Zoonotic Thelazia callipaeda eyeworm in brown bears ( Ursus arctos ): A new host record in Europe

Abstract

Thelazia callipaeda (Spirurida, Thelaziidae) eyeworm, a zoonotic parasite transmitted by lachryphagus drosophilids, causes subclinical to clinical ocular disease in a wide range of vertebrates, including humans. In the past 20 years, the infection spread primarily in areas where the vector thrives, and now is endemic in many European countries. Recently, this nematode has been reported also in the United States. Here, we describe the first record of the brown bear (Ursus arctos) as a host of T. callipaeda. Eight (26.7%) out of 30 bears were found to be infected with T. callipaeda adult worms. In addition, the parasite was detected in 13 wolves (Canis lupus) sharing the same environment with the brown bears. At the molecular characterization, all nematodes belonged to the haplotype 1, which is the only one recorded in Europe, as yet. This finding demonstrates that brown bears may act as hosts for this parasite, suggesting its potential role in the maintenance of the cycle not only in the wild but also in captivity. Under the above circumstances, the brown bear may represent a potential zoonotic risk for humans, both in rural and urban areas where other reservoirs may be infected.

Wild carnivores and Thelazia callipaeda zoonotic eyeworms: A focus on wolves

“…This study reports the first cases of ocular thelaziosis by T. callipaeda in grey wolves from peripheral zones of the Italian Alps. Since the first report of T. callipaeda in wolves in Italy ( Otranto et al, 2007 ), other records on this host species have been published in different European countries such as Romania ( Mihalca et al, 2016 ), Serbia ( Bojan et al, 2019 ), Spain ( Nájera et al, 2020 ), and Greece ( Papadopoulos et al, 2021 ), demonstrating that this ecologically plastic canid is involved in the transmission cycle of T. callipaeda in diverse habitat types in Europe.…”

“…For example, red foxes ( Vulpes vulpes ), have been reported with infection intensity of up to 192 T. callipaeda specimens ( Ionică et al, 2018 ). The infection in carnivore hosts may vary from asymptomatic to clinical signs characterized by conjunctivitis, mucus, corneal ulcers, red eyes, blepharospasm, corneal oedema, and mucopurulent discharge ( Sargo et al, 2014 ; Papadopoulos et al, 2021 ). In addition, the presence of adult worms in the eyes causes discomfort and may expose the animals to opportunistic bacterial infections, which may have more severe consequences ( Rolbiecki et al, 2021 ).…”

“…Among the zoonotic parasites affecting wildlife and humans, Thelazia callipaeda is widely distributed in Europe, representing a health concern for domestic dogs and cats, several wild carnivores (e.g., foxes, wolves, bears), hares, and humans ( Dorchies et al, 2007 ; Otranto et al, 2009 ; Miró et al, 2011 ; Baneth et al, 2016 ; Papadopoulos et al, 2021 ). This nematode is known as eyeworm since its late larval stages (i.e., L3, L4 and L5) and adults develop in the conjunctival sac of the above-mentioned vertebrate hosts ( Otranto et al, 2004 ; Vale et al, 2020 ), after being transmitted by drosophilid flies of the Phortica genus ( Otranto et al, 2005 ).…”

Morphology and Histology of the Orbital Region and Eye of the Asiatic Black Bear (Ursus thibetanus)—Similarities and Differences within the Caniformia Suborder

“…The literature describing the correct structure of the skull while taking into account the anatomical description of the orbital region, the eyeball and the accessory organs of the eye at the macro and microscopic level in the family Ursidae (American black bear Ursus americanus [ 23 , 24 ]; Asiatic black bear Ursus thibetanus [ 25 ]; North American brown bear or Grizzly bear Ursus arctos horribilis [ 26 , 27 ]; brown bear Ursus arctos [ 28 , 29 , 30 , 31 ], sloth bear Melursus ursinus [ 25 , 32 , 33 , 34 ]; Sun Bear Ursus malayanus [ 25 ]; polar bear Ursus maritimus [ 27 ]) are very limited. On the other hand, studies on clinical case descriptions of diseases of the eyeball and accessory organs of the eye in representatives of this family are much more frequent [ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ]. A review of the literature describing the morphology of the eye socket, eye tunics, eyelids and orbital glands in suborder Caniformia is presented in Table S1 .…”

Laboratory breeding of Phortica spp. (Diptera: Drosophilidae), vectors of the zoonotic eyeworm Thelazia callipaeda

“…Thanks to this lachryphagous behaviour, Phortica variegata and Phortica okadai have been identi ed as intermediate hosts and vectors of the zoonotic eyeworm Thelazia callipaeda (Railliet & Henry; Spirurida: Thelaziidae) [9]. This eyeworm infests the ocular apparatus of dogs, cats, wild carnivores (e.g., foxes, wolves, bears), lagomorphs, and humans in Europe and Asia [12,13]. Currently, several cases of human thelaziosis by T. callipaeda have been reported in Asia (i.e., China, Korea, India, Thailand and Japan) and Europe, with an increasing trend in recent decades [14,15,12].…”