Signalment:  

6-week-old Holstein-cross bull calf (Bos taurus).The calf had chronic ear infections since two weeks of age. No improvement was seen with multiple antibiotics or bilateral myringotomy. Intermittent purulent discharge was seen bilaterally. Persistent worsening neurologic signs include severe ataxia, obtundation, and absence of hind limb reflexes, withdrawal, and deep pain sensation. CT exam of the skull revealed expansion of both tympanic bullae with multifocal areas of marked lysis and soft tissue or caseous material filling the bullae. Similar material was seen in both external ear canals.

Gross Description:  

Within the external ear canals, tympanic bullae and inner ears is a severe bilateral white purulent to caseous exudate, with osseous thickening of the tympanic bulla. No gross changes to the meninges are seen.

Histopathologic Description:

Inner ear: Examined is a cross-section of inner ear consisting primarily of the cochlea within the petrous temporal bone, the adjacent vestibule lined by ciliated epithelium containing abundant mucus cells, and associated vestibulocochlear nerve. In the center of the cochlea is a central core of spongy bone which contains the spiral sensory ganglion. The pseudostratified lining epithelium and associated hair cells of the cochlea are necrotic and replaced by abundant granulation tissue. Filling the vestibule and the cochlea, and abutting portions of the cochlear nerve, is a marked inflammatory exudate comprised of neutrophils, lymphocytes, plasma cells, macrophages associated with severe necrosis, which is evidenced by eosinophilic amorphous cellular debris, basophilic karyorrhectic nuclear debris, and multifocal dystrophic mineralization. Similar necrosis, inflammation and granulation tissue fill the middle ear, which is lined by ciliated pseudo stratified epithelium displaying squamous metaplasia. No etiologic agents are seen.

Morphologic Diagnosis:  

Severe, chronic, necrosuppurative otitis interna and media.

Condition:  

Mycoplasma bovis

Contributor Comment:  

Differentials for otitis interna and media in calves includes: Histophilus somnus, Mannheimia haemolytica, Pasteurella multiocida, Streptococcus spp., Actinomyces spp., Arcanobacterium pyogenes, and Mycoplasma bovis.(2,5) A heavy growth of Mycoplasma was cultured from an ear swab collected at necropsy, with a light growth of both E. coli and non-haemolytic Streptococcus. Bacteria were not spectated.

Mycoplasma are extracellular bacteria that lack a cell wall and may be transmitted via infected secretions of the respiratory tract, genital tract, or mammary gland from infected cows or other calves.(1) Mycoplasma evades the host immune system by suppressing neutrophil and lymphocyte activation, as well as inducing lymphocyte apoptosis.(1) Mycoplasma otitis typically affects male dairy calves less than 2 months of age.(3) The pathogenesis of otitis interna and media due to Mycoplasma in calves is not completely understood but is thought to involve one or more of the following mechanisms: (1) ingestion of infected milk causing nasopharyngeal infection, with extension through the Eustachian tube to the middle ear, (2) immunosuppression or a primary viral infection (BVDV, IBRV) allowing overgrowth of resident flora, (3) direct extension from the external ear canal through the tympanic membrane to the middle and inner ear, or (4) hematogenous spread, which is more commonly seen in rodents, lambs, and swine.(3,5) Infection may then ascend via the vestibulocochlear and facial nerves to the brainstem to cause meningitis. Spleen, liver, kidney, and thymus from this case were tested for bovine viral diarrhea virus via a fluorescent antibody test. Testing for herpesvirus (IBRV) was not performed.

Mycoplasma bovis infections are of economic importance, causing widespread systemic disease, including pneumonia, arthritis, and mastitis.(1,3) Antigenic variation of the surface lipoproteins is thought to contribute to a poor response to antibiotic therapy and evasion of the host immune response.(1,2) Therefore, the cellular and humoral immune responses offer no protection, despite the development of antibody titers.(1) Ingestion of infected milk is thought to be the most likely route of infection, therefore, control measures include pasteurization of colostrum and milk being fed to calves, preventing direct contact between calves, and culling infected cows.(2)

JPC Diagnosis:  

Middle and inner ear: Otitis media and labrynthitis, necrosuppurative, severe, with osteonecrosis and osteolysis.

Conference Comment:  

Mycoplasma are small, fastidious, pleomorphic, facultative anaerobic bacteria that generally do not replicate outside the host.(4) Although many species are non-pathogenic, several species cause diseases in both humans and animals. Mycoplasma species are generally found on the mucosal epithelium of the conjunctiva, nasal cavity, oropharynx, intestinal and genital tracts.

Recently some species have been reclassified from the rickettsial group into the genus Mycoplasma; these bacteria are referred to as hemoplasms, as they have a tropism for red blood cells rather than epithelium.(4) In addition to the diseases associated with Mycoplasma bovis that were adeptly described by the contributor, conference participants also discussed a variety of other Mycoplasma species of importance in veterinary medicine(4):

Mycoplasma species	Hosts	Disease
M. mycoides subsp. mycoides (small colony type)	Bovine	Contagious bovine pleuropneumonia
M. bovis	Bovine	Mastitis, pneumonia, arthritis, otitis
M. agalactiae	Ovine, Caprine	Contagious agalactia (mastitis)
M. capricolum subsp. capripneumoniae	Caprine	Contagious caprine pleuropneumonia
M. capricolum subsp. capricolum	Ovine, Caprine	Septicemia, mastitis, polyarthritis, pneumonia
M. mycoides subsp. capri (includes strains previously classified as M. mycoides mycoides large colony type)	Ovine, Caprine	Septicemia, pleuropneumonia, mastitis,arthritis
M. ovioneumoniae	Ovine, Caprine	Pneumonia
M. pulmonis	Rodents--rat and mouse	Colonize nasopharynx and middle ear; affect respiratory and reproductive tracts and joints
M. hyopneumoniae	Swine	Enzootic pneumonia
M. hyosynoviae	Swine (10-30 weeks of age)	Polyarthritis
M. hyorhinis	Swine (3-10 weeks of age)	Polyserositis
M. suis	Swine	Mild anemia, poor growth rates
M. ovipneumoniae		mild pneumonia
M. haemofelis	Feline	Feline infectious anemia
M. cynos	Canine	Implicated in kennel cough complex
M. haemocanis	Canine	Mild or subclinical anema; more severe signs in splenectomized animals
M. gallisepticum	Turkeys and Chickens	Chronic respiratory disease; infectious sinusitis
M. synoviae	Turkeys and Chickens	Infectious synovitis
M. meleagridis	Feline, Equine	Conjunctivitis in cats, pleuritis in horses
M. equigenitalium	Equine	Abortion

Table adapted from Veterinary Microbiology and Microbial Disease. 2nd ed., 2011⁴

Conference participants noted the presence of an inflamed mucosal lining, interpreted as a polyp, that did not appear to be attached to the rest of the tissue. The relationship between the polyp and the other structures was difficult to ascertain in the sections examined. Also, participants noted there is osteolysis of the petrous portion of the temporal bone.

References:

1. Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. 5th ed. New York, NY: Elsevier; 2007:611-613. 2. Foster AP, Naylor RD, Howie NM, Nicholas RAJ, Ayling RD. Mycoplasma bovis and otitis in dairy calves in the United Kingdom. The Veterinary Journal. 2009;179:455-457. 3. Lamm CG, Munson L, Thurmond MC, Barr BC, George LW. Mycoplasma otitis in California calves. J Vet Diagn Invest. 2004;16:397-402. 4. Quinn PJ, Markey BK, Leonard FC, FitzPatrick ES, Fanning S, Hartigan PJ. Mycoplasmas. In: Veterinary Microbiology and Microbial Disease. 2nd ed. Ames, Iowa: Wiley-Blackwell; 2011; Kindle edition. 5. Wilcock BP. Eye and ear. In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. 5th ed. New York, NY: Elsevier; 2007:548-549.

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3-1. Middle and inner ear

3-2. Middle and inner ear

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