What is the relationship between breast milk and infectious disease?

Definition

The female breast is a “factory” of milk production. It is composed of
milk-producing mammary glands
and lactiferous ducts that carry milk to the nipple, which is
surrounded by fatty tissue. Breast milk provides ideal nutrition for a growing newborn and offers significant advantages for the baby’s immune system. It has been known for some time that breast-fed infants contract
fewer infections than those who are formula-fed, but only lately have experts come
to understand and identify the specific immune components that are transferred to
the infant in breast milk.

Breast milk also contains microorganisms, a few of which can be passed to the infant, leading to infection and clinical disease. Rarely, the considerable benefits of breast-feeding must be weighed against the risk of transmitting infection.

Breast-feeding can also be a source of infection in the
breast. Mastitis (infection of the breast tissue) is commonly seen
between one and three months of delivery and may cause pain, fever, and malaise in
the mother, which makes care of the newborn difficult. In almost all cases, it is
recommended that a woman with mastitis continue to breast-feed.

Immunity

During the first months of life, the infant’s immune system is immature and
unable to make the proteins and cells necessary to respond to “foreign” invaders.
Breast milk helps to offer protection in a number of ways. During pregnancy
immunoglobulins cross the placenta to help protect the fetus from infections. Some
types of antibodies can cross the placenta. IgM, the first antibody
to fight acute infection, does not cross the placenta.

All five major antibody types—IgG, IgA, IgM, IgD, and IgE—have been found in human breast milk and are active when ingested by the nursing infant. The most abundant is the type known as secretory IgA, which binds with potential pathogens, preventing them from invading the infant’s system. All antibody types are specific for only one pathogen and do not attack irrelevant or commensal (good) organisms. Other important immune molecules are present in breast milk too. Oligosaccharides (chains of sugars) and mucins (large molecules made of protein and carbohydrates) are able to clump together with invading bacteria, making them harmless.

White blood
cells (leukocytes) are abundant in breast milk; most notably in colostrum, the milky fluid that precedes the flow of milk. Neutrophils, macrophages, and lymphocytes are all present and play a role in protecting the infant from
disease. In addition, studies suggest that some hormones and other factors in
breast milk may induce the infant’s own immune system to mature more rapidly,
allowing breast-fed infants to protect themselves sooner than formula-fed
infants.

Infection Transmission

Few organisms are passed readily by breast milk to cause clinical infection, and it may be difficult to accurately determine the mode of transmission, because breast-feeding requires close contact between mother and infant. Some infections that are spread during the breast-feeding period pass by other means, such as airborne droplets or skin contact. Concern about infection rarely leads to a recommendation against breast-feeding.

Three viruses can be transmitted through breast milk and are of greatest
clinical concern. These include cytomegalovirus (CMV), human immunodeficiency virus
(HIV), which causes acquired immunodeficiency syndrome or
AIDS, and humanT-lymphotrophic virus (HTLV). It is thought that transmission
occurs through exposure to small amounts of virus for several feedings each day
during the prolonged period of breast-feeding.

CMV is a common cause of congenital infection. Most women are infected before becoming pregnant and develop antibodies that cross the placenta to protect the growing fetus and breast-feeding infant. However, if the woman experiences primary infection during pregnancy or breast-feeding, inadequate immune resources and infection can result.

Breast-feeding by an HIV-positive mother increases transmission risk up to 25 percent, in addition to the risk of perinatal transmission. There is no adequate immune protection for mother or infant. HIV-positive mothers should avoid breast-feeding to prevent mother-to-child transmission
.

HTLV is a cause of adult leukemia and other chronic conditions, and it is endemic to several regions of the world. Transmission occurs more often in breast-fed than in formula-fed infants. Mother-to-child transmission can be avoided by not breast-feeding.

Bacterial and other infections are rarely passed to infants through breast
milk. Some infections, including having gonorrhea, group B strep, syphilis, or
tuberculosis, could lead to an interruption of breast-feeding for a brief time,
while the mother or the mother and infant begin antimicrobial therapy. One should
not necessarily stop breast-feeding if using antibiotics.

Infection in the Lactating Breast

Mastitis can occur when bacteria from the infant’s mouth or the mother’s skin enter a duct through a sore, cracked nipple and multiply in breast milk, which is an ideal growth medium. This condition may lead to a localized, minor infection or a more serious deep-breast abscess. Symptoms include tenderness and swelling of the breast, fever, chills, and other flulike symptoms.

Breast infections require treatment with antibiotics. Prevention includes good hygiene and handwashing and proper breast-feeding technique to avoid cracked nipples. Most women with mastitis should continue to breast-feed; doing so does not harm the infant. Also, emptying the breast through feeding speeds healing.

Impact

Breast-feeding provides important protection against disease. The immunologic benefits are well documented and beyond question. For those few circumstances where disease transmission is of concern, more work is needed to develop vaccines and other interventions.

Bibliography

Barbosa-Cesnik, C., K. Schwartz, and B. Foxman. “Lactation Mastitis.” Journal of the American Medical Association 289 (2003): 1609-1612.

Huggins, Kathleen. The Nursing Mother’s Companion. 5th ed. Boston: Harvard Common Press, 2005.

Jackson, Kelly M., and Andrea M. Nazar. “Breastfeeding, the Immune Response, and Long-Term Health.” Journal of the American Osteopathic Association 106, no. 4 (2006): 203-207.

Lawrence, Robert, and Ruth Lawrence, eds. Breastfeeding: A Guide for the Medical Profession. St. Louis, Mo.: Mosby, 1999.

Mestecky, Jim, et al., eds. Immunology of Milk and the Neonate. New York: Plenum Press 1991.

Riordan, Jan, ed. Breastfeeding and Human Lactation. 4th ed. Sudbury, Mass.: Jones and Bartlett, 2010.