Trichinellosis in Badgers in the Rostov Region (Southern Russia)

Introduction. Nematodes of the genus Trichinella of the family Trichinellidae, are the causative agents of trichinellosis, the intestinal and tissue type of helminthiasis deemed to be one of the most serious and widespread zoonotic infections threatening human health [1]. In humans, this disease has been reported in 55 countries worldwide [2]. Apart from its negative impact on public health, trichinellosis causes significant economic damage to agricultural and food industries, particularly with regard to food safety.

Trichinella have a simple yet unique life cycle. The enteric phase begins with the consumption of meat containing tissue parasite capsules. Larvae are released from the capsules due to gastric acid activity and, within a few hours, migrate to the small intestine, where they penetrate into the columnar epithelium. There, they undergo four molts to mature and begin mating 30 hours after infestation. On the fourth day, newborn larvae migrate through the blood-vascular system to the striated muscles and penetrate into muscle cells. Here, encapsulated species form collagen capsules and develop into an invasive form after 15–20 days [3]. Larvae of non-encapsulated species are likely to migrate between muscle layers [4]. Thus, a characteristic feature of the Trichinella life cycle can be identified: any animal they parasitize in becomes for them both a definitive and intermediate host.

At present, the genus Trichinella includes 10 species and 3 genotypes having no taxonomic status. All known species and genotypes are clearly divided into 2 clades. One clade includes Trichinella that encapsulate in the muscle tissue of a host and are capable of infecting mammals. It includes T. spiralis, T. nativa, T. britovi, T. murrelli, T. nelsoni, T. patagoniensis, T. chanchalensis and genotypes designated as T6, T8 and T9. The second clade includes three species of Trichinella that do not encapsulate: among them, one species infests mammals and birds (T. pseudospiralis); and two species parasitize in mammals and reptiles (T. papuae and T. zimbabwensis) [3][5]. All of the above-mentioned species and genotypes of Trichinella pose danger to both animals and humans. Primarily one species was previously reported in the Rostov Region: T. spiralis [e.g., 6]. In the Krasnodar region, cases of finding the non-encapsulated species T. pseudospiralis in pigs have been recorded [7].

In the wildlife, a wide range of animals participate as carriers in circulation of Trichinella, which includes approximately 100 diverse species of carnivorous and omnivorous animals [8]. A badger (Meles meles) is one of the main natural reservoirs of trichinellosis [9]. In the Rostov Region, as well as in the whole country, badgers are often the main prey for hunters. According to data published on the website of the Ministry of Natural Resources and Environment in July 2024¹, the population of badgers in the Rostov Region equals to 2 556 specimens, and the authorised quota for hunting is 3.91% of the population. Although this is quite a high level, poaching is still taking place. As a result, the uninspected meat can be consumed by humans or animals, which can lead to their infectation with trichinellosis.

In the article, we report the first case of detecting Trichinella larvae in a badger in the Rostov Region.

Materials and Methods. The object of the study was a carcass of a badger hunted on the territory of the Veshensky Production and Experimental Hunting Area (Sholokhov District, northern part of Rostov Region) in August 2024. Various muscle groups were sampled, including the crura of the diaphragm, diaphragm, intercostal muscles, neck muscles, and thigh muscles. Larvae and capsules in these samples were isolated and examined using compressor trichinoscopy. Histological sections were then prepared from seperate muscles and stained with hematoxylin and eosin according to the standard techniques. Capsules in native samples were measured and photographed using a Levenhuk MED D45 microscope (Levenhuk Inc., China) and LevenhukLite software. The capsule shape index (V) was calculated as the ratio of the capsule length (L) to its diameter (D). This index is used to evaluate the shape of round objects, including Trichinella capsules [10][11].

Results. Trichinella capsules were found in all the examined muscles of an animal. The largest number was found in the diaphragm and its crura. It has been acknowledged in the previous studies that the most heavily infested muscles in badgers are the head muscles, particularly the mylohyoid muscle [12]. However, these muscles were not within the scope of the present research.

The larvae discovered belong to the encapsulated ones. They were located in capsules in groups or one at a time (Fig. 1 a–b). Histological sections revealed that the capsules had thick shells covered by thin connective tissue membranes formed by the organism of a host (Fig. 1 c–d).

Based on the capsule morphometric data obtained (Table 1), it is possible to state that capsule location in the badger’s body does not affect its size to any significant extent. The shape of capsules in all the muscles was nearly round (V≈0.79).

Discussion and Сonclusion. The capsule shape indices calculated based on the morphometric results correspond more to the respective indices of T. nativa ratether than T. spiralis [11]. The former species used to be registered in the Central Russia, but has not been previously observed in the south of the country or in the Caucasus [13]. The –4 °C isotherm in January is likely to be a southern boundary for this species [4], which makes the possibility of finding this species in the Rostov Region very low. However, it is impossible to draw precise conclusions regarding the species membership of Trichinella detected by us in the badger, since the molecular genetic studies [14] or the use of Western blot technique [15] are required for a reliable diagnosis. Moreover, it is worth noting that most Trichinella species have a sympatric distribution [3]. Thus, in the Rostov region there could potentially be detected two encapsulated species (T. spiralis — reported here before and distributed worldwide, and T. britovi —disseminated from the Iberian Peninsula to Kazakhstan, Turkiye and Iran [4]), and one non-encapsulated species — T. pseudospiralis registered in North America, Eurasia and Tasmania [16]. No evident dependence of different Trichinella species to host animals has been revealed [17], however, different invasion rate by different Trichinella species have been recorded during experimental infestation [18]. All the above makes species identification of Trichinella extremely difficult.

Thus, studying the distribution and species composition of Trichinella remains a highly relevant objective, requiring further research both in south of Russia and worldwide. Badger meat must undergo mandatory trichinoscopy to prevent potential infestations in humans. Unused carcasses and their remains must be disposed of to exclude infestation of domestic and wild animals.