Etiology and pathogenesis

HIV-1 is a retrovirus and member of the genus Lentivirus. These viruses have a characteristically prolonged latency period. There are two molecularly and serologically distinct but related types of HIV: HIV-1 and HIV-2. HIV-2 is a less common cause of the epidemic and is found primarily in West Africa. HIV-1 is categorized by phylo-genetic lineages into three groups (M [main], N [new], and O [outlier]). HIV-1 group M can be further categorized into nine subtypes: A through D, F through H, and J and K. HIV-1 subtype B is primarily responsible for the North American and Western European epidemic.

HIV in humans is believed to result from cross-species transmission from primates infected with simian immunodeficiency virus (SIV). HIV-2 is closely related to the SIV found in sooty mangabeys in West Africa, and HIV-1 is similar to the SIV found in chimpanzees. The earliest known human HIV infection was in central Africa in 1959. Cultural practices such as the preparation and eating of bush-meat, or keeping primates as pets, may have allowed the virus to transmit from animal to human. The rapid spread of the virus throughout the world can be primarily attributed to sexual promiscuity, drug abuse, and high mobility due to modern transportation.

HIV infection occurs through three primary modes of transmission: sexual, par-enteral, and perinatal. The most common method for transmission is receptive anal and vaginal intercourse, with the probability of transmission up to 30% per sexual contact. The probability of transmission increases when the index partner has a high level of viral replication (which occurs at the beginning of infection or late in disease), or when the uninfected partner has ulcerative disease, compromised mucosal surfaces, or (in the case of men) has not been circumcised.

Parenteral transmission of HIV primarily occurs through injection drug use by sharing contaminated needles or injection-related supplies. As a result of a comprehensive North American screening program, less than 1% of all cases of HIV infection occurs as a result of transfusions of contaminated blood or blood products, or infected transplant organs. Health care workers have a 0.3% estimated risk of acquiring HIV infection through percutaneous needlestick injury.

Perinatal infection (also known as vertical transmission or mother-to-child transmission [MTCT]) can occur during gestation, at or near delivery, and during breastfeeding. The risk of MTCT up to and including delivery is approximately 25%, while the risk of transmission during breast-feeding is approximately 15% to 20% within the first 6 months of life. Because a high rate of HIV replication in the blood is a significant risk factor for transmission of HIV, it is important to treat women for their HIV infection during pregnancy. After delivery, mothers are strongly recommended not to breast-feed if safe alternatives are available.

Understanding the life cycle of the virus is important to know how antiretroviral drugs are combined for optimal therapy (Fig. 87-1). Once HIV enters the body, an outer glycoprotein called gp120 binds to CD4 receptors found on the surface of dendritic cells, T lymphocytes, monocytes, and macrophages. This allows further binding to other chemokine receptors on the cell surface called CCR5 and CXCR4. Greater than 95% of newly infected patients have viruses that preferentially use CCR5 to enter the cell, and most patients with advanced disease have viruses that preferentially use CXCR4 to enter the cell. This becomes important in understanding the place in therapy for some of the new drugs in development.

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New Mothers Guide to Breast Feeding

New Mothers Guide to Breast Feeding

For many years, scientists have been playing out the ingredients that make breast milk the perfect food for babies. They've discovered to day over 200 close compounds to fight infection, help the immune system mature, aid in digestion, and support brain growth - nature made properties that science simply cannot copy. The important long term benefits of breast feeding include reduced risk of asthma, allergies, obesity, and some forms of childhood cancer. The more that scientists continue to learn, the better breast milk looks.

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