Rat Bacterial Diseases

Streptococcus pneumoniae

A bacterium that is rare in current laboratory rats and is a common pathogen in humans.

a-hemolytic

A classification of bacteria that partially lyse red blood cells, often associated with Streptococcus pneumoniae.

Natural host of strep

Humans are the primary hosts for Streptococcus pneumoniae, which can be transmitted through aerosol or fomites. Enables rats being good models for strep P.

transmission of strep

Streptococcus pneumoniae typically resides in the nasopharynx of humans, posing a potential zoonotic hazard.

symptoms of strep

Many individuals infected with Streptococcus pneumoniae do not show symptoms.

strep Suppurative rhinitis

A condition characterized by inflammation and pus in the nasal cavity, which can occur due to Streptococcus pneumoniae infection.

strep Otitis media

An infection of the middle ear that can be caused by Streptococcus pneumoniae.

Strep Fibrinopurulent pleuritis

An inflammatory condition of the pleura that can result from Streptococcus pneumoniae infection.

Strep Pericarditis

Inflammation of the pericardium that can be associated with Streptococcus pneumoniae.

Strep Pneumonia

A serious lung infection that can be caused by Streptococcus pneumoniae.

Diagnosis of Strep

The diagnosis of Streptococcus pneumoniae infection is made through nasopharyngeal culture on blood agar. Use the optochin inhibition test for differentiation between other alpha hemolytic strep

Symptomatic rats with strep

The presence of Streptococcus pneumoniae in laboratory rats is only a concern if the rats exhibit symptoms.

Lancefield antigens

Classification system for streptococci based on specific carbohydrate composition of antigens found on the bacteria's cell wall.

Streptococcal enteropathy

Rare condition in suckling rats caused by Lancefield group D enterococci, leading to diarrhea.

Corynebacterium kutscheri

Historic disease-causing bacterium in rats, characterized by vague clinical signs and abscess formation. Can be found in soil, sewage, and marine environments, and has been explored for possible utility of bioremediation of oil spills

Gram positive

Refers to bacteria that retain the crystal violet stain used in the Gram staining procedure, indicating a thick peptidoglycan layer.

Pseudotuberculosis

Disease caused by Corynebacterium kutscheri, primarily affecting rats and mice with potential for abscesses.

Tyzzer’s Disease

Caused by Clostridium piliforme, typically silent but can lead to acute death in young rats.

Gram-negative

Refers to bacteria that do not retain the crystal violet stain, indicating a thinner peptidoglycan layer and an outer membrane.

Salmonella enteritica

Zoonotic bacterium causing salmonellosis, with clinical signs including lethargy and diarrhea in rats.

Pseudomonas aeruginosa

Common environmental bacterium that can cause disease in immunocompromised hosts, often found in contaminated environments.

Streptobacillus moniliformis

Causative agent of rat bite fever, zoonotic and nonpathogenic in rats but can cause disease in humans.

Helicobacteriosis

Infection caused by various Helicobacter species in rats, typically asymptomatic with no documented lesions.

Cilia Associated Respiratory Bacillus

Bacterium associated with respiratory infections in rats, often co-infecting with Mycoplas

Other species affected by C. kutscheri

mice, rats, guinea pigs, hamsters

C. kutscheri transmission, clinical signs and pathology, diagnosis

transmitted direct contact or oronasal exposure

typically clinically silent

Pathology: randomly distributed abscesses, in rats is preferences the lungs (multinucleated giant cells and caseous necrosis)

diagnosis: culture from submandibular LNs, cytology shows branching arrays of gram positive rods (chinese letters).

Bacterial diseases of older animals

mycoplasmosis, CAR Bacillus, and C. Kutscheri

C. piliforme transmission, clinical signs, pathology and diagnosis, prevention

transmission: fecal oral

CS: typically silent, but most likely to clinically affect young and weanlings (nonspecific, sometimes diarrhea)

Pathology: coagulative necrosis of liver, myocarditis, hemorrhagic illeum

Diag: histopath visual of intracellular bacilii (pickup sticks), dont stain well. Sentinal animals in soiled bedding works, PCR, serology (false positives)

Prevention: thorough disinfection (highly resistant), possible wild rat contamination of facility.

Rodentabacter pneumotropica (originally called Pasteurella pneumotropica)

Pasteurella pneumotropica is a gram-negative coccobacillus. It grows aerobically on sheep blood agar without producing hemolysis

R. Pneumotropica transmission, clinical signs, pathology, diagnosis and prevention

transmission: has a high prevalence in infected colonies and is most often isolated from the nasopharynx, cecum, vagina, uterus, and conjunctiva during routine monitoring

CS: The vast majority of animals are asymptomatic, c, with only rare instances of conjunctivitis, metritis, and mastitis

Prevention: Pasteurella pneumotropica is not transmitted to a significant degree by fomites, does not persist or multiply in the environment, and only very rarely colonizes humans. Therefore, once a colony is free of the agent, there is relatively little risk of reinfection except through introduction or incursion of infected animals.

Most common salmonella of rats

S. enterica

Salmonella transmission, CS, pathology, diagnosis, prevention

Transmission: considered nonexistent in the US, transmitted through contaminated bedding, feed, water.

CS: hunched posture, ruffled fur, lethargy, weight loss, and conjunctivitis. Soft stools and diarrhea may also be observed, usually in less than 20% of animals.

pATH: Rats with clinical disease may have evidence of gastrointestinal involvement and septicemia, including mural thickening and mucosal ulcers in the cecum and ileum, as well as splenomegaly. necrosis in the spleen and liver

Diag: tested by culture or PCR of feces, mesenteric lymph nodes, liver, spleen or blood

Prevention: Once S. enterica is detected in a colony, all animals are usually destroyed, and all surfaces and materials either sterilized or safely discarded.

Pseudomonas aeruginosa transmission, clinical signs, pathology, diagnosis, prevention

·       Skin and GI tract, common commensal flora

·       Rarely causes dz unless host deficient in macrophages and neutrophils – steroid administration, irradiation, etc. (so not even common in athymic nudes)

·       Biofilms (sipper tubes, indwelling catheters), resistance to chlorine

·       Diagnosis via culture/ID and/or PCR

·       Acidification pH 2.5-3 or chlorination 10-13 ppm used to prevent colonization in mice (will not eliminate infection)

·       Exclusion from colonies is rare bc you need a Gnotobiotic set up since so ubiquitous

Streptobaccilus moniliformis

·       Gram negative bacillus

·       Causative agent of rat bite fever (RBF). Spirillum muris also associated with RBF (Asian version).

·       Commensal in wild rats inhabiting the nasopharynx, middle ear, respiratory tract

·       Nonpathogenic in rats

·       ZOONOTIC and causes disease in humans (fever, vomiting, arthralgia, rash)

·       Colonies should be monitored via PCR and animals terminated if positive

Helicobacterosis

·       Helicobacter muridarum, H. bilis, H. pullorum, H. trogontum (most prevalent of naturally occurring helicobacters)

·       Gram negative, spiral bacterium

·       Fecal oral transmission in rats assumed

·       No lesions documented in immunocompetent rats

·       Key pathogenic factors for H. pylori include urease, a vacuolating cytotoxin (vacA), and the presence of a pathogenicity island

·       Ddx for proliferative (+/- Ulcerative) large bowel lesions in athymic nude rats

Diag via PCR on fecal pellets

Cilia Associated Respiratory Bacillus (Filobacterium rodentium

·       Rats, mice, rabbits

·       Direct contact; airborne or fomites not an important means of transmission,

·       Usually asymptomatic or nonspecific signs

·       Coinfection with Mycoplasma can lead to suppurative bronchopneumonia (brush border)

·       Warthin starry stain- filamentous bacteria lining respiratory epithelium

·       Not easily transmitted by soiled bedding

·       DX: PCR, serology

·       Ddx: respiratory infections: murine respiratory mycoplasmosis, bacterial pneumonia (Streptococcus pneuominae, Corynabacterium kutscher) and viruses (Sendai, RRV)

Prevention by exclusion from colony

 

Pathogens not transmitted in bedding

Filobacterium rodentium, mycoplasma, and Sendai virus (typically respiratory pathogens not transmitted by bedding)

Mycoplasma pulmonis

·       Causative agent of Murine respiratory mycoplasmosis (MRM)

·       One of several agents that play a role in chronic respiratory disease (CRD) of rats

·       Nonspecific clinical signs in older animals - respiratory and auditory involvement

o   Rales, dyspnea, snuffling, CHATTERING, head tilt, chromodacryorhea, ocular/nasal discharge. Vitamin A or D may potentiate disease.

·       Rats are reservoir for mice. Also a cell line contaminant

·       Passed horizontally (direct contact and aerosol although aerosol transmission is low

·       Transmitted vertically in-utero à hard to re-derive

·       Impairs cilia leading to respiratory or genital tract disease

·       Suppurative rhinitis, otitis media, suppurative bronchopneumonia, arthritis,

·       Histo: peribronchiolar cuffing with lymphocytes and plasma cells

·       **Cobblestone lung

·       Diagnosis: PCR, culture

·       CAR bacillus and other bacterial pneumonias are frequent co-infections

Unlikely transferred via dirty bedding to sentinels b/c organisms desiccate quickly

Mycoplasma Haemomuris (Hemobartonellosis)

·       Gram negative hemotropic mycoplasma

·       Parasitizes erythrocytes of rats and is an obligate parasite (cannot be grown in vitro)

·       Transmitted by spiny rat louse (Polyplax spinulosa)

·       Clinical signs due to erythrocyte destruction

·       Diagnosis via PCR or Blood smears where detection of the organism which can appear as round, elongate, or dumbbell-shaped densities on the erythrocyte surface

Research complications: increase rejection of transplantable tumors, as well as interfering with research in other blood-borne parasitic diseases such as malaria and trypanosomiasis