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Morphometric analyses of canine blood microfilariae isolated by the Knott’s test enables Dirofilaria immitis and D. repens species-specific and Acanthocheilonema (syn. Dipetalonema) genus-specific diagnosis

Johannes Magnis1, Susanne Lorentz2, Lisa Guardone3, Felix Grimm4, Marta Magi3, Torsten J Naucke256 and Peter Deplazes4*

Author Affiliations

1 Kleintierklinik in Iffezheim, An der Rennbahn 16a, Iffezheim, 76473, Germany

2 Parasitus Ex e.V, Vollbergstrasse 37, Niederkassel, 53859, Germany

3 Department of Veterinary Science, University of Pisa, viale delle Piagge 2, Pisa, 56124, Italy

4 Institute of Parasitology, University of Zurich, Winterthurerstr. 266a, Zurich, CH-8057, Switzerland

5 Department of Zoology, Division of Parasitology, University of Hohenheim, Stuttgart, 70599, Germany

6 Laboklin GmbH & Co. KG, Steubenstraße 4, Bad Kissingen, 97688, Germany

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Parasites & Vectors 2013, 6:48  doi:10.1186/1756-3305-6-48

Published: 25 February 2013



Considering the increasing importance of small animals travel medicine and the spread of filariae with zoonotic potential to non-endemic European areas, routine filarial diagnosis in dogs is becoming important. Dirofilaria immitis, D. repens, Acanthocheilonema dracunculoides and A. reconditum are the most common canine filarial nematodes presenting blood circulating microfilariae (mf) which can be differentiated to species level by the acid phosphatase activity patterns or by PCR. Available data on the size of the mf vary considerably in the literature. The aim of this study was to validate morphometric criteria for filarial identification in blood samples of dogs after concentration of mf with the modified Knott’s technique.


Morphometric analysis of 10 mf from samples identified to species level by acid phosphatase activity and partially confirmed by PCR were performed with specimens from 377 dogs.


The mean length and width of D. immitis mf from 60 dogs were 301.77±6.29 μm and 6.30±0.26 μm, of D. repens mf from 171 dogs 369.44±10.76 μm 8.87±0.58 μm, of A. dracunculoides mf from 133 dogs 259.43±6.69 μm and 5.09±0.47 μm and of A. reconditum mf from 13 dogs 264.83±5.47 μm and 4.63±0.52 μm.

For a subset of 30 samples, morphometric analysis was repeated with identical results in two laboratories. Furthermore, the size of mf concentrated and fixed by the Knott’s technique was shown to be stable over 105 days.


The Knott’s test enables to clearly distinguish between D. immitis, D. repens and Acanthocheilonema spp. However, due to the overlapping size ranges of A. dracunculoides and A. reconditum, biochemical or molecular methods are required to distinguish these two species.

Canine blood microfilariae; Laboratory diagnosis; Size of microfilariae