IBK?

The cornea heals, but permanent scarring may occur.

How long does it take for corneal ulcers in IBK to heal?

Healing proceeds from the periphery and takes several weeks, while central scarring can persist for months.

Which cattle are less susceptible to IBK based on ocular pigmentation?

Cattle with darker ocular pigmentation have a lower incidence of IBK.

Which age group of cattle is most susceptible to IBK?

Young cattle under 2 years of age.

Which breed of cattle is more susceptible to IBK?

Bos taurus breeds are more susceptible than Bos indicus breeds.

How do flies contribute to IBK outbreaks?

Flies act as vectors for Moraxella bovis.

List some ocular irritants that can predispose cattle to IBK.

Dust, tall grasses, grass seeds, wind, ultraviolet light, and cold ambient temperatures.

What concurrent infections can exacerbate IBK?

Infection with Bovine herpesvirus 1 or Thelazia spp.

How does vitamin A deficiency relate to IBK?

A deficiency in vitamin A may predispose cattle to IBK.

What are the primary methods used to diagnose IBK?

Clinical signs and isolation of Moraxella bovis from conjunctival swabs or lacrimal secretions.

Why is it important to process IBK diagnostic specimens promptly?

Moraxella bovis is an extremely fragile organism.

What culture conditions are used to grow Moraxella bovis?

Blood agar and MacConkey agar, incubated aerobically at 37°C for 48-72 hours.

What are the colony characteristics of Moraxella bovis?

Small, shiny, friable colonies appear after 48 hours, with virulent strains being hemolytic and embedded in agar.

How does Moraxella bovis grow on MacConkey agar?

Moraxella bovis does not grow on MacConkey agar.

What biochemical tests are positive for Moraxella bovis?

Catalase and oxidase tests, with pitting on Loeffler's agar.

How can Moraxella bovoculi be differentiated from Moraxella bovis?

M. bovoculi tests positive for phenylalanine deaminase.

What are the key components of IBK treatment?

Use of antimicrobials, prevention of ocular irritation, and isolation of affected cattle.

Which antimicrobial treatment has been proven effective for IBK?

Two injections of long-acting oxytetracycline given 72 hours apart.

What are the benefits of using eye patches in IBK treatment?

They reduce irritation caused by environmental factors.

What management strategies help control IBK?

Fly control, management of concurrent diseases, and vitamin A supplementation.

What is the efficacy of fimbriae-derived bacterins in IBK prevention?

Their efficacy is uncertain.

Where is Moraxella bovis typically found in carrier cattle?

It is found on the mucous membranes of carrier cattle.

How does Moraxella bovis survive outside the host?

It is susceptible to desiccation and is short-lived in the environment.

How long can Moraxella bovis survive on flies, and why is this important?

It can survive for up to 72 hours in the salivary organs and on the body surfaces of flies, which act as vectors for transmission.

What are the main virulence factors of Moraxella bovis?

Fimbriae (Q fimbriae, I fimbriae), hemolysin (Mbx A), fibrolysin, phosphatase, hyaluronidase, and aminopeptidase.

What role do fimbriae play in Moraxella bovis pathogenesis?

They help in adherence to the cornea and stimulate type-specific protective immunity.

What is the function of hemolysin (Mbx A) in Moraxella bovis?

It is a calcium-dependent, pore-forming cytolysin that damages the cell membranes of neutrophils.

What type of toxin is Moraxella bovis hemolysin (Mbx A)?

It is an RTX toxin with hemolytic and cytotoxic activity.

What are the functions of fibrolysin, phosphatase, hyaluronidase, and aminopeptidase in Moraxella bovis?

They contribute to tissue breakdown and bacterial invasion.

What biochemical test is used to differentiate Moraxella bovoculi from Moraxella bovis?

Moraxella bovoculi is positive for the phenylalanine deaminase test, while Moraxella bovis is negative.

What are general predisposing factors for otitis externa caused by Malassezia spp.?

Conformation, excessive moisture, obstructive ear disease, systemic disease, and treatment effects.

How does ear conformation contribute to otitis externa?

Pendulous pinna, stenotic ear canals, excessive hair in the canals, and hairy concave pinna can trap moisture and debris, promoting yeast overgrowth.

Why does excessive moisture predispose to Malassezia otitis externa?

Increased humidity from the environment or swimming creates an ideal environment for yeast proliferation.

Name some obstructive ear diseases that can predispose to Malassezia otitis externa.

Neoplasia, polyps, and other conditions that block normal airflow and drainage.

How do systemic diseases contribute to Malassezia otitis externa?

Immune suppression and catabolic states reduce the host's ability to regulate yeast populations.

How can treatment effects predispose dogs to Malassezia otitis externa?

Changes in normal flora from antibiotic use, glucocorticoid therapy, or trauma can disrupt microbial balance.

What is the primary yeast species responsible for otitis externa in dogs?

Malassezia pachydermatis.

What additional condition can Malassezia pachydermatis cause in dogs?

Seborrheic dermatitis.

Where is Malassezia pachydermatis normally found on dogs?

Skin, lips, anus, vagina, anal sacs, and external ear canal.

What factors promote Malassezia overgrowth and disease development?

High humidity, excessive wax accumulation, allergies, neoplasms, seborrhea, and recent antibiotic or glucocorticoid therapy.

How do clinical signs of Malassezia otitis externa develop?

The yeast produces metabolic by-products that can trigger an allergic reaction.

What are common clinical signs of Malassezia otitis externa in dogs?

Head shaking, pruritus, and an offensive odor.

What characteristic discharge is seen in chronic Malassezia otitis externa?

Thick, waxy, brown discharge filling the external ear canal.

What history findings may suggest Malassezia otitis externa?

Poor response to antibiotics, glucocorticoids, and immunotherapy.

What is the most useful diagnostic tool for Malassezia infection?

Cytologic examination of affected areas (impression smears).

How do Malassezia yeast cells appear under cytology?

Slightly elongated oval, broad-based yeast cells with a flask-shaped, "shoe-print," or peanut-shaped morphology.

What are the primary treatment goals for Malassezia otitis externa?

Reduce yeast numbers and identify and eliminate predisposing factors.

What systemic antifungal is commonly used for Malassezia otitis externa?

Ketoconazole.

What alternative antifungal treatment can be used for Malassezia otitis externa?

Itraconazole, administered daily or in pulse therapy.

What is otitis externa?

Inflammation of the external ear canal, commonly seen in dogs and cats.

What are the common clinical signs of otitis externa?

Head shaking, pain, malodor, erythema, erosion, ulceration, swelling, and ceruminous gland inflammation.

How is otitis externa diagnosed?

Otoscopic examination, cytology, and culture.

Why is it important to address the inciting cause of otitis externa?

To prevent recurrence and progression to chronic disease.

What are primary causes of otitis externa?

Conditions that alter the ear environment, often leading to secondary infections.

What are some allergic causes of otitis externa?

Adverse food reactions, atopic dermatitis, and contact allergies.

What parasitic infections can lead to otitis externa?

Otodectes, Demodex, and Sarcoptes infestations.

Name two autoimmune or immune-mediated diseases that can cause otitis externa.

Pemphigus foliaceus and vasculitis.

What endocrine diseases can contribute to otitis externa?

Hypothyroidism and hyperadrenocorticism.

How do epithelialization disorders contribute to otitis externa?

Conditions like sebaceous adenitis and zinc-responsive dermatitis can disrupt normal skin barrier function.

What foreign material can serve as a primary cause of otitis externa?

Foreign bodies lodged in the ear canal.

Name two glandular disorders that can contribute to otitis externa.

Sebaceous gland hyperplasia and excessive cerumen production.

What fungal infection can be a primary cause of otitis externa?

Aspergillus infection.

Name a viral cause of otitis externa.

Canine distemper virus.

What are some miscellaneous primary causes of otitis externa?

Proliferative necrotizing otitis of cats and juvenile cellulitis.

What are secondary causes of otitis externa?

Conditions that create disease in an already abnormal ear, often leading to chronic or recurrent infections.

Name common bacterial pathogens responsible for secondary otitis externa.

Staphylococcus, Streptococcus, Enterococcus, Pseudomonas, Proteus, and other bacteria.

What yeast species is a common secondary cause of otitis externa?

Malassezia spp.

How can medication reactions contribute to secondary otitis externa?

They can disrupt the normal ear flora, leading to dysbiosis and inflammation.

Why is overcleaning a risk factor for secondary otitis externa?

Excessive cleaning can cause trauma, disrupt normal flora, and increase susceptibility to infections.

What is the principal pathogen causing infectious bovine keratoconjunctivitis (IBK)?

Moraxella bovis.

What age group is most affected by IBK?

Animals under 2 years of age.

How does IBK impact the cattle industry economically?

Causes decreased weight gain in beef breeds, loss of milk production, short-term breeding disruptions, and treatment costs.

What factor contributes to age-related immunity in IBK?

Previous exposure to Moraxella bovis.

Where do asymptomatic carriers of Moraxella bovis harbor the bacteria?

Nasolacrimal ducts, nasopharynx, and vagina.

What are the main transmission routes of Moraxella bovis?

Direct contact, aerosols, and mechanical transmission by flies.

What is the Gram reaction and morphology of Moraxella spp.?

Short Gram-negative rods, usually in pairs.

What are the optimal growth conditions for Moraxella spp.?

Growth on enriched media under aerobic conditions.

Are Moraxella spp. motile?

No, they are non-motile.

What are two key enzymatic characteristics of Moraxella spp.?

Catalase-positive and oxidase-positive.

How do Moraxella spp. interact with sugar substrates?

They are proteolytic and unreactive with sugar substrates.

What virulence factors are associated with pathogenic Moraxella strains?

Virulent strains are fimbriated and hemolytic.

Besides Moraxella bovis, which other Moraxella species are associated with disease in animals?

M. bovoculi, M. ovis, and M. equi.