Etiology of chronic pneumonia in rats and a study of the experimental disease in mice

Approved and novel strategies in diagnostics of rat bite fever and other Streptobacillus infections in humans and animals

Rat bite fever (RBF), a worldwide occurring and most likely under-diagnosed zoonosis caused by Streptobacillus moniliformis, represents the most prominent disease of Streptobacillus infections. Recently, novel members have been described, from which a reservoir in rats and other animal species and a zoonotic potential can be assumed. Despite regularly published case reports, diagnostics of RBF continues to represent a 'diagnostic dilemma', because the mostly applied 16S rRNA sequence analysis may be uncertain for proper pathogen identification. Virtually nothing is known regarding prevalence in humans and animal reservoirs. For a realistic assessment of the pathogen's spread, epidemiology and virulence traits, future studies should focus on the genomic background of Streptobacillus. Full genome sequence analyses of a representative collection of strains might facilitate to unequivocally identify and type isolates. Prevalence studies using selective enrichment mechanisms may also enable the isolation of novel strains and candidate species of this neglected group of microorganisms.

Rat bite fever

Rat bite fever (RBF) is a bacterial zoonosis for which two causal bacterial species have been identified: Streptobacillis moniliformis and Spirillum minus. Haverhill fever (HF) is a form of S. moniliformis infection believed to develop after ingestion of contaminated food or water. Here the infectious agents, their host species, pathogenicity (virulence factors and host susceptibility), diagnostic methods, therapy, epidemiology, transmission and prevention are described. Special emphasis is given on information from the field of laboratory animal microbiology and suggestions for future research.

Streptobacillus moniliformis infection in Swiss white mice

An epizootic of disease attributed to infection with Streptobacillus moniliformis occurred in a colony of Swiss white mice. The mortality rate among the 180 breeding females in the 6 affected pens was 100%, and most of the sucking young died from starvation. Acute septicemia, subacute septicemia, and polyarthritis were the 3 forms of disease observed. Clinically, septicemic mice either were found dead or were depressed and hunched for 1-2 days prior to death. About a half of these mice had brown skin crusts overlying the mammae. Pathologic findings in cases of acute septicemia were few; in mice with subacute septicemia, there was acute, multifocal, suppurative, embolic interstitial nephritis, and the arthritic form was characterized by many subcutaneous and periarticular abscesses. Severe, acute, diffuse neutrophilic dermatitis was responsible for the brown skin crusts. The S. moniliformis isolate conformed morphologically and physiologically to classical descriptions of the organism. The infection may have gained entry to the colony via wild rats.

Spontaneous glomerular sclerosis in aging Sprague-Dawley rats. I. Lesions associated with mesangial IgM deposits

The present studies examined the pathogenesis of focal glomerular sclerosis in aging rats. A marked difference in development of the lesion was noted between males and females, and strain variability was an important factor. Increased glomerular basement membrane permeability with loss of selectivity unrelated to changes in glomerular sialoprotein occurred with aging and was accompanied by increasing proteinuria. Noncomplement-fixing mesangial deposits of rat IgM were present after 1 month of age and were also found in lesser amounts in germfree rats. Fluoresceinated eluates of rat kidneys did not have antibody activity against rat serum or tissue antigens. There was no evidence for a pathogenetic role of IgM deposits. Rat IgG, IgA, IgE, C3, and fibrin were occasionally found in sclerotic areas. Analysis of multiple histologic sections revealed a close correlation between aging and glomerular pathology, with a poor correlation between tubular damage and aging. Glomerular damage appeared to be the initial event leading to tubular damage. Indirect evidence suggests that a relative thymic deficiency may play an important role in the pathogenesis of the lesion.

Experimental Mycoplasma pulmonis infection in pathogen-free mice. Models for studying mycoplasmosis of the respiratory tract

Mice of a Swiss substrain, reared under rigid pathogen-free (PF) conditions, were inoculated intranasally with broth cultures of Mycoplasma pulmonis ranging in dose from 10(1) to 9 x 10(9) colony forming units (CFU). A highly reproducible disease resulted with an LD(50) of 1.3 x 10(8) CFU and a PD(50) (dose producing pneumonia in 50% of mice) of 3.4 x 10(5) CFU. The inoculating dose of M pulmonis was found to be the critical determinant of the severity, duration and pathologic character of the respiratory disease produced. PF mice given 10(4) CFU or less developed a transient illness characterized by low frequencies of rhinitis, otitis media, laryngotracheitis and focal pneumonia. This was proposed as a low dose model. Doses of 10(5) to 10(9) CFU resulted in high frequencies of rhinitis, otitis media, laryngotracheitis and pneumonia. Within the first 10 days the pneumonia often was fatal, being characterized by an outpouring of neutrophils and edema fluid into alveolar spaces, pulmonary congestion and hemorrhage and, occasionally, pleuritis. This high dose-acute disease model was shown to be the result of seeding alveoli with large numbers of organisms at the time of intranasal inoculation. In animals surviving doses of 10(5) to 10(9) CFU beyond approximately 10 days postinoculation, the larger concentration of organisms was present in bronchi and bronchioles, giving rise to a third model, the high dose-chronic disease model. The predominant lesions were chronic suppurative bronchitis and bronchiolitis, marked peribronchial lymphoid cuffing, variable numbers of neutrophils and macrophages in alveoli, and complications such as bronchiectasis and pulmonary abscesses. Identical lesions were observed in axenic mice infected with M pulmonis. The infection in PF mice is considered a highly useful experimental system, both for comparative study of respiratory mycoplasmosis and for investigations directed toward understanding and eliminating the natural disease this agent causes in conventional mice and rats.