January 2017



Signalment (JPC# POLA-1):  Guinea pig




HISTOPATHOLOGIC DESCRIPTION:  Cerebrum at the level of the hippocampus and thalamus:  Multifocally, filling the third ventricle and obscuring ependymal cells, as well as expanding the leptomeninges up to 20 um, there is a cellular infiltrate composed of numerous macrophages, lymphocytes, and heterophils admixed with fibrin and proteinaceous fluid (edema). These inflammatory cells often infiltrate or obscure vessel walls. Multifocally vessels within the leptomeninges and underlying neuropil are congested and often exhibit hypertrophied (reactive) endothelium.  In the subjacent gray matter, there are increased numbers of glial cells (gliosis) with rare heterophils and the neuropil is pale and multifocally vacuolated (spongiosis).


MORPHOLOGIC DIAGNOSIS:  Cerebrum:  Meningitis, ependymitis and ventriculitis, fibrinous, heterophilic and lymphohistiocytic, subacute, multifocal, moderate, guinea pig, (Cavia porcellus).


ETIOLOGIC DIAGNOSIS: Streptococcal meningitis


CAUSE:  Streptococcus pneumoniae  


ETIOLOGY SYNONYMS:  Pneumonococcus pneumoniae and Diplococcus pneumoniae



  • Important streptococcal (gram positive) pathogens in guinea pigs:
    • S. equi subsp. zooepidemicus (beta-hemolytic; Lancefield group B): Cervical lymphadenitis (“lumps”)
    • S. pneumonia (encapsulated diplococci; alpha-hemolytic, do not lyse erythrocytes): Pneumonia and/or meningitis
      • Capsular polysaccharide type 19 and type 4 cause disease in guinea pigs; serotypes identical to human isolates- interspecies transmission possible (not proven)
      • Normal guinea pigs and nonhuman primates can carry S. pneumoniae in upper respiratory tract asymptomatically
    • +/- S. pyogenes (beta-hemolytic, Lancefield group A): Hemorrhagic septicemia (adults in a single colony); necrohemorrhagic and fibrinopurulent pneumonia, metritis, hemopericardium/thorax



  • Epizootics typically occur in winter; young animals/pregnant sows at risk
    • Other predisposing factors: Changes in temperature, poor husbandry, experimental procedures, inadequate nutrition

·       Aerosol transmission > colonizes nasopharynx > ear or lung infection  > bacteremia > invades CNS > meningitis

·       Virulence factors:

o   Polysaccharide capsule is antiphagocytic by forming a hydrophilic gel, which shields from antibodies and complement proteins (don’t produce toxins)

o   Several serotypes produce tissue damage by activation of the alternative complement pathway> this may stimulate early tissue changes



·       Weakness, ataxia, lethargy, anorexia, muscle tremors, flaccid paralysis, clonic seizures, constricted pupils, delayed light reflexes, nystagmus, torticollis

·       Dyspnea, nasal/ocular discharge

·       Abortion, stillbirth

  • Sudden death



·       Opaque/hyperemic meninges, accumulation of grayish-yellow fibrinopurulent exudate

·       Fibrinopurulent pleuritis, pericarditis, peritonitis, conjunctivitis, lung consolidation with abscessation and hemorrhage, and otitis media



·       Diffuse fibrinous exudate, gram positive paired cocci, heterophilic, lympoplasmacytic, histiocytic inflammation

·       Fibrinopurulent meningitis

  • Acute bronchopneumonia with fibrin and polymorphonuclear cell infiltration; elongated/fusiform infiltrating cells forming palisading patterns in airways and alveoli

o   +/- Thrombosis of pulmonary vessels in acute cases

·       Splenitis, metritis, ovarian abscessation, hepatic necrosis, lymphadenitis

·       Suppurative arthritis and osteomyelitis reported in guinea pigs with borderline vitamin C deficiency



·       Gram stain

·       Culture - isolation of bacteria



·       For histologic finding of meningitis in guinea pigs:

o   Bordetella bronchiseptica: Gram-negative; typically causes suppurative bronchopneumonia but may see meningitis if septicemic

o   Streptococcus zooepidemicus: Gram positive; typically causes suppurative lymphadenitis but meningitis may be seen if septicemic

o   Lymphocytic choriomeningitis (arenavirus): Rare; lymphocytic    inflammation of the meninges, ependyma, and choroid plexus



·       Nonhuman primatesThe most common cause of fibrinopurulent meningitis/meningoencephalitis in NHPs is S. pneumoniae; also causes fibrinous pleuropneumonia, septicemia, polyserositis, conjuncitivitis/panophthalmitis, peritonitis, sudden death

o   Stress, viral infection, and waning neonatal passive immunity predispose infection

o   Differential diagnosis for meningitis in non-human primates: Bacillus anthracis (anthrax): Necrohemorrhagic meningitis (“Cardinal’s cap”)

·       Rat: Outbreaks rare in well-managed facilities; organism carried in nasoturbinates and tympanic bullae of normal rats; typically opportunistic/2o invader; as in guinea pigs, some serotypes isolated from sick rats are the same as those from human cases- interspecies transmission?

o   Fibrinopurulent polyserositis, pleuropneumonia, pericarditis, peritonitis, meningitis, rhinitis, and otitis media +/- embolic suppurative lesions in liver, spleen, kidney

·       Hamster: S. pneumonia has been associated with upper respiratory disease, otitis and bronchopneumonia



  1. Percy DH, Barthold SW. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Iowa State University Press; 2016: 144-145, 186, 229-230.
  2. Simmons J and Gibson S. Bacterial and mycotic disesases in nonhuman primates. In: Abee CR, Mansfield K, Tardif S, Morris T, eds. Nonhuman Primates in Biomedical Research: Diseases. 2nd ed. London, UK: Academic Press; 2012:107-109.
  3. Stewart GC. Streptococcus and Enterococcus. In: McVey DS, Kennedy M, Chengappa MM, eds. Veterinary Microbiology. 3rd ed. Ames, IA. Wiley-Blackwell; 2013: 194-199.

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