Detection of circulating microfilariae in canine EDTA blood using lens-free technology: preliminary results

Abstract

Dirofilaria immitis causes life-threatening heart disease in dogs, thus screening of dog populations is important. Lens-free technology (LFT) is a low-cost imaging technique based on light diffraction that allows computerized recognition of small objects in holographic images. We evaluated an algorithm capable of recognizing microfilariae in canine whole blood using the LFT. We examined 3 groups of 10 EDTA blood specimens, from dogs with microfilaremia (group A), healthy dogs (B), and dogs with hematologic modifications other than microfilaremia (C). The LFT analyzer photographed repeated series of 5 images of all samples. The algorithm declared a sample positive if a microfilaria was detected on ≥1, ≥2, or ≥3 of the 5 images of a series. Microfilariae were detected visually in the images in 9 of 10 cases in group A; no microfilariae were seen in the images from groups B and C. Of the 30 cases, there were 14, 4, and only 3 false-positives with the 1 of 5, 2 of 5, and 3 of 5 image cutoffs, respectively. There were no false-negatives, regardless of cutoff. LFT seems useful for detecting microfilaria and could have application in clinical pathology.

Keywords: Dirofilaria immitis; dogs; lens-free imaging; microfilaria.

Figure 1.

The steps of the algorithm for image reconstruction and detection of regions of interest, based on eccentricity and solidity characteristics.

Figure 2.

Scatterplot of the percentage of series with visual lens-free technology identification of microfilariae versus microfilariae count on blood films.

Figure 3.

Lens-free technology image (hologram) of a microfilaria surrounded by red blood cells in a canine whole blood specimen. Figure 4. Lens-free technology image (hologram) of agglutinated red blood cells in the blood of a dog with immune-mediated hemolytic anemia. Agglutinated red blood cells were the main source of false-positive results in group C.