Toxocara eggs shed by dogs and cats and their molecular and morphometric species-specific identification: Is the finding of T. cati eggs shed by dogs of epidemiological relevance?

Abstract

Intestinal infections with Toxocara cati and Toxocara canis in their definitive host (felids
and canids, respectively) are diagnosed by egg identification in faeces using coproscopical
techniques. The Toxocara species is assumed to comply with the species from which
the examined faeces were obtained, i.e. T. cati in cats and T. canis in dogs. We isolated
and measured Toxocara eggs from faecal samples of 36 cats and 35 dogs from Switzerland
and identified the Toxocara species by PCR. Amongst the isolates originating from dogs,
24 (68.5%) were determined as T. canis and 11 (31.5%) as T. cati. In all samples originating
from cats, only T. cati was identified. Based on PCR identification, eggs of T. canis (n = 241)
and T. cati (n = 442) were measured, revealing statistically significant different (p < 0.001)
mean sizes of 62.3 by 72.7um for T. cati and 74.8 by 86.0um for T. canis eggs. Considering
that coprophagy is not unusual for dogs, a considerable percentage of Toxocara infections
coproscopically diagnosed in dogs, as well as assumptions on anthelminthic resistance in
regularly treated dogs, might in fact relate to intestinal passages of eggs following the
uptake of other animals’ faeces.