Research article

Hepatitis B virus genotypes and resistance mutations in patients under long term lamivudine therapy: characterization of genotype G in Brazil

Marcelle Bottecchia¹ , Francisco JD Souto² , Kycia MR Ó^1,3 , Marcia Amendola⁴ , Carlos E Brandão⁴ , Christian Niel¹ and Selma A Gomes¹

¹Laboratório de Virologia Molecular, Instituto Oswaldo Cruz, FIOCRUZ. Av. Brasil 4365, 21045-900 Rio de Janeiro, RJ, Brazil

²Núcleo de Estudos de Doenças Infecciosas e Tropicais, Faculdade de Ciências Médicas, Universidade Federal de Mato Grosso, Av. Amarílio de Almeida 215, 78010-060 Cuiabá, MT, Brazil

³Hospital Alcides Carneiro, Fundação Municipal de Sáude de Petrópolis, Rua Vigário Correas 1345, 25720-320 Petrópolis, RJ, Brazil

⁴Hospital Universitário Gaffrée e Guinle, Rua Mariz e Barros 775, 20270-004 Rio de Janeiro, RJ, Brazil

author email corresponding author email

BMC Microbiology 2008, 8:11doi:10.1186/1471-2180-8-11

Published:	22 January 2008

Abstract

Background

Lamivudine is an oral nucleoside analogue widely used for the treatment of chronic hepatitis B. The main limitation of lamivudine use is the selection of resistant mutations that increases with time of utilization. Hepatitis B virus (HBV) isolates have been classified into eight genotypes (A to H) with distinct geographical distributions. HBV genotypes may also influence pathogenic properties and therapeutic features. Here, we analyzed the HBV genotype distribution and the nature and frequency of lamivudine resistant mutations among 36 patients submitted to lamivudine treatment for 12 to 84 months.

Results

Half of the patients were homosexual men. Only 4/36 (11%) patients were HBV DNA negative. As expected for a Brazilian group, genotypes A (24/32 positive individuals, 75%), D (3/32, 9.3%) and F (1/32, 3%) were present. One sample was from genotype C, which is a genotype rarely found in Brazil. Three samples were from genotype G, which had not been previously detected in Brazil. Lamivudine resistance mutations were identified in 20/32 (62%) HBV DNA positive samples. Mean HBV loads of patients with and without lamivudine resistance mutations were not very different (2.7 × 10⁷ and 6.9 × 10⁷ copies/mL, respectively). Fifteen patients showed the L180M/M204V lamivudine resistant double mutation. The triple mutant rt173V/180M/204V, which acts as a vaccine escape mutant, was found in two individuals. The three isolates of genotype G were entirely sequenced. All three showed the double mutation L180M/M204V and displayed a large genetic divergence when compared with other full-length genotype G isolates.

Conclusion

A high (55%) proportion of patients submitted to long term lamivudine therapy displayed resistant mutations, with elevated viral load. The potential of transmission of such HBV mutants should be monitored. The identification of genotypes C and G, rarely detected in South America, seems to indicate a genotype distribution different to that observed in non treated patients. Disparities in routes of transmission (genotype G seems to be linked to homosexual behavior) and in pathogenic properties (genotype C is very aggressive) among HBV genotypes may explain the presence of rare genotypes in the present work.