Seroprevalence and incidence of human toxocarosis in Russia

Molecular identification of Baylisascaris melis (Gedoelst, 1920) from the Eurasian badger (Meles meles) and ascarids from other wild carnivores in Kazakhstan

Introduction

The presence of gastrointestinal nematodes, including zoonotic ascarids, in wild canids, felids and mustelids as definitive hosts in Central Asian countries has been documented in many studies based on traditional morphological methods. In contrast, relevant data for the badger are scarce. The aim of this study was the molecular identification of ascarid nematodes from five wild carnivore species in different regions of Kazakhstan.

Methods

A total of 211 adult ascarids were collected from gray wolves (Canis lupus, 8 of 83 infected with 2-6 Toxascaris leonina), red foxes (Vulpes vulpes, 26 of 53, with 2-8 Toxascaris leonina), corsac foxes (Vulpes corsac, 6 of 11, 3-6 Toxascaris leonina), lynx (Lynx lynx, 2 of 3, with 2-5 Toxocara cati) and badgers (Meles meles, 2 of 4, with 2-7 Baylisascaris melis). Genomic DNA was extracted from the worms and ribosomal DNA, including the first and second internal transcribed spacer genes, was amplified by polymerase chain reaction using specific oligonucleotide primers and then sequenced.

Results

Toxascaris leonina, but not Toxocara canis, was molecularly identified in the wild canids, Toxocara cati in the lynx and Baylisascaris melis in the badger. The maximum likelihood phylogenetic tree showed three distinct clades: the canid Toxascaris leonina was placed in one clade, Toxocara cati in another and Baylisascaris melis in a third.

Discussion

The study provides the world's first molecular data and phylogenetic analysis of Baylisascaris melis, identified for the second time since its description over 100 years ago. This species was shown to be genetically distinct from other Baylisascaris spp. (B. columnaris, B. procyonis, B. transfuga, B. devosi). The possible zoonotic significance of ascarids from wild carnivores is discussed in the light of conditions in Central Asia.

Toxocara prevalence in dogs, cats and the environment in Russia

The toxocariasis incidence in Russia is relatively low (1.8 cases per 100,000 individuals) and the parasite is not a major healthcare concern. However, the proportion of primary hosts testing positive for the parasite is high and varies between 3% and 100% in dogs (on average 33%), and between 6% and 52% in cats. Higher prevalence was observed in Volga, Urals and Siberia regions. Levels of contamination of soil, children's playgrounds and sandboxes is also high, with up to 100% contamination rates determined in some studies, but more commonly prevalence of contamination around 40% was reported. There is a pronounced seasonality in the prevalence of Toxocara in primary hosts and the soil, with peaks in the summer and autumn. Most likely, a lack of permissive conditions for the development of eggs in the winter determines observed seasonal patterns, which are different than those observed in most other countries. Toxocara eggs were found in 4-10% of vegetables and greenery samples tested, suggesting that they can contribute to the transmission of Toxocara.