Abstract
BackgroundThelazia callipaeda is a zoonotic parasitic nematode of the family Thelaziidae, with Phortica okadai as its intermediate host and only confirmed vector in China. China has the largest number of human cases of thelaziosis in the world. It is generally believed that infected domestic animals (dogs and cats) are the most important reservoir hosts of T. callipaeda, and thus pose a direct threat to humans. At present, there is little research or attention focused on the role of wildlife in the transmission cycle of thelaziosis in nature reserves.MethodsWe selected locations in four national nature reserves across China to monitor P. okadai and wildlife. We used a fly-trap method to monitor P. okadai density. Morphological analysis of the parasites collected from the conjunctival sac of the infected wildlife was undertaken as the first step in species identification, and polymerase chain reaction (PCR) was used for species confirmation.ResultsIn 2019, the density of P. okadai in Foping National Nature Reserve in China increased sharply, and infected P. okadai were newly found in the reserve. Giant panda, wild boar, leopard cat, and black bear were found to be newly infected with T. callipaeda (one individual of each species). A total of four worms were collected, one from each species of wildlife. The four worms were identified as T. callipaeda by their morphological characteristics; species identification was confirmed by PCR amplification.ConclusionsTo the best of our knowledge, this is the first report of T. callipaeda infection in P. okadai as well as in a variety of wildlife, including giant panda, in nature reserves in China. These results indicate that there is a transmission cycle of T. callipaeda among wildlife in these nature reserves. The increasing number of case reports of thelaziosis in wildlife suggest a likely risk of T. callipaeda infection for the inhabitants of villages situated around nature reserves.
Highlights
Thelazia callipaeda is a zoonotic parasitic nematode of the family Thelaziidae, with Phortica okadai as its intermediate host and only confirmed vector in China
Monitoring locations for P. okadai and wildlife We selected locations in the following four national nature reserves, which are situated across China, for the monitoring of P. okadai and wildlife between 2016 and 2019: Foping National Nature Reserve, Shaanxi (FNNR; 33°38′43"N, 107°47′38"E); Tangjiahe National Nature Reserve, Sichuan (32°34′44"N, 104°45′43"E); Wolong National Nature Reserve, Sichuan (WNNR; 31°02′20"N, 103°11′52"E); and Fengtongzhai National Nature Reserve, Sichuan (30°22′05"N, 102°48′52"E) (Fig. 1)
Before 2019, there were fewer P. okadai in the wildlife home ranges than in the surrounding villages; no infected P. okadai were found in the wildlife home ranges during this period (Tables 1, 2, 3)
Summary
Thelazia callipaeda is a zoonotic parasitic nematode of the family Thelaziidae, with Phortica okadai as its intermediate host and only confirmed vector in China. China has the largest number of human cases of thelaziosis in the world. It is generally believed that infected domestic animals (dogs and cats) are the most important reservoir hosts of T. callipaeda, and pose a direct threat to humans. Thelazia callipaeda is a zoonotic parasitic nematode of the family Thelaziidae, with Phortica okadai (Diptera, Drosophilidae, Steganinae) as its intermediate host. China has the largest number of human cases of thelaziosis in the world, and saw a significant increase in cases between 1970 and 1999. An increase in the number of P. okadai coupled with the proliferation of domestic animals (dogs and cats) has led to increased vigilance towards T. callipaeda infection
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