Veterinary Microbiology by McVey D. Scott Kennedy Melissa Chengappa M. M. & Melissa Kennedy & M.M. Chengappa

Author:McVey, D. Scott, Kennedy, Melissa, Chengappa, M. M. & Melissa Kennedy & M.M. Chengappa
Language: eng
Format: epub
ISBN: 9781118650622
Publisher: Wiley
Published: 2013-05-16T04:00:00+00:00

N. helminthoeca

Descriptive Features

N. helminthoeca causes salmon poisoning in dogs. This pathogen multiplies in the cytoplasm of monocytes and macrophages. This infection is very similar to E. canis and E. chaffeensis in dogs, except that the organism is not transmitted by ticks. After staining a sample with a Giemsa stain, the organism may be visible as cytoplasmic inclusions in the macrophages of a lymph node tissue or in the monocytes from a blood smear made from a clinically ill animal.

Ecology

Reservoir and Transmission

The reservoir of infection for N. helminthoeca is the fluke, Nanophyetus salmincola. The life cycle of the fluke includes passage through a fish and a snail. Dogs eating raw fish infested with a fluke containing N. helminthoeca are likely to acquire infection and the disease. The geographical distribution of salmon poisoning pathogens is limited by the range of the snail, intermediate hosts of the fluke. In particular, the distribution of the snail includes North American coastal regions, such as northern cost of California, Oregon, Washington, and British Columbia. Dogs are the definitive hosts of the fluke, harboring the adults in their intestine. If N. helminthoeca fluke gains entry into a dog as a result of eating fluke-infected fish, the pathogen infection establishes in the dog. Fluke eggs are shed in canine feces and hatch miracidia, which reach to a snail in the environment. Cercaria emerges from the fluke-infected snail and invades a fish.

Pathogenesis

Exposure to an infected raw fish in an endemic area is the primary cause for acquiring the N. helminthoeca infection by dogs as a result of fluke gaining entry from the fish. The fluke then matures in the dog's gastrointestinal tract where N. helminthoeca organisms are released, which enters into the canine bloodstream and lymph nodes. In blood, the organism infects monocytes. The replication of the organism in the dog results in the clinical signs associated with the disease. Within 1–2 weeks of exposure, dogs develop fever, anorexia, depression, weight loss, swollen lymph nodes, and often hemorrhagic enteritis. Vomiting and diarrhea are also common clinical signs. Mortality can be up to 90% in untreated animals, which can occur within 2 weeks.

Immunologic Aspects

Dogs recovered from the clinical disease appear to be protected from the disease.

Laboratory Diagnosis

The presence of organisms within the cytoplasmic vacuoles of monocytes in a stained blood smear or in lymph node aspirates is an evidence of the disease. The organisms may be cultured, but it is a time-consuming method. Molecular methods can be used to detect the rickettsial nucleic acids from a blood or lymph node sample.

Treatment and Control

Tetracycline, chloramphenicol, and sulfonamides are effective in treating N. helminthoeca infections. Supportive treatment is also necessary. The best preventive measure is the exclusion of infected salmon from the canine diet. Flukes and N. helminthoeca are killed by cooking at high temperatures or by freezing for 24 h.

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