A graduate student who died last week in Mammoth Lakes and a Santa Barbara County ranch hand were infected with the deadly hantavirus--the same virus that caused a fatal outbreak in the Four Corners area of the Southwest earlier this year, state health officials announced late Monday.
The two are the only confirmed cases of hantavirus infection in California, the sixth state where the disease has been identified since the illness was discovered among Navajos in New Mexico in May.
At least 17 people--and possibly as many as 31--have died after being infected.
State health officials have not ordered quarantines in the two isolated areas where the California patients were believed to have been infected, nor have they asked that campgrounds be closed where rodents thought to transmit the virus might be present in large numbers.
Instead, they are urging Californians, primarily those who live or travel in remote or rural areas to avoid contact with wild rodents and to use caution in cleaning up rodent urine and droppings.
Both individuals who were infected had “heavy rodent exposures,” said Dr. George W. Rutherford, deputy director of the state Department of Health Services.
“Where (the disease) has occurred in the United States, it has occurred in rural areas, in places that have heavy infestations of mice, specifically deer mice,” Rutherford said.
Laboratory tests conducted by the U.S. Centers for Disease Control and Prevention in Atlanta confirmed that Jeanne Messier, 27, a UC San Diego wildlife biology student working near Mammoth Lakes in Mono County, and an unidentified 50-year-old Santa Barbara County ranch hand died of hantavirus infections.
Messier’s case illustrates how rapidly the disease, which often begins with fever, headache and breathing difficulty, can quickly escalate into a life-threatening illness.
Messier, who was studying birds at the Valentine Ecological Reserve, sought treatment for flu-like symptoms last Wednesday. Rutherford said that after being seen at a hospital she went back to her research station.
She returned to the hospital the next day and was flown to a Reno hospital, where she died Friday. Rutherford said that the cabin she lived in was infested with rodents.
The Santa Barbara County ranch hand died last September, soon after he began suffering from similar respiratory illness. That was months before the Four Corners outbreak was discovered and hantavirus was known to be the cause of deaths in the United States.
Initially, public health officials thought he might have died of plague, a bacterial disease that periodically flares up in the rodent population in the state and can be transmitted to humans.
But a test of the dead man’s lung tissue confirmed that the hantavirus was present. The man reportedly often trapped mice and other rodents to feed his cats.
Officials are planning to trap animals in Mono and Santa Barbara counties to determine the spread of the hantavirus in the rodent populations in both areas.
Health authorities have ruled out hantavirus as the cause of death in a third case, that of an Orange County man who died of respiratory distress without a known cause. Tests showed that the man was once infected with hantavirus, but long before his most recent illness.
Public health officials believe that deer mice are the most common carriers of the disease. The rodents have been found in all 58 California counties. Animals without symptoms can be carriers of the virus.
Rutherford said investigators can only speculate on why there has never been an outbreak of hantavirus identified before this year. He said that the virus has probably been present in deer mice and other rodents for a long time.
Increased rain and snow has contributed to a sudden rise in vegetation, which has led to an increase in the rodent population throughout the West, they said. And that could lead to increased exposure to humans.
The virus is easily transmitted and health officials are warning the public to avoid direct contact with wild animals and to use extreme caution in cleanup of dead animals or their droppings.
The disease has a fatality rate of up to 40% among people in whom the disease is diagnosed. But only those with the most severe symptoms are likely to be diagnosed.
The disease, officially known as the hantavirus associated respiratory distress syndrome, is believed to have caused a total of 31 deaths in California, Arizona, Colorado, New Mexico, Nevada and Texas. Only 17 of the deaths have been confirmed as linked to hantavirus.