Buffy coat smear or Knott's test: which to choose for canine microfilaria screening in field studies?

BACKGROUND

In recent years, an increasing number of cases of canine dirofilariasis have been reported worldwide. However, the rate of infection in dogs is largely unknown in many remote areas, and the importance of field studies for determination of the prevalence of canine dirofilariasis in such areas is well recognized. The detection of microfilariae by the modified Knott's test (MKT) is a recommended screening method for canine dirofilariasis.

OBJECTIVES

The purposes of this study were to compare the diagnostic sensitivity of the MKT with the buffy coat smear method (BCS), and to evaluate the utility of these 2 methods under field study conditions.

METHODS

One hundred and fifty dogs of the Maio Island of Republic of Cabo Verde, were screened for microfilariae using MKT and BCS. The results of the 2 methods were generated in a blinded manner and statistically compared.

RESULTS

The detection rate was 4.67% with the MKT and 5.33% with BCS, which is statistically not different. The latter allowed a morphologic identification of Dirofilaria repens (later confirmed by molecular biology methods) and an estimation of parasite load, which varied from 15 to 185 microfilariae/mL.

CONCLUSIONS

The methods MKT and BCS were comparable in terms of diagnostic sensitivity. However, the BCS was technically less demanding and produced permanent preparations, in which co-infection with other hematologic pathogens can easily be assessed. Overall, this method is well suited to assess microfilariae in a large number of animals, and it could replace the MKT in studies devoted to dirofilariasis.