Fresno County’s top health official and a vector control manager urged people to protect themselves from mosquito bites as they announced Friday that a Fresno man is the county’s first confirmed patient with West Nile virus this year.
The timing of the announcement also coincided with national reports that four cases of Zika infection in the Miami area were likely the first local transmissions of the mosquito-borne virus in the continental United States. The virus, which can be spread by mosquitoes and sex, causes brain damage and neurological problems in babies and has been linked to neurological problems in adults.
Zika and West Nile viruses are spread by mosquitoes – but each is unique to an individual species. Fresno and Clovis have both types of mosquitoes.
Public health officials have feared a local transmission of Zika virus could occur in areas such as Florida, where the Aedes aegypti mosquito that transmits the virus has become entrenched. The mosquito has been found in regions of Fresno County but is not as widely dispersed here as it is in Florida, said Fresno County Health Officer Dr. Kenneth Bird.
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On the other hand, the common southern house mosquito that spreads West Nile virus is well-established in the central San Joaquin Valley and California.
It’s really important that people recognize the need to be protecting themselves from mosquito bites in general.
Steve Mulligan, manager Consolidated Mosquito Abatement District
Researchers are studying the southern house mosquito to see if it could spread Zika in addition to West Nile. But Steve Mulligan, manager of the Consolidated Mosquito Abatement District that covers Clovis, said it has not been shown to be capable of doing so. “At this point, this mosquito is more important as a vector of West Nile.”
But the message for the public: “It’s really important that people recognize the need to be protecting themselves from mosquito bites in general,” Mulligan said. The Aedes aegypti typically bites during the day but also can bite at night. The southern house mosquito bites at dusk and night.
Bird said the man infected with West Nile virus was hospitalized with a neuroinvasive condition. His case “is a strong reminder that West Nile virus is still present in our county and everyone should increase efforts to protect themselves and their families from mosquito bites.”
The county has had one other confirmed West Nile case identified during blood donor testing, but that person had no symptoms. Most people infected with West Nile virus have no or only mild flu-like ailments. But the disease can cause neurological and other serious conditions, and can be fatal. In 2015, Fresno County reported eight West Nile cases. There were no deaths. Statewide, there were 783 cases and 53 deaths.
West Nile activity has increased this summer statewide. Los Angeles and Yuba counties also have had a case each.
Until Friday, there had been 1,658 Zika cases reported in the continental United States, but none from the bite of a local mosquito. Fifteen of the cases were from sexual transmission and one from laboratory exposure. Zika is widespread in portions of southern Mexico, in Central and South American countries and in the Caribbean.
Fresno County has had one case of travel-associated Zika infection, which health officials reported earlier this month.
Bird said Friday that he was not surprised that Florida was the first state to have a local transmission. The state has a lot of travelers to countries where the virus is endemic. The concern of public health officials is that an infected person returning home who is bitten by a mosquito can set off a chain of infections.
We want to be very careful that we don’t overburden our county and state lab. They should rule out everything else that it possibly could be.
Dr. Kenneth Bird, Fresno County health officer
The health officer has asked doctors in the county to be alert for Zika infections, and to request testing for suspected cases. “But we want to be very careful that we don’t overburden our county and state lab,” he said. “They should rule out everything else that it possibly could be.”
Travelers to Zika-infested areas should use insect repellent for three weeks after returning home, whether or not they have symptoms of Zika – fever, muscle aches, rash, red eyes. “That’s really critical. We can stop local transmission by preventing people coming back who are infected” from being bitten by a mosquito who then could carry the virus to another person, Mulligan said.
The federal Centers for Disease Control and Prevention recommends that everyone in areas where the Aedes aegpyti mosquitoes are present, and especially pregnant women, take steps to avoid mosquito bites.
The Food and Drug Administration has ordered blood banks in Miami-Dade and Broward counties in Florida to stop collecting blood because of the local Zika transmissions. Nationwide, blood banks are asking people who have traveled to countries that have widespread Zika transmission to delay donating blood for a month after their return.
The federal agency has not asked blood banks to stop accepting blood from people who have traveled to Florida, said Leslie Botos, spokeswoman for the Central California Blood Center. But Botos said the local blood bank would ask those who have traveled to Florida to report it when donating blood.
Blood donations are always affected by Zika stories, Botos said. Right now, the Central California Blood Center has about 30 percent of the blood supply it needs, she said. “It’s every single type, and this is a shortage that is being mirrored across the United States.”