Rat Bacterial Diseases

Streptococcus pneumoniae (Rare in current laboratory rats)

·       a-hemolytic

·       Humans are natural host, transmitted via aerosol or fomites, colonizes nasopharynx: Potential zoonotic hazard!

·       Usually asymptomatic

o   suppurative rhinitis and otitis media, Fibrinopurulent pleuritis, pericarditis, and/or pneumonia

·       dx: nasopharyngeal culture unto blood agar, only a problem though if rats are symptomatic

Other Streptococcal species

·       B hemolytic rarely cause disease in rats

o   Divided into groups based on Lancefield antigens, with Lancefield groups B and G most commonly isolated from rats

·       Exclusion from colonies is not necessary- humans often carriers and only a single report of disease/symptoms is noted

·       In rare cases streptococcal enteropathy occurs- only suckling rats – caused by Lancefield group D enterococci à pups develop bright yellow pasty feces (ddx for diarrhea) à still no need to exclude enterococcus from colonies, again rare to cause disease

Pseudotuberculosis, Corynebacterium kutscheri (Historic disease)

·       Gram positive, club-shaped bacteria found in environment

·       Rats, mice, guinea pigs, hamsters; clinical disease only in rats and mice

·       Transmission via direct contact/oronasal exposure

·       Usually no clinical signs, vague when present: hunched, poor grooming, dyspnea, rales, porphyria, nasal discharge, lethargy, lameness, acute death

·       Multiple randomly distributed abscesses in the lung, liver, kidney, skin, and joints due to septic emboli (hematogenous spread)

o   Lung most frequently involved in the rat

·       Dx: culture of submandibular (cervical) lymph nodes, PCR , histo: “Chinese letters”

Ddx: multiple abscess- streptococcosis, streptobacillosis, mycoplasmosis, CAR

Tyzzer’s Disease, Clostridium piliforme

·       Gram-negative, spore-forming rod

·       Transmitted horizontally through spores, fecal-oral

·       Usually clinically silent, symptoms are usually only present in young, recently weaned pups and are non-specific: Hunched/ lethargic, acute death, diarrhea +/- blood

·       Necrosis on surface of liver, heart and megaloileitis (dilated, hyperemic ileum)

o   Coagulative necrosis of liver hallmark lesion (Triad = ileum, liver, heart)

·       Intracellular bacilli in “pick up” stick arrangement

·       Warthin Starry (best), Giemsa, and methylene blue stains

·       PCR can be used but animals may have already cleared infection resulting in false positives

Ddx: necrotizing hepatitis: Corynebacterium kutscheri or rat virus; adynamic ileus d/t chloral hydrate

 Pasteurella pneumotropica

·       Gram negative coccobacillus

·       Isolated from respiratory, GI, and urogenital systems

·       Usually asymptomatic, rare cases of conjunctivitis, metritis, and mastitis

·       Direct contact and fecal transmission

·       Rarely a primary pathogen but commonly an opportunistic infection secondary to M. pulmonis or Sendai virus infections

·       Relatively easy to re-derive and eliminate from colony

o   Not transmitted via fomites

o   Does not persist in environment

o   Rarely colonizes humans

·       Direct animal or Plenum PCR and/or culture works. TX: Enrofloxacin/rederivation 

 Salmonella enteritca (Salmonellosis)

·       ZOONOTIC

·       Serotypes Enteritidis and Typhimurium most frequently implicated with disease

·       Clinical signs rare but include hunched/ lethargy, weight loss, soft stool or diarrhea (in less than 20% of animals)

·       If GI involvement, mural thickening with focal mucosal ulcers in cecum and ileum – flecks of blood in soft stool

·       Ddx diarrhea rats: Tyzzer’s disease, rotavirus, enteroccocal enteropathy, cryptosporidiosis

·       Diagnosis: Culture and isolation (mesenteric lymph node is a good choice) – if fecal may need to repeat due to intermittent shedding

·       Tx may not be wise given potential for chronic carrier state and zoonosis

 Pseudomonas aeruginosa (Pseudomoniasis)

·       Gram negative, aerobic, bacillus

·       Common contaminant of food, bedding, water bottles, bottle stoppers, sipper tubes

·       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

 Helicobacteriosis

·       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 rats

 Cilia Associated Respiratory Bacillus (Filobacterium rodentium)

·       Rats, mice, rabbits

·       Direct contact; airborne 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)

 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

·       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