Strongyloides stercoralis infection in imported and local dogs in Switzerland: from clinics to molecular genetics

Abstract

16Strongyloides stercoralis is a worldwide distributed intestinal nematode affecting mainly humans and 17 dogs. Canine strongyloidosis is generally characterized by diarrhoea, malabsorption and 18 bronchopneumonia, and may be fatal in cases of impaired immunity. In recent years, molecular and 19 epidemiological studies suggested that host-adapted populations of S. stercoralis with different 20 zoonotic potential may exist. Clinical and subclinical cases of S. stercoralis infection have been 21 increasingly diagnosed in imported (France, Belgium, Bulgaria) and locally born dogs in Switzerland, 22showing that this parasite is currently circulating in Europe. Three of these clinical cases will be 23 described here. All three dogs presented severe disease, characterised by harsh diarrhoea, 24 dehydration, vomiting, respiratory and/or neurologic signs, and needed intensive care and 25 hospitalisation. One of these dogs was related to a Swiss breeding kennel, in which the infection was 26 subsequently diagnosed in several other dogs. Faeces were analysed by three coproscopical methods 27 including (i) the Baermann technique, which consistently identified the typical S. stercoralis first-stage 28 larvae in both clinical and subclinical infections, (ii) the sedimentation-zinc chloride flotation and (iii) 29 sodium acetate -acetic acid -formalin concentration (SAFC) methods, which allowed the additional 30 identification of parasitic females and/or eggs in two of the clinical cases. Interestingly, S. stercoralis 31 source: https://doi.org/10.7892/boris.122740 | downloaded: 9.8.2020 isolated from all three independent clinical cases exhibited an identical genetic background on the 32 nuclear 18S rDNA (fragment involving hypervariable regions I and IV) and the mitochondrial 33 cytochrome oxidase subunit I (cox1) loci, similar to that of zoonotic isolates from other geographical 34 regions, and not to that of dog-adapted variants. Due to the clinical relevance and zoonotic potential of 35 this parasite, the awareness of both diagnosticians and clinicians is strongly required. 36 37 38 Introduction 39 40 Strongyloides stercoralis is a worldwide distributed intestinal nematode that affects mainly humans 41 and dogs. Higher prevalences are generally observed in tropical and subtropical regions (Thamsborg 42 et al. 2017). S. stercoralis undergoes a complex life cycle involving both parasitic and free-living 43 generations. Parasitic females are located in the small intestine mucosa and produce eggs containing 44 first-stage rhabditoid larvae (L1) by parthenogenesis, which hatch in the intestine and are shed with 45 the faeces. In the environment, they develop either directly through second-stage rhabditoid larvae 46 (L2) into infective third-stage filariform larvae (L3) (homogonic development) or alternatively, through 47 several stages and moultings into free-living female and male worms that mate and produce a

Detection of classic and cryptic Strongyloides genotypes by deep amplicon sequencing: A preliminary survey of dog and human specimens collected from remote Australian communities

“…(2017) and Basso et al . (2018), we discovered two new HVR-I haplotypes; haplotypes VIII and X (Figure 2, Table 1), in addition to the six haplotypes previously described (Jaleta et al, 2017, Basso et al, 2018), Due to the existence of noteworthy similarities (> 99% in all cases) between sequences of S. stercoralis , Strongyloides procyonis , a sequence assigned to Strongyloides sp. Okayama (GB: LC038066.1), and our novel dog sequences, we expanded the Jaletta et al .…”

“…We also identified haplotype VI in a single Australian dog. Following the genotype nomenclature developed by Jaleta et al (2017) and Basso et al (2018), in addition to these six haplotypes previously described (Jaleta et al, 2017, Basso et al, 2018), we discovered two new HVR-I haplotypes; haplotypes VIII and X (Figure 2, Table 1). Due to the existence of noteworthy similarities (> 99% in all cases) between sequences of S. stercoralis, Strongyloides procyonis , a sequence assigned to Strongyloides sp.…”

“…A graphical representation of the novel Strongyloides genotypes discovered in this study compared to haplotypes identified in previous reports. The location of sites that were genotypically informative based on the original genotyping method described by Jaletta et al (2017) and Basso et al (2018) are indicated, as well as new SNP/indel sites that have been incorporated into the typing scheme based on the results of this study (Jaleta et al, 2017, Basso et al, 2018). For hypervariable region I, we introduce two novel types (VIII and X), and assign new haplotype names to published sequences that had not been previously considered in this typing scheme (VII and IX).…”

“…Jaleta et al (2017) previously sequenced the SSU HVR-I region of S. stercoralis worms from Cambodian dog and human specimens and identified five different haplotypes (HVR-I haplotypes I-V) (Jaleta et al, 2017). A recent study of European dogs identified a new haplotype from the HVR-I region (haplotype VI) (Basso et al, 2018). In our Australian samples we found haplotype II in both human and dog samples and haplotype IV in dog samples only, which is consistent with the findings from Jaleta et al (2017).…”

“…There are two regions of the S. stercoralis nuclear and mitochondrial genome that are considered to be conserved within the Strongyloides genus and can be used as markers for molecular typing of S. stercoralis . Hyper-variable regions (HVR) I and IV of the small Subunit ( SSU ) 18s ribosomal DNA and the cytochrome c-oxidase subunit 1 ( cox 1) gene of the mitochondrial DNA (mtDNA) have been widely used to study relationships between S. stercoralis from different hosts and different geographic locations (Hasegawa et al, 2009, Hasegawa et al, 2010, Jaleta et al, 2017, Nagayasu et al, 2017, Basso et al, 2018). Based on genetic analysis of these genetic loci, it has been recently found that there are two genetically different S. stercoralis strains, one is dog and human infective, and the other is dog specific.…”