ISSN 2398-2942      

Neorickettsia helminthoeca

icanis
Contributor(s):

Prof. William Foreyt

Synonym(s): N. helminthoeca


Introduction

Classification

Taxonomy

  • Order: Rickettsiales.
  • Family: Rickettsiaceae.
  • Tribe: Ehrlichieae.
  • Genus: Neorickettsia.

Etymology

  • Neorickettsia - new Rickettsia; helminthoeca - worm dwelling.

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Clinical Effects

Epidemiology

Habitat

  • Salmon disease is endemic to the area where the snail intermediate host (Oxytrema silicula) of the salmon fluke (Nanophyetus salmincola) is found.

Lifecycle

Nanophyetus salmincola

  • Dogs (and bears, raccoons, wolves, foxes, cats etc) are the definitive hosts of the fluke.
  • Eggs are shed by the adults in the intestine of the host; they embryonate and hatch miracidia which invade the snail.
  • Cercariae emerge from the snail, invade a fish and become sessile metacercariae encysted in the kidney, and other host tissues.
  • After ingestion by the dog, they become adults in 6-7 days.

Transmission

  • Ingestion of N. helminthoeca via fluke-infected fish kidney, or other fish tissues.

Pathological effects

  • Affects lymphoreticular tissues of Canidae and is characterized by fever, swollen lymph nodes, lethargy, inappetence, weight loss, depression, and often a hemorrhagic enteritis with vomiting and diarrhea. A non-suppurative meningoencephalitis is common.
  • Metacercarial flukes emerge from the ingested fish kidney or tissues into the dog's intestine where they attach and develop into adults and release N. helminthoeca which colonizes lymphoid tissue.
  • Enlargement of lymphoid tissue occurs and clinical signs develop from 5 days to several weeks after infection.
  • Rickettsiae spread via blood to liver, lungs and brain.
  • If untreated, dogs may die approximately 2 weeks after clinical signs begin.

Control

Control via animal

  • Exclusion of infected salmon from the diet. The flukes and the N. helminthoeca are killed by cooking or freezing at -20°C for 24 hours.

Control via chemotherapies

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Dumler J, Barbet A F, Bekker C P et al (2001) Reorganization of genera in the families Rickettsiaceae and Anaplasmataceae in the order Rickettsiales: unification of some species of Ehrlichia with AnaplasmaCowdria with Ehrlichia and Ehrlichia with Neorickettsia, descriptions of six new species combinations and designation of Ehrlichia equi and 'HGE agent' as subjective synonyms of Ehrlichia phagocytophilia. Int J Syst Evol Microbiol 51 (Pt 6), 2145-2165 PubMed.
  • Pretzman C, Ralph D, Stothard D R et al (1995) 16S rRNA sequence of Neorickettsia helminthoeca and its phylogenetic alignment with members of the genus Ehrlichia. International Journal of Systematic Bacteriology 45 (2), 207-211 PubMed.
  • Rikihisa Y (1991) Cross-reacting antigens between Neorickettsia helminthoeca and Ehrlichia species, shown by immunofluorescence and Western blotting. J Clin Microbiol 29 (9), 2024-2029 PubMed.
  • Rikihisa Y, Stills H, & Zimmerman G (1991) Isolation and continuous culture of Neorickettsia helminthoeca in a macrophage cell line. J Clin Microbiol 29 (9), 1928-1933 PubMed.

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