West Nile virus has been detected in breast milk, raising the possibility
that the microbe could be transmitted through nursing as well as by blood
transfusion, organ donation and the usual route, mosquito bite, government
officials said yesterday.
There have been no known cases of West Nile fever acquired through breast
milk, and it's not known whether such transmission is possible, officials from
the Centers for Disease Control and Prevention emphasized. However, viruses
similar to West Nile can be passed in milk and infect humans, they said.
The agency made no recommendation on whether mothers diagnosed with West Nile
virus should stop nursing. Only four of the 2,206 reported cases in the United
States this year have been in children younger than 1, suggesting that
transmission through nursing is rare, if it occurs at all.
"We need to investigate the potential role of breast milk in
transmission," said Lyle R. Petersen, one of the CDC's West Nile experts.
The new finding came in the case of a 40-year-old woman in southeastern
Michigan who delivered a baby Sept. 2. She received a transfusion of one unit of
blood that day and another unit the following day. She became feverish and ill
after returning home, and was readmitted to the hospital Sept. 17. The West Nile
diagnosis was made the next day, Michigan state epidemiologist Matthew Boulton
said in a telephone news conference.
The woman had been breast-feeding her infant during that two-week period. The
child never fell ill, and the woman has recovered, Boulton said, although she
has not resumed breast-feeding.
The initial tests of her milk found genetic material from the West Nile
virus. Tests are underway to learn whether the virus is whole, live and capable
of infecting a person.
Birds have been experimentally infected with West Nile virus orally, Petersen
said, although no studies have been done on milk.
Other insect-borne viruses in the same family as West Nile can be transmitted
through milk. Tick-borne encephalitis virus, which is confined to Western Europe
and the former Soviet Union, has infected people who drank milk from infected
goats and cows, Petersen said. Animal-to-animal transmission through milk has
also been reported in Kyasanur forest disease virus (found in monkeys in Western
India) and louping-ill virus (found in sheep in the British Isles).
The Michigan and CDC investigators say they are certain the nursing mother
was infected through blood transfusion, because a 47-year-old man who received
blood from one of the same donors also developed West Nile. A stored sample from
that donor tested positive for the virus.
Studies done in the 1950s, when West Nile virus was given experimentally to
cancer patients to induce fevers thought to be possibly therapeutic, showed that
the virus circulated in the bloodstream for only about five days.
Consequently, Petersen said, "we would expect that virus would be
present in the breast milk for a very short period of time."
As of Thursday, 2,206 cases of West Nile infection, and 108 deaths, had been
reported in 32 states and the District. About three-quarters of those infections
caused either encephalitis or meningitis -- severe, life-threatening brain
infection. In the other quarter, the patients had fever, headache, weakness and
other milder symptoms. And a few patients have developed poliolike paralysis
from the infection.