Streptococcus pneumoniae Infection: Pneumococcal or Diplococcal Infection

In the past, diplococcal (pneumococcal) infections due to S. pneumoniae were recognized to be a common prob­lem in laboratory rats. Today, outbreaks of clinical dis­ease are rarely recognized in well-managed, barrier- maintained facilities.

Pathology

Clinical signs may include serosanguinous nasal dis­charge, rhinitis, sinusitis, conjunctivitis, and vestibular signs consistent with middle ear infection. At necropsy, there may be serous to mucopurulent exudate present in the nasal passages, with variable involvement of the tympanic bullae. In the acute systemic form of the disease, there are variable patterns of characteristic fibri- nopurulent polyserositis, including pleuritis, pericarditis (Fig. 2.43), peritonitis, periorchitis, and meningitis. Fibrinopurulent lesions may be confined to the lepto- meninges in some fatal cases. There may be consolida­tion of one or more lung lobes. Affected areas are dark red to dull tan and relatively firm and nonresilient.

FIG. 2.43. Fibrinous pericarditis and pleuritis in a young rat with acute diplococcal (Streptococcus pneumoniae^ infection.

infections have been associated with suppurative bron­chopneumonia in chronic respiratory disease, as well as otitis media.

Diagnosis

The presence of fibrinopurulent serositis is characteristic when present, and demonstration of the typical encap­sulated diplococci in Gram-stained smears from lesions will provide a provisional diagnosis. Confirmation of streptococcosis requires the collection and culture of material from lesions and identification of the alpha- hemolytic organism. Nasal lavage at necropsy is a recommended procedure to recover the organism for bacterial culture. Differential diagnoses include cory- nebacteriosis, salmonellosis, pseudomoniasis, and pasteurellosis.

Bacterial PyelonephritisZNephritis

Suppurative pyelonephritis is more commonly encoun­tered in male rats, and may be associated with a concur­rent disease process, such as cystitis or prostatitis. A variety of bacteria have been recovered from affected kidneys, including Escherichia coli, Klebsiella sp., P. aer­uginosa, Corynebacterium sp., Streptococcus sp., Enterococ­cus spp., and Proteus sp. The lower urinary tract is considered to be the most likely portal of entry in pyelonephritis. Excavation of the renal papilla, dilation of the renal pelves, and the accumulation of suppurative inflammatory exudates are typical findings. In cases of suppurative nephritis involving the renal interstitium, descending infections with bacterial emboli are the usual source of the infection. Streptococci are the most common isolates. Lesions are similar to those seen in other species with suppurative disease processes of this system.