Global Distribution and Clinical Features of Pythiosis in Humans and Animals

Abstract

Pythiosis is a difficult-to-treat infectious disease caused by Pythium insidiosum. The condition is unfamiliar among healthcare workers. Manifestation of pythiosis is similar to other fungal infections, leading to misdiagnosis and delayed treatment. The geographical extent of pythiosis at a global scale is unclear. This study aimed to analyze the clinical information recorded in the scientific literature to comprehensively project epidemiological characteristics, clinical features, and future trends of pythiosis. From 1980 to 2021, 4203 cases of pythiosis in humans (n = 771; 18.3%) and animals (primarily horse, dog, and cow; n = 3432; 81.7%), with an average of 103 cases/year, were recruited. Pythiosis case reports significantly increased in the last decade. Pythiosis spanned 23 tropical, subtropical, and temperate countries worldwide. Some patients acquired pythiosis from a trip to an endemic country. Strikingly, 94.3% of human cases were in India and Thailand, while 79.2% of affected animals were in the U.S.A. and Brazil. Clinical features of pythiosis varied. Vascular and ocular pythiosis were only observed in humans, whereas cutaneous/subcutaneous and gastrointestinal infections were predominant in animals. Mortality depended on host species and clinical forms: for example, none in patients with ocular pythiosis, 0.7% in cows with a cutaneous lesion, 26.8% in humans with vascular disease, 86.4% in dogs with gastrointestinal pathology, and 100% in several animals with disseminated infection. In summary, this study reports up-to-date epidemiological and clinical features of pythiosis in humans and animals. It increases awareness of this life-threatening disease, as the illness or outbreak can exist in any country, not limited to the endemic areas.

Keywords: Pythium insidiosum; clinical feature; distribution; epidemiology; pythiosis.

Figure 1

The number of included and excluded pythiosis cases from 270 reports published from 1980–2021. Clinical information of 1042 patients from 65 reports is excluded from the study due to considerably duplicated or repeated cases reported in other publications or lacking information on animal species. Eleven reports (as indicated by the asterisks) contain both included (n = 1830) and excluded (n = 133) cases of pythiosis. Four thousand two hundred and three pythiosis cases from 216 reports were recruited for epidemiological analyses.

Figure 2

Distribution of 216 published articles reporting 4203 pythiosis cases in humans and animals during 1980–2021. The number above each bar graph indicates the total reported cases in each respective year.

Figure 3

The world map shows the geographic distribution of pythiosis in humans and animals. The case numbers and percentages (in the parenthesis) are added to the countries where the patients acquired pythiosis. The color scale represents case density (ranging from 1 to 1890 cases). Stars indicate the areas or countries where P. insidiosum has been successfully isolated from the environment.