Molecular epidemiology of cytic echinococcosis in Italy, Portugal, Slovak Republic and Argentina

BUSI, M.; SNABEL, V.; DENEGRI, G.; DOPCHIZ, M.C.; ELISSONDO, M.C. & D’AMELIO, S.

Italia

Congreso; XXII Congresso della Società Italiana di Parassitologia; 2002

Società Italiana di Parassitologia

A considerable degree of attention has been addressed in the recent past to the taxonomy of the causative agents of hydatid disease, Echinococcus spp.. Until recently it was believed that the genus Echinococcus consisted of only 4 species, Le. E. granulosus, E. multilocularis, E. vogeli and E. oligarthrus plus a large number 9f intraspecific variants, or strains, recognised principalIy on the basis oí host occurrence. Molecular genetic studies, however, have shown that many strains warrant species status (Bowles J et al. 1995, Parasitology, 110: 317-328; Thompson RC et al. 1995, Adv Parasitol, 35: 145-76). The species and strains tm now detected have shown a considerable amount of diversity in their ecology, and in particular in their geographic distributions and occurrence in intermediate and definitive host. Such differences reflects a marked differentiation at genetie level, probably as a result of a spatial structuring in genetic variation of Echinococcus spp. populations, after splitting of small. isolated populations which went through genetic drift and local adaptation in absence of gene flow or as a resuJt oí cross-inseminations and high outcrossing rates in genetically different worms. The genetie differentiation of speeies and strains is remarkably meaningful, since the correet definition and identification of the taxa involved in a selected study area is a first step for the correct understanding oí the epidemíology of this disease. The present research was aimed to study the genetic variation in Echinococcus granulosus in different regions (Italy, Portugal, Slovak Republic and Argentina), as a tool for the detection and identification of the species and strains ¡nvolved in the transmission of such disease to humans. While strain charaeterisation studies have been carried out in the Slovak Republic (Snabel V et al, 2000, J Helminth 74: 177-181) and in Argentina (Rozenzvit MC et al, 1999, ParasitoJogy, 118: 523-530), no data on the genetic characterisation of E. granulosus strains in Italy and Portugal are tm now availabJe. Isolates from hydatid cysts coJlected in humans and in infected sheep, bovines and pigs were analysed by DNA sequencing of the mitochondrial cytochrome e oxidase 1 (COI) and NADH dehydrogenase 1 (ND 1) genes. Conceming ItaUan samples, most of the ¡solates collected in sheep and bovínes from Sardinia were identífied as G 1 sheep strain, with the exception of one isolate that showed a COI sequence identical to the 02 Tasmanian sheep strain. In collecting sites in Rome surrounding areas most of the ¡solates showed identical sequences to the 01 sheep strain, while few specimens showed, at one or two nueleotide positions, character state_ typical of the Tasmanian sheep strain (e.g. G2 genotype). E. granulosus isolates from human cases from Rome were a11 identified as G 1 sheep strain, thus confirming the role of this variant in the zoonotie transmission. The occurrence of the Tasmanian sheep strain outside its original geographic area is not surprising, sinee ovine are often exported from a region to another. The introgression of G2 haplotypes into G 1 genetie pools, or vice versa, could índicate that a certain amount of gene flow between genetie variants of E. granulosus sti1l oecurs. A similar picture was observed in samples from Portugal, where the G 1 and G 1/02 individuals were found. This study represents the fírst strain identificatíon, using markers based on mitochondrial gene sequencing, of Italian and Portuguese E. granulosus populations. All the Slovak isolates were -identified as befonging to the G7 pig strain. This result ís consistent with prevíous investigations in the same region and confirms the prominent role of the pig strain in the transmission oí eystic hydatidosis in central Europe. Al1 the isolated coIlected from bovines in the Buenos Aires province, Argentina and from sheep in Portugal were identified as belonging to the G 1 sheep strain. This strain, the most widespread E. granulosus strain tm now detected, was previously found in Argentina in the Chubut and the Rio Negro provinces, but nOl in the areas here under study. In Argentina cystic hydatic disease represents an emerging problem, being endemic in many areas of the country. where numerous human cases are reported.