Breeding systems in Echinococcus granulosus (Cestoda; Taeniidae): selfing or outcrossing?

K. L. HAAG a1c1, A. M. ARAÚJO a1, B. GOTTSTEIN a3, M. SILES-LUCAS a3, R. C. A. THOMPSON a4 and A. ZAHA a2
a1 Departamento de Genética, Universidade Federal do Rio Grande do Sul, Caixa Postal 15053, Porto Alegre, 91501-970, Brazil
a2 Departamento de Biotecnologia, Universidade Federal do Rio Grande do Sul, Caixa Postal 15005, Porto Alegre, 91501-970, Brazil
a3 Institute of Parasitology, University of Berne, Laengass Strasse 122, PO Box 8466, Berne, CH-3001, Switzerland
a4 World Health Organization Collaborating Centre for the Molecular Epidemiology of Parasitic Infections, Division of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, Western Australia 6150, Australia


We used the PCR–SSCP method followed by sequencing in order to assess the genetic variability of coding and non- coding parts of the genome of Echinococcus granulosus (Cestoda; Taeniidae) and to test whether or not the parasite populations are mainly self-fertilizing. For this, we analysed a sample of 110 E. granulosus metacestode isolates collected from different geographical regions (Southern Brazil, Europe and Australia) and from different intermediate hosts (ovine, bovine, human, macropod, swine and equine). Using appropriate controls, we were able to identify 4 strains in that sample (sheep, cattle, pig and horse strains). The high degree of genetic differentiation between strains, but not within, and the monomorphism found in most loci (EgAg4, EgActII, EgHbx2 and EgAg6 – non-coding – EgAgB/1 and EgND1 – coding) indicated that they are largely selfed. On the other hand, outcrossing was also shown to occur, since 5 potential hybrid genotypes between cattle and sheep strains were found in populations of Southern Brazil, but absent in other geographical areas. We suggest that both processes are adaptive. The article also reports, for the first time, the occurrence of the E. granulosus cattle strain in South America.

(Received April 10 1998)
(Revised June 20 1998)
(Accepted June 20 1998)

Key Words: Echinococcus granulosus; SSCP; strain; genetic variability; selfing.

c1 Corresponding author: Departamento de Genética, UFRGS, Caixa Postal 15053, 91501-970, Porto Alegre, Brazil. Tel: 0055 51 316 6717. Fax: 0055 51 319 2011. E-mail: