ISSN 2398-2993      

Stephanofilaria stilesi

obovis
Contributor(s):

Mike Reynolds

Andrew Forbes


Introduction

Classification

Taxonomy

  • Several species of the genus Stephanofilaria have been described as causing disease in animals.
  • Stephanofilaria stilesi has been described based on the asymmetry of the cephalic armature, the size of the left spicule of the male and the distance of the vulva from the anterior end of the female.

Etymology

  • Stephanofilaria stilesi are small, approximately 3-6 mm nematodes which are found in the dermis of the skin of affected animals.

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Clinical Effects

Epidemiology

Habitat

  • Adult nematodes live in the dermis of the skin.

Lifecycle

  • Infective microfilariae are ingested by the intermediate host of Stephanofilaria stilesi in North America, the horn fly, Haematobia irritans during its normal feeding behavior Cattle flies and larvae: overview.
  • Transmission occurs optimally when ambient temperatures exceed ~27°C/80.6°F and horn flies feed preferentially in the shade of the lower abdomen of cattle, where the lesions occur.
  • Upon ingestion, microfilariae migrate to the salivary glands of the vector.
  • Over a 14–21 day period, microfilariae undergo two molts within the vector to become the infective larval form.
  • After transmission via infective vector species, approximately 6-8 weeks later, adult nematodes commence the release of microfilariae into the host’s skin.

Transmission

  • Transmission occurs during the normal feeding behavior of Haematobia irritans, as during the feeding process, infective larvae migrate from the insect’s mouth parts and into the skin of the host.

Pathological effects

  • In North America, lesions are confined to the ventral midline of the animal, particularly the area between the brisket and umbilicus .
  • In acute disease, lesions appear hemorrhagic in nature, often with serous exudate, papules and crusting. Lesions can cause irritation and over 2-3 years, become chronic in nature with alopecia, skin thickening and hyperkeratosis.
  • Typically, multiple animals are affected.
  • In addition to ventral midline lesions, clinical cases in Russia have also described dermatitis of the ears.

Other Host Effects

  • Production losses and compromised animal welfare secondary to severe skin pathology and irritation associated with clinical disease.

Control

Control via animal

  • Prevention or a reduction in disease incidence in cattle depends upon adequate control of the disease vector, Haematobia irritans.
  • The use of chemotherapeutic agents, for example, synthetic pyrethroids Parasiticides - overview to control fly numbers. However, this may be difficult to achieve in extensively farmed livestock.
  • Housing animals during periods of peak fly activity.

Control via chemotherapies

  • There are no approved therapies for the control of Stephanofilaria stilesi in cattle.
  • Anecdotal reports suggest clinical resolution can be achieved using systemic treatments of levamisole Levamisole or ivermectin Ivermectin; the latter has been shown to be an effective therapy in stephanofilariosis caused by the related species, Stephanofilaria assamensis.
  • Anthelmintics do not appear to be active against adult worms, hence repeat treatments may be necessary to remove microfilariae.

Control via environment

  • Dung beetles have been successfully utilized in some regions of the world, eg Australia, to reduce fly numbers via a reduction in the number of viable coprophilous larvae in cow pats.

Vaccination

  • No vaccination for cattle is currently available.

Other countermeasures

  • Bos indicus breeds are less susceptible to external parasites than Bos taurus Bos taurus.

Diagnosis

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Mosca M, Vabret M, Randleff-Rasmussen P & Pin D (2018. Skin lesions in Aubrac cows strongly associated with fly bites (Haematobia irritans). Vet Dermatol 29 (3), 254–e94 PubMed
  • Oyarzún M P, Quiroza & Birkett M A (2008) Insecticide resistance in the horn fly: alternative control strategies. Med Vet Entomol 22 (3), 188–202 PubMed.
  • Johnson S J (1987) Stephanofilariasis - a review. Helminthological Abstracts (Series A) 56 (8), 287-299 VetMedResource.
  • Dies K H & Pritchard J (1985) Bovine stephanofilarial dermatitis in alberta. Can Vet J 26 (11), 361-362 PubMed.
  • Ishihara K, Sasaki Y & Kitagawa H (1982) Occurrence of cutaneous haemorrhagic parafilariasis in cattle. Jpn J Vet Sci 44 (4), 669-673 PubMed.

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