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.
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.Â No gross changes to
the meninges are seen.
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.Â In the center of the cochlea is a central core of
spongy bone which contains the spiral sensory ganglion.Â The pseudostratified lining epithelium and associated hair cells of the cochlea are necrotic and
replaced by abundant granulation tissue.Â 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.Â Similar necrosis, inflammation and granulation tissue fill the middle ear,
which is lined by ciliated pseudo stratified epithelium displaying squamous metaplasia.Â No etiologic agents are seen.
Severe, chronic, necrosuppurative otitis interna and media.
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.Â coli and non-haemolytic Streptococcus.Â 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.Â Spleen, liver, kidney, and thymus from this case were tested for bovine viral diarrhea virus via a fluorescent antibody test.Â 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)
Middle and inner ear: Otitis media and labrynthitis, necrosuppurative, severe, with osteonecrosis and osteolysis.
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):
|M.Â mycoides subsp.Â mycoides (small colony type)||Bovine||Contagious bovine pleuropneumonia|
|M.Â bovis||Bovine||Mastitis, pneumonia, arthritis, otitis|
|M.Â agalactiae||Ovine, Caprine||Contagious agalactia (mastitis)|
|M.Â capricolum subsp.Â capripneumoniae||Caprine||Contagious caprine pleuropneumonia|
|M.Â capricolum subsp.Â capricolum||Ovine, Caprine||Septicemia, mastitis, polyarthritis, pneumonia|
|M.Â mycoides subsp.Â capri (includes strains previously classified as M.Â mycoides mycoides large colony type)||Ovine, Caprine||Septicemia, pleuropneumonia, mastitis,arthritis|
|M.Â ovioneumoniae||Ovine, Caprine||Pneumonia|
|M.Â pulmonis||Rodents--rat and mouse||Colonize nasopharynx and middle ear; affect respiratory and reproductive tracts and joints|
|M.Â hyopneumoniae||Swine||Enzootic pneumonia|
|M.Â hyosynoviae||Swine (10-30 weeks of age)||Polyarthritis|
|M.Â hyorhinis||Swine (3-10 weeks of age)||Polyserositis|
|M.Â suis||Swine||Mild anemia, poor growth rates|
|M.Â ovipneumoniae||mild pneumonia|
|M.Â haemofelis||Feline||Feline infectious anemia|
|M.Â cynos||Canine||Implicated in kennel cough complex|
|M.Â haemocanis||Canine||Mild or subclinical anema; more severe signs in splenectomized animals|
|M.Â gallisepticum||Turkeys and Chickens||Chronic respiratory disease; infectious sinusitis|
|M.Â synoviae||Turkeys and Chickens||Infectious synovitis|
|M.Â meleagridis||Feline, Equine||Conjunctivitis in cats, pleuritis in horses|
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.Â The relationship between the polyp and the other structures was difficult to ascertain in the sections examined.Â Also, participants noted there is osteolysis of the petrous portion of the temporal bone.
1.Â Caswell JL, Williams KJ.Â Respiratory system.Â In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. 5th ed.Â New York, NY:
2.Â Foster AP, Naylor RD, Howie NM, Nicholas RAJ, Ayling RD.Â Mycoplasma bovis and otitis in dairy calves in the United Kingdom.Â The Veterinary Journal.
3.Â Lamm CG, Munson L, Thurmond MC, Barr BC, George LW.Â Mycoplasma otitis in California calves.Â J Vet Diagn Invest. 2004;16:397-402.
4.Â Quinn PJ, Markey BK, Leonard FC, FitzPatrick ES, Fanning S, Hartigan PJ.Â Mycoplasmas.Â In: Veterinary Microbiology and Microbial Disease. 2nd ed.Â Ames,
Iowa: Wiley-Blackwell; 2011; Kindle edition.
5.Â Wilcock BP.Â Eye and ear.Â In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals.Â 5th ed.Â New York, NY: Elsevier; 2007:548-549.