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Journal of Virology, August 2000, p. 6992-7004, Vol. 74, No. 15
Special Pathogens Branch, Division of Viral
and Rickettsial Diseases, National Center for Infectious Diseases,
Centers for Disease Control and Prevention, Atlanta, Georgia 30333
Received 7 January 2000/Accepted 4 May 2000
The arenavirus Lassa virus causes Lassa fever, a viral hemorrhagic
fever that is endemic in the countries of Nigeria, Sierra Leone,
Liberia, and Guinea and perhaps elsewhere in West Africa. To determine
the degree of genetic diversity among Lassa virus strains, partial
nucleoprotein (NP) gene sequences were obtained from 54 strains and
analyzed. Phylogenetic analyses showed that Lassa viruses comprise four
lineages, three of which are found in Nigeria and the fourth in Guinea,
Liberia, and Sierra Leone. Overall strain variation in the partial NP
gene sequence was found to be as high as 27% at the nucleotide level
and 15% at the amino acid level. Genetic distance among Lassa strains
was found to correlate with geographic distance rather than time, and
no evidence of a "molecular clock" was found. A method for
amplifying and cloning full-length arenavirus S RNAs was developed and
used to obtain the complete NP and glycoprotein gene (GP1 and GP2)
sequences for two representative Nigerian strains of Lassa virus.
Comparison of full-length gene sequences for four Lassa virus strains
representing the four lineages showed that the NP gene (up to 23.8%
nucleotide difference and 12.0% amino acid difference) is more
variable than the glycoprotein genes. Although the evolutionary order
of descent within Lassa virus strains was not completely resolved, the
phylogenetic analyses of full-length NP, GP1, and GP2 gene sequences
suggested that Nigerian strains of Lassa virus were ancestral to
strains from Guinea, Liberia, and Sierra Leone. Compared to the New
World arenaviruses, Lassa and the other Old World arenaviruses have either undergone a shorter period of diverisification or are evolving at a slower rate. This study represents the first large-scale examination of Lassa virus genetic variation.
0022-538X/00/$04.00+0
Genetic Diversity among Lassa Virus
Strains


*
Corresponding author. Mailing address: Special
Pathogens Branch, Mailstop G14, Division of Viral and Rickettsial
Diseases, National Center for Infectious Diseases, Centers for Disease
Control and Prevention, Atlanta, GA 30333. Phone: (404) 639-1115. Fax: (404) 639-1118. E-mail: stn1{at}cdc.gov.
Present address: Bioterrorism Preparedness and Response Program,
National Center for Infectious Diseases, Centers for Disease Control
and Prevention, Atlanta, GA 30333.
Present address: Tuberculosis/Mycobacteriology Branch, Division of
Bacterial and Mycotic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333.
§
Present address: Emerging Bacterial and Mycotic Disease Branch,
Division of Bacterial and Mycotic Diseases, National Center for
Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333.
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