S2.4a Pythiosis: An emerging disease in Hong Kong

Abstract

S2.4 Veterinary mycology research, September 21, 2022, 3:00 PM - 4:30 PM Oomycosis is an emerging disease of humans and animals caused by oomycetes in the Stramenopiles-Alveolata-Rhizaria super group, mainly Pythium insidiosum and occasionally Lagenidium giganteum or Paralagenidum species. In surface freshwater, oomycetes produce motile biflagellate asexual zoospores with marked chemotactic attraction to epithelial surfaces of vertebrate hosts. Infection is the result of encystation and invasion of damaged skin or gastrointestinal mucosa. Of ∼ 4200 cases of pythiosis reported globally between 1980 and 2021 only ∼ 20% involved humans while 80% involved animals, mainly horses, dogs, and cattle. Most human cases occur in India and Thailand, whereas most animal infections were reported in the United States and Brazil. Pythiosis has been reported in mainland China, but the burden of the disease is low and comprises <1% of overall cases in humans. Neither pythiosis nor lagenidiosis has been previously reported in humans or animals in Hong Kong. From January 2018 to January 2022, the Veterinary Diagnostic Laboratory of City University of Hong Kong diagnosed 10 cases of oomycosis (5 canine, 5 feline) after identification of non-parallel walled, irregularly branching, and poorly septate hyphae in the center of necrotic regions of histological sections of formalin-fixed paraffin-embedded tissues (FFPET). Species identity was confirmed by PCR and sequencing of 28S rDNA from DNA extracts of FFPET. There were 8 cases of P. insidiosum and 2 of L. giganteum infection. Serum ELISA was positive for Pythium antibodies in 5/6 cases tested and negative for Pythium/Lagenidium/Paralagenidum antibodies in a German shepherd dog (GSD) with disseminated disease caused by L. giganteum. Affected dogs were young to middle-aged at presentation (9 months to 5 years old). Two dogs had focal cutaneous infections, two had extensive gastrointestinal involvement, and the GSD had disseminated disease with cutaneous, mediastinal, and abdominal involvement. Affected cats were young (8 weeks to 18 months) and presented with subcutaneous/cutaneous disease. Three cats had a distinctive perianal ring of bulging subcutaneous granulation tissue, including one that also had an ulcerated, proliferative and necrotic lesion involving two adjacent hind-limb digits. One cat had facial subcutaneous swelling with mandibular lymph node enlargement and the remaining cat presented with extensive circumferential swelling of one hind limb from the distal paw to the mid-stifle. All cats tested negative for the Feline leukemia virus and Feline immunodeficiency virus. Traumatic or surgical wounds preceding infection were identified in a kitten caught in a rodent glue-trap with skin wounds, in a cat with facial involvement that had an injured globe surgically enucleated, and in a dog with cutaneous pythiosis that had chronic dermatitis. Treatment data were available for one canine case. The GSD with lagenidiosis was treated with combination antimicrobial therapy including voriconazole, terbinafine, minocycline, and azithromycin. The dog responded poorly. Mefenoxam was substituted for voriconazole and hyperbaric oxygen therapy was administered. After initial response, the dog succumbed 4 months from diagnosis. We have had success with the treatment of four feline cases using combination therapy including surgical debridement, immunotherapy with a Pythium vaccine, and combinations of antifungal drugs (posaconazole and terbinafine), and/or antimicrobials (doxycycline/minocycline and azithromycin).