Canine strongyloidosis in Central Europe: clinics, diagnostics, genetics and the risk of zoonotic transmission

trongyloides stercoralis is an intestinal nematode, primarily affecting humans and dogs. Infection is frequently reported in tropical and subtropical regions worldwide and considered rare in Central Europe. However, during the last years, several cases of S. stercoralis infection in dogs have been diagnosed in Switzerland, Austria, and in neighbouring countries. This parasite has a complex life cycle involving parasitic and free-living generations. Infection mainly occurs percutaneously or through the oral mucosa by penetration of infective larvae. The infection can be asymptomatic; however, in cases of impaired immunity, large worm burdens, or in young dogs, life-threatening disease characterized by diarrhoea, malabsorption and bronchopneumonia may occur. Further, autoinfection, hyperinfection, and extraintestinal dissemination of the parasite was reported in dogs. In recent years, molecular and epidemiological studies suggested that both, dog-adapted and zoonotic populations of S. stercoralis may exist. In 2017, canine strongyloidosis was diagnosed at the Institute of Parasitology in Bern in a breeding kennel with 37 Yorkshire terriers, which had previously imported animals from France and Bulgaria. Since then, the infection has been diagnosed in eight further unrelated individual dogs: two French Bulldogs, two Chihuahuas, two Pomeranians, one West Highland White Terrier, and one American Staffordshire Terrier. All animals were younger than two years, most of them younger than six months. In addition, we have diagnosed strongyloidosis in three dogs from Austria (one French Bulldog and two Pomeranians). Some of these cases had an import history (France, Italy, Croatia, Slovakia or Belgium). Main clinical manifestations were a poor general condition and chronic, severe gastrointestinal signs. In some cases, further clinical signs (respiratory or neurological signs), coinfections with other parasites (Giardia duodenalis, Cystoisospora spp.), concomitant diseases (portosystemic shunt, intestinal leiomyositis, immunosuppression), and lethal outcome were observed. Faecal samples were analysed using flotation, SAFC and Baermann methods in all cases. Diagnosis was more frequently successful using the Baermann method. All cases were confirmed by molecular methods and all S. stercoralis isolates characterised so far in Switzerland (n=9) and Austria (n=1) exhibited a similar genetic background to that of zoonotic isolates from other geographical regions. Attempted treatments included fenbendazole, ivermectin or a combination of both with variable results. Breeding kennels and animal trade seem to play an important epidemiological role in the dissemination of S. stercoralis. Due to clinical relevance, zoonotic potential, and difficulties in treatment, increased awareness for S. stercoralis of both, diagnosticians and clinicians is required.