Page 568 - Clinical Immunology_ Principles and Practice ( PDFDrive )

39

Human Immunodeficiency Virus Infection and

Acquired Immunodeficiency Syndrome

Susan L. Gillespie, Javier Chinen, Mary E. Paul, William T. Shearer

In recent years, there has been a stabilization and possible reversal KEY CONCEPTS
of the overall growth of the global acquired immunodeficiency
syndrome (AIDS) epidemic. The number of new infections has Trends in Human Immunodeficiency Virus
steadily declined since the late 1990s, and there are fewer AIDS- (HIV) Infection
related deaths as a result of the scale-up of antiretroviral therapy • Global rates of HIV infection have stabilized, but there is great het-
(ART) since 2004. People living with human immunodeficiency erogeneity in disease incidence among countries and regions.
virus (HIV) are now living longer and healthier lives. • Although most countries had a reduction in disease incidence between
According to the Joint United Nations Programme on HIV/ 2001 and 2009, seven countries had increases in disease incidence
AIDS (UNAIDS), 36.9 million people worldwide were estimated by more than 25% over that period.
1
to be living with HIV or AIDS at the end of 2014 (Fig. 39.1). • The age demographic most affected in the developing world, that is,
New HIV infections are declining in most countries. The annual those aged 25–44 years, includes men and women who are economi-
cally productive and women of childbearing potential.
number of incident HIV infections peaked at >3 million in the • Worldwide, most infections are acquired through heterosexual contact.
late 1990s and has steadily declined thereafter. In 2014, 2 million • In the United States, African Americans and men who have sex with
people were newly infected, with approximately 1% of these men (MSM) are disproportionately infected.
infections (220 000 cases) occurring in children younger than • The numbers of infections transmitted from mother to child are declining
1
15 years of age. Globally, however, adolescents, particularly as access to prophylactic medications to prevent infection improves.
adolescent girls, are at particular risk for acquiring HIV infection.
In 2012, there were 300 000 new infections reported among
adolescents aged 15–19 years, which accounted for about 13% of HIV infection, the number of newly diagnosed infections in
of all new infections. In sub-Saharan Africa, 70% of new infections the United States has remained unchanged from 2006–14,
2
in adolescents occurred among girls. There has been a slow but approximately 40 000–50 000 per year. Within the United States,
continued reduction in the number of people dying from AIDS- there is great variability in both the geographical and demographic
related conditions worldwide. AIDS mortality peaked at 2.1 distribution of the disease, with certain segments of the American
million in 2004, and by the end of 2014, it was down to 1.2 population being disproportionately affected, specifically men
1
million deaths resulting from AIDS-related illnesses. The decline who have sex with men (MSM) and ethnic and racial minorities,
3
reflects increased access to ART and improvements in the care including African Americans and Hispanic Americans (Fig. 39.2).
and support of infected individuals. Mortality among children In the United States and other developed countries, in contrast
younger than 15 years of age has also declined as a result of the to more resource-limited parts of the world, the number of
expansion of services to prevent mother-to-infant transmission children newly infected with HIV has decreased dramatically
of HIV and an increase in access to care and treatment for as a consequence of successful interventions against perinatal
children. Although access to care and treatment services for mother-to-child transmission. In 2014, 174 children were
HIV-infected children in resource-limited settings is expanding, diagnosed with HIV infection, 73% of whom had acquired the
4
it is estimated that only 31% of children in need of life-saving infection through perinatal transmission. At the same time,
ART received it, and an estimated 150 000 children had died of new pediatric AIDS cases and AIDS deaths also have plummeted,
AIDS-related illnesses in 2014. Of concern, HIV/AIDS is the in large part as a result of powerful combinations of antiretroviral
most common cause of death among adolescents in sub-Saharan (ARV) drugs.
Africa and the second leading cause of death among adolescents
globally. HIV PATHOGENESIS
US Perspective HIV Lifecycle
The Centers for Disease Control and Prevention (CDC) estimate HIV is a lentivirus that targets CD4 T cells by specifically
that almost 1.2 million adults and adolescents were living with binding the viral Env protein to two cell surface proteins, the
HIV in the United States at the end of 2014, including 156 300 CD4 receptor, and either the CCR5 or the CXCR4 chemokine
(12.8%) whose infection was undiagnosed. Despite ongoing receptor (Fig. 39.3). Other cell targets for HIV are monocytes
prevention efforts designed to reduce the number of new cases and dendritic cells (DCs), although they present less expression

545