Worldwide distribution of human pythosis and biological characteristics of a Pythium insidiosum strain susceptible to antibiotics from China: a dual-scale study

Xiaoyun Liu¹Qiuyue Diao²Mingliang Li³Yuting Yang²Jiayin Liang⁴Ze-Hua Cui²Haiyan Zhang¹Huiling He²Jiabao Huang¹Hao Ren²Fengli Zhou¹Tijiang Shan⁵Xiaoping Liao²Jian Sun^2*Kouxing Zhang^1*

• ¹Department of General medicine, Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
• ²National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, China
• ³Department of General ICU, Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
• ⁴Department of Clinical Laboratory, Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
• ⁵College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China

Introduction: Pythiosis, caused by Pythium insidiosum (P. insidiosum), is an emerging disease with high mortality and morbidity. Despite its clinical severity and geographical strain variations, diagnostic and treatment challenges persist. Materials and methods: We queried PubMed and Google Scholar for "P. insidiosum" and "pythiosis," 1084 human pythiosis cases to generate a corresponding distribution map. Molecular biology, morphology, modified sporulation technique, and microscopic observation were employed to understand the biological properties of P. insidiosum with a strain of P. insidiosum isolated from a patient in Guangzhou. Drug susceptibility studies on the isolate were conducted both in vitro and in vivo. Results: Molecular biology, morphology, and biological processes confirmed that this strain was P. insidiosum. Epidemiological investigations have revealed that India and Thailand are hotspots for human pythiosis, and sporadic cases are increasing in China, the Americas, and Europe. The modified method of zoospore induction achieved 250-fold greater than the traditional method within 24 h. In vitro drug testing demonstrated superior antibiotic sensitivity (doxycycline (DOX) MIC 4 μg/mL; azithromycin (AZM) MIC 8 μg/mL) versus antifungals (>128 μg/mL). Subcutaneous infection models in immunocompromised mice showed 80% and 90% survival with oral AZM/DOX monotherapy versus 20% in controls (P<0.05), correlating with reduced hepatic fungal burdens and attenuated neutrophilic periarteritis. Conclusion: The distribution map underscores pythiosis as a growing climate-sensitive disease that requires enhanced surveillance in non-endemic regions. The modified method of zoospore induction and microstructure observation with Transmission Electron Microscopy (TEM) may be helpful for the rapid and sensitive detection of P. insidiosum. We also provided theoretical and technical support for the effective treatment of pythiosis in humans and animals with DOX and AZM in China, which offers novel insights into the potential of certain antibiotics as effective treatments.