West Nile Worries Are No Reason to Give Up Breast-feeding

West Nile virus infections are spreading like wildfire–and not just through bug bites. Although the vast majority of the nearly 2,800 U.S. cases reported to the Centers for Disease Control and Prevention (CDC) so far this year were picked up from mosquitoes, at least 3 people–and possibly 15–appear to have acquired the virus from infected blood or transplanted organs. But the case of the youngest person in the United States thought to have been infected–a newborn–almost certainly resulted from transmission of the virus in breast milk, federal officials say.

The good news: Though tests of the mom’s blood and spinal fluid confirmed the presence of the virus, her infant has exhibited no symptoms of disease.

Until this Michigan incident, there was no evidence that West Nile virus might be transmitted in humans via ingestion, although some experiments showed birds could contract West Nile disease orally. In fact, West Nile virus belongs to a family of germs known as flaviviruses, and several tickborne flaviviruses, such as the ones causing encephalitis and Kyasanur Forest disease, can be spread via the milk of infected animals, notes Lyle Petersen, CDC’s West Nile expert. He says that people have sometimes picked up those other flaviviruses by drinking milk from diseased livestock.

Still, he cautions, the new Michigan findings don’t warrant changing current breast-feeding guidelines.

Babies derive plenty of benefits from breast-feeding, beyond the mere acquisition of nutritious calories. Studies have shown that in addition to fostering the bonding of mother and child, consumption of this special milk can speed the maturation of the infant’s gut and vision and supply infection-fighting agents, including retinoic acids. Some recent epidemiological studies have also found evidence that consumption of mother’s milk, instead of commercial formulas, might also reduce the risk of celiac disease (see “On Wheat and Weaning” at On Wheat and Weaning). For all of these reasons, pediatricians generally recommend that during the first months of life, mother’s milk is best.

Only two infectious conditions preclude breast-feeding, Petersen says: when a mom is either HIV-positive or carries a leukemia virus known as T-cell type 1. However, he concedes, in light of the neonatal case, “women with documented–and I emphasize ‘documented’–West Nile virus infection may wish to consult their physician about breast-feeding.”

Petersen and his colleagues published a preliminary account of the neonatal case in the Oct. 4 Morbidity and Mortality Weekly Report, a CDC publication.

An editorial accompanying that report notes that since the virus reached the United States in 1999, only four other babies–ages 2, 3, 9, and 11 months old–have been diagnosed with West Nile virus infection. All turned up this year. “Retrospective investigations are underway to determine if these infants were potentially infected with [the virus] through breast-feeding,” the editorial says. Additional CDC surveys will attempt to confirm the presence of this virus in the breast milk of infected women.

Concludes the editorial: “Until live virus is cultured from breast milk, or until definitive data are obtained to document [virus] transmission through breast milk, the findings in this report should be interpreted with caution.”

The youngest victim

Hours after delivering a healthy baby on Sept. 2., a 40-year-old Michigan woman required blood transfusions to combat anemia. She received two units of blood. Soon, the woman, who had a history of migraines, began complaining of headaches. On and off she ran a fever, and she still didn’t feel very well when she left the hospital on Sept. 4.

Eight days later, the woman developed a severe, unremitting headache that she recognized as something other than a migraine. Several days after that, she was readmitted to the hospital with a fever, where tests for West Nile virus were performed. They proved positive, indicating the woman had developed West Nile meningitis.

Her disease appears to have been triggered by a transfusion of infected blood, Petersen says. Both the new mother and another patient received blood from a donor who later was diagnosed with West Nile disease. Both of the blood recipients developed their disease shortly after their transfusions.

Despite feeling sick since the delivery of her baby, the new mom continued to nurse her child from the breast. When the woman’s West Nile infection was confirmed, the hospital sampled her milk, beginning on the 16th day after the birth of her child–and confirmed that it hosted antibodies to the virus. A second test of the milk, performed on the 24th day, failed to find any live virus, indicating that the woman probably was no longer infectious.

Though her baby never developed symptoms of West Nile disease, blood tests at 3.5 weeks of age confirmed the infant had antibodies to the virus. Those antibodies might have been transferred from the mother via breast milk, the editorial concedes–except that transmission of antibodies through milk “is inefficient.” It therefore concludes that the robust numbers of antibodies in the infant suggest that they were produced in response to an infection in the baby.

Ironically, Petersen says, although West Nile infections have been endemic in Africa and western Asia for a long time, no one ever analyzed breast milk as a source of infection in infants. The expectation was always that children picked up the disease as adults did–from mosquito bites.

In fact, the Michigan woman and her infant could have each contracted their infection from bug bites. However, CDC epidemiologists note, neither spent much time outside where they might have encountered a mosquito.

So far this year, West Nile disease has claimed the lives of more than 145 people in the United States. Though infections appear to have peaked for the year in the South, Petersen says it may be a few weeks before they do so farther north.

What is West Nile disease?

Many people with the virus show no signs of illness other than perhaps transient high fevers and other flulike symptoms. In other people, especially the elderly or those with impaired immunity, encephalitis or meningitis may occur.

Encephalitis is an inflammation of the brain. Symptoms typically include sudden fever, headache, vomiting, unusual sensitivity to light, a stiff neck or back, confusion, drowsiness, clumsiness, and irritability. In critical cases, the victim may lose consciousness, endure seizures, suffer muscle weakness, or develop sudden severe dementia. Meningitis, in contrast, is an infection of the membranes surrounding the brain and spinal cord. Many of its symptoms resemble those of encephalitis. The National Institutes of Health recommends that anyone experiencing symptoms of encephalitis or meningitis should see a doctor immediately.

More recently, a new form of West Nile disease has emerged. Its symptoms, polio-like paralysis, have been confirmed in seven people thus far.

As no vaccine exists to prevent disease, the best approach to limit risk of infection is to avoid contact with mosquitoes, to cover up the body when working in the yard and walking in the woods, and to wear a bug repellent. To limit the spread of mosquitoes, eliminate standing water–including that in birdbaths–unless it’s been treated to kill the insect’s larvae.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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