Classification

Small Gram-positive rod with one end wider than the other

Family

Corynebacteriaceae

Affected species

Mice and rats; nude, hairless, and SCID animals

Frequency

Common in some research and testing facilities. It is not known whether wild rodents carry this bacterium.

Transmission

Transmission is between animals by direct contact or via fomites such as the gloves of an animal caretaker. C. bovis may also be transmitted through transplantable tumor lines. Rarely, immunocompetent animals may be asymptomatic carriers of C. bovis, but infections of immunocompetent animals are usually transient.

Clinical Signs and Lesions

Clinical signs associated with C. bovis infection in nude or SCID mice include a wide-spread scaly dermatitis, hence the name “scaly skin disease”. In nude mice, the signs are most commonly seen on the dorsum, and in SCID mice, the scaling is accompanied by alopecic areas. Microscopically, skin sections reveal epidermal hyperplasia (acanthosis) and an orthokeratotic hyperkeratosis. Macrophages and neutrophils infiltrate the dermis.

C. bovis rapidly causes clinical signs in naïve animals. Lesions that appear 7-10 days after exposure to infection (for example, exposure to infected animals or a contaminated facility) are consistent with, and characteristic of, a new C. bovis infection. If animals survive the infection (most do), the hyperkeratosis disappears, but the acanthosis remains, as does a slight increase in inflammatory cells in the dermis. Animals remain infected after clinical signs have resolved and continue to shed organisms. Animals from a colony that is enzootically infected with C. bovis are persistently infected, but may show signs less frequently than would naïve animals.

Diagnosis

C. bovis may be cultured from the skin (site of choice), feces, or oropharynx of affected animals or the contaminated environment. PCR testing is also available for tumor lines, environmental swabs, or affected animals.

Interference with Research

Infection with C. bovis may cause weight loss, probably due to dehydration through skin lesions, or from anorexia, and pruritis. It is also associated with decreased transplantable tumor take. Animals infected with C. bovis are not suitable for research use.

Prevention and Treatment

Health monitoring for C. bovis should be performed regularly for nude, hairless, and SCID animals. Animals should be sourced from regularly tested colonies. Aseptic hysterectomy rederivation with fostering onto clean females or embryo transfer rederivation will remove C. bovis from a colony. Animals may also be treated with antibiotics to reduce clinical signs while waiting to rederive or receive new animals. C. bovis isolates have been shown to be sensitive to tetracycline, enrofloxacin, and ampicillin.

C. bovis is persistent in the environment, since it is lipophilic and survives well on skin flakes and other organic material. Aggressive decontamination with autoclaving of materials, discarding of non-sterilizable materials, and chlorine dioxide disinfection has been reported as a means of ridding a facility of C. bovis. Any environmental decontamination should be verified by PCR or culture of the environment. Anecdotally, it has been necessary for some facilities to close old animal areas and open new ones as the only way to truly remove C. bovis from the environment.

  • References

    Baker DG. Natural Pathogens of Laboratory Animals: Their effects on research. Washington, D.C.: ASM Press; 2003. 385 pp.

    Clifford CB, Walton BJ, Reed TH, Coyle MB, White WJ, Amyx HL. Hyperkeratosis in athymic nude mice caused by a coryneform bacterium: Microbiology, transmission, clinical signs, and pathology. 1995. Lab. Anim. Sci. 45:131-139.

    Fox JG, Anderson LC, Lowe FM, and Quimby FW, editors. Laboratory Animal Medicine. 2nd ed. San Diego: Academic Press; 2002. 1325 pp.

    Fox J, Barthold S, Davisson M, Newcomer C, Quimby F, and Smith A, editors. The Mouse in Biomedical Research: Diseases. 2nd ed. New York: Academic Press; 2007. 756 pp.

    Percy DH, Barthold SW. Pathology of Laboratory Rodents and Rabbits. Ames: Iowa State University Press; 2007. 325 pp.