Short Communication Molecular evidence of horizontal transmission of hepatitis C virus within couples Isabel Maria Vicente Guedes de Carvalho-Mello, 1,2 Jose ´ Eymard Medeiros Filho, 2 Michele Soares Gomes-Gouve ˆ a, 2 Fernanda de Mello Malta, 2 Artur Trancoso Lopo de Queiro ´z, 3 Joa ˜ o Renato Rebello Pinho 2 and Flair Jose ´ Carrilho 2 Correspondence Isabel Maria Vicente Guedes de Carvalho-Mello imvgcmello@butantan.gov.br 1 Laborato ´ rio de Imunologia Viral, Instituto Butantan, Av. Vital Brasil 1500, 05503-900 Sa ˜ o Paulo, SP, Brazil 2 Department of Gastroenterology, University of Sa ˜ o Paulo School of Medicine, Av. Dr. Ene ´ as de Carvalho de Aguiar 500, 05403-000 Sa ˜ o Paulo, SP, Brazil 3 Instituto de Biocie ˆ ncias, Universidade de Sa ˜ o Paulo, 05508-090 Sa ˜ o Paulo, SP, Brazil Received 5 August 2009 Accepted 4 November 2009 Hepatitis C virus (HCV) transmission has decreased with the adoption of universal blood donor screening and social policies to reduce the risk of infection in intravenous drug users, but remains a worldwide health problem. The objective of this study was to evaluate the phylogenetic relationships among sequences from different HCV genomic regions from sexual partners of infected patients. Nine couples with a stable relationship and without other risk factors for HCV infection and 42 control patients were selected, and the NS3 and NS5B regions were analysed. Phylogenetic analysis showed that viruses from five of the couples had a common origin, clustering in the same monophyletic group, with bootstrap values greater than 70. For the other couples, monophyletic groups were observed, but without bootstrap support. Thus, using two different viral genome regions, a common source of infection was observed in both members of five couples. These data strongly support HCV transmission within couples. Hepatitis C virus (HCV) infection constitutes a major health problem throughout the world and is related to severe liver cirrhosis, end-stage liver disease and hepato- cellular carcinoma (Chevaliez & Pawlotsky, 2007). The only member of the genus Hepacivirus of the family Flaviviridae, HCV is an enveloped virus with a positive- sense, single-stranded RNA genome of approximately 9.6 kb, encoding a single polyprotein of approximately 3000 aa that is cleaved into structural and non-structural proteins. HCV is classified into six genotypes, HCV-1 to -6, with each genotype further subdivided into subtypes, such as HCV-1a and -1b (Simmonds, 2004). Although intrafamilial transmission is not well documen- ted, several studies have reported sexual and vertical transmission and close contacts as sources of contamina- tion (Cavalheiro, 2004; Cavalheiro et al., 2009; Chiaramonte et al., 1996; Keiserman et al., 2003; Mastromatteo et al., 2001). Sexual transmission is not well determined, although studies have indicated a low effec- tiveness of infection via this route (Akahane et al., 1994). The estimated risk for sexual transmission is 0–0.6 % year 21 for partners who maintain monogamous relation- ships for a long period of time, and 1 % year 21 for those with multiple partners (Terrault, 2002). Some studies show high serum anti-HCV positivity rates among sex profes- sionals, men who have sex with other men, and healthcare professionals (Nakashima et al., 1992; Ndimbie et al., 1996; Thomas et al., 1995). If the index case is co-infected with human immunodeficiency virus (HIV), the sexual trans- mission risk is higher (Filippini et al., 2001). As with sexual and vertical transmission, occupational exposure has been documented but is rare (Alter, 2002; Alter et al., 1999). At least 10 % of HCV-infected patients do not report exposure to any of the known risk factors, and these are considered sporadic cases. Detailed molecular analysis may be able to establish the common ancestry of viruses circulating in a family and to support the hypothesis that close familial contact and sexual intercourse are important methods of HCV transmission. The present study had the objective of supporting the hypothesis of horizontal transmission within couples. The GenBank/EMBL/DDBJ accession numbers for the HCV sequences determined in this study are EF406133–EF406248. A maximum-likelihood tree constructed from the NS5B region and two supplementary tables showing patient data and primer sequences are available with the online version of this paper. Journal of General Virology (2010), 91, 691–696 DOI 10.1099/vir.0.015594-0 015594 G 2010 SGM Printed in Great Britain 691