Traces of West Nile Virus Found in Breast Milk

By DENISE GRADY

races of West Nile virus have been found in the breast milk of a mother who contracted the disease, probably from blood transfusions, health officials said yesterday. But so far her baby is healthy, despite being breast-fed while the mother was ill.

The case does not mean that current recommendations in favor of breast-feeding should change, according to the Centers for Disease Control and Prevention. Women should still be encouraged to breast-feed because it is so beneficial to infants, the C.D.C. said. But the centers also issued a statement saying women with documented West Nile infections might want to consult their doctors about breast-feeding.

But their doctors may not know what to advise. Dr. Lyle Petersen, a West Nile expert at the disease centers, said it was not known whether breast milk could transmit the virus to babies.

The mother in the new case, a 40-year-old from southeastern Michigan, gave birth on Sept. 2 and had one transfusion that day and another on Sept. 3. She ran a fever while in the hospital but was sent home on Sept. 4 and continued to suffer from fever, headaches, malaise and nausea. She was readmitted to the hospital 13 days later and was found to be infected with West Nile.

Tests showed that the transfusion on Sept. 3 carried the virus and that another patient who had received blood from the same donor also became ill. The woman's breast milk was found to contain genetic material from West Nile, but that finding does not prove that whole live viruses were present. Genetic material from West Nile has never been found in breast milk before, the disease centers said.

The baby is being tested for infection, and samples of the milk are being tested to find out whether the virus can be grown from them. That would indicate that live virus was present in the milk.

It is a good sign that the baby has remained healthy, Dr. Petersen said. But he added that the incubation period of 2 to 14 days was not over and that in theory the baby could still become sick if the virus was transmitted in the milk. The mother nursed until Sept. 19, when the West Nile diagnosis was made.

"We would expect the virus in breast milk to be present for only a very short period of time," Dr. Petersen said, adding that he would expect the risk to become negligible very quickly as the virus disappeared from the milk.

It is not known whether the virus can cause illness if it enters the body through the mouth and digestive tract, as opposed to entering the bloodstream through a mosquito bite, transfusion or organ transplant.

Dr. Petersen said that two other viruses in the same family as West Nile had been transmitted to people from drinking milk from cows or goats. Neither of those viruses has been found in North America. One is from India and the other from eastern Europe and parts of Asia. There is no information about whether those viruses pass into human breast milk.

Dr. Petersen said there were just two viral infections in which women are told not to breast-feed, H.I.V. and a very rare illness, human T-cell leukemia virus type 1. With other viral illnesses like colds and flu, he said, women are generally told to continue nursing because the illnesses are not severe enough to justify stopping.

"The benefits of breast-feeding are so great, we wouldn't want women to stop," he said.

Although mosquitoes are by far the most important source of infection, Dr. Petersen said, the illness in two transfusion recipients was further evidence that the virus could spread through blood and blood products. Transmission via blood is thought to have occurred in three other transfusion recipients. Officials theorize that four people, including one who died, contracted the disease from organ transplants.

There is no screening test to detect West Nile in the blood supply. Dr. Jesse Goodman of the Food and Drug Administration said his agency was "urgently working with manufacturers and others with potential blood screening tests to try to facilitate their availability."

The disease centers said that as of Thursday the reported West Nile cases this year totaled 2,206, with 108 deaths.

The agency also said the epidemic appeared to have peaked in the Southern states last month and in the last two weeks in Northern states. The tropical storm that struck Louisiana this week may be beneficial, Dr. Petersen said, because the mosquitoes that carry West Nile multiply better in small puddles of water than in floods.