Refrigerated modified Knott concentrate enables long-term morphological viability of canine blood microfilariae


diagnosis, Dirofilaria immitis, teaching.

How to Cite

Zanfagnini, L. G., da Silva, T. P., Campos, D. R., de Souza, S. F., Malavazi, P. F. N. da S., de Oliveira, R. S., … Pacheco, A. D. (2023). Refrigerated modified Knott concentrate enables long-term morphological viability of canine blood microfilariae . Brazilian Journal of Veterinary Medicine, 45, e000223.


There are several methods of laboratory diagnosis of filarids, the most used are the thick smear and the Knott method. Both are quick to perform, have a low cost and allow observing the presence, quantifying and analyzing the morphological characteristics of microfilariae. Knowing the morphological viability of fixed microfilariae is of practical importance, as it allows the transport of samples to a laboratory, facilitates epidemiological studies , and allows the storage of samples for didactic. Thus, the aim of this study was to evaluate the morphological viability of microfilariae fixed in the refrigerated modified knott test using 2% formalin. To perform the modified Knott technique, 10 samples of microfilaremic dogs aged over 6 months were used. To evaluate the morphological viability time of the microfilariae in the modified Knott concentrate, the evaluations were repeated after intervals of 0, 1, 7, 30, 60, 120, 180, 240, and 304 days. In the present study, we did not verify any difference in the morphology of the microfilariae in any of the analyzed intervals from day 0 to 304 days, and it is possible to conclude that the use of 2% formalin in the modified Knott technique allows the microfilariae to be identified in a period of 304 days. days after processing the sample without changes in its morphology.


Bendas, A. J. R., Branco, A. S., da Silva, B. R. S. A., Paiva, J. P., de Miranda, M. G. N., Mendes-de-Almeida, F., & Labarthe, N. V. (2019). Mosquito abundance in a Dirofilaria immitis hotspot in the eastern state of Rio de Janeiro, Brazil. Veterinary Parasitology. Regional Studies and Reports, 18, 100320. vprsr.2019.100320. PMid:31796177.

De Andrade Vieira, V. M., Martiniano, N. O. M., da Silva, P. P., Paulino, É. T., do Amaral Fernandes, P., Labarthe, N., Gazêta, G. S., & de Moraes Neto, A. H. A. (2022). Molecular characterization of canine filarioids in a previously non-endemic area of Rio de Janeiro State, Brazil. Parasitology Research, 121(3), 925-932. PMid:35083588.

Genchi, M., Ciuca, L., Vismarra, A., Ciccone, E., Cringoli, G., Kramer, L., & Rinaldi, L. (2021). Evaluation of alternative reagents on the performance of the modified Knott’s test. Veterinary Parasitology, 298, 109555. PMid:34425345.

Latrofa, M. S., Weigl, S., Dantas-Torres, F., Annoscia, G., Traversa, D., Brianti, E., & Otranto, D. (2012). A multiplex PCR for the simultaneous detection of species of filarioids infesting dogs. Acta Tropica, 122(1), 150-154. PMid:22248527.

Little, S., Saleh, M., Wohltjen, M., & Nagamori, Y. (2018). Prime detection of Dirofilaria immitis: Understanding the influence of blocked antigen on heartworm test performance. Parasites & Vectors, 11(1), 186. PMid:29554955.

Long, S. A., Rhinehart, J., Shrake, J., & Marsh, A. E. (2020). Feasibility and comparative analysis of Dirofilaria immitis microfilaria freezing and fixation for student instruction and assessment of clinical parasitology skills. BMC Veterinary Research, 16(1), 31. PMid:32005240.

Magnis, J., Lorentz, S., Guardone, L., Grimm, F., Magi, M., Naucke, T. J., & Deplazes, P. (2013). 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. Parasites & Vectors, 6(1), 48. PMid:23442771.

Moraes, M. F. D., da Silva, M. X., Magalhães-Matos, P. C., de Albuquerque, A. C. A., Tebaldi, J. H., Mathias, L. A., & Lux Hoppe, E. G. (2017). Filarial nematodes with zoonotic potential in ring-tailed coatis (Nasua nasua Linnaeus, 1766, Carnivora: Procyonidae) and domestic dogs from Iguaçu National Park, Brazil. Veterinary Parasitology. Regional Studies and Reports, 8, 1-9. PMid:31014622.

Peribáñez, M. A., Lucientes, J., Arce, S., Morales, M., Castillo, J. A., & Gracia, M. J. (2001). Histochemical differentiation of Dirofilaria immitis, Dirofilaria repens and Acanthocheilonema dracunculoides microfilariae by staining with a commercial kit, Leucognost-SP. Veterinary Parasitology, 102(1-2), 173-175. S0304-4017(01)00516-7. PMid:11705664.

Silva, R. C., & Langoni, H. (2009). Dirofilariose: Zoonose emergente negligenciada. Ciência Rural, 39(5), 1615-1624.

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Copyright (c) 2023 Leticia Gomes Zanfagnini, Tatiane Paula da Silva, Diefrey Ribeiro Campos, Soraia Figueiredo de Souza, Patrícia Fernandes Nunes da Silva Malavazi, Rômulo Silva de Oliveira, Cíntia Daudt, Acácio Duarte Pacheco