Onchocerca spp

From Dog
Conjunctiva excision of the fibrous mass tissue with the extracted O. lupi tightly beneath the sub-conjunctiva[1]
Dog with keratitis and uveitis that was found to be positive for Onchocerca lupi nematodes by parasitologic examination[2]
Episcleral granuloma in a dog due to O. lupi[3]

Onchocerca spp are an endemic zoonotic nematode parasite of many tropical and subtropical countries worldwide, particularly in the United States and Europe[4].

This parasite is normally found in Caucasian wolves[5] and are morphologically indistinguishable from O. lienalis[6].

Patent infections in domestic dogs are usually seen in accidental infections in dogs which frequent areas where natural wolves reside[7], but autochonous infections have been reported in Germany[8].

Species which are pathogenic to dogs include:

  • Onchocerca lupi

These zoonotic filariids, like Dirofilaria immitis and Brugia malayi, are transmitted by blood-feeding insects, particularly blackflies (Simulium spp) and/or biting midges (Culicoides spp).

The alphaproteobacteria Wolbachia spp are intimate to the survival, reproduction and growth of this parasite[9]

These parasites reside in subcutaneous tissue and are associated with ocular onchocerciasis. Clinical symptoms include acute or chronic conjunctivitis, photophobia, lacrimation, ocular discharge, keratitis, episclera and retrobulbar granuloma[10] and exophthalmia[11].

Diagnosis is based on physical identification of the parasite from infected tissue and PCR assay speciation[12].

A differential diagnosis would include other ocular parasites such as Cuterebra spp and Thelazia callipaeda.

Treatment of ocular onchocerciases usually requires surgical intervention, with physical removal of the parasite if possible and parenteral ivermectin.

Because the obligatory endosymbiontic alphaproteobacteria Wolbachia spp is intimately involved in reproduction and growth of this parasite[13], elective use of doxycycline is recommended to help eliminate any adult larvae which cannot be physically remove or in dogs that are sensitive to macrocylic lactones.

References

  1. Otranto D et al (2012) Human ocular filariasis: further evidence on the zoonotic role of Onchocerca lupi. Parasit Vectors 5:84
  2. Otranto D et al (2012) Tracking the vector of Onchocerca lupi in a rural area of Greece. Emerg Infect Dis 18(7):1196-1200
  3. Telenet.be
  4. Otranto D et al (2011) Case report: First evidence of human zoonotic infection by Onchocerca lupi (Spirurida, Onchocercidae). Am J Trop Med Hyg 84(1):55-58
  5. Sréter-Lancz Z et al (2007) Molecular genetic comparison of Onchocerca sp. infecting dogs in Europe with other spirurid nematodes including Onchocerca lienalis. Vet Parasitol 148(3-4):365-370
  6. Zarfoss MK et al (2005) Canine ocular onchocerciasis in the United States: two new cases and a review of the literature. Vet Ophthalmol 8(1):51-57
  7. Sréter T & Széll Z (2008) Onchocercosis: a newly recognized disease in dogs. Vet Parasitol 151(1):1-13
  8. Hermosilla C et al (2005) First autochthonous case of canine ocular onchocercosis in Germany. Vet Rec 156(14):450-452
  9. Ferri E et al (2011) New insights into the evolution of Wolbachia infections in filarial nematodes inferred from a large range of screened species. PLoS One 6(6):e20843
  10. Faísca P et al (2010) A case of canine ocular onchocercosis in Portugal. Vet Ophthalmol 13(2):117-121
  11. Sænchez MD et al (2012) Pathology in practice. Focally extensive granulomatous and eosinophilic conjunctivitis with numerous intralesional nematodes, consistent with Onchocerca spp. J Am Vet Med Assoc 240(4):385-387
  12. Rishniw M et al (2006) Discrimination between six species of canine microfilariae by a single polymerase chain reaction. Vet Parasitol 135(3-4):303-314
  13. Egyed Z et al (2002) Molecular phylogenetic analysis of Onchocerca lupi and its Wolbachia endosymbiont. Vet Parasitol 108(2):153-161