The human immunodeficiency virus, or HIV, is the causative agent of acquired immunodeficiency syndrome, better known as AIDS. The World Health Organization (WHO) estimates 33.4 million people globally were living with HIV infection at the end of 2008. The U.S. Centers for Disease Control and Prevention (CDC) estimates 1.1 million Americans were living with HIV as of 2006. There are two types of HIV, HIV-1 and HIV-2. HIV-1 causes the overwhelming majority of HIV infections in the United States.
HIV-1
CDC reports HIV-1 was first discovered in 1984. According to WHO, HIV-1 is the most common type of HIV worldwide and is responsible for the global HIV pandemic. In the article "Molecular Epidemiology of HIV" published in "The Indian Journal of Medical Research," Dr. A. Kandathil and colleagues note that HIV-1 predominates in all areas of the world except in certain regions of West Africa. WHO reports HIV-1 causes a more rapidly progressive illness than HIV-2.
HIV-1 Groups
HIV-1 is categorized into three groups: M for main or major; N for new or non-M/non-O; and O for outlier or other. Group M is the predominant HIV-1 group globally. In the same article, Kandathil reports HIV-1 group M is the causative agent of more than 90 percent of infections worldwide. He further states that HIV-1 groups O and N are rare, occurring predominantly in Cameroon and Gabon.
HIV-1 Group M Subtypes
In an article on HIV-1 genetic variation published in CDC's journal "Emerging Infectious Diseases," Dr. M. Kalish and colleagues explain HIV-1 group M is further subdivided into nine subtypes based on small differences in structure. The subtypes are denoted by letters and include A, B, C, D, F, G, H, J and K. In a hallmark study on the global distribution of HIV-1 subtypes published in the journal "AIDS" in 2004, Dr. Joris Hemelaar of the World Health Organization reported group M, subtype B, causes 98 percent of HIV-1 infections in the United States.
HIV-2
In a summary statement on HIV-2, CDC states only 79 cases of HIV-2 have been reported in the United States. Two-thirds of those affected were born in West Africa. CDC advises HIV-2 is most common in the African nations of Cape Verde, Côte d'Ivoire, Gambia, Guinea-Bissau, Mali, Nigeria and Sierra Leone. Despite the low incidence and prevalence of HIV-2 in the United States, screening of all blood donations includes testing for both HIV-1 and HIV-2.
References
- Centers for Disease Control and Prevention: HIV/AIDS in the United States
- World Health Organization: HIV/AIDS Questions and Answers
- World Health Organization: Overview of HIV Infection
- Centers for Disease Control and Prevention: Human Immunodeficiency Virus Type 2
- University of South Carolina School of Medicine, Microbiology and Immunology Online: Human Immunodeficiency Virus and AIDS--Types, Subtypes and Co-receptors
