Otitis media in guinea pigs: pathology and bacteriology

Research-Relevant Conditions and Pathology of Laboratory Mice, Rats, Gerbils, Guinea Pigs, Hamsters, Naked Mole Rats, and Rabbits

Animals are valuable resources in biomedical research in investigations of biological processes, disease pathogenesis, therapeutic interventions, safety, toxicity, and carcinogenicity. Interpretation of data from animals requires knowledge not only of the processes or diseases (pathophysiology) under study but also recognition of spontaneous conditions and background lesions (pathology) that can influence or confound the study results. Species, strain/stock, sex, age, anatomy, physiology, spontaneous diseases (noninfectious and infectious), and neoplasia impact experimental results and interpretation as well as animal welfare. This review and the references selected aim to provide a pathology resource for researchers, pathologists, and veterinary personnel who strive to achieve research rigor and validity and must understand the spectrum of "normal" and expected conditions to accurately identify research-relevant experimental phenotypes as well as unusual illness, pathology, or other conditions that can compromise studies involving laboratory mice, rats, gerbils, guinea pigs, hamsters, naked mole rats, and rabbits.

Modeling asthma: Pitfalls, promises, and the road ahead

Asthma is a chronic, heterogeneous, and recurring inflammatory disease of the lower airways, with exacerbations that feature airway inflammation and bronchial hyperresponsiveness. Asthma has been modeled extensively via disease induction in both wild-type and genetically manipulated laboratory mice (Mus musculus). Antigen sensitization and challenge strategies have reproduced numerous important features of airway inflammation characteristic of human asthma, notably the critical roles of type 2 T helper cell cytokines. Recent models of disease induction have advanced to include physiologic aeroallergens with prolonged respiratory challenge without systemic sensitization; others incorporate tobacco, respiratory viruses, or bacteria as exacerbants. Nonetheless, differences in lung size, structure, and physiologic responses limit the degree to which airway dynamics measured in mice can be compared to human subjects. Other rodent allergic airways models, including those featuring the guinea pig (Cavia porcellus) might be considered for lung function studies. Finally, domestic cats (Feline catus) and horses (Equus caballus) develop spontaneous obstructive airway disorders with clinical and pathologic features that parallel human asthma. Information on pathogenesis and treatment of these disorders is an important resource.

Mannheimia caviae sp. nov., isolated from epidemic conjunctivitis and otitis media in guinea pigs

Strains T138021-75T, Pg19 and Pg20 (taxon 25 of Bisgaard) were isolated from guinea pigs and characterized. Strains T138021-75T and Pg20 showed identical 16S rRNA gene sequences and were distantly related to the published strain P224 with the highest 16S rRNA similarity of 98.6 %. These two strains showed 97.8 % sequence similarity with the type strain and other strains of Mannheimia glucosida and 97.3 % similarity with the type strain of Mannheimia varigena, but <97 % similarity with all other type strains of the genus Mannheimia, including Mannheimia haemolytica (96.9 %). Phylogenetic analysis of rpoB gene sequences showed that strain P224 had a distant position (89.9 % gene sequence similarity) compared with the three other strains (T138021-75T, Pg20 and Pg19), which had identical gene sequences. These three novel strains also shared identical recN gene sequences. Phylogenetic analysis of the recN gene sequences showed a close relationship between the three novel strains and strain P224. The DNA–DNA reassociation value between strain T138021-75T and P224 was 81.6 % and 40.3 % between strain T138021-75T and the type strain of M. glucosida. Based on the DNA–DNA reassociation data, strain T138021-75T belonged to a separate species that was closely related to strain P224. Strain P224 differed from strains T138021-75T, Pg20 and Pg19 in the following phenotypic characteristics: activity of ornithine carboxylase, hydrolysis of glycosides, and acid formation from maltose, dextrin, melibiose and raffinose, as well as reactions for α-galactosidase and β-xylosidase. Whole genome similarity calculations based on recN gene sequences showed that strains T138021-75T and P224 were related at the species level (0.932), whereas 16S rRNA and partial rpoB gene sequence comparisons showed a more divergent position of strain P224 compared with the novel strains, including a different host of isolation. The results showed that the three strains of taxon 25 represent a novel species for which the name Mannheimia caviae sp. nov. is proposed. The type strain, T138021-75T ( = CCUG 59995T = DSM 23207T) was isolated from purulent conjunctivitis in guinea pigs. Previous publications have documented both ubiquinones and demethylmenaquinone to be present in the type strain. The G+C content of the DNA of the type strain has been found to be 41.4 mol% (T m).

Gross pathology of small mammals

A review is presented on how to perform a meaningful necropsy of the rabbit, ferret, and guinea pig. Brief descriptions of gross findings of significant diseases are provided in sufficient detail for identification in practice. Diseases are organized by organ systems affected and included based on their clinical significance, incidence, and importance in the United States.

Demonstration of Mycoplasma hyorhinis as a possible primary pathogen for porcine otitis media

A study of the pathology of the ear was performed on 479 pigs ranging in age from 1 day to 1 year. Histologically, 364 (76.0%) of 479 pigs were affected with otitis. Eustachitis was the most common and preceded an inflammation of other sites of the ear, and an acute eustachitis occurred from as early as 1 week of life. Immunohistochemical examination of frozen cryostat sections revealed Mycoplasma hyorhinis (Mhr) antigens on the luminal surface of the eustachian epithelia in 14 (50.0%) of 28 piglets examined. All the pigs positive for Mhr had an acute eustachitis. Ultrastructural examination on the auditory tubes with positive immunostaining disclosed many mycoplasmas among the cilia. Mhr was isolated from the auditory tubes and tympanic cavities of 19 (67.9%) and 16 (57.1%) of 28 piglets examined, respectively. Porcine otitis media may be caused primarily by Mhr infection in the auditory tube.

A pathologic and bacteriologic study on otitis media in swine

A pathologic and bacteriologic study on otitis media in swine was performed on 237 swine, ranging in age from 1 day to 1 year. These 237 swine from eight selected farms were slaughtered due to unfavorable prognosis associated with clinical signs of illness. One hundred sixty-three (68.8%) of the 237 swine were found to be affected with otitis, though only a few swine showed clinical signs characteristic of the disease. One hundred fifty-one (63.7%), 53 (22.4%), and 39 (16.5%) had lesions in the middle, external, and internal ear, respectively. Of the 151 cases with otitis media, bilateral and unilateral infection accounted for 114 (75.5%) and 37 (24.5%), respectively. Only 5/53 swine with otitis externa and 6/39 swine with otitis interna failed to show otitis media. All swine with infection in the tympanic cavity had inflammatory lesions in the auditory tube. Examination of the swine grouped by age revealed that, regardless of age, incidence of otitis media was 50-70%. In swine younger than 1 month old, otitis media tended to center on the auditory tube, where a mild infiltration of neutrophils into the mucous membrane was frequent. Thereafter, otitis media increased in degree and extent with age. Forty (26.5%) of the 151 swine affected with otitis media were accompanied by a substantial amount of inflammatory exudate in the tympanic cavity and bulla. Purulent exudate was found in 20/40 (50%) swine. Severe otitis media prevailed in swine between 1 and 4 months of age, showing inspissation of a suppurative exudate in the tympanic cavity and lysis of the underlying osseous wall of the tympanic bulla with subsequent fibrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Incidence of amikacin ototoxicity: a sigmoid function of total drug exposure independent of plasma levels

A sigmoid curve was found to closely describe the relationship between the incidence of amikacin ototoxicity (greater than or equal to 15 dB hearing loss at a given frequency) and either (1) total dose, or (2) the area under the curve (AUC) describing plasma drug concentration v time over the total period of amikacin administration (total AUC) in continuously infused guinea pigs. Total dose or total AUC estimates of the drug exposure required to produce ototoxicity in 50% of the animals (ED50s) were not significantly different over an eight-fold range of dosing rates or plasma concentrations. A theoretical explanation for this result is that ototoxicity occurs only when a critical amount of drug is accumulated at the ototoxic site by an essentially unidirectional process with a rate that is slow and linearly related to the extracellular drug concentration. The sigmoid relationships for pooled data were parallel in slope for all hearing frequencies from 2 to 32 kHz, and the ED50s showed a strong negative linear relationship to the log of the hearing frequency over this range. The magnitude of ototoxicity expressed as the number of octaves (frequency ratios of 2) for which hearing loss damage was continuous from 32 kHz downward, was correlated to both total dose (r = .605) and total AUC (r = 0.703). No relationship between ototoxicity and plasma level or dosing rate was found. The extreme steepness of the dose-effect curve for the incidence of ototoxicity greatly amplified the variability between individuals and offers an explanation for the unpredictability of aminoglycoside ototoxicity in human patients. The results indicate that either total dose or total AUC (in cases of highly unpredictable blood levels), and not peak or trough serum levels, should be used as an index of ototoxic risk and that the safety limits of drug exposure should be set conservatively.