Evaluación del rol de los jabalíes y roedores en el ciclo silvestre de Trichinella spp. en el noreste de Patagonia

Abstract

The genus Trichinella consists of 9 species and 4 genotypes. Parasites of the genus Trichinella are morphologically indistinguishable and potentially zoonotic. They are distributed in a wide range of hosts that includes mammals, birds and reptiles. Trichinella spp. are characterized by developing two generations in the same host to complete its biological cycle, autoheteroxen. Infection with Trichinella spp. it is transmitted only by the consumption of infected meat, and develops in the same way in all hosts. A domestic cycle (rural or urban) is identified that depends on the management of pig production and a wild cycle that is maintained in parallel thanks to carnivorism, scavenging and cannibalism among species of free life. Trichinella spp. have an anaerobic metabolism that allows the survival in decaying muscle tissue and in frozen muscles of carnivorous mammals for long periods of time. Scavenging is one of the main ways of dissemination and it is among the wildlife (mainly the mesocarnivores of the Canidae Family) where the parasite biomass is sustained. In Argentina, until the present, 4 species have been recorded: T. spiralis, T. patagoniensis, T. pseudospiralis and T. britovi. Although, in recent years the number of surveillance studies in wild species has increased, there are still regions with no large-scale studies. The aims of the present study were to elaborate a distribution and prevalence map of Trichinella spp., establish the possible wild cycle of Trichinella spp. in the northeastern region of Patagonia, defining the role of wild boar (Sus scrofa) and rodents in the transmission of Trichinella spp. in the study area, the genotyping of larvaes of Trichinella spp. before the appearance of positive diagnoses and study the possible relationship between the composition of the Sus scrofa diet and its role as a transmitter of Trichinella spp. To achieve the aims, samples of wild boar muscle tissue were collected between 2014 and 2019 from contact with hunters and hunting tournaments. At the same time, muscle samples were taken from various wild species (including mammals, birds and reptiles) and between 2016 and 2018, 12 sessions of capture and removal of wild rodents were carried out. The samples were analyzed by the artificial digestion (AD) method. Between 10 and 40 grams of mainly diaphragm muscle (wild boar), limbs (other mammals, birds and reptiles) or the entire carcass (rodents) were digested. A total of 832 individuals from 32 species were sampled and analyzed with a negative result in the presence of Trichinella spp. Mammals: 508 Sus scrofa, 174 wild rodents of 8 species belonging to Muridae and Cricetidae family, 35 Lycalopex gymnocercus, 19 Chaetophractus villosus, 15 Didelphis albiventris, 13 Galictis cuja, 11 Leopardus geoffroyi, 9 Puma concolor, 2 Myocastor coipo, 1 Neovison vison, 1 Conepatus chinga,1 Tursiops truncatus. Aves: 9 Tyto alba, 9 Athene cunicularia, 4 Larus dominicanus, 2 Buteo polysoma, 2 Guira guira, 2 Asio flammeus, 2 Bubo virginianus, 2 Milvago chimango, 1 Polyborus plancus, 1 Macronectes giganteus, 1 Cathartes aura, 1 Falco sparverius, 1 Sterna hirudinacea. Reptiles: 9 Philodryas patagoniensis. Also, the content of 11 wild boar stomach were analyzed, in which 6 food items of plant origin (grasses and herbs/sub-bushes/shrubs) and animal origin (insects, hairs, undifferentiated tissue) were identified. The analysis of stomach contents coincides with other research that states that wild boars have a preference towards the consumption of plant matter. The absence of wild boars positive to the presence of Trichinella spp. by artificial digestion, coincides with research by several authors around the world. In Argentina, the results presented contrast with the prevalence reported in the population of wild boars, mainly from the west of northern Patagonia. This difference could be the combined consequence of environmental factors, of the variation in the availability of plant food (cultivated areas) and of human practices in the discarding of corpses in relation to hunting activity. In addition to the aims of this study, 125 wild boar sera and 304 wild boar muscle juices were obtained and analyzed by indirect methods (ELISA). Antibodies against Trichinella spp. were detected in 3/125 sera (2.4%; 95% CI 0.42-4.38) and in 5/304 (1.64%; 95% CI 0-3.24) muscle juices. The difference between direct and indirect methods could be explained by their relative sensitivity: 1-3 larva per gram for the AD method and (antibody to values equivalent to) 0.01 larva per gram for the indirect method. Also, it could happen that among the free-living wild boars that inhabit the northeastern of Patagonia Trichinella spp. circulate with a very low parasitic loads. According to the results, it could not be demonstrated that wild rodents participate in the wild cycle of Trichinella spp. in the studied area. For the first time in South America an active surveillance study of Trichinella spp. that includes birds and reptiles. The negative results obtained suggest that, in northeast Patagonia, the infection rate with Trichinella spp. it is very low among the wild species analyzed. However, the sudden emergence of foci that describes this parasite justifies the need to sustain action plans from a public health perspective, which considers: active surveillance in wildlife, control of existing health programs in domestic animals and programs of awareness aimed at producers, hunters, consumers, policy makers and the general public.