Abstract
On February 15, 2014, a carcass of a subadult male northern fur seal Callorhinus ursinus was found stranded at the coast of Niigata, Japan (37:55:26 N, 139:01:34 E). It was 172 cm long, weighed 116.6 kg, and was in good body condition with thick blubber.
Gross necropsy revealed pneumonia with diffused abscess of all lung lobes and massive necrosis of kidney and liver. Swollen or enlarged lymph nodes were not detected. Major histologic findings of lung were necrotizing and fibrinous pneumonia infiltrated by band neutrophils with intraluminal abscess of bronchi containing heavy gram-positive cocci in chain-like arrangement. Kidney cortex showed interstitial nephritis with multifocal perivascular infiltration of inflammatory cells, renal tubule necrosis and thrombosis, but Gram and Warthin-Starry stain were negative. Kidney medullar and bladder were histologically normal. Liver did not have adequate conditions for histologic assessments.
Cultures of the lung and blood were submitted to a local human commercial laboratory, and both samples cultured positive for unidentified two strains of beta-hemolytic streptococci (Lancefield's group G and unknown), Enterococcus faecalis, Corynebacterium sp., and Proteus vulgaris. 16S ribosome RNA sequences were performed to the two isolates of streptococci and they were identified as Streptococcus canis (Group G) and S. phocae (unknown type).
Based on these findings, it was concluded that acute pneumonia and septicemia were the major cause of death of the animal. Either or both of isolated streptococcal species were suspected as causative agents.
Streptococcus canis is one normal flora of dogs and cats, but sometimes causes severe and fatal diseases.2 Pinniped infections are also known in Europe, South Africa, New Zealand and Canada.1,3,5,9 Streptococcus phocae was first described in 1994 in harbor seals of Norway with morbillivirus infections.9 Since this first description, pinniped infection cases including otariids have been reported from other geographic regions such as the northeast Pacific, Caspian Sea and in South Africa.3,6-8 Most of reported pinniped infection cases involving the two streptococcal species are implicated to secondary infections after other diseases such as viral infections and starvation,3,5,7,9 or in subclinical cases4,6. Fatal pneumonia of Canadian harbor seals, in which S. phocae is the primary agent, are also reported.8
This is the first report of fatal streptococcal disease in a northern fur seal in East Asia that indicates highly virulent streptococcal strains which are fatal to healthy animals. These fatal strains are now identified and existing in wild pinnipeds around Japan.
* Presenting author
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