Is strongyloidiasis currently autochthonous in Croatia? A retrospective study

Seroprevalence and microscopy detection rates of strongyloidiasis in Croatian patients with eosinophilia

Infection with the parasitic nematode Strongyloides stercoralis is characteristic for tropical and subtropical regions of the world, but autochthonous cases have been reported in European countries as well. Here we present the first nation-wide survey of S. stercoralis seroprevalence in Croatian individuals presenting with eosinophilia, and evaluate the fraction of positive microscopy rates in stool specimens of seropositive individuals. In our sample of 1407 patients tested between 2018 and 2021, the overall prevalence of strongyloidiasis was 9.31%, with significantly higher rates in those older than 60 years of age (P = 0.005). Of those, one-quarter (25.95%) were also positive following microscopy examination of faeces after using the merthiolate-iodine-formaldehyde concentration method. Our findings reinforce the notion of endemic strongyloidiasis transmission in Croatia, particularly in older individuals, and highlight the need to consider the presence of S. stercoralis in patients with eosinophilia.

Using newly optimized genetic tools to probe Strongyloides sensory behaviors

The oft-neglected human-parasitic threadworm, Strongyloides stercoralis, infects roughly eight percent of the global population, placing disproportionate medical and economic burden upon marginalized communities. While current chemotherapies treat strongyloidiasis, disease recrudescence and the looming threat of anthelminthic resistance necessitate novel strategies for nematode control. Throughout its life cycle, S. stercoralis relies upon sensory cues to aid in environmental navigation and coordinate developmental progression. Odorants, tastants, gases, and temperature have been shown to shape parasite behaviors that drive host seeking and infectivity; however, many of these sensory behaviors remain poorly understood, and their underlying molecular and neural mechanisms are largely uncharacterized. Disruption of sensory circuits essential to parasitism presents a promising strategy for future interventions. In this review, we describe our current understanding of sensory behaviors - namely olfactory, gustatory, gas sensing, and thermosensory behaviors - in Strongyloides spp. We also highlight the ever-growing cache of genetic tools optimized for use in Strongyloides that have facilitated these findings, including transgenesis, CRISPR/Cas9-mediated mutagenesis, RNAi, chemogenetic neuronal silencing, and the use of fluorescent biosensors to measure neuronal activity. Bolstered by these tools, we are poised to enter an era of rapid discovery in Strongyloides sensory neurobiology, which has the potential to shape pioneering advances in the prevention and treatment of strongyloidiasis.

Strongyloides stercoralis infection in dogs in Austria: two case reports

Background

Strongyloides stercoralis is endemic in tropical and subtropical regions, but reports of infections in central and northern Europe have been recently increasing. Infections occur mainly in humans and dogs. In dogs, both dog-adapted and zoonotic S. stercoralis genotypes seem to occur. Clinical manifestations mainly include gastrointestinal and respiratory signs. The severity of the disease can vary greatly and depends on the immune status of the host. The infection is potentially fatal in immunosuppressed individuals, either medically induced or due to an underlying disease, in which hyperinfections and disseminated infections with extraintestinal parasite dissemination may occur.

Methods

Diagnosis was based on coproscopy, including flotation and the Baermann funnel technique, histology of small intestinal biopsies and molecular analysis of mitochondrial cytochrome oxidase subunit I (COI) and hypervariable regions I and IV (HVR I and HVR IV) of the nuclear 18S rDNA loci.

Results

Two independent cases of severe canine S.stercoralis infection in Austria are presented. In both cases, S. stercoralis was detected in histological sections of the small intestine and with the Baermann funnel technique. Molecular analysis revealed strains with zoonotic potential. Case 1 was a 1-year-old female French bulldog with a long history of respiratory and gastrointestinal signs, severe emaciation and apathy before S.stercoralis infection was diagnosed. Treatment with moxidectin (2.5 mg/kg body weight [BW], oral route) did not eliminate the infection, but treatment with ivermectin (0.2 mg/kg BW, subcutaneously) was successful. Case 2 consisted of two 2-month-old Pomeranian puppies, one female and one male, from a litter of four, which died soon after presenting dyspnoea and haemorrhagic diarrhoea (female) or torticollis (male); S.stercoralis infection was first diagnosed post-mortem.

Conclusion

More attention should be paid to this nematode because although it appears to be rare in Austria, it is easily overlooked on standard coproscopy unless a Baermann funnel technique is used, and even then, it can be missed. Moxidectin is not always successful in eliminating the infection, and treatment with ivermectin should be considered in cases of infection.

Graphical Abstract

Strongyloidiasis – diagnostic and therapeutic dilemmas in hyperinfection patients: a case series

The helminth infection caused by Strongyloides stercoralis is widespread in tropical regions, but rare in European countries. Unfamiliarity with the disease and diagnostic obstacles could contribute to its lethal outcome. Frequent use of corticosteroids during the COVID-19 pandemic could increase its significance. The aim of this retrospective descriptive study was to explore disease patterns and discuss clinical dilemmas in patients with S. stercoralis hyperinfection treated at the University Hospital for Infectious Diseases ‘Dr. Fran Mihaljević’ in Zagreb, Croatia, between 2010 and 2021. Five out of 22 (22.7%) immunosuppressed patients treated due to strongyloidiasis developed hyperinfection. All patients were male, median 64 years; four were immunosuppressed by corticosteroids (although ileum resection could have been the trigger in one) and one by rituximab. The diagnosis was established after a median of 1.5 months of symptom duration, accidentally in all patients, by visualizing the parasite in the gastric/duodenal mucosa in four cases, and bronchial aspirate in one. All patients were cachectic, four out of five had severe hypoalbuminemia and all suffered secondary bacterial/fungal infection. Despite combined antibiotic, antifungal and antihelmintic therapy, three out of five of the patients died, after failing to clear living parasites from stool samples. We can conclude that significant delays in diagnosis and lack of clinical suspicion were observed among our patients with the most severe clinical presentations of strongyloidiasis. Although being beyond diagnostic recommendations for strongyloidiasis, an early upper gastrointestinal endoscopy with mucosal sample analysis could expedite diagnosis in severe, immunosuppressed patients. The persistence of viable parasites in the stool despite antihelmintic therapy should be further investigated.