Journal of General Virology (1997), 78, 2225–2233. Printed in Great Britain ............................................................................................................................................................................................................... SHORT COMMUNICATION Evolution of human immunodeficiency virus subtype A in women seroconverting post partum and in their offspring post-natally infected by ingestion of breast milk A. Simonon, 1 † G. A. Mulder-Kampinga, 2,3 ‡ P. van de Perre, 1 E. Karita, 1 P. Msellati, 4 C. Kuiken 2 § and J. Goudsmit 2 1 The AIDS Reference Laboratory, National AIDS Control Program, Kigali, Rwanda 2,3 Department of Human Retrovirology 2 and Department of Obstetrics and Gynaecology 3 , Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands 4 ORSTOM, Abidjan, Co  te d’Ivoire The evolution of genomic RNA of human immuno- deficiency virus type 1 (HIV-1), subtype A, was studied in three Rwandan mother–child pairs over a period of 12–30 months. In two pairs a homo- geneous subtype A V3 sequence population was observed at seroconversion and the virus popu- lations in the children resembled those in the mothers. One of these mother–child pairs was infected with an A/C recombinant virus (A p17 /C p24 ). In the third pair, a heterogeneous V3 sequence population was observed in the maternal sero- conversion sample but the V3 sequence population in the child’s sample was homogeneous. In each individual the intra- and intersample variation (between the seroconversion and follow-up samples) increased over time in both the V3 region and p17 gag . Independent evolution for 1–2 years did not abolish the epidemiological relationship between virus populations in mother and child. Author for correspondence : Jaap Goudsmit Fax 31 20 6916531. e-mail j.GoudsmitAMC.UVA.NL † Present address : Centre Muraz/OCCGE, Bobo Dioulasso, Burkina Faso. ‡ Present address : Department of Medical Microbiology, University of Groningen, Groningen, The Netherlands. § Present address : Los Alamos National Library, Los Alamos, N. Mex., USA. Nucleotide sequences reported in this paper have been assigned the accession numbers Z47881–Z47902, Z47951–Z47997, Z478010, Z478011, Z76706–Z76734, Z75958–Z76462, Z76649 and Z76650. In sub-Saharan Africa human immunodeficiency virus type 1 (HIV-1) infections are caused by a wide variety of HIV-1 subtypes. Infections with the subtypes A, C and D are the most frequently reported (Myers et al., 1995). HIV-1 subtypes co- circulate in several central African countries and as a conse- quence subtype recombinants are found (Robertson et al., 1995). The present study focused on the evolution of the V3 region of env and p17 region of gag of HIV-1 subtype A in mother–child pairs. HIV-1 genomic RNA was isolated from serum samples from three mother–child pairs originating from a prospective cohort study in Kigali, Rwanda. The women seroconverted after childbirth and their children became infected through breast milk. The design of the cohort study and details of serological and diagnostic PCR data are given elsewhere (van de Perre et al., 1991, 1992). The pairs designated 10, 12 and 16 in the reports of van de Perre et al. (1991, 1992) correspond to 538, 566 and 564 in this study. Children 538 and 566 seroconverted within the same 3 month period as did their mothers, suggesting vertical transmission during the acute phase of maternal infection (van de Perre et al., 1991). Child 564 seroconverted 18 months after maternal seroconversion (van de Perre et al., 1992). Some of the sequence results of pair 564 have been published previously and are included in the present paper for comparison only (Mulder-Kampinga et al., 1995). None of the mothers and children fulfilled the WHO clinical case definition of AIDS (World Health Organization, 1986, 1994). No information was available about CD4 + and CD8 + T-cell numbers. The procedures for RNA isolation, reverse transcription, amplification of cDNA by nested PCR, cloning and sequencing have been published previously (Mulder-Kampinga et al., 1993, 1995). For each of the tested samples from these mother–child pairs, a specific signal was obtained after a single PCR amplification procedure (data not shown). The detection limit of the first PCR is 10–100 copies of DNA for both the V3 0001-4709  1997 SGM CCCF