Updating Taenia asiatica in humans and pigs.

An epidemiological study on taeniasis and cysticercosis in northern India has recently updated the epidemiology of Taenia asiatica. Practically, all the detected cases of taeniasis were caused by T. asiatica, cited for the first time in humans in that country. The finding widens the geographical distribution of T. asiatica, a species wrongly considered an exclusive South-Eastern Asian parasite. Due to the introduction of molecular techniques in Taenia diagnosis, the species is slowly showing its true distribution. A human Taenia species with cosmopolitan hosts (the same as the other two Taenia species) but limited to a specific geographical area and not affected by globalisation would certainly be hard to believe. Regarding cysticercosis, there is a remarkable finding concerning T. asiatica pig cysticercosis, specifically the presence of the cysticercus of T. asiatica not only in the liver (its preferential infection site) but also in muscle. This is the first time that the cysticercus of T. asiatica has been found in muscle in a naturally infected pig. This fact is actually relevant since people are at a greater risk of becoming infected by T. asiatica than previously expected since the liver is no longer the only site of pig infection. The Taenia species causing Taenia saginata-like taeniasis around the world, as well as pig and human cysticercosis, should always be molecularly confirmed since T. asiatica could be involved.

First ultrastructural data on the human tapeworm Taenia asiatica eggs by scanning and transmission electron microscopy (SEM, TEM).

Humans are definitive hosts of three species of the Taenia genus, namely Taenia solium, Taenia saginata and Taenia asiatica. The relative novelty of the latter explains the lack of knowledge concerning certain relevant aspects related to this parasite, such as its definite geographical distribution and whether its eggs can infect humans or not. So far, only the eggs of T. solium are known to be infective for humans, producing cysticercosis. Although eggs contain the infective stage, the oncosphere, there is a lack of research on the ultrastructure of eggs of human taeniids. We show, for the first time, the ultrastructure of eggs of T. asiatica by means of SEM and TEM analyses. We detected all the envelopes, namely the egg shell, vitelline layer, outer embryophoric membrane, embryophore, granular layer, basal membrane, oncospheral membrane and oncospheral tegument. Hooks surrounded by myofibrils and glycogen-like particles, the two types of secretory granules of the penetration glands, as well as several nuclei and mitochondria were also revealed in the oncospheres. In addition to the already known structures in eggs from other Taenia species, the presence of two types of small vesicles is described herein, possibly corresponding to exosomes and ectosomes because of their shape and size, which could participate in the host/parasite intercellular communication.

Taenia asiatica: the most neglected human Taenia and the possibility of cysticercosis.

Not only Taenia solium and Taenia saginata, but also Taenia asiatica infects humans. The last species is not included in the evaluation of the specificity of the immunodiagnostic techniques for taeniasis/cysticercosis. There is currently no specific immunodiagnostic method for T. asiatica available. Therefore, due to the fact that molecular techniques (the only tool to distinguish the 3 Taenia species) are normally not employed in routine diagnostic methods, the 2 questions concerning T. asiatica (its definite geographic distribution and its ability to cause human cysticercosis), remain open, turning T. asiatica into the most neglected agent of human taeniasis-cysticercosis.